Merge branch 'fix-msys2-quoting-bugs'

These patches fix several bugs in quoting arguments when spawning shell
scripts on Windows.

Note: these bugs are Windows-only, as we have to construct a command
line for the process-to-spawn, unlike Linux/macOS, where `execv()`
accepts an already-split command line.

Furthermore, these fixes were not included in the CVE-2019-1350 part of
v2.14.6 because the Windows-specific quoting when spawning shell scripts
was contributed from Git for Windows into Git only in the v2.21.x era.

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

compat/mingw.c

diff --git a/compat/mingw.c b/compat/mingw.c
index 0e14cab..2c55c34 100644
--- a/compat/mingw.c
+++ b/compat/mingw.c
@@ -1120,13 +1120,14 @@ static const char *quote_arg_msys2(const char *arg)
 
 	for (p = arg; *p; p++) {
 		int ws = isspace(*p);
-		if (!ws && *p != '\\' && *p != '"' && *p != '{')
+		if (!ws && *p != '\\' && *p != '"' && *p != '{' && *p != '\'' &&
+		    *p != '?' && *p != '*' && *p != '~')
 			continue;
 		if (!buf.len)
 			strbuf_addch(&buf, '"');
 		if (p != p2)
 			strbuf_add(&buf, p2, p - p2);
-		if (!ws && *p != '{')
+		if (*p == '\\' || *p == '"')
 			strbuf_addch(&buf, '\\');
 		p2 = p;
 	}
@@ -1136,7 +1137,7 @@ static const char *quote_arg_msys2(const char *arg)
 	else if (!buf.len)
 		return arg;
 	else
-		strbuf_add(&buf, p2, p - p2),
+		strbuf_add(&buf, p2, p - p2);
 
 	strbuf_addch(&buf, '"');
 	return strbuf_detach(&buf, 0);
@@ -1391,7 +1392,10 @@ static inline int match_last_path_component(const char *path, size_t *len,
 
 static int is_msys2_sh(const char *cmd)
 {
-	if (cmd && !strcmp(cmd, "sh")) {
+	if (!cmd)
+		return 0;
+
+	if (!strcmp(cmd, "sh")) {
 		static int ret = -1;
 		char *p;
 
@@ -1411,6 +1415,16 @@ static int is_msys2_sh(const char *cmd)
 		}
 		return ret;
 	}
+
+	if (ends_with(cmd, "\\sh.exe")) {
+		static char *sh;
+
+		if (!sh)
+			sh = path_lookup("sh", 0);
+
+		return !fspathcmp(cmd, sh);
+	}
+
 	return 0;
 }
 
@@ -1426,7 +1440,8 @@ static pid_t mingw_spawnve_fd(const char *cmd, const char **argv, char **deltaen
 	BOOL ret;
 	HANDLE cons;
 	const char *(*quote_arg)(const char *arg) =
-		is_msys2_sh(*argv) ? quote_arg_msys2 : quote_arg_msvc;
+		is_msys2_sh(cmd ? cmd : *argv) ?
+		quote_arg_msys2 : quote_arg_msvc;
 
 	do_unset_environment_variables();