Spec-Driven

Spec-Driven C++: Dirnav

traversal, admission, matching, and emission in one class template

Process Behavior C++ Rust C# Python
Synopsis:
This page covers Cpp_TextFinder_Dirnav, which walks, selects, reads, matches, and formats. It is the only component that touches file contents, and it writes to no stream.
  • A class template constrained on the Output base class it declares and does not implement, so the polymorphism is a compile-time check rather than a runtime dispatch.
  • One instance serves every root path, so the expression compiles once per run.
  • search returns nothing - every failure it meets is announced through Output, so the caller has nothing to report on its behalf.
Several standard-library calls are rejected by name, because the plausible call is the wrong one.
  • path::extension() returns nothing for .gitignore, where the specification gives it an extension.
  • recursive_directory_iterator would have to be told after the fact about /s and the skip list.
  • generic_string() is the instructive one - it silently passes invalid bytes on POSIX and throws out of the walk on Windows, so renderPath replaces it and behaves the same on both.
 Two behaviors are worth reading for how little code they take.
  • The no-content case is two constructor flags, after which a selected file produces a path line without ifstream ever being opened for it.
  • The run counts are two increments, each at the one point that decides the count, so everything the specification excludes is excluded by where the lines sit rather than by a test of its own.
  • Section 6 covers the linkage rule the build taught: the reflex answer compiles and does not link.

1.  Public Interface

Cpp_TextFinder_Dirnav walks a directory tree, reads each selected file, evaluates the expression against each line, and formats every matching file into the block Spec_TextFinder.md §3.4 fixes, emitting each of its lines as it is produced. It is the only component that touches file contents, and it writes to no stream. The module interface unit exports three things at global scope. 
export class Output {
public:
    virtual ~Output() = default;
    virtual void output(const std::string& text) = 0;
};

export using SkipList = std::vector<std::string>;

export template <typename Out>
    requires std::derived_from<Out, Output>
class Cpp_TextFinder_Dirnav {
public:
    Cpp_TextFinder_Dirnav(Out& out, const SkipList& skips, const ProgramCommands& commands);
    void search(const std::filesystem::path& root);
    void emitRunSummary();
};
The class template declares the Output base class it does not implement, which is what puts Cpp_TextFinder_Output downstream of it in the import chain. The concept constraint makes the base class the requirement and the template parameter makes the call direct, so the polymorphism is a compile-time check rather than a runtime dispatch. The constructor compiles commands.regexText with std::regex, constructed with std::regex::ECMAScript - the engine Spec_TextFinder.md §6.1 assigns to C++ - and lets std::regex_error propagate when it will not compile. Cpp_TextFinder_Cmdline guarantees the text is non-empty, so the constructor never sees an empty expression. All three arguments are retained by reference and owned by Cpp_TextFinder_Entry; the skip list and the commands are consulted but never modified. search returns nothing. Every failure it meets is announced through Output, so the caller has nothing to report on its behalf. That return type is a review outcome rather than a first draft: the original bool came back false both for a root that could not be opened and for one that was neither file nor directory, which would have had the binary print cannot open for /dev/null. Once Dirnav announces root failures itself, the bool has no consumer. A single instance is reused across every root path, so the compiled expression is built once per run. search carries no state from one call to the next but for the two run counts of Section 5.1, which accumulate across calls by design. Member definitions live in the interface unit, since the class is a template. emitRunSummary writes the run summary Spec_TextFinder.md §3.6 requires. It takes no argument and returns nothing, the counts being this instance's own, and Cpp_TextFinder_Entry calls it once after the last search returns. The split is deliberate: the counts belong here because nothing else sees the entries, and the call belongs to the caller because nothing here knows which root was the last. No accessor is exported for either count - the line is the whole of what they are for, and the unit suite reads them by reading that line through its own Output.

2.  Traversal

search resolves a root before walking it. A symbolic link or a status query that fails draws cannot open; a regular file is examined as a single file; a directory is walked; anything else draws cannot open. The skip list is never consulted for the root, which Spec_TextFinder.md §3.2 exempts because the user named it explicitly. The recursion is written explicitly. walk iterates one directory and calls itself on each subdirectory it decides to enter, so entries are handled as std::filesystem::directory_iterator yields them, without being collected or reordered. Two standard-library choices are stated in the specification by name, and each rules out a plausible alternative.
  • recursive_directory_iterator is not used. The library controls its own descent, because /s and the skip list both decide whether to enter a directory and a recursive iterator would have to be told after the fact.
  • directory_iterator enumerates a single level only. Its order is unspecified by the standard and is whatever readdir or FindFirstFileW returns, which is exactly the platform facility Spec_TextFinder.md §3.2 requires an implementation to enumerate through. Entries are neither sorted nor grouped, as §3.2 forbids.
 The loop advances with entry.increment(error) rather than ++, because the throwing overload would turn a directory that becomes unreadable mid-iteration into an exception the library has no way to report through Output. Each of the three entry queries - is_symlink, is_directory, is_regular_file - takes its own std::error_code for the same reason. The order of those three queries matters. A symbolic link is tested first and passed over silently whatever its target, since no attempt is made to open it, so a link to a directory never reaches the descent branch. A pruned directory draws no announcement either: pruning is work the library chose not to do, and cannot open reports work it could not do. One gate sits between the link test and everything after it, and §5 rule 6 fixes its position: an entry whose own name will not render as text is announced with cannot open and skipped. It runs before the skip-list test, before the extension filter, and before any attempt to open, so such a name is announced whatever /p holds - Spec_TextFinder.md §3.4 writes that rule over every such file rather than over the selected ones. A symbolic link is still tested first, so a link with an unrenderable name stays silent: rule 5 turns on the entry's kind, which costs no conversion, and §3.2 asks for silence there. The gate is what lets the rest of the library assume it holds a name. Everything after it takes text as a std::string, and Section 5 covers the helper that produces that text and decides whether an entry passes.

