windows: simplify DLL init test and improve README

src/main_c.zig

@@ -17,53 +17,6 @@ const state = &@import("global.zig").state;
 const apprt = @import("apprt.zig");
 const internal_os = @import("os/main.zig");
 
-// On Windows, Zig's _DllMainCRTStartup does not initialize the MSVC C
-// runtime when targeting MSVC ABI. Without initialization, any C library
-// function that depends on CRT internal state (setlocale, malloc from C
-// dependencies, C++ constructors in glslang) crashes with null pointer
-// dereferences. Declaring DllMain causes Zig's start.zig to call it
-// during DLL_PROCESS_ATTACH/DETACH, and we forward to the CRT bootstrap
-// functions from libvcruntime and libucrt (already linked).
-//
-// This is a workaround. Zig handles MinGW DLLs correctly (via dllcrt2.obj)
-// but not MSVC. No upstream issue tracks this exact gap as of 2026-03-26.
-// Closest: Codeberg ziglang/zig #30936 (reimplement crt0 code).
-// Remove this DllMain when Zig handles MSVC DLL CRT init natively.
-pub const DllMain = if (builtin.os.tag == .windows and
-    builtin.abi == .msvc) struct
-{
-    const BOOL = std.os.windows.BOOL;
-    const HINSTANCE = std.os.windows.HINSTANCE;
-    const DWORD = std.os.windows.DWORD;
-    const LPVOID = std.os.windows.LPVOID;
-    const TRUE = std.os.windows.TRUE;
-    const FALSE = std.os.windows.FALSE;
-
-    const DLL_PROCESS_ATTACH: DWORD = 1;
-    const DLL_PROCESS_DETACH: DWORD = 0;
-
-    const __vcrt_initialize = @extern(*const fn () callconv(.c) c_int, .{ .name = "__vcrt_initialize" });
-    const __vcrt_uninitialize = @extern(*const fn (c_int) callconv(.c) c_int, .{ .name = "__vcrt_uninitialize" });
-    const __acrt_initialize = @extern(*const fn () callconv(.c) c_int, .{ .name = "__acrt_initialize" });
-    const __acrt_uninitialize = @extern(*const fn (c_int) callconv(.c) c_int, .{ .name = "__acrt_uninitialize" });
-
-    pub fn handler(_: HINSTANCE, fdwReason: DWORD, _: LPVOID) callconv(.winapi) BOOL {
-        switch (fdwReason) {
-            DLL_PROCESS_ATTACH => {
-                if (__vcrt_initialize() < 0) return FALSE;
-                if (__acrt_initialize() < 0) return FALSE;
-                return TRUE;
-            },
-            DLL_PROCESS_DETACH => {
-                _ = __acrt_uninitialize(1);
-                _ = __vcrt_uninitialize(1);
-                return TRUE;
-            },
-            else => return TRUE,
-        }
-    }
-}.handler else void;
-
 // Some comptime assertions that our C API depends on.
 comptime {
     // We allow tests to reference this file because we unit test
@@ -203,6 +156,52 @@ pub export fn ghostty_string_free(str: String) void {
     str.deinit();
 }
 
+// On Windows, Zig's _DllMainCRTStartup does not initialize the MSVC C
+// runtime when targeting MSVC ABI. Without initialization, any C library
+// function that depends on CRT internal state (setlocale, malloc from C
+// dependencies, C++ constructors in glslang) crashes with null pointer
+// dereferences. Declaring DllMain causes Zig's start.zig to call it
+// during DLL_PROCESS_ATTACH/DETACH, and we forward to the CRT bootstrap
+// functions from libvcruntime and libucrt (already linked).
+//
+// This is a workaround. Zig handles MinGW DLLs correctly (via dllcrt2.obj)
+// but not MSVC. No upstream issue tracks this exact gap as of 2026-03-26.
+// Closest: Codeberg ziglang/zig #30936 (reimplement crt0 code).
+// Remove this DllMain when Zig handles MSVC DLL CRT init natively.
+pub const DllMain = if (builtin.os.tag == .windows and
+    builtin.abi == .msvc) struct {
+    const BOOL = std.os.windows.BOOL;
+    const HINSTANCE = std.os.windows.HINSTANCE;
+    const DWORD = std.os.windows.DWORD;
+    const LPVOID = std.os.windows.LPVOID;
+    const TRUE = std.os.windows.TRUE;
+    const FALSE = std.os.windows.FALSE;
+
+    const DLL_PROCESS_ATTACH: DWORD = 1;
+    const DLL_PROCESS_DETACH: DWORD = 0;
+
+    const __vcrt_initialize = @extern(*const fn () callconv(.c) c_int, .{ .name = "__vcrt_initialize" });
+    const __vcrt_uninitialize = @extern(*const fn (c_int) callconv(.c) c_int, .{ .name = "__vcrt_uninitialize" });
+    const __acrt_initialize = @extern(*const fn () callconv(.c) c_int, .{ .name = "__acrt_initialize" });
+    const __acrt_uninitialize = @extern(*const fn (c_int) callconv(.c) c_int, .{ .name = "__acrt_uninitialize" });
+
+    pub fn handler(_: HINSTANCE, fdwReason: DWORD, _: LPVOID) callconv(.winapi) BOOL {
+        switch (fdwReason) {
+            DLL_PROCESS_ATTACH => {
+                if (__vcrt_initialize() < 0) return FALSE;
+                if (__acrt_initialize() < 0) return FALSE;
+                return TRUE;
+            },
+            DLL_PROCESS_DETACH => {
+                _ = __acrt_uninitialize(1);
+                _ = __vcrt_uninitialize(1);
+                return TRUE;
+            },
+            else => return TRUE,
+        }
+    }
+}.handler else void;
+
 test "ghostty_string_s empty string" {
     const testing = std.testing;
     const empty_string = String.empty;

