[PATCH v4] Expand ~ and ~user in core.excludesfile, commit.template

@@ -346,7 +346,8 @@ Common unit suffixes of 'k', 'm', or 'g' are supported.
 core.excludesfile::
 	In addition to '.gitignore' (per-directory) and
 	'.git/info/exclude', git looks into this file for patterns
-	of files which are not meant to be tracked.  See
+	of files which are not meant to be tracked.  "~" and "~user"
+	are expanded to the user's home directory.  See
 	linkgit:gitignore[5].
 
 core.editor::

@@ -554,6 +555,7 @@ color.status.<slot>::
 
 commit.template::
 	Specify a file to use as the template for new commit messages.
+	"~" and "~user" are expanded to the user's home directory.
 
 color.ui::
 	When set to `always`, always use colors in all git commands which

@@ -891,7 +891,7 @@ static void print_summary(const char *prefix, const unsigned char *sha1)
 static int git_commit_config(const char *k, const char *v, void *cb)
 {
 	if (!strcmp(k, "commit.template"))
-		return git_config_string(&template_file, k, v);
+		return git_config_pathname(&template_file, k, v);
 
 	return git_status_config(k, v, cb);
 }

@@ -527,6 +527,7 @@ int git_config_perm(const char *var, const char *value);
 int adjust_shared_perm(const char *path);
 int safe_create_leading_directories(char *path);
 int safe_create_leading_directories_const(const char *path);
+extern char *expand_user_path(char *buf, const char *path, int sz);
 char *enter_repo(char *path, int strict);
 static inline int is_absolute_path(const char *path)
 {

@@ -748,6 +749,7 @@ extern unsigned long git_config_ulong(const char *, const char *);
 extern int git_config_bool_or_int(const char *, const char *, int *);
 extern int git_config_bool(const char *, const char *);
 extern int git_config_string(const char **, const char *, const char *);
+extern int git_config_pathname(const char **, const char *, const char *);
 extern int git_config_set(const char *, const char *);
 extern int git_config_set_multivar(const char *, const char *, const char *, int);
 extern int git_config_rename_section(const char *, const char *);

@@ -334,6 +334,15 @@ int git_config_string(const char **dest, const char *var, const char *value)
 	return 0;
 }
 
+int git_config_pathname(const char **dest, const char *var, const char *value) {
+	if (!value)
+		return config_error_nonbool(var);
+	*dest = expand_user_path(NULL, value, 0);
+	if (!*dest)
+		die("Failed to expand user dir in: '%s'", value);
+	return 0;
+}
+
 static int git_default_core_config(const char *var, const char *value)
 {
 	/* This needs a better name */

@@ -457,7 +466,7 @@ static int git_default_core_config(const char *var, const char *value)
 		return git_config_string(&editor_program, var, value);
 
 	if (!strcmp(var, "core.excludesfile"))
-		return git_config_string(&excludes_file, var, value);
+		return git_config_pathname(&excludes_file, var, value);
 
 	if (!strcmp(var, "core.whitespace")) {
 		if (!value)

@@ -137,46 +137,68 @@ int validate_headref(const char *path)
 	return -1;
 }
 
-static char *user_path(char *buf, char *path, int sz)
+static inline struct passwd *getpw_str(const char *username, size_t len)
 {
+	if (len == 0)
+		return getpwuid(getuid());
+
 	struct passwd *pw;
-	char *slash;
-	int len, baselen;
+	char *username_z = xmalloc(len + 1);
+	memcpy(username_z, username, len);
+	username_z[len] = '\0';
+	pw = getpwnam(username_z);
+	free(username_z);
+	return pw;
+}
 
-	if (!path || path[0] != '~')
-		return NULL;
-	path++;
-	slash = strchr(path, '/');
-	if (path[0] == '/' || !path[0]) {
-		pw = getpwuid(getuid());
-	}
-	else {
-		if (slash) {
-			*slash = 0;
-			pw = getpwnam(path);
-			*slash = '/';
-		}
-		else
-			pw = getpwnam(path);
-	}
-	if (!pw || !pw->pw_dir || sz <= strlen(pw->pw_dir))
-		return NULL;
-	baselen = strlen(pw->pw_dir);
-	memcpy(buf, pw->pw_dir, baselen);
-	while ((1 < baselen) && (buf[baselen-1] == '/')) {
-		buf[baselen-1] = 0;
-		baselen--;
-	}
-	if (slash && slash[1]) {
-		len = strlen(slash);
-		if (sz <= baselen + len)
+/*
+ * Return a string with input strings concatenated.  If buf != NULL, then
+ * it is the output buffer with size bufsz (including terminator); else the
+ * return buffer is xmalloced.  Second string can be NULL, in which case the
+ * first string is simply strduped/strcpyed.  Returns NULL if bufsz is too
+ * small.
+ */
+static inline char *concatstr(char *buf, const char *str1, const char *str2,
+			      size_t bufsz)
+{
+	size_t len1 = strlen(str1);
+	size_t len2 = str ? strlen(str2) : 0;
+	size_t needbuflen = len1 + len2 + 1;
+	if (buf) {
+		if (needbuflen > bufsz)
 			return NULL;
-		memcpy(buf + baselen, slash, len + 1);
+	} else {
+		buf = xmalloc(needbuflen);
 	}
+	memcpy(buf, str1, len1);
+	if (str2)
+		memcpy(buf+len1, str2, len2+1);
 	return buf;
 }
 
 /*
+ * Return a string with ~ and ~user expanded via getpw*.  If buf != NULL, then
+ * it is the output buffer with size bufsz (including terminator); else the
+ * return buffer is xmalloced.  Returns NULL on getpw failure or if the input
+ * buffer is too small.
+ */
+char *expand_user_path(char *buf, const char *path, int bufsz)
+{
+	if (path == NULL)
+		return NULL;
+
+	if (path[0] != '~')
+		return concatstr(buf, path, NULL, bufsz);
+
+	const char *username = path + 1;
+	size_t username_len = strchrnul(username, '/') - username;
+	struct passwd *pw = getpw_str(username, username_len);
+	if (!pw)
+		return NULL;
+	return concatstr(buf, pw->pw_dir, username+username_len, bufsz);
+}
+
+/*
  * First, one directory to try is determined by the following algorithm.
  *
  * (0) If "strict" is given, the path is used as given and no DWIM is

@@ -221,7 +243,7 @@ char *enter_repo(char *path, int strict)
 		if (PATH_MAX <= len)
 			return NULL;
 		if (path[0] == '~') {
-			if (!user_path(used_path, path, PATH_MAX))
+			if (!expand_user_path(used_path, path, PATH_MAX))
 				return NULL;
 			strcpy(validated_path, path);
 			path = used_path;