3.  File Selection

Selection follows the /p rules of Spec_TextFinder.md §5, and the list arrives from Cpp_TextFinder_Cmdline already normalized to bare extensions. An empty list selects every file; a non-empty list selects a file whose extension matches an entry. std::filesystem::path::extension() does not implement those rules, and the specification rejects it by name: it returns an empty string for .gitignore, whereas §5 gives that file the extension gitignore. The extension is therefore taken as the text after the last . in the file name, with no special case for a leading dot, and a name holding no . at all has no extension. The name itself comes from baseName, which routes through the renderPath of Section 5 rather than calling path::filename().string() - that call converts on Windows and can throw. Nothing here has to handle the failure, because the Section 2 gate has already refused every entry whose name will not render: selection sees a name and never a failure. u8string() is rejected by name too, for a duller reason: it returns std::u8string, which will not compare against the std::string extensions the parser supplies. Both warnings survived every trimming pass, on the ground that each stops an implementer writing something plausible and wrong. Comparison goes through sameName, which is case-sensitive on POSIX and case-insensitive on Windows per §3.2 and §5. The same function serves the skip list, since the platform rule is the same for both, and it is the one place in the file where _WIN32 changes behavior rather than only including a header. Selection applies uniformly: a root path that is a regular file is filtered by /p like any other file. A root named on /P escapes the skip list and does not escape the extension filter.

4.  Admission and the No-Content Case

examine applies the three admission tests of Spec_TextFinder.md §3.3 in the order the specification fixes. The size test reads filesystem metadata, so a file above the limit is never read into memory; the NUL and UTF-8 tests read bytes. The constructor records once, for the whole run, whether the no-content case applies - regexText equal to . with lineNumbers and matchedLine both false. Two flags carry it: 
pathOnly_{!commands.lineNumbers && !commands.matchedLine},
contentNotNeeded_{pathOnly_ && commands.regexText == "."}
When contentNotNeeded_ holds, a selected file that passes the size test and is not empty produces a block of its path line alone, and std::ifstream is never opened for it. No file announcement accompanies that block: searched reports a file that was read and matched nothing and skipped reports one a content test rejected, and neither happened, so the library emits neither whatever /h says. A selected file of zero size produces no block and draws no announcement either. Both error announcements still work in this case, because both rest on metadata: a file above the limit draws too large, and one whose metadata cannot be read draws cannot open. A file that needs reading is read in full, so one failing a later test is skipped entirely rather than searched in part. The read allocates a string of the reported size, reads into it, and resizes to gcount(), which is what makes a file that shrank between the file_size call and the read produce a correct short string rather than a buffer with garbage at the end. validUtf8 rejects truncated sequences, overlong encodings, encoded surrogates, and scalar values above U+10FFFF. All four rejections are one line each in the source, with the reason named in the comment, because "valid UTF-8" is a phrase two implementers read differently and four named rejections are four test cases. A leading BOM is erased after the tests, not before, so the three bytes count toward the size limit and toward the NUL scan like any others.

5.  Matching and Emission

splitLines divides the bytes at LF, CRLF, or bare CR, and treats a final unterminated run as a line. It returns std::string_view into the buffer rather than copies, so a 10 MB file costs one allocation for its contents and one vector of views. Line numbers count every line, matching or not. Each line is evaluated with std::regex_search, which gives the anywhere-in-the-line match §3.3 requires. The line is passed as its bytes, so ., a character class, and a class escape each match one byte rather than one Unicode scalar value; §6.1 records that as this implementation's divergence from the other three on a non-ASCII line, and the divergence is a consequence of std::regex over char rather than a choice made here. scan writes the block and answers whether the file matched. Three rules govern it, and all three are visible in a dozen lines:
  1. The path line goes out at the first match, ahead of the detail line for that same match, and an opened flag makes sure it goes out once. A file that never matches produces no line at all; a file that matches many produces its path line once.
  2. With neither /n nor /L, the loop returns as soon as the path line is written. The block has no detail lines, so the first match settles the file.
  3. Otherwise the loop runs to the end of the file, writing one detail line - two spaces of indent, then the fields /n and /L select - as each matching line is evaluated.
 Nothing is accumulated for the file. Output receives each line as it is produced, which is the pipeline behavior §3.4's "as they occur" requires. Announcements go through the same Output, at the point the failure or the finding is met, and an error announcement is not gated on /h. The /h gate is one line, announceNoMatch, and it reads as the rule it implements: emit unless suppressOnNoMatch. A file announcement reports only a file that produced no block, so it never repeats a path the output already carries - searched at the moment the last line has been evaluated, which is the first moment the library knows the file matched nothing, and skipped at the point of rejection. Path rendering strips a leading ./ contributed by a root of ., per §3.4. generic_u8string() is rejected by name for the same reason u8string() is: Output::output takes a std::string. generic_string() is rejected too, and its rejection is the most instructive of the three, because the function looks correct and behaves differently on the two platforms this implementation targets. On POSIX the native string is already char, so it copies bytes and cannot fail - and a name holding bytes that are not valid UTF-8 passes straight through, unexamined. On Windows the native string is wchar_t, so it must convert UTF-16 to narrow, and an unpaired surrogate has no encoding; the standard has that conversion throw std::system_error. One platform never reports the condition §3.4 defines, and the other reports it by throwing out of the walk, where nothing catches it. renderPath replaces it and behaves the same on both. It produces the generic form, substitutes U+FFFD REPLACEMENT CHARACTER for each unit that will not render, and reports through a reference parameter whether it substituted any. On POSIX it walks the bytes with the same sequence test validUtf8 applies to file contents, copying each valid sequence and substituting for each byte that begins none. On Windows it walks the UTF-16 units, mapping the separator, encoding each scalar value, and substituting for each surrogate not part of a pair. It calls neither generic_string() nor filename().string(), so there is no conversion left to throw and nothing to catch - a stronger guarantee than wrapping the old calls in a try would give. That second return is what the Section 2 gate consumes, through a one-line renderable. Every name that survives the gate renders without substitution, so baseName and a block's path line receive text that is the name, and the U+FFFD form appears in exactly one place: the cannot open announcement naming the entry that failed the gate. Adding renderPath also split the old validUtf8 in two. utf8Sequence now returns the length of the valid sequence beginning at an offset, or 0 where none does, and validUtf8 is a loop over it. The specification requires the POSIX branch to use "the same validity test validUtf8 applies to file contents", so the two share one definition rather than carrying two that can drift.

