fix: rebuild and relink on what changed, submodules at their revisions, and mingw found where it is

- Shaders record the files glslang opened (a depfile) and their settings
  (source path, stage, entry point, defines, include directories) in the
  build directory, and rebuild when an included file or a setting changes,
  not only the shader's own source.
- An executable relinks when its link command changed, not only when an
  object is newer: a link flag in project.cpp, or a dependency's library
  that moved (an ExternalDependency built into a new cache directory). The
  command is recorded beside the objects; its flags come from ordered sets,
  so the order the dependency threads finish in can't change it.
- An external's newest artifact counts its libDirs and versioned .so names.
- Submodules are checked out at the revisions the fetched commit records,
  from the URLs its .gitmodules gives, after every clone, switch, checkout
  and pull, so a pinned commit builds against its own submodules, and one
  moved by hand is put back; with no .gitmodules, git isn't asked.
- Each external clone's fetch and build hold a file lock: parallel builds
  pulled into one clone at once ("cannot lock ref").
- mingw:
  - -stdlib=libstdc++ always;
  - the std module's source is found through libstdc++.modules.json in the
    mingw toolchain's own library directories (the generic lib/ holds the
    host's Linux one), asking the compiler once a run;
  - a toolchain that isn't there is a build error saying where it looked,
    not std::terminate;
  - CRAFTER_MINGW_DIR names the prefix, the directory holding
    x86_64-w64-mingw32/ and lib/gcc/;
  - inside the Flatpak the host's /usr mingw is used.
- RunScript's exit-status check reads as the one range it is.
- Tests: ConcurrentExternalFetch, ExternalArtifactTime, GitSubmodules,
  LinkFlagsChange, MingwMissing, ShaderIncludeChange; ShaderCompile and
  ToolchainResolve extended.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/ShaderIncludeChange/main.cpp

@@ -0,0 +1,126 @@
+// SPDX-License-Identifier: LGPL-3.0-only
+// SPDX-FileCopyrightText: Copyright (C) 2026 Catcrafts®
+
+import std;
+import Crafter.Build;
+namespace fs = std::filesystem;
+using namespace Crafter;
+
+// A shader's output is stale when anything that went into it changed, not
+// only its own source. Check() used to compare the .spv against the source's
+// mtime alone, so:
+//   - editing a file the shader #includes left the .spv built against the old
+//     contents, the GLSL twin of IncrementalHeaderChange;
+//   - changing an entry's defines without touching the source did too.
+// Each pass changes one thing and checks both directions: the shader it
+// reaches is recompiled, to new contents, and the shader that includes
+// nothing is left alone. A build with nothing changed compiles nothing.
+namespace {
+    std::int32_t failures = 0;
+
+    void Check(bool cond, std::string_view msg) {
+        if (!cond) {
+            std::println(std::cerr, "FAIL: {}", msg);
+            ++failures;
+        }
+    }
+
+    // The fixture is edited between passes, so work on a copy outside the repo.
+    fs::path StageFixture() {
+        fs::path source = fs::current_path() / "tests" / "ShaderIncludeChange" / "fixture";
+        fs::path staged = fs::temp_directory_path() / "crafter-build-shader-include-change";
+        fs::remove_all(staged);
+        fs::copy(source, staged, fs::copy_options::recursive);
+        return staged;
+    }
+
+    Configuration MakeApp(const fs::path& staged) {
+        Configuration app;
+        app.path = staged;
+        app.name = "lit";
+        app.outputName = "lit";
+        app.target = HostTarget();
+        app.type = ConfigurationType::Executable;
+        std::array<fs::path, 0> ifaces = {};
+        std::array<fs::path, 1> impls = { "main" };
+        app.GetInterfacesAndImplementations(ifaces, impls);
+        app.shaders.emplace_back(staged / "lit.frag", std::string("main"), ShaderType::Fragment);
+        app.shaders.emplace_back(staged / "plain.frag", std::string("main"), ShaderType::Fragment);
+        // Puts include/ on the shaders' #include path.
