fix(workspace): anchor an inherited include_dirs to the workspace root

Found by re-reading the merge, not by a failure. `[workspace.build]
include_dirs = ["shared/inc"]` was prepended to each member verbatim, so every
member resolved it against its OWN directory — looking for
`<member>/shared/inc` for a directory that lives at `<workspace>/shared/inc`.

This is #224 for a new key. `[indices].path` and `[workspace.dependencies]
path` are anchored to the workspace root for exactly this reason, and a third
relative-path key that skipped it fails as a missing header three members deep,
naming neither the manifest that declared it nor the root it was written
against. Anchored rather than refused: `expandIncludeDirs` already accepts an
absolute include directory, so the anchored form needs nothing downstream.

321 now includes a header from the workspace root, so the anchoring has an
assertion rather than a comment.

Author: speak-agent

src/project.cppm

@@ -201,9 +201,32 @@ export void inherit_workspace_config(mcpp::manifest::Manifest& member,
         prepend(b.ldflags,  w.ldflags);
         prepend(b.defines,  w.defines);
         prepend(b.dialectCxxflags, w.dialectCxxflags);
-        prepend(b.includeDirs,        w.includeDirs);
-        prepend(b.includeDirsAfter,   w.includeDirsAfter);
-        prepend(b.privateIncludeDirs, w.privateIncludeDirs);
+        // A RELATIVE INCLUDE DIRECTORY IN THE WORKSPACE MANIFEST WAS WRITTEN
+        // AGAINST THE WORKSPACE ROOT, and every member would otherwise resolve
+        // it against its own directory.
+        //
+        // This is #224 for a new key: `[indices].path` and
+        // `[workspace.dependencies] path` are anchored for exactly this reason,
+        // and a third relative-path key that skipped it would silently point at
+        // `<member>/shared/inc` for a directory that lives at
+        // `<workspace>/shared/inc`. The failure is a missing header, three
+        // members deep, naming neither the manifest that declared it nor the
+        // root it was declared against.
+        //
+        // Anchored rather than refused: an absolute include directory is
+        // already accepted by `expandIncludeDirs`, so the anchored form needs
+        // no new handling downstream.
+        auto anchored = [&](const std::vector<std::filesystem::path>& src) {
+            std::vector<std::filesystem::path> out;
+            out.reserve(src.size());
+            for (auto const& d : src)
+                out.push_back(d.is_absolute() ? d
+                                              : (wsRoot / d).lexically_normal());
+            return out;
+        };
+        prepend(b.includeDirs,        anchored(w.includeDirs));
+        prepend(b.includeDirsAfter,   anchored(w.includeDirsAfter));
+        prepend(b.privateIncludeDirs, anchored(w.privateIncludeDirs));
         if (b.cStandard.empty())            b.cStandard            = w.cStandard;
         if (b.linkage.empty())              b.linkage              = w.linkage;
         if (b.target.empty())               b.target               = w.target;

tests/e2e/321_workspace_inheritance.sh

@@ -24,7 +24,8 @@ TMP=$(mktemp -d)
 trap "rm -rf $TMP" EXIT
 cd "$TMP"
 
-mkdir -p silent/src pinned/src adds/src
+mkdir -p silent/src pinned/src adds/src shared/inc
+printf '#define SHARED_HEADER_FOUND 1\n' > shared/inc/shared.h
 
 cat > mcpp.toml <<'EOF'
 [workspace]
@@ -36,7 +37,8 @@ version  = "0.4.2"
 license  = "Apache-2.0"
 
 [workspace.build]
-cxxflags = ["-DFROM_WORKSPACE=1"]
+cxxflags     = ["-DFROM_WORKSPACE=1"]
+include_dirs = ["shared/inc"]
 EOF
 
 # `version` is deliberately absent from every member: it is a required field,
@@ -46,7 +48,12 @@ printf '[package]\nname = "silent"\n' > silent/mcpp.toml
 printf '[package]\nname = "pinned"\nstandard = "c++23"\n' > pinned/mcpp.toml
 printf '[package]\nname = "adds"\n\n[build]\ncxxflags = ["-DFROM_MEMBER=1"]\n' > adds/mcpp.toml
 for m in silent pinned adds; do
-    printf '#ifndef FROM_WORKSPACE\n#error "workspace [build] did not reach the member"\n#endif\nint main(){return 0;}\n' > "$m/src/main.cpp"
+    # The include also proves the workspace-relative path was anchored to the
+    # WORKSPACE ROOT and not to each member: `shared/inc` lives at
+    # `<workspace>/shared/inc`, and resolving it per-member would look for
+    # `<member>/shared/inc` and fail with a missing header three members deep,
+    # naming neither the manifest that declared it nor the root it meant.
+    printf '#include <shared.h>\n#if !defined(FROM_WORKSPACE) || !defined(SHARED_HEADER_FOUND)\n#error "workspace [build] did not reach the member"\n#endif\nint main(){return 0;}\n' > "$m/src/main.cpp"
 done
 
 flags_of() {  # $1 = member dir