From 0c5d95a80ad9b80fa09bf7515043cf458333ed3c Mon Sep 17 00:00:00 2001
From: Alexander Medvednikov <alexander@medvednikov.com>
Date: Sun, 24 May 2026 19:10:47 +0300
Subject: [PATCH] pref: fall back to bundled tcc on Windows when gcc is not in
 PATH (fix #27119) (#27233)

---
 vlib/v/pref/default.v                   | 26 ++++++++++-
 vlib/v/pref/default_tcc_compiler_test.v | 61 +++++++++++++++++++++++++
 2 files changed, 86 insertions(+), 1 deletion(-)

diff --git a/vlib/v/pref/default.v b/vlib/v/pref/default.v
index 6b99e48fc..f1394df37 100644
--- a/vlib/v/pref/default.v
+++ b/vlib/v/pref/default.v
@@ -468,6 +468,23 @@ pub fn default_tcc_compiler() string {
 	return usable_system_tcc_compiler()
 }
 
+// windows_default_c_compiler picks the host C compiler to default to on Windows.
+// `gcc` is the historical default, but plenty of Windows users only have the
+// bundled tcc that `makev.bat` provisions under `thirdparty/tcc/tcc.exe`.
+// Falling back to the bundled tcc when `gcc` isn't on PATH avoids confusing
+// "'gcc' is not recognized as an internal or external command" errors during
+// `v install`, `v outdated`, etc. (https://github.com/vlang/v/issues/27119).
+fn windows_default_c_compiler(vroot string) string {
+	if os.find_abs_path_of_executable('gcc') or { '' } != '' {
+		return 'gcc'
+	}
+	bundled_tcc := usable_bundled_tcc_compiler(vroot)
+	if bundled_tcc != '' {
+		return bundled_tcc
+	}
+	return 'gcc'
+}
+
 fn (mut p Preferences) clear_gc_options() {
 	p.compile_defines = p.compile_defines.filter(it !in windows_default_gc_defines)
 	p.compile_defines_all = p.compile_defines_all.filter(it !in windows_default_gc_defines)
@@ -503,7 +520,14 @@ fn (mut p Preferences) clear_gc_options() {
 pub fn (mut p Preferences) default_c_compiler() {
 	// TODO: fix $if after 'string'
 	$if windows {
-		p.ccompiler = 'gcc'
+		// -prealloc and -prod intentionally avoid the bundled tcc (see
+		// try_to_use_tcc_by_default); preserve that here so the Windows fallback
+		// does not silently re-select an incompatible compiler.
+		if p.prealloc || p.is_prod {
+			p.ccompiler = 'gcc'
+			return
+		}
+		p.ccompiler = windows_default_c_compiler(os.dir(vexe_path()))
 		return
 	}
 	if p.os == .ios {
diff --git a/vlib/v/pref/default_tcc_compiler_test.v b/vlib/v/pref/default_tcc_compiler_test.v
index bf107ca58..e74aeb18f 100644
--- a/vlib/v/pref/default_tcc_compiler_test.v
+++ b/vlib/v/pref/default_tcc_compiler_test.v
@@ -220,6 +220,67 @@ fn test_try_to_use_tcc_by_default_resolves_explicit_tcc_to_system_tcc_on_termux(
 	assert prefs.ccompiler == system_tcc
 }
 
+fn test_windows_default_c_compiler_prefers_gcc_when_available() {
+	$if windows {
+		return
+	}
+	test_root := os.join_path(os.vtmp_dir(), 'v_pref_default_c_compiler_test')
+	prepare_test_tcc_binary(test_root, 'exit 0')
+	fake_gcc := prepare_test_executable(test_root, 'bin/gcc', 'exit 0')
+	old_path := os.getenv('PATH')
+	os.setenv('PATH', os.dir(fake_gcc), true)
+	defer {
+		os.setenv('PATH', old_path, true)
+		os.rmdir_all(test_root) or {}
+	}
+	assert windows_default_c_compiler(test_root) == 'gcc'
+}
+
+fn test_windows_default_c_compiler_falls_back_to_bundled_tcc_when_no_gcc() {
+	$if windows {
+		return
+	}
+	test_root := os.join_path(os.vtmp_dir(), 'v_pref_default_c_compiler_test')
+	tcc_path := prepare_test_tcc_binary(test_root, 'exit 0')
+	old_path := os.getenv('PATH')
+	os.setenv('PATH', os.join_path(test_root, 'no_such_path'), true)
+	defer {
+		os.setenv('PATH', old_path, true)
+		os.rmdir_all(test_root) or {}
+	}
+	assert windows_default_c_compiler(test_root) == tcc_path
+}
+
+fn test_windows_default_c_compiler_keeps_gcc_when_bundled_tcc_is_broken() {
+	$if windows {
+		return
+	}
+	test_root := os.join_path(os.vtmp_dir(), 'v_pref_default_c_compiler_test')
+	prepare_test_tcc_binary(test_root, 'exit 1')
+	old_path := os.getenv('PATH')
+	os.setenv('PATH', os.join_path(test_root, 'no_such_path'), true)
+	defer {
+		os.setenv('PATH', old_path, true)
+		os.rmdir_all(test_root) or {}
+	}
+	assert windows_default_c_compiler(test_root) == 'gcc'
+}
+
+fn test_windows_default_c_compiler_keeps_gcc_when_neither_is_available() {
+	$if windows {
+		return
+	}
+	test_root := os.join_path(os.vtmp_dir(), 'v_pref_default_c_compiler_test')
+	os.rmdir_all(test_root) or {}
+	old_path := os.getenv('PATH')
+	os.setenv('PATH', os.join_path(test_root, 'no_such_path'), true)
+	defer {
+		os.setenv('PATH', old_path, true)
+		os.rmdir_all(test_root) or {}
+	}
+	assert windows_default_c_compiler(test_root) == 'gcc'
+}
+
 fn prepare_test_executable(test_root string, relative_path string, exit_line string) string {
 	path := os.join_path(test_root, relative_path)
 	os.mkdir_all(os.dir(path)) or { panic(err) }
-- 
2.39.5