object-name: fix resolution of object names containing curly braces

Given a branch name of 'foo{bar', commands like

    git cat-file -p foo{bar:README.md

should succeed (assuming that branch had a README.md file, of course).
However, the change in cce91a2 (Change 'master@noon' syntax to
'master@{noon}'., 2006-05-19) presumed that curly braces would always
come after an '@' or '^' and be paired, causing e.g. 'foo{bar:README.md'
to entirely miss the ':' and assume there's no object being referenced.
In short, git would report:

    fatal: Not a valid object name foo{bar:README.md

Change the parsing to only make the assumption of paired curly braces
immediately after either a '@' or '^' character appears.

Add tests for this, as well as for a few other test cases that initial
versions of this patch broke:
  * 'foo@@{...}'
  * 'foo^{/${SEARCH_TEXT_WITH_COLON}}:${PATH}'

Note that we'd prefer duplicating the special logic for "@^" characters
here, because if get_oid_basic() or interpret_nth_prior_checkout() or
get_oid_basic() or similar gain extra methods of using curly braces,
then the logic in get_oid_with_context_1() would need to be updated as
well.  But it's not clear how to refactor all of these to have a simple
common callpoint with the specialized logic.

Reported-by: Gabriel Amaral <gabriel-amaral@github.com>
Helped-by: Michael Haggerty <mhagger@github.com>
Signed-off-by: Elijah Newren <newren@gmail.com>

object-name.c

@@ -2051,12 +2051,14 @@ static enum get_oid_result get_oid_with_context_1(struct repository *repo,
 		return -1;
 	}
 	for (cp = name, bracket_depth = 0; *cp; cp++) {
-		if (*cp == '{')
+		if (strchr("@^", *cp) && cp[1] == '{') {
+			cp++;
 			bracket_depth++;
-		else if (bracket_depth && *cp == '}')
+		} else if (bracket_depth && *cp == '}') {
 			bracket_depth--;
-		else if (!bracket_depth && *cp == ':')
+		} else if (!bracket_depth && *cp == ':') {
 			break;
+		}
 	}
 	if (*cp == ':') {
 		struct object_id tree_oid;

t/t1006-cat-file.sh

@@ -240,7 +240,8 @@ test_expect_success "setup" '
 	git config extensions.objectformat $test_hash_algo &&
 	git config extensions.compatobjectformat $test_compat_hash_algo &&
 	echo_without_newline "$hello_content" > hello &&
-	git update-index --add hello
+	git update-index --add hello &&
+	git commit -m "add hello file"
 '
 
 run_blob_tests () {
@@ -602,6 +603,34 @@ test_expect_success FUNNYNAMES '--batch-check, -Z with newline in input' '
 	test_cmp expect actual
 '
 
+test_expect_success 'setup with curly braches in input' '
+	git branch "foo{bar" HEAD &&
+	git branch "foo@" HEAD
+'
+
+test_expect_success 'object reference with curly brace' '
+	git cat-file -p "foo{bar:hello" >actual &&
+	git cat-file -p HEAD:hello >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'object reference with at-sign' '
+	git cat-file -p "foo@@{0}:hello" >actual &&
+	git cat-file -p HEAD:hello >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'setup with commit with colon' '
+	git commit-tree -m "testing: just a bunch of junk" HEAD^{tree} >out &&
+	git branch other $(cat out)
+'
+
+test_expect_success 'object reference via commit text search' '
+	git cat-file -p "other^{/testing:}:hello" >actual &&
+	git cat-file -p HEAD:hello >expect &&
+	test_cmp expect actual
+'
+
 test_expect_success 'setup blobs which are likely to delta' '
 	test-tool genrandom foo 10240 >foo &&
 	{ cat foo && echo plus; } >foo-plus &&