zencore: implement SearchPathForExecutable on POSIX (#981)

- The Linux/macOS branch of `SearchPathForExecutable` was previously a no-op that returned the input unchanged. Callers passing a bare executable name (e.g. `llvm-symbolizer`) got the same bare name back even when the binary lived elsewhere on `PATH`.
- Now walks `$PATH` like `execvp` does: skip the search if the input contains a `/`, try each colon-separated entry (empty entry == cwd), and return the first candidate that is both a regular file and executable by the current user. Falls back to returning the input unchanged if nothing matches, preserving the previous behavior for the no-match case.
- Windows branch is unchanged (still uses `SearchPathW`).

1 files changed, 32 insertions, 1 deletions

diff --git a/src/zencore/filesystem.cpp b/src/zencore/filesystem.cpp
index 08e921293..03e04c77c 100644
--- a/src/zencore/filesystem.cpp
+++ b/src/zencore/filesystem.cpp
@@ -3183,7 +3183,38 @@ SearchPathForExecutable(std::string_view ExecutableName)
 
 	return PathBuffer.get();
 #else
-	return ExecutableName;
+	// If the name already contains a path separator, don't search PATH
+	// (matches the shell / execvp semantics).
+	if (ExecutableName.find('/') != std::string_view::npos)
+	{
+		return std::filesystem::path(ExecutableName);
+	}
+
+	const char* PathEnv = ::getenv("PATH");
+	if (PathEnv == nullptr || *PathEnv == '\0')
+	{
+		return std::filesystem::path(ExecutableName);
+	}
+
+	std::string_view PathView(PathEnv);
+	while (!PathView.empty())
+	{
+		size_t			 Sep = PathView.find(':');
+		std::string_view Dir = (Sep == std::string_view::npos) ? PathView : PathView.substr(0, Sep);
+		PathView			 = (Sep == std::string_view::npos) ? std::string_view{} : PathView.substr(Sep + 1);
+
+		// An empty entry in PATH is interpreted as the current directory.
+		std::filesystem::path Candidate = Dir.empty() ? std::filesystem::path(".") : std::filesystem::path(Dir);
+		Candidate /= ExecutableName;
+
+		std::error_code Ec;
+		if (std::filesystem::is_regular_file(Candidate, Ec) && ::access(Candidate.c_str(), X_OK) == 0)
+		{
+			return Candidate;
+		}
+	}
+
+	return std::filesystem::path(ExecutableName);
 #endif
 }