Add a windows launcher program to replace the current .bat files

This is still just an experiment but eventually I hope to remove
the `.bat` files in favor of this executable.

There are several reasons to want to do this:

1. Batch files are notoriously painful to work with and mis-understood.
2. Should be faster (no need to launch cmd.exe).
3. Works around several known issues with .bat files including one that
   is known unsolvable one (see emcc.bat for more details)

Author: sbc100

.circleci/config.yml

@@ -1077,10 +1077,17 @@ jobs:
       EMTEST_BROWSER: "0"
     steps:
       - checkout
+      - run:
+          name: Setup Visual Stdio
+          shell: cmd.exe
+          command: dir 'C:\Program Files (x86)\Microsoft Visual Studio'
+      #"C:/Program Files (x86)/Microsoft Visual Studio/2019/Community/VC/Auxiliary/Build/vcvarsall.bat" x86
+      - run:
+          name: Build Python Launcher
+          command: cd tools/maint/win32_launcher && ./build.bat
       - run:
           name: Install packages
-          command: |
-            choco install -y cmake.portable ninja pkgconfiglite
+          command: choco install -y cmake.portable ninja pkgconfiglite
       - run:
           name: Add python to bash path
           command: echo "export PATH=\"$PATH:/c/Python27amd64/\"" >> $BASH_ENV

tools/maint/win32_launcher/README.md

@@ -0,0 +1,11 @@
+Windows Python Script Launcher
+==============================
+
+This directory contains a simple launcher program for windows which is used to
+execute the emscripten compiler entry points using the python interpreter.  It
+uses the its own name (the name of the currently running executable) to
+determine which python script to run and serves the same purpose as the
+``run_python.sh`` script does on non-windows platforms.
+
+We build this executable statically using ``/MT`` so that it is maximally
+portable.

tools/maint/win32_launcher/build.bat

@@ -0,0 +1 @@
+cl launcher.c /Fe:launcher.exe /MT

tools/maint/win32_launcher/launcher.c

@@ -0,0 +1,107 @@
+/*
+ * Copyright 2025 The Emscripten Authors.  All rights reserved.
+ * Emscripten is available under two separate licenses, the MIT license and the
+ * University of Illinois/NCSA Open Source License.  Both these licenses can be
+ * found in the LICENSE file.
+ */
+
+#include <process.h> // For _spawnvp
+#include <stdio.h>
+#include <stdlib.h> // For _splitpath_s, _makepath_s, GetEnvironmentVariable
+#include <string.h>
+#include <windows.h>
+
+#if 1
+#define dbg printf
+#else
+#define dbg(...)
+#endif
+
+void findPythonExePath(char* pythonExePath, size_t bufferSize) {
+  char envPythonPath[MAX_PATH]; // Temporary buffer for environment variable
+
+  // Attempt to retrieve the value of the "PYTHON" environment variable.
+  DWORD result = GetEnvironmentVariable("PYTHON", envPythonPath, MAX_PATH);
+
+  if (result > 0 && result < MAX_PATH) {
+    // If the "PYTHON" environment variable is set and its value fits within the
+    // buffer, use this explicit path. strncpy_s is used for safe string
+    // copying.
+    strncpy_s(pythonExePath, bufferSize, envPythonPath, _TRUNCATE);
+    dbg("Launcher: Using PYTHON environment variable: %s\n", pythonExePath);
+    return;
+  }
+
+  // If "PYTHON" environment variable is not set or its value is too long,
+  // default to "python.exe". The _spawnvp function in main() will then
+  // search for "python.exe" in the system's PATH.
+  strcpy(pythonExePath, "python.exe");
+  dbg("Launcher: PYTHON environment variable not found or invalid, defaulting "
+      "to 'python.exe' (will use PATH search).\n");
+}
+
+int main() {
+  char exePath[MAX_PATH];
+  char drive[_MAX_DRIVE];
+  char dir[_MAX_DIR];
+  char fname[_MAX_FNAME];
+  char ext[_MAX_EXT];
+  char pythonScriptPath[MAX_PATH];
+  char pythonExeToLaunch[MAX_PATH]; // Buffer to store the determined Python
+                                    // executable path
+
+  // Call the subroutine to determine the Python executable path and its
+  // discovery method. The return value (discoveryMethod) is no longer used for
+  // adding -Xutf8.
+  findPythonExePath(pythonExeToLaunch, MAX_PATH);
+
+  // 1. Get the full path of the current executable.
+  if (GetModuleFileName(NULL, exePath, MAX_PATH) == 0) {
+    fprintf(stderr, "Error: Could not get executable path (Error code: %lu)\n", GetLastError());
+    return 1;
+  }
+
+  // 2. Split the executable path into its components (drive, directory, file
+  // name, extension).
+  _splitpath_s(exePath, drive, _MAX_DRIVE, dir, _MAX_DIR, fname, _MAX_FNAME, ext, _MAX_EXT);
+
+  // 3. Construct the Python script path. It uses the same base name as the
+  // launcher but with a ".py" extension, residing in the same directory.
+  _makepath_s(pythonScriptPath, MAX_PATH, drive, dir, fname, ".py");
+
+  dbg("Launcher: Executable path: %s\n", exePath);
+  dbg("Launcher: Python script to run: %s\n", pythonScriptPath);
+
+  // 4. Prepare arguments for the Python executable.
+  // The arguments are now always 3: python_exe, script_path, and NULL
+  // terminator.
+  char* argv[] = {
+    pythonExeToLaunch, // Use the path determined by findPythonExePath
+    pythonScriptPath,
+    NULL};
+
+  // Check for EM_WORKAROUND_PYTHON_BUG_34780 environment variable
+  if (GetEnvironmentVariable("EM_WORKAROUND_PYTHON_BUG_34780", NULL, 0) > 0) {
+    dbg("Launcher: EM_WORKAROUND_PYTHON_BUG_34780 is set so closing stdin\n");
+    fclose(stdin);
+  }
+
+  // 5. Launch the Python executable and wait for it to finish.
+  // _spawnvp searches for the program specified in argv[0] in the system's PATH
+  // (if argv[0] is not a full path) and executes it. _P_WAIT ensures the
+  // launcher waits for the Python process to complete before continuing.
+  intptr_t result = _spawnvp(_P_WAIT, argv[0], argv);
+
+  if (result == -1) {
+    // If _spawnvp returns -1, an error occurred during the launch of the child
+    // process.
+    perror("Launcher Error: Failed to launch python.exe");
+    return 1; // Set a specific exit code to indicate launch failure.
+  }
+
+  // If successful, the return value of _spawnvp is the exit code of the spawned
+  // process.
+  int exitCode = (int)result;
+  dbg("Launcher: python.exe exited with code: %d\n", exitCode);
+  return exitCode;
+}