mingw: move MSys2 specific environment tweaks to setup_windows_environment

Lets keep the environment initialization and conversion section as lean as
possible and move recently added tweaks to setup_windows_environment().

This fixes the following potential problems:

 * Prevent duplicate TZ variables if both TZ and MSYS2_TZ are set.
 * Some of the higher level x* APIs from wrapper.c require a working
   getenv(), using e.g. xstrdup() during initialization is dangerous.
 * Slashifying the Windows TMP variable may break native Windows programs,
   use POSIX TMPDIR instead.
 * Properly slashify TMPDIR even if it is already set, and also if we only
   have TEMP, but not TMP.
 * Reduce complexity from O(n) to O(log n).

Signed-off-by: Karsten Blees <blees@dcon.de>

Author: kblees

compat/mingw.c

@@ -2211,15 +2211,31 @@ int handle_long_path(wchar_t *path, int len, int max_path, int expand)
 
 static void setup_windows_environment()
 {
+	char *tmp;
+
 	/* on Windows it is TMP and TEMP */
 	if (!getenv("TMPDIR")) {
-		const char *tmp = getenv("TMP");
-		if (!tmp)
+		if (!(tmp = getenv("TMP")))
 			tmp = getenv("TEMP");
 		if (tmp)
 			setenv("TMPDIR", tmp, 1);
 	}
 
+	if ((tmp = getenv("TMPDIR"))) {
+		/*
+		 * Convert all dir separators to forward slashes,
+		 * to help shell commands called from the Git
+		 * executable (by not mistaking the dir separators
+		 * for escape characters).
+		 */
+		for (; *tmp; tmp++)
+			if (*tmp == '\\')
+				*tmp = '/';
+	}
+
+	if (!getenv("TZ") && (tmp = getenv("MSYS2_TZ")))
+		setenv("TZ", tmp, 1);
+
 	/* simulate TERM to enable auto-color (see color.c) */
 	if (!getenv("TERM"))
 		setenv("TERM", "cygwin", 1);
@@ -2294,26 +2310,8 @@ void mingw_startup()
 	__argv[0] = wcstoutfdup_startup(buffer, _wpgmptr, maxlen);
 	for (i = 1; i < argc; i++)
 		__argv[i] = wcstoutfdup_startup(buffer, wargv[i], maxlen);
-	for (i = 0; wenv[i]; i++) {
+	for (i = 0; wenv[i]; i++)
 		environ[i] = wcstoutfdup_startup(buffer, wenv[i], maxlen);
-		if (!strncasecmp(environ[i], "MSYS2_TZ=", 9)) {
-			char *to_free = environ[i];
-			environ[i] = xstrdup(to_free + 6);
-			free(to_free);
-		}
-		if (!strncasecmp(environ[i], "TMP=", 4)) {
-			/*
-			 * Convert all dir separators to forward slashes,
-			 * to help shell commands called from the Git
-			 * executable (by not mistaking the dir separators
-			 * for escape characters).
-			 */
-			char *p;
-			for (p = environ[i]; *p; p++)
-				if (*p == '\\')
-					*p = '/';
-		}
-	}
 	environ[i] = NULL;
 	free(buffer);