Merge branch 'unc-path-w-backslashes'

This topic branch addresses a problem identified in
https://github.com/git-for-windows/git/issues/439: while
cloning/fetching/pushing from "POSIX-ified UNC paths" (i.e. UNC paths
whose backslashes have been converted to forward slashes) works for some
time now, true UNC paths (with backslashes left intact) were handled
incorrectly. Example:

	git clone //myserver/folder/repo.git

works, but

	git clone \\myserver\folder\repo.git

(in CMD; in Git Bash, the backslashes would need to be doubled) used to
fail. The reason was an unexpected difference in command-line handling
between Win32 executables and MSYS2 ones (such as the shell that is used
by git-clone.exe to spawn git-upload-pack.exe).

This topic branch features a workaround *just* for the case where Git
passes stuff through sh.exe (which covers quite a few use cases,
though).

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

compat/mingw.c

@@ -963,7 +963,7 @@ char *mingw_getcwd(char *pointer, int len)
  * See http://msdn2.microsoft.com/en-us/library/17w5ykft(vs.71).aspx
  * (Parsing C++ Command-Line Arguments)
  */
-static const char *quote_arg(const char *arg)
+static const char *quote_arg_msvc(const char *arg)
 {
 	/* count chars to quote */
 	int len = 0, n = 0;
@@ -1018,6 +1018,37 @@ static const char *quote_arg(const char *arg)
 	return q;
 }
 
+#include "quote.h"
+
+static const char *quote_arg_msys2(const char *arg)
+{
+	struct strbuf buf = STRBUF_INIT;
+	const char *p2 = arg, *p;
+
+	for (p = arg; *p; p++) {
+		int ws = isspace(*p);
+		if (!ws && *p != '\\' && *p != '"' && *p != '{')
+			continue;
+		if (!buf.len)
+			strbuf_addch(&buf, '"');
+		if (p != p2)
+			strbuf_add(&buf, p2, p - p2);
+		if (!ws && *p != '{')
+			strbuf_addch(&buf, '\\');
+		p2 = p;
+	}
+
+	if (p == arg)
+		strbuf_addch(&buf, '"');
+	else if (!buf.len)
+		return arg;
+	else
+		strbuf_add(&buf, p2, p - p2),
+
+	strbuf_addch(&buf, '"');
+	return strbuf_detach(&buf, 0);
+}
+
 static const char *parse_interpreter(const char *cmd)
 {
 	static char buf[100];
@@ -1179,6 +1210,34 @@ struct pinfo_t {
 static struct pinfo_t *pinfo = NULL;
 CRITICAL_SECTION pinfo_cs;
 
+static int is_msys2_sh(const char *cmd)
+{
+	if (cmd && !strcmp(cmd, "sh")) {
+		static int ret = -1;
+		char *p;
+
+		if (ret >= 0)
+			return ret;
+
+		p = path_lookup(cmd, 0);
+		if (!p)
+			ret = 0;
+		else {
+			size_t len = strlen(p);
+			ret = len > 15 &&
+				is_dir_sep(p[len - 15]) &&
+				!strncasecmp(p + len - 14, "usr", 3) &&
+				is_dir_sep(p[len - 11]) &&
+				!strncasecmp(p + len - 10, "bin", 3) &&
+				is_dir_sep(p[len - 7]) &&
+				!strcasecmp(p + len - 6, "sh.exe");
+			free(p);
+		}
+		return ret;
+	}
+	return 0;
+}
+
 static pid_t mingw_spawnve_fd(const char *cmd, const char **argv, char **deltaenv,
 			      const char *dir,
 			      int prepend_cmd, int fhin, int fhout, int fherr)
@@ -1190,6 +1249,8 @@ static pid_t mingw_spawnve_fd(const char *cmd, const char **argv, char **deltaen
 	unsigned flags = CREATE_UNICODE_ENVIRONMENT;
 	BOOL ret;
 	HANDLE cons;
+	const char *(*quote_arg)(const char *arg) =
+		is_msys2_sh(*argv) ? quote_arg_msys2 : quote_arg_msvc;
 
 	do_unset_environment_variables();
 

t/t0061-run-command.sh

@@ -177,4 +177,14 @@ test_expect_success 'GIT_TRACE with environment variables' '
 	)
 '
 
+test_expect_success MINGW 'verify curlies are quoted properly' '
+	: force the rev-parse through the MSYS2 Bash &&
+	git -c alias.r="!git rev-parse" r -- a{b}c >actual &&
+	cat >expect <<-\EOF &&
+	--
+	a{b}c
+	EOF
+	test_cmp expect actual
+'
+
 test_done

t/t5580-clone-push-unc.sh

@@ -49,6 +49,11 @@ test_expect_success clone '
 	git clone "file://$UNCPATH" clone
 '
 
+test_expect_success 'clone with backslashed path' '
+	BACKSLASHED="$(echo "$UNCPATH" | tr / \\\\)" &&
+	git clone "$BACKSLASHED" backslashed
+'
+
 test_expect_success push '
 	(
 		cd clone &&