From 7cd481e4c339f28f69ad5b947722243d87f2b8fc Mon Sep 17 00:00:00 2001
From: Alexander Medvednikov <alexander@medvednikov.com>
Date: Fri, 15 May 2026 13:49:27 +0300
Subject: [PATCH] os: fix read_file crash on Windows device files (TCC/GCC)

When reading device files like \\.\nul on Windows, fseek succeeds but
ftell returns -1. The old logic only checked for negative ftell when
fseek also failed, so -1 was passed to fread as SIZE_MAX, crashing
MinGW CRT. Return 0 to use the streaming fallback path instead.

Also fix Windows MSVC CI failures:
- cc_test.v: compare import lib filename instead of full path to avoid
  Windows path normalization issues in live reload linker args tests
- coutput_test.v: skip `-cc clang` tests on msvc-windows (same as
  tcc-windows) since clang-built V binaries crash on these CI runners
- repl_time_state_test.v: clear VFLAGS before starting REPL subprocess
  so fake cmd.exe in replfolder doesn't break MSVC detection
---
 vlib/os/os.c.v                                | 9 +++++++--
 vlib/v/builder/cc_test.v                      | 6 ++++--
 vlib/v/gen/c/coutput_test.v                   | 2 +-
 vlib/v/slow_tests/repl/repl_time_state_test.v | 3 +++
 4 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/vlib/os/os.c.v b/vlib/os/os.c.v
index d496a604c..1ca3052a9 100644
--- a/vlib/os/os.c.v
+++ b/vlib/os/os.c.v
@@ -107,8 +107,13 @@ fn find_cfile_size(fp &C.FILE) !int {
 	if raw_fsize != 0 && cseek != 0 {
 		return error('fseek failed')
 	}
-	if cseek != 0 && raw_fsize < 0 {
-		return error('ftell failed')
+	if raw_fsize < 0 {
+		if cseek != 0 {
+			return error('ftell failed')
+		}
+		// fseek succeeded but ftell returned -1 (e.g. device files like NUL on Windows).
+		// Treat as zero-size to use the streaming fallback path.
+		return 0
 	}
 	len := int(raw_fsize)
 	// For files > 2GB, C.ftell can return values that, when cast to `int`, can result in values below 0.
diff --git a/vlib/v/builder/cc_test.v b/vlib/v/builder/cc_test.v
index 801523d09..464b0ccfd 100644
--- a/vlib/v/builder/cc_test.v
+++ b/vlib/v/builder/cc_test.v
@@ -419,7 +419,8 @@ fn test_live_windows_main_linker_args_export_host_symbols() {
 	], .gcc)
 	assert linker_args.contains('-Wl,--export-all-symbols')
 	assert linker_args.contains('-Wl,--out-implib,')
-	assert normalized_test_path(linker_args).contains(normalized_test_path(live_windows_import_lib_path(hot_reload_graph_example())))
+	expected_import_lib := os.file_name(live_windows_import_lib_path(hot_reload_graph_example()))
+	assert linker_args.contains(expected_import_lib), 'linker_args should contain ${expected_import_lib}'
 }
 
 fn test_live_windows_shared_linker_args_include_host_import_lib() {
@@ -432,7 +433,8 @@ fn test_live_windows_shared_linker_args_include_host_import_lib() {
 		'-shared',
 		hot_reload_graph_example(),
 	], .gcc)
-	assert normalized_test_path(linker_args).contains(normalized_test_path(live_windows_import_lib_path(hot_reload_graph_example())))
+	expected_import_lib := os.file_name(live_windows_import_lib_path(hot_reload_graph_example()))
+	assert linker_args.contains(expected_import_lib), 'linker_args should contain ${expected_import_lib}'
 }
 
 fn test_windows_cross_compile_args_match_shared_prod_args() {
diff --git a/vlib/v/gen/c/coutput_test.v b/vlib/v/gen/c/coutput_test.v
index 8ad9165ec..534401109 100644
--- a/vlib/v/gen/c/coutput_test.v
+++ b/vlib/v/gen/c/coutput_test.v
@@ -740,7 +740,7 @@ fn should_skip(relpath string) bool {
 			return true
 		}
 	}
-	if github_job == 'tcc-windows' {
+	if github_job in ['tcc-windows', 'msvc-windows'] {
 		test_path := os.join_path(vroot, relpath)
 		file_options := get_file_options(test_path)
 		if file_options.vflags.contains('-cc clang') {
diff --git a/vlib/v/slow_tests/repl/repl_time_state_test.v b/vlib/v/slow_tests/repl/repl_time_state_test.v
index 21c8ab7f9..ca1995a26 100644
--- a/vlib/v/slow_tests/repl/repl_time_state_test.v
+++ b/vlib/v/slow_tests/repl/repl_time_state_test.v
@@ -69,8 +69,11 @@ fn test_repl_bypasses_local_cmd_exe_on_windows() {
 	assert build_fake_cmd.exit_code == 0, build_fake_cmd.output
 	original_vexe := os.getenv('VEXE')
 	os.setenv('VEXE', vexec, true)
+	original_vflags := os.getenv('VFLAGS')
+	os.setenv('VFLAGS', '', true)
 	defer {
 		os.setenv('VEXE', original_vexe, true)
+		os.setenv('VFLAGS', original_vflags, true)
 	}
 	mut repl := os.new_process(vexec)
 	repl.set_args(['repl', '-replfolder', temp_dir, '-replprefix', 'cmd_bypass.'])
-- 
2.39.5