exewrapper: add .dll to LoadLibrary() argument

LoadLibrary() changes behavior depending on whether the argument
passed to it contains a period. From the MSDN docs:

If no file name extension is specified in the lpFileName parameter,
the default library extension .dll is appended. However, the file name
string can include a trailing point character (.) to indicate that the
module name has no extension. When no path is specified, the function
searches for loaded modules whose base name matches the base name of
the module to be loaded. If the name matches, the load succeeds.
Otherwise, the function searches for the file.

As the subsequent patch will show, some environments on Windows
define their Python library as e.g. "libpython2.7.dll." The existing
code would pass "libpython2.7" into LoadLibrary(). It would assume
"7" was the file extension and look for a "libpython2.dll" to load.

By passing ".dll" into LoadLibrary(), we force it to search for the
exact basename we want, even if it contains a period.

mercurial/exewrapper.c

@@ -1,174 +1,175 b''
 /*
  exewrapper.c - wrapper for calling a python script on Windows
 
  Copyright 2012 Adrian Buehlmann <[e-mail]> and others
 
  This software may be used and distributed according to the terms of the
  GNU General Public License version 2 or any later version.
 */
 
 #include <stdio.h>
 #include <windows.h>
 
 #include "hgpythonlib.h"
 
 #ifdef __GNUC__
 int strcat_s(char *d, size_t n, const char *s)
 {
 	return !strncat(d, s, n);
 }
 int strcpy_s(char *d, size_t n, const char *s)
 {
 	return !strncpy(d, s, n);
 }
 #endif
 
 
 static char pyscript[MAX_PATH + 10];
 static char pyhome[MAX_PATH + 10];
 static char envpyhome[MAX_PATH + 10];
 static char pydllfile[MAX_PATH + 10];
 
 int main(int argc, char *argv[])
 {
 	char *p;
 	int ret;
 	int i;
 	int n;
 	char **pyargv;
 	WIN32_FIND_DATA fdata;
 	HANDLE hfind;
 	const char *err;
 	HMODULE pydll;
 	void (__cdecl *Py_SetPythonHome)(char *home);
 	int (__cdecl *Py_Main)(int argc, char *argv[]);
 
 	if (GetModuleFileName(NULL, pyscript, sizeof(pyscript)) == 0)
 	{
 		err = "GetModuleFileName failed";
 		goto bail;
 	}
 
 	p = strrchr(pyscript, '.');
 	if (p == NULL) {
 		err = "malformed module filename";
 		goto bail;
 	}
 	*p = 0; /* cut trailing ".exe" */
 	strcpy_s(pyhome, sizeof(pyhome), pyscript);
 
 	hfind = FindFirstFile(pyscript, &fdata);
 	if (hfind != INVALID_HANDLE_VALUE) {
 		/* pyscript exists, close handle */
 		FindClose(hfind);
 	} else {
 		/* file pyscript isn't there, take <pyscript>exe.py */
 		strcat_s(pyscript, sizeof(pyscript), "exe.py");
 	}
 
 	pydll = NULL;
 	/*
 	We first check, that environment variable PYTHONHOME is *not* set.
 	This just mimicks the behavior of the regular python.exe, which uses
 	PYTHONHOME to find its installation directory (if it has been set).
 	Note: Users of HackableMercurial are expected to *not* set PYTHONHOME!
 	*/
 	if (GetEnvironmentVariable("PYTHONHOME", envpyhome,
 				   sizeof(envpyhome)) == 0)
 	{
 		/*
 		Environment var PYTHONHOME is *not* set. Let's see if we are
 		running inside a HackableMercurial.
 		*/
 
 		p = strrchr(pyhome, '\\');
 		if (p == NULL) {
 			err = "can't find backslash in module filename";
 			goto bail;
 		}
 		*p = 0; /* cut at directory */
 
 		/* check for private Python of HackableMercurial */
 		strcat_s(pyhome, sizeof(pyhome), "\\hg-python");
 
 		hfind = FindFirstFile(pyhome, &fdata);
 		if (hfind != INVALID_HANDLE_VALUE) {
 			/* path pyhome exists, let's use it */
 			FindClose(hfind);
 			strcpy_s(pydllfile, sizeof(pydllfile), pyhome);
-			strcat_s(pydllfile, sizeof(pydllfile), "\\" HGPYTHONLIB);
+			strcat_s(pydllfile, sizeof(pydllfile),
+				 "\\" HGPYTHONLIB ".dll");
 			pydll = LoadLibrary(pydllfile);
 			if (pydll == NULL) {
 				err = "failed to load private Python DLL "
 				      HGPYTHONLIB ".dll";
 				goto bail;
 			}
 			Py_SetPythonHome = (void*)GetProcAddress(pydll,
 							"Py_SetPythonHome");
 			if (Py_SetPythonHome == NULL) {
 				err = "failed to get Py_SetPythonHome";
 				goto bail;
 			}
 			Py_SetPythonHome(pyhome);
 		}
 	}
 
 	if (pydll == NULL) {
-		pydll = LoadLibrary(HGPYTHONLIB);
+		pydll = LoadLibrary(HGPYTHONLIB ".dll");
 		if (pydll == NULL) {
 			err = "failed to load Python DLL " HGPYTHONLIB ".dll";
 			goto bail;
 		}
 	}
 
 	Py_Main = (void*)GetProcAddress(pydll, "Py_Main");
 	if (Py_Main == NULL) {
 		err = "failed to get Py_Main";
 		goto bail;
 	}
 
 	/*
 	Only add the pyscript to the args, if it's not already there. It may
 	already be there, if the script spawned a child process of itself, in
 	the same way as it got called, that is, with the pyscript already in
 	place. So we optionally accept the pyscript as the first argument
 	(argv[1]), letting our exe taking the role of the python interpreter.
 	*/
 	if (argc >= 2 && strcmp(argv[1], pyscript) == 0) {
 		/*
 		pyscript is already in the args, so there is no need to copy
 		the args and we can directly call the python interpreter with
 		the original args.
 		*/
 		return Py_Main(argc, argv);
 	}
 
 	/*
 	Start assembling the args for the Python interpreter call. We put the
 	name of our exe (argv[0]) in the position where the python.exe
 	canonically is, and insert the pyscript next.
 	*/
 	pyargv = malloc((argc + 5) * sizeof(char*));
 	if (pyargv == NULL) {
 		err = "not enough memory";
 		goto bail;
 	}
 	n = 0;
 	pyargv[n++] = argv[0];
 	pyargv[n++] = pyscript;
 
 	/* copy remaining args from the command line */
 	for (i = 1; i < argc; i++)
 		pyargv[n++] = argv[i];
 	/* argv[argc] is guaranteed to be NULL, so we forward that guarantee */
 	pyargv[n] = NULL;
 
 	ret = Py_Main(n, pyargv); /* The Python interpreter call */
 
 	free(pyargv);
 	return ret;
 
 bail:
 	fprintf(stderr, "abort: %s\n", err);
 	return 255;
 }