[PATCH 2/5] get_sha1: allow custom SHA-1 mapping with $SHA1^{~alias} syntax

["Nguyễn Thái Ngọc Duy" <pclouds@gmail.com>]

"alias" is defined in config as sha1.alias. %sha1% and %arg% in the
alias command will be substituted.

The alias command is supposed to return a piece of text that
get_sha1() can consume, preferably straight SHA-1.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 Documentation/config.txt    |    9 ++++
 Documentation/revisions.txt |    7 +++
 alias.c                     |   23 +++++++++--
 cache.h                     |    1 +
 sha1_name.c                 |   86 +++++++++++++++++++++++++++++++++++++++++++
 t/t1511-rev-parse-caret.sh  |   45 ++++++++++++++++++++++
 6 files changed, 166 insertions(+), 5 deletions(-)

diff --git a/Documentation/config.txt b/Documentation/config.txt
index 0f85793..0c4fb66 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -588,6 +588,15 @@ it will be treated as a shell command.  For example, defining
 executed from the top-level directory of a repository, which may
 not necessarily be the current directory.
 
+sha1.*::
+	Extended SHA-1 syntax aliases. These aliases are similar to alias.*
+	but each will correspond to a '{caret}\{{tilde}alias\}' syntax (see
+	linkgit:gitrevisions[7]). '%sha1%' in the alias command will be
+	substituted with resolved SHA-1 before the caret. If
+	'{caret}\{{tilde}alias:extra\}' syntax is used, '%arg%' in the
+	alias command will be substituted with 'extra'. The command is
+	supposed to return an extended SHA-1 syntax.
+
 am.keepcr::
 	If true, git-am will call git-mailsplit for patches in mbox format
 	with parameter '--keep-cr'. In this case git-mailsplit will
diff --git a/Documentation/revisions.txt b/Documentation/revisions.txt
index 174fa8e..413f91c 100644
--- a/Documentation/revisions.txt
+++ b/Documentation/revisions.txt
@@ -106,6 +106,13 @@ the `$GIT_DIR/refs` directory or from the `$GIT_DIR/packed-refs` file.
   and dereference the tag recursively until a non-tag object is
   found.
 
+* A suffix '{caret}' followed by an SHA-1 alias with a leading
+  '{tilde}', all enclosed in brace pair (e.g.
+  `v0.998{caret}\{{tilde}alias\}`) will invoke the corresponding
+  alias command, specified in config (see linkgit:git-config[1],
+  key 'sha1.*'). The command is supposed to return an extended
+  SHA-1.
+
 * A suffix '{caret}' to a revision parameter followed by a brace
   pair that contains a text led by a slash (e.g. `HEAD^{/fix nasty bug}`):
   this is the same as `:/fix nasty bug` syntax below except that
diff --git a/alias.c b/alias.c
index 6626bb0..29a9903 100644
--- a/alias.c
+++ b/alias.c
@@ -1,12 +1,12 @@
 #include "cache.h"
 #include "run-command.h"
 
-static const char *alias_key;
 static char *alias_val;
 
 static int alias_lookup_cb(const char *k, const char *v, void *cb)
 {
-	if (!prefixcmp(k, "alias.") && !strcmp(k+6, alias_key)) {
+	const char *key = cb;
+	if (!strcmp(k, key)) {
 		if (!v)
 			return config_error_nonbool(k);
 		alias_val = xstrdup(v);
@@ -15,14 +15,27 @@ static int alias_lookup_cb(const char *k, const char *v, void *cb)
 	return 0;
 }
 
-char *alias_lookup(const char *alias)
+static char *generic_alias_lookup(const char *alias, const char *namespase)
 {
-	alias_key = alias;
+	struct strbuf key = STRBUF_INIT;
+	strbuf_addstr(&key, namespase);
+	strbuf_addstr(&key, alias);
 	alias_val = NULL;
-	git_config(alias_lookup_cb, NULL);
+	git_config(alias_lookup_cb, key.buf);
+	strbuf_release(&key);
 	return alias_val;
 }
 
+char *alias_lookup(const char *alias)
+{
+	return generic_alias_lookup(alias, "alias.");
+}
+
+char *sha1_alias_lookup(const char *alias)
+{
+	return generic_alias_lookup(alias, "sha1.");
+}
+
 #define SPLIT_CMDLINE_BAD_ENDING 1
 #define SPLIT_CMDLINE_UNCLOSED_QUOTE 2
 static const char *split_cmdline_errors[] = {
diff --git a/cache.h b/cache.h
index 20a37ff..56a1b18 100644
--- a/cache.h
+++ b/cache.h
@@ -1120,6 +1120,7 @@ struct alias_param {
 };
 
 char *alias_lookup(const char *alias);
+char *sha1_alias_lookup(const char *alias);
 int split_cmdline(char *cmdline, const char ***argv);
 /* Takes a negative value returned by split_cmdline */
 const char *split_cmdline_strerror(int cmdline_errno);
diff --git a/sha1_name.c b/sha1_name.c
index c5c59ce..3a98a50 100644
--- a/sha1_name.c
+++ b/sha1_name.c
@@ -529,6 +529,76 @@ struct object *peel_to_type(const char *name, int namelen,
 	}
 }
 
