Set the long path bit for embedded interpreters too

`rb_w32_sysinit` is documented as being for `ruby(1)`, so a program which embeds libruby may skip it and keep the 260 character limit while `ruby.exe` does not. Call the same initialization from `ruby_setup`, which every embedder reaches through `ruby_init`.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

NEWS.md

@@ -245,9 +245,10 @@ Ruby 4.0 bundled RubyGems and Bundler version 4. see the following links for det
     * BSD/OS (BSDi)
 
 * Windows 10 1703 or later no longer needs the `LongPathsEnabled` registry
-  value to use paths longer than 260 characters.  Each path component is still
-  limited to 255 characters, and a child process still starts with the
-  `MAX_PATH` limited current directory. [[Bug #18947]]
+  value to use paths longer than 260 characters.  This applies to any process
+  running the interpreter, including a program which embeds libruby.  Each path
+  component is still limited to 255 characters, and a child process still
+  starts with the `MAX_PATH` limited current directory. [[Bug #18947]]
 
 ## Compatibility issues
 

eval.c

@@ -76,6 +76,9 @@ ruby_setup(void)
      */
 #if defined(__linux__) && defined(PR_SET_THP_DISABLE)
     prctl(PR_SET_THP_DISABLE, 1, 0, 0, 0);
+#endif
+#if defined(_WIN32)
+    rb_w32_init_long_paths();
 #endif
     Init_BareVM();
     rb_vm_encoded_insn_data_table_init();

internal.h

@@ -64,6 +64,11 @@
 /* internal/symbol.h */
 #define rb_sym_intern_ascii_cstr(...) rb_nonexistent_symbol(__VA_ARGS__)
 
+#ifdef _WIN32
+/* win32/win32.c */
+void rb_w32_init_long_paths(void);
+#endif
+
 
 /* MRI debug support */
 

win32/win32.c

@@ -851,19 +851,27 @@ static int w32_cmdvector(const WCHAR *, char ***, UINT, rb_encoding *);
  * when that registry value is set, so the manifest alone is not enough on a
  * stock machine.  Undocumented, and taken from initLongPathSupport in Go's
  * runtime <https://go.dev/src/runtime/os_windows.go>, whose maintainers have
- * proposed to drop it <https://github.com/golang/go/issues/66560>. */
-static void
-init_long_path_support(void)
+ * proposed to drop it <https://github.com/golang/go/issues/66560>.
+ *
+ * Called from rb_w32_sysinit, which runs before the VM exists, and from
+ * ruby_setup, so that a program which embeds libruby without calling
+ * ruby_sysinit gets it as well. */
+void
+rb_w32_init_long_paths(void)
 {
     /* PEB.BitField, and the IsLongPathAwareProcess bit in it */
     enum {peb_bit_field_offset = 3, is_long_path_aware_process = 0x80};
     typedef long (WINAPI version_func)(OSVERSIONINFOW *);
     typedef void *(WINAPI peb_func)(void);
+    static int done = 0;
     version_func *pRtlGetVersion;
     peb_func *pRtlGetCurrentPeb;
     OSVERSIONINFOW osvi;
     BYTE *bit_field;
 
+    if (done) return;
+    done = 1;
+
     pRtlGetVersion = (version_func *)get_proc_address("ntdll.dll", "RtlGetVersion", NULL);
     if (!pRtlGetVersion) return;
     memset(&osvi, 0, sizeof(osvi));
@@ -892,7 +900,7 @@ rb_w32_sysinit(int *argc, char ***argv)
     SetErrorMode(SEM_FAILCRITICALERRORS|SEM_NOGPFAULTERRORBOX);
 
     get_version();
-    init_long_path_support();
+    rb_w32_init_long_paths();
 
     //
     // subvert cmd.exe's feeble attempt at command line parsing