5.1  The Run Summary

Spec_TextFinder.md §3.6 puts the two run counts in this library, for every implementation alike, and fixes the line they produce. Two std::size_t members hold them, both zero on construction, and neither is reset by search, so they accumulate over every root the instance is given. Each increment sits at the one point that decides the count, which is what keeps the rule to two lines of code and no second test.
  • Files are counted in examine, immediately after the /p test of Section 3 admits the file and before std::filesystem::file_size is called. A file admitted and then announced too large or cannot open is therefore counted, the increment standing ahead of both.
  • Directories are counted at the head of walk, before directory_iterator is constructed, so a directory that cannot be enumerated is counted and announced alike.
 Everything §3.6 excludes is excluded by where those two lines sit rather than by a test of its own. An entry refused by /p, a symbolic link, an entry beneath a pruned directory, an entry whose name will not render, and an entry that is neither a regular file nor a directory all fail or bypass the /p test and never reach the increment - though the last two draw cannot open on the way past, which is why the file count can be smaller than the number of announcements a run writes. A root that resolved to a directory reaches walk and is counted; a pruned directory and, under /s false, every subdirectory never reach it. emitRunSummary composes the line with std::to_string on each count and sends it through the same Output as every other line, in §3.6's fixed form and with neither noun inflected: 
accessed <files> files, <directories> directories
It is not gated on /h, which governs file announcements alone, and it names no path, so this section's rendering rules do not reach it. Eleven unit-suite assertions cover it, and the one worth naming reads accessed 1 files, 0 directories from a root that is a regular file - the uninflected singular, asserted rather than left to be noticed.

6.  Module Linkage and the inline Helpers

Every helper sits at module scope, not exported and marked inline: sameName, utf8Sequence, validUtf8, renderPath, baseName, displayPath, renderable, splitLines, and appendUtf8 on Windows. The combination is deliberate and the source says why. They were written first in an anonymous namespace, which is the reflex for "private to this file". That gives them internal linkage, and the class template that calls them is instantiated in main.cpp's translation unit, which therefore could not resolve them: the build compiled every translation unit and failed at link with five unresolved externals. Non-exported inline functions at module scope solve both halves. Module linkage keeps them invisible to importers, so the module's interface is still the three exported names. inline lets the instantiating translation unit emit its own copy, so the template's calls resolve. This is the one place in the project where the code carries a comment about the language rather than about the specification, and it earns it: the reflex answer compiles and does not link, and the failure names five symbols rather than the rule that was broken.

7.  Source

Cpp_TextFinder_Dirnav.ixx in full - 353 lines, the largest file in the project. The comments cite the C++ specification's sections, which cite Spec_TextFinder.md in turn.
Cpp_TextFinder_Dirnav.ixx
// Cpp_TextFinder_Dirnav.ixx - traversal, file admission, matching, and emission per Spec_Cpp_TextFinder_Dirnav.md

export module Cpp_TextFinder_Dirnav;

import std;
import Cpp_TextFinder_Cmdline;

export class Output {
public:
    virtual ~Output() = default;
    virtual void output(const std::string& text) = 0;
};

export using SkipList = std::vector<std::string>;

// These helpers are not exported, so they have module linkage and stay invisible to importers.
// They are inline because the class template below is instantiated in the importing translation unit.

inline constexpr std::uintmax_t sizeLimit = 10u * 1024u * 1024u;   // Spec_TextFinder.md §3.3

// Case-sensitive on POSIX, case-insensitive on Windows, per Spec_TextFinder.md §3.2 and §5.
inline bool sameName(std::string_view left, std::string_view right) {
#ifdef _WIN32
    if (left.size() != right.size()) return false;
    for (std::size_t i = 0; i < left.size(); ++i) {
        const auto l = std::tolower(static_cast<unsigned char>(left[i]));
        const auto r = std::tolower(static_cast<unsigned char>(right[i]));
        if (l != r) return false;
    }
    return true;
#else
    return left == right;
#endif
}

inline constexpr std::string_view replacement{"\xEF\xBF\xBD"};   // U+FFFD, per §8

// §7: the length of the valid UTF-8 sequence beginning at i, or 0 if none does. Rejects
// truncated sequences, overlong encodings, encoded surrogates, and values above U+10FFFF.
inline std::size_t utf8Sequence(std::string_view bytes, std::size_t i) {
    const auto lead = static_cast<unsigned char>(bytes[i]);
    std::size_t trailing = 0;
    char32_t point = 0;

    if (lead < 0x80) return 1;
    else if ((lead & 0xE0) == 0xC0) { trailing = 1; point = lead & 0x1Fu; }
    else if ((lead & 0xF0) == 0xE0) { trailing = 2; point = lead & 0x0Fu; }
    else if ((lead & 0xF8) == 0xF0) { trailing = 3; point = lead & 0x07u; }
    else return 0;

    if (i + trailing >= bytes.size()) return 0;
    for (std::size_t k = 1; k <= trailing; ++k) {
        const auto next = static_cast<unsigned char>(bytes[i + k]);
        if ((next & 0xC0) != 0x80) return 0;
        point = (point << 6) | (next & 0x3Fu);
    }

    if (trailing == 1 && point < 0x80) return 0;        // overlong
    if (trailing == 2 && point < 0x800) return 0;       // overlong
    if (trailing == 3 && point < 0x10000) return 0;     // overlong
    if (point > 0x10FFFF) return 0;                     // beyond Unicode
    if (point >= 0xD800 && point <= 0xDFFF) return 0;   // encoded surrogate

    return trailing + 1;
}

// §7: the admission test of Spec_TextFinder.md §3.3, over the same sequence rule §8 renders with.
inline bool validUtf8(std::string_view bytes) {
    for (std::size_t i = 0; i < bytes.size();) {
        const std::size_t length = utf8Sequence(bytes, i);
        if (length == 0) return false;
        i += length;
    }
    return true;
}

