From be9ce00fc8850ff647b5b9d5e3034f97f5d08b40 Mon Sep 17 00:00:00 2001
From: Alexander Medvednikov <alexander@medvednikov.com>
Date: Thu, 23 Apr 2026 18:17:14 +0300
Subject: [PATCH] builder: fix Cross compiling for Linux on Windows does not
 work (fixes #12128)

---
 vlib/v/builder/builder_test.v      | 22 ++++++++++++++++++++++
 vlib/v/builder/cbuilder/cbuilder.v | 12 +++++++-----
 vlib/v/builder/compile.v           |  7 ++++++-
 vlib/v/pref/pref_test.v            |  1 +
 4 files changed, 36 insertions(+), 6 deletions(-)

diff --git a/vlib/v/builder/builder_test.v b/vlib/v/builder/builder_test.v
index fa9753360..27d163e3b 100644
--- a/vlib/v/builder/builder_test.v
+++ b/vlib/v/builder/builder_test.v
@@ -1,6 +1,8 @@
 module main
 
 import os
+import v.builder
+import v.pref
 
 const vexe = @VEXE
 const test_path = os.join_path(os.vtmp_dir(), 'run_check')
@@ -226,6 +228,26 @@ fn test_missing_library_is_reported_without_compiler_bug_hint() {
 	assert !normalized_output.contains('This is a V compiler bug')
 }
 
+fn test_windows_host_c_compiler_probe_is_skipped_for_non_windows_targets() {
+	assert builder.should_find_windows_host_c_compiler(&pref.Preferences{
+		backend: .c
+		os:      .windows
+	})
+	assert !builder.should_find_windows_host_c_compiler(&pref.Preferences{
+		backend: .c
+		os:      .linux
+	})
+	assert !builder.should_find_windows_host_c_compiler(&pref.Preferences{
+		backend:        .c
+		os:             .windows
+		output_cross_c: true
+	})
+	assert !builder.should_find_windows_host_c_compiler(&pref.Preferences{
+		backend: .js_browser
+		os:      .windows
+	})
+}
+
 fn test_run_with_obscure_source_filenames() {
 	if os.user_os() == 'windows' {
 		return
diff --git a/vlib/v/builder/cbuilder/cbuilder.v b/vlib/v/builder/cbuilder/cbuilder.v
index 719143b1d..c1a331118 100644
--- a/vlib/v/builder/cbuilder/cbuilder.v
+++ b/vlib/v/builder/cbuilder/cbuilder.v
@@ -18,11 +18,12 @@ pub fn compile_c(mut b builder.Builder) {
 		println('all .v files before:')
 	}
 	$if windows {
-		b.find_win_cc() or {
-			if b.pref.ccompiler_set_by_flag && b.pref.ccompiler != 'msvc' {
-				builder.verror(err.msg())
-			}
-			builder.verror('
+		if builder.should_find_windows_host_c_compiler(b.pref) {
+			b.find_win_cc() or {
+				if b.pref.ccompiler_set_by_flag && b.pref.ccompiler != 'msvc' {
+					builder.verror(err.msg())
+				}
+				builder.verror('
 ==================
 Error: no C compiler detected.
 
@@ -37,6 +38,7 @@ You can also use `v doctor`, to see what V knows about your current environment.
 
 You can also seek #help on Discord: https://discord.gg/vlang
 ')
+			}
 		}
 	}
 	mut files := b.get_builtin_files()
diff --git a/vlib/v/builder/compile.v b/vlib/v/builder/compile.v
index 8e587187c..e23948fd2 100644
--- a/vlib/v/builder/compile.v
+++ b/vlib/v/builder/compile.v
@@ -10,11 +10,16 @@ import v.vmod
 
 pub type FnBackend = fn (mut b Builder)
 
+// should_find_windows_host_c_compiler reports whether Windows host compiler probing is needed.
+pub fn should_find_windows_host_c_compiler(pref_ &pref.Preferences) bool {
+	return pref_.backend == .c && pref_.os == .windows && !pref_.output_cross_c
+}
+
 pub fn compile(command string, pref_ &pref.Preferences, backend_cb FnBackend) {
 	check_if_input_file_exists(pref_)
 	check_if_output_folder_is_writable(pref_)
 	$if windows {
-		if pref_.backend == .c {
+		if should_find_windows_host_c_compiler(pref_) {
 			// Resolve the effective Windows C compiler before builder initialization.
 			mut probe := Builder{
 				pref: unsafe { pref_ }
diff --git a/vlib/v/pref/pref_test.v b/vlib/v/pref/pref_test.v
index 1a653d847..18acab9b0 100644
--- a/vlib/v/pref/pref_test.v
+++ b/vlib/v/pref/pref_test.v
@@ -230,6 +230,7 @@ fn test_cross_compile_defaults_linux_to_amd64() {
 	target := os.join_path(vroot, 'examples', 'hello_world.v')
 	prefs, _ := pref.parse_args_and_show_errors([], ['', '-os', 'linux', target], false)
 	assert prefs.arch == .amd64
+	assert prefs.ccompiler == 'clang'
 }
 
 fn test_cross_compile_infers_android_arch_from_vcross_compiler_name() {
-- 
2.39.5