+/*
+ * Handle $SHA1^{~alias} syntax. Config key sha1.alias will be used.
+ * The following parameters are substituted:
+ *
+ *  - %sha1%  SHA-1 before ^{~alias}, required
+ *  - %arg%   extra arguments after colon in SHA1^{~alias:args}
+ *
+ * The alias returns a string, preferabbly SHA-1.
+ */
+static int peel_alias(const char *name, int len, const char *sp,
+		      const unsigned char *input_sha1,
+		      struct strbuf *result)
+{
+	struct alias_param *params, *param;
+	struct strbuf alias = STRBUF_INIT;
+	struct strbuf cmd = STRBUF_INIT;
+	char *s;
+	int ret, arg_len = 0;
+
+	if (name[len-1] != '}')
+		return -1;
+	len -= sp - name + 1; /* remove $SHA1^{~ and } */
+	if (!len)
+		return error("$SHA1^{~alias} syntax with no alias");
+
+	s = strchr(sp, ':');
+	if (s) {
+		arg_len = (sp + len) - (s + 1);
+		len = s - sp;
+	}
+	strbuf_add(&alias, sp, len);
+	s = sha1_alias_lookup(alias.buf);
+	if (!s) {
+		ret = error("unable to find SHA-1 alias '%s'", alias.buf);
+		goto done;
+	}
+	strbuf_attach(&cmd, s, strlen(s), strlen(s)+1);
+
+	extract_alias_params(cmd.buf, &params);
+	param = lookup_alias_param(params, "%sha1%");
+	if (!param) {		/* %sha1% is mandatory */
+		ret = error("%%sha1%% not found in alias '%s'", alias.buf);
+		goto done;
+	}
+	param->value = xstrdup(sha1_to_hex(input_sha1));
+
+	param = lookup_alias_param(params, "%arg%");
+	if (param && arg_len)
+		param->value = xstrndup(sp + len + 1,arg_len);
+	else if (param) {
+		ret = error("Alias '%s' needs arguments", alias.buf);
+		goto done;
+	}
+	else if (arg_len) {
+		ret = error("Arguments are given but alias '%s' does not need them", alias.buf);
+		goto done;
+	}
+
+	expand_alias_params(&cmd, params);
+	free_alias_params(params);
+
+	trace_printf("trace: sha1 alias expansion: %s => %s\n",
+		     alias.buf, cmd.buf);
+	ret = get_alias_oneline(alias.buf, cmd.buf, result);
+done:
+	strbuf_release(&alias);
+	strbuf_release(&cmd);
+	return ret;
+}
+
 static int peel_onion(const char *name, int len, unsigned char *sha1)
 {
 	unsigned char outer[20];
@@ -566,6 +636,22 @@ static int peel_onion(const char *name, int len, unsigned char *sha1)
 		expected_type = OBJ_NONE;
 	else if (sp[0] == '/')
 		expected_type = OBJ_COMMIT;
+	else if (sp[0] == '~') {
+		struct strbuf new_name = STRBUF_INIT;
+
+		if (get_sha1_1(name, sp - name - 2, outer))
+			return -1;
+
+		if (peel_alias(name, len, sp + 1, outer, &new_name))
+			return -1;
+		if (get_sha1_1(new_name.buf, new_name.len, sha1)) {
+			strbuf_release(&new_name);
+			return -1;
+		}
+
+		strbuf_release(&new_name);
+		return 0;
+	}
 	else
 		return -1;
 
diff --git a/t/t1511-rev-parse-caret.sh b/t/t1511-rev-parse-caret.sh
index e043cb7..b99bfa2 100755
--- a/t/t1511-rev-parse-caret.sh
+++ b/t/t1511-rev-parse-caret.sh
@@ -70,4 +70,49 @@ test_expect_success 'ref^{/Initial}' '
 	test_cmp expected actual
 '
 
+test_expect_success 'ref^{~}' '
+	test_must_fail git rev-parse HEAD^{~}
+'
+
+test_expect_success 'ref^{~non-existent}' '
+	test_must_fail git rev-parse HEAD^{~non-existent}
+'
+
+test_expect_success 'ref^{~simple}' '
+	git config sha1.simple "rev-parse %sha1%" &&
+	test_must_fail git rev-parse master^{~simple:something} &&
+	git rev-parse master^{~simple} >actual &&
+	git rev-parse master >expected &&
+	test_cmp expected actual
+'
+
+test_expect_success 'ref^{~external}' '
+	git config sha1.external "!echo %sha1%" &&
+	test_must_fail git rev-parse master^{~external:something} &&
+	git rev-parse master^{~external} >actual &&
+	git rev-parse master >expected &&
+	test_cmp expected actual
+'
+
+test_expect_success 'ref^{~witharg:args}' '
+	git config sha1.witharg "!echo %sha1%^{%arg%}" &&
+	test_must_fail git rev-parse master^{~witharg} &&
+	git rev-parse master^{~witharg:tree} >actual &&
+	git rev-parse master^{tree} >expected &&
+	test_cmp expected actual
+'
+
+test_expect_success 'ref^{~simple}^{~external}' '
+	git rev-parse master^{~simple}^{~external} >actual &&
+	git rev-parse master >expected &&
+	test_cmp expected actual
+'
+
+test_expect_success 'ref^{~mapping}' '
+	git config sha1.mapping "!echo %sha1%^{~simple}" &&
+	git rev-parse master^{~mapping} >actual &&
+	git rev-parse master >expected &&
+	test_cmp expected actual
+'
+
 test_done
-- 
1.7.3.3.476.g10a82