#ifdef _WIN32
inline void appendUtf8(std::string& text, char32_t point) {
    if (point < 0x80) text += static_cast<char>(point);
    else if (point < 0x800) {
        text += static_cast<char>(0xC0 | (point >> 6));
        text += static_cast<char>(0x80 | (point & 0x3F));
    }
    else if (point < 0x10000) {
        text += static_cast<char>(0xE0 | (point >> 12));
        text += static_cast<char>(0x80 | ((point >> 6) & 0x3F));
        text += static_cast<char>(0x80 | (point & 0x3F));
    }
    else {
        text += static_cast<char>(0xF0 | (point >> 18));
        text += static_cast<char>(0x80 | ((point >> 12) & 0x3F));
        text += static_cast<char>(0x80 | ((point >> 6) & 0x3F));
        text += static_cast<char>(0x80 | (point & 0x3F));
    }
}
#endif

// §8: the generic form Spec_TextFinder.md §3.4 fixes, with U+FFFD for each unit that will not
// render and a report of whether any was substituted. Calls neither generic_string() nor
// filename().string(): on Windows both convert and can throw out of the walk, and on POSIX
// both pass invalid bytes through unexamined, so neither reports the condition §3.4 defines.
inline std::string renderPath(const std::filesystem::path& path, bool& lossy) {
    lossy = false;
    std::string text;

#ifdef _WIN32
    // The native string is UTF-16. Walk its units, mapping the separator and encoding each
    // scalar value, and substitute for a surrogate that is not part of a pair.
    const std::wstring& native = path.native();
    for (std::size_t i = 0; i < native.size(); ++i) {
        char32_t point = static_cast<unsigned short>(native[i]);
        if (point == L'\\') point = U'/';

        if (point >= 0xD800 && point <= 0xDBFF) {
            const bool paired = i + 1 < native.size() &&
                                static_cast<unsigned short>(native[i + 1]) >= 0xDC00 &&
                                static_cast<unsigned short>(native[i + 1]) <= 0xDFFF;
            if (!paired) { text += replacement; lossy = true; continue; }
            const char32_t low = static_cast<unsigned short>(native[++i]);
            point = 0x10000 + ((point - 0xD800) << 10) + (low - 0xDC00);
        }
        else if (point >= 0xDC00 && point <= 0xDFFF) { text += replacement; lossy = true; continue; }

        appendUtf8(text, point);
    }
#else
    // The native string is bytes and the separator is already /. Copy each valid sequence and
    // substitute for each byte that begins none.
    const std::string& native = path.native();
    for (std::size_t i = 0; i < native.size();) {
        const std::size_t length = utf8Sequence(native, i);
        if (length == 0) { text += replacement; lossy = true; ++i; continue; }
        text.append(native, i, length);
        i += length;
    }
#endif

    if (text.starts_with("./")) text.erase(0, 2);   // a root of . contributes no leading ./
    return text;
}

inline std::string baseName(const std::filesystem::path& path) {
    const std::filesystem::path base = path.has_filename() ? path : path.parent_path();
    bool lossy = false;
    return renderPath(base.filename(), lossy);
}

inline std::string displayPath(const std::filesystem::path& path) {
    bool lossy = false;
    return renderPath(path, lossy);
}

// §5 rule 6: whether this entry's own name renders without substitution.
inline bool renderable(const std::filesystem::path& path) {
    bool lossy = false;
    renderPath(path, lossy);
    return !lossy;
}

// LF, CRLF, and bare CR terminate a line; a final unterminated run is still a line.
inline std::vector<std::string_view> splitLines(std::string_view text) {
    std::vector<std::string_view> lines;
    std::size_t start = 0;
    for (std::size_t i = 0; i < text.size();) {
        if (text[i] == '\n') {
            lines.push_back(text.substr(start, i - start));
            start = ++i;
        }
        else if (text[i] == '\r') {
            lines.push_back(text.substr(start, i - start));
            i += (i + 1 < text.size() && text[i + 1] == '\n') ? 2 : 1;
            start = i;
        }
        else ++i;
    }
    if (start < text.size()) lines.push_back(text.substr(start));
    return lines;
}

export template <typename Out>
    requires std::derived_from<Out, Output>
class Cpp_TextFinder_Dirnav {
public:
    // §4: all three arguments are retained by reference and outlive this instance. The
    // expression is compiled once here; std::regex_error propagates to Cpp_TextFinder_Entry.
    Cpp_TextFinder_Dirnav(Out& out, const SkipList& skips, const ProgramCommands& commands)
        : out_{out}, skips_{skips}, commands_{commands},
          expression_{commands.regexText, std::regex_constants::ECMAScript},
          pathOnly_{!commands.lineNumbers && !commands.matchedLine},
          contentNotNeeded_{pathOnly_ && commands.regexText == "."} {}

    // §5 rule 1. Carries no state from one call to the next.
    void search(const std::filesystem::path& root) {
        std::error_code error;

        const bool link = std::filesystem::is_symlink(root, error);
        if (error || link) { announceCannotOpen(root); return; }

