convert: refactor code to clarify ownership of check_roundtrip_encoding

The `check_roundtrip_encoding` variable is tracked in a `const char *`
even though it may contain allocated strings at times. The result is
that those strings may be leaking because we never free them.

Refactor the code to always store allocated strings in this variable.
The default value is handled in `check_roundtrip()` now, which is the
only user of the variable.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

config.c

@@ -1564,8 +1564,10 @@ static int git_default_core_config(const char *var, const char *value,
 		return 0;
 	}
 
-	if (!strcmp(var, "core.checkroundtripencoding"))
-		return git_config_string(&check_roundtrip_encoding, var, value);
+	if (!strcmp(var, "core.checkroundtripencoding")) {
+		FREE_AND_NULL(check_roundtrip_encoding);
+		return git_config_string((const char **) &check_roundtrip_encoding, var, value);
+	}
 
 	if (!strcmp(var, "core.notesref")) {
 		if (!value)

convert.c

@@ -345,30 +345,32 @@ static int check_roundtrip(const char *enc_name)
 	 * space separated encodings (eg. "UTF-16, ASCII, CP1125").
 	 * Search for the given encoding in that string.
 	 */
-	const char *found = strcasestr(check_roundtrip_encoding, enc_name);
+	const char *encoding = check_roundtrip_encoding ?
+		check_roundtrip_encoding : "SHIFT-JIS";
+	const char *found = strcasestr(encoding, enc_name);
 	const char *next;
 	int len;
 	if (!found)
 		return 0;
 	next = found + strlen(enc_name);
-	len = strlen(check_roundtrip_encoding);
+	len = strlen(encoding);
 	return (found && (
 			/*
-			 * check that the found encoding is at the
-			 * beginning of check_roundtrip_encoding or
-			 * that it is prefixed with a space or comma
+			 * Check that the found encoding is at the beginning of
+			 * encoding or that it is prefixed with a space or
+			 * comma.
 			 */
-			found == check_roundtrip_encoding || (
+			found == encoding || (
 				(isspace(found[-1]) || found[-1] == ',')
 			)
 		) && (
 			/*
-			 * check that the found encoding is at the
-			 * end of check_roundtrip_encoding or
-			 * that it is suffixed with a space or comma
+			 * Check that the found encoding is at the end of
+			 * encoding or that it is suffixed with a space
+			 * or comma.
 			 */
-			next == check_roundtrip_encoding + len || (
-				next < check_roundtrip_encoding + len &&
+			next == encoding + len || (
+				next < encoding + len &&
 				(isspace(next[0]) || next[0] == ',')
 			)
 		));

convert.h

@@ -92,7 +92,7 @@ void convert_attrs(struct index_state *istate,
 		   struct conv_attrs *ca, const char *path);
 
 extern enum eol core_eol;
-extern const char *check_roundtrip_encoding;
+extern char *check_roundtrip_encoding;
 const char *get_cached_convert_stats_ascii(struct index_state *istate,
 					   const char *path);
 const char *get_wt_convert_stats_ascii(const char *path);

environment.c

@@ -64,7 +64,7 @@ char *excludes_file;
 enum auto_crlf auto_crlf = AUTO_CRLF_FALSE;
 enum eol core_eol = EOL_UNSET;
 int global_conv_flags_eol = CONV_EOL_RNDTRP_WARN;
-const char *check_roundtrip_encoding = "SHIFT-JIS";
+char *check_roundtrip_encoding;
 enum branch_track git_branch_track = BRANCH_TRACK_REMOTE;
 enum rebase_setup_type autorebase = AUTOREBASE_NEVER;
 enum push_default_type push_default = PUSH_DEFAULT_UNSPECIFIED;