+        app.buildFiles = { staged / "include" / "palette.glsl" };
+        return app;
+    }
+
+    bool BuildOk(Configuration& app, std::string_view label) {
+        // A fresh depResults per pass: the map memoizes a Configuration's
+        // build for the duration of one pass.
+        std::unordered_map<fs::path, std::shared_future<BuildResult>> depResults;
+        std::mutex depMutex;
+        BuildResult r = Build(app, depResults, depMutex);
+        Check(r.result.empty(), std::format("{} builds: {}", label, r.result));
+        return r.result.empty();
+    }
+
+    std::string ReadAll(const fs::path& file) {
+        std::ifstream stream(file, std::ios::binary);
+        return std::string(std::istreambuf_iterator<char>(stream), std::istreambuf_iterator<char>());
+    }
+}
+
+int main() {
+    const fs::path staged = StageFixture();
+    Configuration app = MakeApp(staged);
+    const fs::path lit = app.BinDir() / "lit.spv";
+    const fs::path plain = app.BinDir() / "plain.spv";
+    const fs::path palette = staged / "include" / "palette.glsl";
+
+    // Pass 1: everything from scratch.
+    if (!BuildOk(app, "the first pass")) return 1;
+    Check(fs::exists(lit) && fs::exists(plain), "both shaders are in the bin dir");
+    const fs::file_time_type plainBuilt = fs::last_write_time(plain);
+    const std::string green = ReadAll(lit);
+
+    // Pass 2: nothing changed.
+    fs::file_time_type litBuilt = fs::last_write_time(lit);
+    BuildOk(app, "an unchanged project");
+    Check(fs::last_write_time(lit) == litBuilt && fs::last_write_time(plain) == plainBuilt, "with nothing changed, no shader is recompiled");
+
+    // Pass 3: the included file changes. Dated just after the output it must
+    // outdate, so the rebuilt output is newer than it again.
+    {
+        std::ofstream out(palette, std::ios::trunc);
+        out << "const vec4 kTint = vec4(1.0, 0.0, 0.0, 1.0);\n";
+    }
+    fs::last_write_time(palette, litBuilt + std::chrono::milliseconds(1));
+    BuildOk(app, "an edited include");
+    const std::string red = ReadAll(lit);
+    Check(fs::last_write_time(lit) > litBuilt && red != green, "editing an included file recompiles the shader that includes it, to new contents");
+    Check(fs::last_write_time(plain) == plainBuilt, "and leaves the shader that includes nothing alone");
+
+    // Pass 4: the entry's defines change, no file does.
+    app.shaders[0].defines = { "LIT_DIM" };
+    litBuilt = fs::last_write_time(lit);
+    BuildOk(app, "a new define");
+    const std::string dim = ReadAll(lit);
+    Check(fs::last_write_time(lit) > litBuilt && dim != red, "a define added to the entry recompiles it, taking the #ifdef branch");
+    Check(fs::last_write_time(plain) == plainBuilt, "and leaves the other entry alone");
+
+    // Pass 5: and back.
+    app.shaders[0].defines = {};
+    BuildOk(app, "the define taken out");
+    Check(ReadAll(lit) == red, "taking the define out again recompiles it as it was");
+
+    // Pass 6: nothing changed again; what the passes above recorded holds.
+    litBuilt = fs::last_write_time(lit);
+    BuildOk(app, "an unchanged project, again");
+    Check(fs::last_write_time(lit) == litBuilt && fs::last_write_time(plain) == plainBuilt, "with nothing changed since, no shader is recompiled");
+
+    std::error_code ec;
+    fs::remove_all(staged, ec);
+
+    if (failures > 0) {
+        std::println(std::cerr, "{} assertions failed", failures);
+        return 1;
+    }
+    return 0;
+}