        // §5 rule 6: a root whose text will not render is announced and not traversed.
        if (!renderable(root)) { announceCannotOpen(root); return; }

        const std::filesystem::file_status status = std::filesystem::status(root, error);
        if (error) { announceCannotOpen(root); return; }

        if (std::filesystem::is_regular_file(status)) { examine(root); return; }
        if (!std::filesystem::is_directory(status)) { announceCannotOpen(root); return; }

        // §5 rule 4: the skip list is never consulted for a root path.
        walk(root);
    }

    // §8.1: the run summary of Spec_TextFinder.md §3.6, written once after the last root.
    void emitRunSummary() {
        emit("accessed " + std::to_string(files_) + " files, " +
             std::to_string(directories_) + " directories");
    }

private:
    // §5 rule 2: one level per call, entries taken as directory_iterator yields them -
    // neither collected nor reordered - with explicit recursion into each subdirectory entered.
    void walk(const std::filesystem::path& directory) {
        ++directories_;   // §8.1: counted before enumeration, so one that fails is counted too

        std::error_code error;
        std::filesystem::directory_iterator entry{directory, error};
        if (error) { announceCannotOpen(directory); return; }

        const std::filesystem::directory_iterator end;
        for (; entry != end; entry.increment(error)) {
            if (error) { announceCannotOpen(directory); return; }
            const std::filesystem::path& path = entry->path();

            std::error_code kind;
            const bool link = entry->is_symlink(kind);
            if (kind) { announceCannotOpen(path); continue; }
            if (link) continue;   // §5 rule 5: passed over silently, never opened

            // §5 rule 6: after the link test and before the skip list, the extension filter,
            // and any open, so a name that will not render is announced whatever /p holds.
            if (!renderable(path.filename())) { announceCannotOpen(path); continue; }

            const bool folder = entry->is_directory(kind);
            if (kind) { announceCannotOpen(path); continue; }
            if (folder) {
                if (commands_.recurse && !pruned(path)) walk(path);
                continue;
            }

            const bool file = entry->is_regular_file(kind);
            if (kind) { announceCannotOpen(path); continue; }
            if (file) examine(path);
            else announceCannotOpen(path);
        }
    }

    // §7: the three admission tests of Spec_TextFinder.md §3.3.
    void examine(const std::filesystem::path& file) {
        if (!selected(file)) return;
        ++files_;   // §8.1: after the /p test admits it, ahead of every later outcome

        std::error_code error;
        const std::uintmax_t size = std::filesystem::file_size(file, error);
        if (error) { announceCannotOpen(file); return; }
        if (size > sizeLimit) { emit("too large " + displayPath(file)); return; }

        // §7: with the default expression and neither /n nor /L, every non-empty file
        // matches and its block is the path line, so no file is opened and - nothing
        // having been read or rejected - no file announcement arises under either /h.
        if (contentNotNeeded_) {
            if (size == 0) return;
            emit(displayPath(file));
            return;
        }

        std::ifstream input{file, std::ios::binary};
        if (!input) { announceCannotOpen(file); return; }

        // Read in full, so a file failing a later test is skipped entirely, not searched in part.
        std::string bytes(static_cast<std::size_t>(size), '\0');
        input.read(bytes.data(), static_cast<std::streamsize>(size));
        if (input.bad()) { announceCannotOpen(file); return; }
        bytes.resize(static_cast<std::size_t>(input.gcount()));

        if (bytes.find('\0') != std::string::npos || !validUtf8(bytes)) {
            announceNoMatch("skipped " + displayPath(file));
            return;
        }
        if (bytes.starts_with("\xEF\xBB\xBF")) bytes.erase(0, 3);

        // §8: a file that matched names itself in its block, so only one that did not is announced.
        if (!scan(file, bytes)) announceNoMatch("searched " + displayPath(file));
    }

    // §8: writes the block of Spec_TextFinder.md §3.4 and answers whether the file matched.
    bool scan(const std::filesystem::path& file, const std::string& bytes) {
        bool opened = false;
        std::size_t number = 0;

        for (std::string_view line : splitLines(bytes)) {
            ++number;
            if (!std::regex_search(line.begin(), line.end(), expression_)) continue;

            if (!opened) {
                emit(displayPath(file));   // the block's path line, written once
                opened = true;

                // With neither /n nor /L the block has no detail lines, so the first
                // match settles the file.
                if (pathOnly_) return true;
            }

            std::string detail = "  ";
            if (commands_.lineNumbers) detail += std::to_string(number);
            if (commands_.lineNumbers && commands_.matchedLine) detail += " - ";
            if (commands_.matchedLine) detail += std::string{line};
            emit(detail);
        }

        return opened;
    }

    // §6: the extension is the text after the last dot in the file name, dot-files included.
    bool selected(const std::filesystem::path& file) const {
        if (commands_.extensions.empty()) return true;

        const std::string name = baseName(file);
        const std::size_t dot = name.rfind('.');
        if (dot == std::string::npos) return false;

        const std::string_view extension{name.data() + dot + 1, name.size() - dot - 1};
        return std::ranges::any_of(commands_.extensions,
                                   [&](const std::string& item) { return sameName(item, extension); });
    }

    bool pruned(const std::filesystem::path& directory) const {
        const std::string name = baseName(directory);
        return std::ranges::any_of(skips_,
                                   [&](const std::string& item) { return sameName(item, name); });
    }

    void emit(const std::string& text) { out_.output(text); }
    void announceNoMatch(const std::string& text) { if (!commands_.suppressOnNoMatch) emit(text); }
    void announceCannotOpen(const std::filesystem::path& path) { emit("cannot open " + displayPath(path)); }

    Out&                    out_;
    const SkipList&         skips_;
    const ProgramCommands&  commands_;
    std::regex              expression_;
    bool                    pathOnly_;
    bool                    contentNotNeeded_;
    std::size_t             files_{0};          // §8.1: never reset between roots
    std::size_t             directories_{0};
};

8.  Prompt Records

The two conversations that produced Spec_Cpp_TextFinder_Dirnav.md. The first covers the draft, the move of traversal order into the parent specification, and the decision to write the recursion by hand over directory_iterator; the second covers the 13-item review whose answers promoted ten rules upward, the discussion that removed sibling sorting, and a text reduction.
Prompts_Spec_Cpp_TextFinder_Dirnav.md 
# Prompts and Replies — Spec_Cpp_TextFinder_Dirnav Development

This file records the prompts and replies that produced [Spec_Cpp_TextFinder_Dirnav.md](Spec_Cpp_TextFinder_Dirnav.md). Two of the turns below also changed [Spec_TextFinder.md](../../Spec_TextFinder.md) and [Project_Tree.md](../../Project_Tree.md).

