v3: clean up transform helpers/inits; cmd/v: fix v3.v bootstrap dispatch on macOS (#28157)

Author: medvednikov

cmd/v/macos_v3_args.c.v

@@ -19,6 +19,27 @@ fn macos_v3_non_compilation_command(command string) bool {
 		'interpret', 'get', 'translate']
 }
 
+// is_macos_v3_compiler_bootstrap reports whether `normalized_path` targets the
+// `vlib/v3/v3.v` compiler bootstrap, which must build with the compatibility
+// compiler rather than the embedded V3 driver. It matches the repo-relative path
+// and any path ending in it, and also resolves a bare `v3.v` (for example when
+// invoked from inside `vlib/v3`) through its real path, so the bootstrap is
+// recognized regardless of the working directory. Both dispatch gates rely on
+// it, so keep the detection in one place to stop them drifting.
+@[markused]
+fn is_macos_v3_compiler_bootstrap(normalized_path string) bool {
+	if normalized_path == 'vlib/v3/v3.v' || normalized_path.ends_with('/vlib/v3/v3.v') {
+		return true
+	}
+	// Only a file literally named `v3.v` can be the bootstrap; skip the real-path
+	// resolution (a filesystem lookup) for every other compilation target.
+	if os.base(normalized_path) != 'v3.v' {
+		return false
+	}
+	real_path := os.real_path(normalized_path).replace('\\', '/').trim_right('/')
+	return real_path == 'vlib/v3/v3.v' || real_path.ends_with('/vlib/v3/v3.v')
+}
+
 // macos_v3_force_requested reports whether `-new-compiler` should hand this
 // invocation to the embedded V3 compiler. It gates on `-old-compiler`
 // precedence, options/modes V3 cannot honor yet, and whether the command is an
@@ -44,7 +65,7 @@ fn macos_v3_force_requested(command string, prefs &pref.Preferences) bool {
 	normalized_path := prefs.path.replace('\\', '/').trim_right('/')
 	if normalized_path == 'cmd/v' || normalized_path.starts_with('cmd/v/')
 		|| normalized_path.contains('/cmd/v/') || normalized_path.ends_with('/cmd/v')
-		|| normalized_path == 'vlib/v3/v3.v' || normalized_path.ends_with('/vlib/v3/v3.v') {
+		|| is_macos_v3_compiler_bootstrap(normalized_path) {
 		return false
 	}
 	return command in ['run', 'build'] || prefs.is_script || os.is_dir(prefs.path)

cmd/v/macos_v3_darwin.c.v

@@ -95,7 +95,7 @@ fn is_macos_v3_relevant_command(command string, prefs &pref.Preferences) bool {
 	// modes use V3 by default.
 	if normalized_path == 'cmd/v' || normalized_path.starts_with('cmd/v/')
 		|| normalized_path.contains('/cmd/v/') || normalized_path.ends_with('/cmd/v')
-		|| normalized_path == 'vlib/v3/v3.v' || normalized_path.ends_with('/vlib/v3/v3.v')
+		|| is_macos_v3_compiler_bootstrap(normalized_path)
 		|| is_macos_v3_internal_tool_bootstrap(normalized_path, os.getenv('VCHILD') == 'true') {
 		return false
 	}

cmd/v/macos_v3_test.v

@@ -217,6 +217,47 @@ fn test_macos_v3_relevant_command_selects_user_compilation_and_tests() {
 	}
 }
 
+fn test_macos_v3_compiler_bootstrap_is_detected_from_any_cwd() {
+	// Repo-relative and absolute spellings are recognized directly.
+	assert is_macos_v3_compiler_bootstrap('vlib/v3/v3.v')
+	assert is_macos_v3_compiler_bootstrap('/home/user/v/vlib/v3/v3.v')
+	// Non-bootstrap targets stay on the V3 path.
+	assert !is_macos_v3_compiler_bootstrap('main.v')
+	assert !is_macos_v3_compiler_bootstrap('cmd/v')
+	assert !is_macos_v3_compiler_bootstrap('some/other/place/v3.v')
+
+	// A bare `v3.v` invoked from inside vlib/v3 must resolve to the bootstrap so
+	// it builds with the compatibility compiler instead of the embedded V3 driver.
+	// Use an isolated <tmp>/vlib/v3/v3.v so this exercises the real-path
+	// resolution unconditionally, independent of where this test file lives.
+	root := os.join_path(os.real_path(os.vtmp_dir()), 'macos_v3_bootstrap_${os.getpid()}')
+	v3_dir := os.join_path(root, 'vlib', 'v3')
+	other_dir := os.join_path(root, 'elsewhere')
+	os.rmdir_all(root) or {}
+	os.mkdir_all(v3_dir) or { panic(err) }
+	os.mkdir_all(other_dir) or { panic(err) }
+	defer {
+		os.rmdir_all(root) or {}
+	}
+	os.write_file(os.join_path(v3_dir, 'v3.v'), 'module main\n') or { panic(err) }
+	os.write_file(os.join_path(other_dir, 'v3.v'), 'module main\n') or { panic(err) }
+
+	saved := os.getwd()
+	defer {
+		os.chdir(saved) or {}
+	}
+	os.chdir(v3_dir) or { panic(err) }
+	bare := is_macos_v3_compiler_bootstrap('v3.v')
+	dotted := is_macos_v3_compiler_bootstrap('./v3.v')
+	// A bare `v3.v` that is not under vlib/v3 must stay on the V3 path.
+	os.chdir(other_dir) or { panic(err) }
+	non_bootstrap := is_macos_v3_compiler_bootstrap('v3.v')
+	os.chdir(saved) or {}
+	assert bare
+	assert dotted
+	assert !non_bootstrap
+}
+
 fn test_macos_v3_dispatch_allows_the_implicit_gc_default() {
 	$if macos {
 		implicit_gc, _ := pref.parse_args_and_show_errors([], ['', 'main.v'], false)