test/windows/.gitignore

@@ -0,0 +1,3 @@
+*.exe
+*.pdb
+*.dll

test/windows/README.md

@@ -10,12 +10,17 @@ runtime is properly initialized.
 
 ### Build
 
+First build ghostty.dll, then compile the test:
+
 ```
+zig build -Dapp-runtime=none -Demit-exe=false
 zig cc test_dll_init.c -o test_dll_init.exe -target native-native-msvc
 ```
 
 ### Run
 
+From this directory:
+
 ```
 copy ..\..\zig-out\lib\ghostty.dll . && test_dll_init.exe
 ```
@@ -24,5 +29,8 @@ Expected output (after the CRT fix):
 
 ```
 ghostty_info: <version string>
-ghostty_init: 0
 ```
+
+The ghostty_info call verifies the DLL loads and the CRT is initialized.
+Before the fix, loading the DLL would crash with "access violation writing
+0x0000000000000024".

test/windows/test_dll_init.c

@@ -2,16 +2,19 @@
  * Minimal reproducer for the libghostty DLL CRT initialization issue.
  *
  * Before the fix (DllMain calling __vcrt_initialize / __acrt_initialize),
- * ghostty_init crashed with "access violation writing 0x0000000000000024"
- * because Zig's _DllMainCRTStartup does not initialize the MSVC C runtime
- * for DLL targets.
+ * loading ghostty.dll and calling any function that touches the C runtime
+ * crashed with "access violation writing 0x0000000000000024" because Zig's
+ * _DllMainCRTStartup does not initialize the MSVC C runtime for DLL targets.
+ *
+ * This test loads the DLL and calls ghostty_info, which exercises the CRT
+ * (string handling, memory). If it returns a version string without
+ * crashing, the CRT is properly initialized.
  *
  * Build:  zig cc test_dll_init.c -o test_dll_init.exe -target native-native-msvc
  * Run:    copy ..\..\zig-out\lib\ghostty.dll . && test_dll_init.exe
  *
  * Expected output (after fix):
  *   ghostty_info: <version string>
- *   ghostty_init: 0
  */
 
 #include <stdio.h>
@@ -24,7 +27,6 @@ typedef struct {
 } ghostty_info_s;
 
 typedef ghostty_info_s (*ghostty_info_fn)(void);
-typedef int (*ghostty_init_fn)(size_t, char **);
 
 int main(void) {
     HMODULE dll = LoadLibraryA("ghostty.dll");
@@ -34,18 +36,13 @@ int main(void) {
     }
 
     ghostty_info_fn info_fn = (ghostty_info_fn)GetProcAddress(dll, "ghostty_info");
-    if (info_fn) {
-        ghostty_info_s info = info_fn();
-        fprintf(stderr, "ghostty_info: %.*s\n", (int)info.version_len, info.version);
+    if (!info_fn) {
+        fprintf(stderr, "GetProcAddress(ghostty_info) failed: %lu\n", GetLastError());
+        return 1;
     }
 
-    ghostty_init_fn init_fn = (ghostty_init_fn)GetProcAddress(dll, "ghostty_init");
-    if (init_fn) {
-        char *argv[] = {"ghostty"};
-        int result = init_fn(1, argv);
-        fprintf(stderr, "ghostty_init: %d\n", result);
-        if (result != 0) return 1;
-    }
+    ghostty_info_s info = info_fn();
+    fprintf(stderr, "ghostty_info: %.*s\n", (int)info.version_len, info.version);
 
     /* Skip FreeLibrary -- ghostty's global state cleanup and CRT
      * teardown ordering is not yet handled. The OS reclaims everything