---

## Turn 1

### User

> create Spec_Cpp_TextFinder_Dirnav in directory Cpp_Spec_driven_Dirnav.  You may use the project spec Spec_TextFinder.md for content and Spec_Cpp_TextFinder_Cmdline.md for structure and style example

### Assistant

Read [Spec_TextFinder.md](../../Spec_TextFinder.md), [Spec_Cpp_TextFinder_Cmdline.md](../Cpp_Spec_driven_Cmdline/Spec_Cpp_TextFinder_Cmdline.md), [Spec_Cpp_TextFinder_Entry.md](../Cpp_Spec_driven_TextFinder_Entry/Spec_Cpp_TextFinder_Entry.md), and [Cpp_TextFinder_Structure.md](../Cpp_TextFinder_Structure.md), then created [Spec_Cpp_TextFinder_Dirnav.md](Spec_Cpp_TextFinder_Dirnav.md) with ten sections mirroring the Cmdline spec's shape:

1. **Purpose** — the only component that touches file contents; writes to no stream.
2. **Scope** — parsing, skip-list ownership, and the destination of emitted strings belong to the other three specs.
3. **Responsibilities** — defines `Output`, compiles the expression once, traverses, selects files, formats records and announcements.
4. **Public Interface** — the `Output` abstract base class, `SkipList`, and the `Cpp_TextFinder_Dirnav<Out>` class template with its constructor and `search`.
5. **Traversal Rules** — root paths, order, recursion, skip list, symbolic links, unopenable subdirectories.
6. **File Selection** — the `/p` extension filter and its platform-dependent comparison.
7. **Content Decoding and Line Splitting** — whole-file UTF-8 validation, BOM handling, line terminators.
8. **Matching and Emission** — `regex_search` per line, the four record forms under `/n` and `/L`, and the `/h` announcement rules.
9. **Build** — C++23, CMake library target, C++ module, dependency on `Cpp_TextFinder_Cmdline` for `ProgramCommands`.
10. **Non-Goals** — no parsing, no skip-list ownership, no stream writing, no file modification.

Interface decisions taken from the surrounding specs: the constructor compiles the expression and lets `std::regex_error` propagate, since Entry already owns reporting the malformed-regex diagnostic; `search` returns `false` for a root that cannot be opened, because Entry formats that notice itself; and all three constructor arguments are held by reference, matching the `ProgramCommands` lifetime rule already fixed in the Cmdline spec.

Reported one finding: parent §6 requires every implementation to emit matches in the same order, but nothing fixed the order of entries within a directory, and every language's directory iterator returns them in filesystem order. Two implementations would diverge at the first directory with more than one entry.

Flagged five decisions made where the parent was silent, three of them affecting emitted output and therefore candidates for the parent:

- **Traversal order** — ascending basename, bytewise, files and directories interleaved.
- **Path rendering** — generic form with `/` separators on every platform.
- **Announcement wording** — `searched <path>`, `skipped <path>`, `cannot open <path>`, the last reusing the string Entry already fixed; distinct wording is needed because `/n false /L false` makes a match record a bare path.
- **Skip list versus root paths** — a root named on `/P` traversed even when its basename is in the list.
- **Symbolic links and UTF-8** — a symlink skipped whatever its target; a file validated in full before any line is evaluated, since parent §7 says such files are *skipped* and streaming would emit matches from the valid prefix of a file the spec says to skip.

---

## Turn 2

### User

> Specify traversal order as DFS in the project level spec

### Assistant

Added the visit order to parent [Spec_TextFinder.md](../../Spec_TextFinder.md) §3.2, where it binds all four implementations: depth-first descent completing each subtree before returning to the parent, and within a directory, entries visited in ascending order of basename compared bytewise, files and directories interleaved rather than grouped.

Included the sibling ordering alongside DFS because depth-first alone does not fix the order — it says how to descend, not which entry to take first, so §6 still could not be satisfied without it.

Repaired two cross-references while there: §6 pointed at §3.4 for "directory-traversal order," but §3.4 only used the phrase without defining it. Both now point at §3.2.

Reduced §5 rule 2 of the Dirnav spec to a deferral, keeping only the C++-specific consequence — `directory_iterator` returns entries in an unspecified order, so a directory's entries must be collected and sorted before any is visited.

---

## Turn 3

### User

> Don't use directory_iterator.  write code to traverse the directory recursively in DFS order.  Prevent using directory name in skiplist

### Assistant

Applied the skip-list decision first, since it was unambiguous: §5 rule 4 lost its carve-out, so the list is consulted for every directory including root paths, and `/P build` is pruned before any entry is read. `search` returns `true` for a pruned root rather than `false`, which is reserved for a root that cannot be opened and drives Entry's `cannot open` notice. Noted that no parent change was needed — parent §3.2 already said any directory whose name appears in the list has its subtree pruned, so the carve-out had been the deviation.

Asked which API should list a single directory level, since hand-written recursion still needs one and the standard library offers only the filesystem iterators. Presented two options with code previews: `directory_iterator` for one level with the recursion hand-written, or POSIX `opendir`/`readdir` and Windows `FindFirstFileW`/`FindNextFileW` behind a platform shim — noting the second costs a platform-abstraction section and conflicts with parent §6, which restricts implementations to the standard library.

