test: sibling projects inherit the loading project's args

ProjectArgs loads a chain app -> lib -> leaf of LocalProjects with --debug
and a project flag. lib, loaded without .args, has to see both, and so
does its own sibling, which takes the default one level further down.
Copies loaded with `.args = {}` and with an explicit list get nothing and
exactly that list. The GitProjectSpec default is checked on the spec
itself, since a GitProject would need a repository to clone. Without the
defaults, five of its checks fail.

ProjectDependency now also loads its consumer with a project flag: the
pragma dependency must still come back with no args. Without the explicit
`.args = {}` in the pragma path it gets the consumer's flag.

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

tests/ProjectArgs/main.cpp

@@ -0,0 +1,91 @@
+// 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 GitProject or LocalProject without `.args` forwards the args of the
+// project file that declares it: both specs default their args to
+// ProjectArgs(). Before that default, every project.cpp with a sibling
+// dependency copied its span into a std::vector<std::string> for each spec,
+// and a spec that missed the copy built its sibling with none of the
+// project's flags: for the host while the project cross-compiled, and in
+// release while the project built --debug. The fixture is a chain
+// app -> lib -> leaf of LocalProjects; app also loads lib with an empty and
+// with a replaced list, and checks the GitProjectSpec default itself, which
+// a clone would need a repository for.
+namespace {
+    std::int32_t Failures = 0;
+
+    void Check(bool cond, std::string_view msg) {
+        if (!cond) {
+            std::println(std::cerr, "FAIL: {}", msg);
+            ++Failures;
+        }
+    }
+
+    // The single sibling lib and leaf declare, or nullptr.
+    const Configuration* OnlyDependency(const Configuration& cfg) {
+        return cfg.dependencies.size() == 1 ? cfg.dependencies[0] : nullptr;
+    }
+}
+
+int main() {
+    const fs::path installedHome = GetCrafterBuildHome();
+    if (!fs::exists(installedHome / "Crafter.Build.cppm")) {
+        std::println(std::cerr, "SKIP: no module sources at {}", installedHome.string());
+        return 77;
+    }
+
+    // Staged because LoadProject drops a build/ tree next to every project
+    // file it compiles.
+    const fs::path fixture = fs::current_path() / "tests" / "ProjectArgs" / "fixture";
+    const fs::path scratch = fs::temp_directory_path() / "crafter-build-project-args";
+    std::error_code ec;
+    fs::remove_all(scratch, ec);
+    fs::create_directories(scratch);
+    fs::copy(fixture, scratch, fs::copy_options::recursive);
+
+    Check(ProjectArgs().empty(), "no project args outside a project file");
+
+    // Loaded from the project's own directory, as crafter-build runs it: the
+    // fixture's LocalProject paths are relative to the working directory.
+    const fs::path cwd = fs::current_path();
+    fs::current_path(scratch / "app");
+    std::array<std::string_view, 2> args = { "--debug", "--flavor=x" };
+    const std::vector<std::string> flavor = { "--flavor=x" };
+    const std::vector<std::string> only = { "--only" };
+    try {
+        Configuration cfg = LoadProject("project.cpp", args);
+        Check(std::ranges::contains(cfg.compileFlags, "-DGIT_DEFAULT=1"), "a GitProjectSpec's args default to the project's own");
+        Check(cfg.dependencies.size() == 3, std::format("the project declared its three siblings (got {})", cfg.dependencies.size()));
+        if (cfg.dependencies.size() == 3) {
+            const Configuration& inherited = *cfg.dependencies[0];
+            const Configuration& none = *cfg.dependencies[1];
+            const Configuration& replaced = *cfg.dependencies[2];
+            Check(inherited.debug && inherited.projectArgs == flavor, std::format("a LocalProject without .args gets the project's args (debug {}, projectArgs {})", inherited.debug, inherited.projectArgs));
+            Check(!none.debug && none.projectArgs.empty(), std::format("`.args = {{}}` forwards nothing (debug {}, projectArgs {})", none.debug, none.projectArgs));
+            Check(!replaced.debug && replaced.projectArgs == only, std::format("an explicit list replaces the args rather than adding to them (debug {}, projectArgs {})", replaced.debug, replaced.projectArgs));
+            Check(&inherited != &none && &inherited != &replaced && &none != &replaced, "each list loads its own configuration");
+
+            // One sibling further down, the same default passes on what the
+            // middle project was given, not what the top one was.
+            const Configuration* inheritedLeaf = OnlyDependency(inherited);
+            Check(inheritedLeaf && inheritedLeaf->debug && inheritedLeaf->projectArgs == flavor, "the project's args reach its sibling's sibling");
+            const Configuration* noneLeaf = OnlyDependency(none);
+            Check(noneLeaf && !noneLeaf->debug && noneLeaf->projectArgs.empty(), "a sibling loaded with nothing passes nothing on");
+            const Configuration* replacedLeaf = OnlyDependency(replaced);
+            Check(replacedLeaf && !replacedLeaf->debug && replacedLeaf->projectArgs == only, "a sibling passes on the list it was given");
+        }
+    } catch (const std::exception& e) {
+        fs::current_path(cwd);
+        std::println(std::cerr, "FAIL: LoadProject threw: {}", e.what());
+        return 1;
+    }
+    fs::current_path(cwd);
+
+    Check(ProjectArgs().empty(), "no project args once the project file has returned");
+    return Failures > 0 ? 1 : 0;
+}