From d02eaf28353db02fd0583e809352c99611032042 Mon Sep 17 00:00:00 2001
From: Alexander Medvednikov <alexander@medvednikov.com>
Date: Thu, 23 Apr 2026 19:45:46 +0300
Subject: [PATCH] pref: fix invalid option -- '-bt25' (fixes #18199)

---
 vlib/v/builder/cc_test.v    | 16 ++++++++++++++++
 vlib/v/builder/cc_windows.v |  1 +
 vlib/v/pref/default.v       |  6 +++---
 vlib/v/pref/pref_test.v     | 16 ++++++++++++++++
 4 files changed, 36 insertions(+), 3 deletions(-)

diff --git a/vlib/v/builder/cc_test.v b/vlib/v/builder/cc_test.v
index c319a894b..2c1bb7cfb 100644
--- a/vlib/v/builder/cc_test.v
+++ b/vlib/v/builder/cc_test.v
@@ -429,6 +429,22 @@ fn test_shared_windows_builds_do_not_add_subsystem_flags() {
 	assert !compile_args.contains('-mconsole')
 }
 
+fn test_shared_tcc_compile_args_skip_bt25_after_late_compiler_resolution() {
+	mut full_args := ['']
+	full_args << ['-shared', hello_world_example()]
+	mut prefs, _ := pref.parse_args_and_show_errors([], full_args, false)
+	prefs.ccompiler = 'tcc'
+	prefs.ccompiler_type = .tinyc
+	prefs.normalize_gc_defaults_for_resolved_ccompiler()
+	assert 'no_backtrace' in prefs.compile_defines_all
+
+	mut builder := new_builder(prefs)
+	builder.out_name_c = os.join_path(os.vtmp_dir(), 'builder_cc_test.tmp.c')
+	builder.setup_ccompiler_options(prefs.ccompiler)
+
+	assert !builder.get_compile_args().contains('-bt25')
+}
+
 fn test_should_use_rsp_for_linux_by_default() {
 	builder := new_test_builder([hello_world_example()])
 	assert builder.should_use_rsp(['-o', builder.out_name_c])
diff --git a/vlib/v/builder/cc_windows.v b/vlib/v/builder/cc_windows.v
index 9984aa984..f31a09bf4 100644
--- a/vlib/v/builder/cc_windows.v
+++ b/vlib/v/builder/cc_windows.v
@@ -40,6 +40,7 @@ pub fn (mut v Builder) find_win_cc() ! {
 				}
 				v.pref.ccompiler = thirdparty_tcc
 				v.pref.ccompiler_type = .tinyc
+				v.pref.normalize_gc_defaults_for_resolved_ccompiler()
 				return
 			}
 			v.cached_msvc = msvc
diff --git a/vlib/v/pref/default.v b/vlib/v/pref/default.v
index 57db5e087..1717e90d0 100644
--- a/vlib/v/pref/default.v
+++ b/vlib/v/pref/default.v
@@ -246,7 +246,6 @@ pub fn (mut p Preferences) fill_with_defaults() {
 	}
 	p.ccompiler_type = cc_from_string(p.ccompiler)
 	p.normalize_gc_defaults_for_resolved_ccompiler()
-	p.disable_tcc_shared_backtraces()
 	p.is_test = p.path.ends_with('_test.v') || p.path.ends_with('_test.vv')
 		|| p.path.all_before_last('.v').all_before_last('.').ends_with('_test')
 	p.is_vsh = p.path.ends_with('.vsh') || p.raw_vsh_tmp_prefix != ''
@@ -302,9 +301,10 @@ pub fn (mut p Preferences) fill_with_defaults() {
 	}
 }
 
-// normalize_gc_defaults_for_resolved_ccompiler clears stale default GC state
-// after the effective C compiler has been resolved.
+// normalize_gc_defaults_for_resolved_ccompiler clears stale compiler-dependent
+// defaults after the effective C compiler has been resolved.
 pub fn (mut p Preferences) normalize_gc_defaults_for_resolved_ccompiler() {
+	p.disable_tcc_shared_backtraces()
 	if p.os != .windows || p.ccompiler_type != .msvc || p.gc_set_by_flag {
 		return
 	}
diff --git a/vlib/v/pref/pref_test.v b/vlib/v/pref/pref_test.v
index 50adee0f2..f72249429 100644
--- a/vlib/v/pref/pref_test.v
+++ b/vlib/v/pref/pref_test.v
@@ -539,3 +539,19 @@ fn test_tcc_shared_builds_disable_backtraces() {
 	regular_prefs.fill_with_defaults()
 	assert 'no_backtrace' !in regular_prefs.compile_defines_all
 }
+
+fn test_late_resolved_tcc_shared_builds_disable_backtraces() {
+	mut shared_prefs := &pref.Preferences{
+		path:      'libfoo.v'
+		is_shared: true
+		ccompiler: 'gcc'
+	}
+	shared_prefs.fill_with_defaults()
+	assert 'no_backtrace' !in shared_prefs.compile_defines_all
+
+	shared_prefs.ccompiler_type = .tinyc
+	shared_prefs.normalize_gc_defaults_for_resolved_ccompiler()
+
+	assert 'no_backtrace' in shared_prefs.compile_defines_all
+	assert shared_prefs.build_options.contains('-d no_backtrace')
+}
-- 
2.39.5