### User

Selected: **directory_iterator, one level only**

### Assistant

Rewrote §5 rule 2 as "Order and descent": the recursion is written explicitly as one function that lists a directory, sorts its entries, then calls itself on each subdirectory it decides to enter; `std::filesystem::recursive_directory_iterator` is excluded by name so the library controls its own descent; `std::filesystem::directory_iterator` enumerates a single level only, with the sort still required because it yields entries in an unspecified order.

---

## Turn 4

### User

> create file Prompts_Spec_Cpp_TextFinder_Dirnav.md with content with prompts and replies used to create Spec_Cpp_TextFinder_Dirvnav.md

### Assistant

Created this file, [Prompts_Spec_Cpp_TextFinder_Dirnav.md](Prompts_Spec_Cpp_TextFinder_Dirnav.md), covering the initial draft, the move of traversal order into the parent, and the recursion and skip-list decisions. User prompts are quoted verbatim. Assistant replies are summarized from the actual responses; tool calls are noted as effects rather than transcribed.
Prompts_Fix_Spec_Cpp_TextFinder_Dirnav.md 
# Prompts and Replies — Spec_Cpp_TextFinder_Dirnav Refinement

This file records the prompts and replies exchanged while refining [Spec_Cpp_TextFinder_Dirnav.md](Spec_Cpp_TextFinder_Dirnav.md) after its initial draft. The four turns that produced it are recorded in [Prompts_Spec_Cpp_TextFinder_Dirnav.md](Prompts_Spec_Cpp_TextFinder_Dirnav.md). Most turns below changed [Spec_TextFinder.md](../../Spec_TextFinder.md) as well, and the last two also changed [Spec_Cpp_TextFinder_Cmdline.md](../Cpp_Spec_driven_Cmdline/Spec_Cpp_TextFinder_Cmdline.md), [Spec_Cpp_TextFinder_Entry.md](../Cpp_Spec_driven_TextFinder_Entry/Spec_Cpp_TextFinder_Entry.md), and [Cpp_TextFinder_Structure.md](../Cpp_TextFinder_Structure.md).

---

## Turn 1

### User

> thinking carfully, analyze this spec or ambiguities and parts that need improvement

### Assistant

Reviewed the spec and listed thirteen items in six groups, without editing.

**Internal inconsistencies:**

1. §8 said a record is emitted "before the next line is read," but §7 reads the whole file first — every line is already read. Introduced when whole-file validation was added.
2. `search` returned `false` both for a root that cannot be opened and for one that is neither file nor directory, so Entry would report `cannot open` for `/dev/null`.

**Gaps:**

3. A file that cannot be opened or read was unspecified — §5 rule 6 covered directories only, §7 covered UTF-8 failure only.
4. A root path that is itself a symbolic link fell through to rule 1, which would follow it.
5. The sort key was unspecified in C++ terms: on Windows `path::filename().native()` is UTF-16, which orders differently from UTF-8 above the BMP, defeating the cross-platform order the rule existed to guarantee.

**Behavior worth confirming:**

6. Under `/h true`, a matching file was announced and then emitted its records, printing the path twice — the literal reading of parent §5 and Entry §7, but not the common expectation.
7. "Last dot-suffix" disagrees with `std::filesystem::path::extension()`, which returns `""` for `.gitignore`.
8. With the default root `.`, every record would read `./src/foo.cpp`.

**Claims that may not hold:**

9. The assertion that an empty `/r` compiles and matches every line — `std::regex` handling of an empty pattern has varied across implementations.
10. A UTF-16LE file of ASCII text is valid UTF-8, so it passed validation and was searched fruitlessly, though parent §7 says binary files are not searched.

**Parent candidates:** 11. extension case-sensitivity by platform; 12. generic path rendering and the announcement wording, both raised before and still only in this spec.

**Practical:** 13. no size bound on the whole-file read.

Noted that items 1, 3, 5, and 10 were worth fixing whatever the preferences on the rest.

---

## Turn 2

### User

Provided decisions on all thirteen items:

> 1. fix
> 2. wording change in Entry
> 3. Intent is to react to any file or directory opening attempt that fails, with an identifying error message.
> 4. A rootpath failure is treated like any other failure (child directories will not be opened)
> 5. name u8string()
> 6. skip announcement, just show the match
> 7. show .[somefile] unless it is in the skiplist
> 8. normalize it away
> 9. The intent is to never have empty regex, e.g., use "." default to match all files
> 10. Use NUL-byte test
> 11. move to parent spec
> 12. fix
> 13. set bound at 10 MBytes, provide error message if exceeded.
>
> It looks like all of these belong in the Project spec

### Assistant

Agreed, and put ten of the thirteen in the parent, since each changes emitted output and so binds all four implementations.

[Spec_TextFinder.md](../../Spec_TextFinder.md) gained: symlink and non-file/non-directory root handling in §3.2; the three admission tests in §3.3 — 10 MB, no NUL byte, valid UTF-8 — with whole-file reading justified by "skipped entirely rather than searched in part"; path rendering and a four-row announcement table in §3.4 (`searched`, `skipped`, `too large`, `cannot open`) with the `/h` gating; the dotfile rule, extension case-sensitivity, the non-empty-regex requirement, and the new `/h` meaning across the `/p`, `/r`, and `/h` rows of §5; an empty-`/r` row in §5.2; and the NUL test named in §7.

This spec kept only the C++ bindings: `u8string()` as the extension source with the UTF-16 hazard stated, `path::extension()` rejected by name because it disagrees with §5 on dotfiles, `generic_u8string()` for records, and the size test applied to the filesystem-reported size so an oversized file is never read into memory. [Spec_Cpp_TextFinder_Cmdline.md](../Cpp_Spec_driven_Cmdline/Spec_Cpp_TextFinder_Cmdline.md) now rejects an empty `/r`; [Spec_Cpp_TextFinder_Entry.md](../Cpp_Spec_driven_TextFinder_Entry/Spec_Cpp_TextFinder_Entry.md) no longer formats root-path notices.

Flagged three consequences that went beyond the literal decisions:

- **`search` returns `void`.** Once Dirnav announces root failures too, the `bool` had no consumer, which dissolves item 2 rather than rewording it — Entry has nothing left to mislabel.
- **`too large` and `cannot open` ignore `/h`; `searched` and `skipped` obey it.** Item 6 suppressed announcements but item 3 wanted failures visible; silencing a 10 MB skip under the default would hide requested work that did not happen.
- **Symlinks are asymmetric.** One met during traversal is passed over silently, since no open is attempted and there is no failure to report; one named on `/P` is announced, per item 4.

---

## Turn 3

### User

> I don't like the idea of sorting filenames while processing a directory.  I think DFS requires visiting the elements, e.g., both files and subdirectories, in the order presented by the std library. Do you have any comments? Don't implement without my authorization

### Assistant

Gave comments without editing, including a correction.

On the definition: sorting does not stop it being DFS. Depth-first constrains descent — finish a subtree before moving on — not which sibling is taken first, so sorted order and library order are both DFS. The choice is about determinism.

On the risk, which the earlier review had overstated: the claim that two implementations would diverge at the first multi-entry directory is too strong. `directory_iterator`, Rust's `read_dir`, Python's `os.scandir`, and C#'s `EnumerateFileSystemEntries` all bottom out in `readdir` or `FindFirstFileW`, so on one machine against one tree the four implementations agree, and the cross-implementation purpose of parent §6 largely survives without sorting.

What does not survive: cross-platform runs, since NTFS returns uppercased-name index order while ext4 with `dir_index` returns hash order; stability over time, since ext4 hash order shifts as entries are added and removed, making golden-file tests unreliable; and agreement across filesystems. Also noted that the C++ standard leaves `directory_iterator` order unspecified, so "the order presented by the std library" is not itself a fixed thing.

Acknowledged the merit of the objection — library order streams instead of buffering a level, and reads more cleanly, which counts for a teaching codebase — and listed the three places that must change together so the spec would not claim what it no longer delivers: parent §3.2, parent §6 Consistency, and this spec's §5 rule 2.

---

## Turn 4

### User

> eliminate the file sorting

### Assistant

Removed sorting from all three places. Parent §3.2 keeps depth-first descent but visits entries in the order the platform's directory-reading facility presents them, with no reordering. Parent §6 Consistency now claims only what it delivers: the match set always agrees, and the full emission order is reproducible over the same tree on the same platform and filesystem, where all four implementations agree by reading through the same facility. Parent §3.4's emission paragraph stopped claiming a fixed cross-implementation order and points at §6.

In this spec, §5 rule 2 became one function that iterates a directory and recurses, entries handled as `directory_iterator` yields them, nothing collected; the `u8string()` sort key is gone, while `recursive_directory_iterator` remains excluded so the library keeps control of its own descent. Noted that `u8string()` survives in §6 for the unrelated purpose of extracting an extension.

---

## Turn 5

### User

> is there any text that can be removed without significantly affecting quality of the specification? Don't implement without my authorization

### Assistant

Read all four specs and reported removable text in three groups, without editing.

**Cross-document duplication:** toolchain minimums appeared verbatim in three component specs, and `Language: C++23` in those three plus the structure doc — a four-place edit whenever a floor moves.

**Duplication inside this spec:** six Responsibilities bullets all restated below; the same three root failures enumerated in §4 and §5 rule 1 four lines apart; the POSIX/Windows comparison rule restated in §5 rule 4 while also citing §3.2; §5 rule 5's second sentence pointing back to rule 1; §7's BOM and line-terminator sentences duplicating parent §3.3; §8's "occurs anywhere" and "one record per line" duplicating parent §3.3 and §3.4; and "everything leaves through `Output`" stated four times.

**Rationale in the parent:** nine tails a spec can leave implicit — the separator justification, the `/h` gating reason, the duplicate `/H` sentence, the UTF-16 explanation, the fixed-text reason, §7's announcement clause, §2's restatement of Constitution rule 1, §3.1's restatement of §4 and §5, and a five-sentence Consistency paragraph.

Recommended keeping the §5.1 help block and §5.2 table, whose redundancy against §5 is deliberate, and this spec's two warnings — `path::extension()` and `directory_iterator` — because each stops an implementer writing something plausible and wrong.

---

## Turn 6

### User

> cut all the text you recommend

### Assistant

Applied every cut. `Language: C++23`, the CMake declaration, and the toolchain floors moved to [Cpp_TextFinder_Structure.md](../Cpp_TextFinder_Structure.md), leaving each component spec's Build section with its own target name and module-versus-TU status. This spec went 105 to 99 lines and the parent 181 to 176; across the four specs, 460 to 446 lines and roughly 300 words, with no rule changed.

Noted afterward that parent §3.3 is now a denser paragraph carrying the whole-file read, all three admission tests, the NUL rationale, BOM handling, and the failure route, and that splitting the tests back into a list would cost about three lines.

---

## Turn 7

### User

> create Prompts_Fix_Cpp_TextFinder_Dirnav.md using all the prompts and replies not already recorded in Prompts_Cpp_TextFinder_Dirnav.md

### Assistant

Created this file, [Prompts_Fix_Spec_Cpp_TextFinder_Dirnav.md](Prompts_Fix_Spec_Cpp_TextFinder_Dirnav.md), covering the thirteen-item review, the decisions applied, the sorting discussion and its removal, and the text reduction. User prompts are quoted verbatim. Assistant replies are summarized from the actual responses; tool calls are noted as effects rather than transcribed.