More tests for ambiguous OIDs across packs

The test coverage for ambiguous OIDs was pretty thin.  This adds
a bunch of new objects both in packs, across packs, and loose that
match to 8 characters so that we can test various cases of
ambiguous lookups.

include/git2/odb.h

@@ -120,7 +120,7 @@ GIT_EXTERN(int) git_odb_read(git_odb_object **out, git_odb *db, const git_oid *i
  * @param db database to search for the object in.
  * @param short_id a prefix of the id of the object to read.
  * @param len the length of the prefix
- * @return 
+ * @return
  * - 0 if the object was read;
  * - GIT_ENOTFOUND if the object is not in the database.
  * - GIT_EAMBIGUOUS if the prefix is ambiguous (several objects match the prefix)

tests-clar/odb/mixed.c

@@ -18,8 +18,72 @@ void test_odb_mixed__dup_oid(void) {
 	const char hex[] = "ce013625030ba8dba906f756967f9e9ca394464a";
 	git_oid oid;
 	git_odb_object *obj;
+
 	cl_git_pass(git_oid_fromstr(&oid, hex));
 	cl_git_pass(git_odb_read_prefix(&obj, _odb, &oid, GIT_OID_HEXSZ));
 	git_odb_object_free(obj);
 }
 
+/* some known sha collisions of file content:
+ *   'aabqhq' and 'aaazvc' with prefix 'dea509d0' (+ '9' and + 'b')
+ *   'aaeufo' and 'aaaohs' with prefix '81b5bff5' (+ 'f' and + 'b')
+ *   'aafewy' and 'aaepta' with prefix '739e3c4c'
+ *   'aahsyn' and 'aadrjg' with prefix '0ddeaded' (+ '9' and + 'e')
+ */
+
+void test_odb_mixed__dup_oid_prefix_0(void) {
+	char hex[10];
+	git_oid oid;
+	git_odb_object *obj;
+
+	/* ambiguous in the same pack file */
+
+	strncpy(hex, "dea509d0", sizeof(hex));
+	cl_git_pass(git_oid_fromstrn(&oid, hex, strlen(hex)));
+	cl_assert_equal_i(
+		GIT_EAMBIGUOUS, git_odb_read_prefix(&obj, _odb, &oid, strlen(hex)));
+
+	strncpy(hex, "dea509d09", sizeof(hex));
+	cl_git_pass(git_oid_fromstrn(&oid, hex, strlen(hex)));
+	cl_git_pass(git_odb_read_prefix(&obj, _odb, &oid, strlen(hex)));
+	git_odb_object_free(obj);
+
+	strncpy(hex, "dea509d0b", sizeof(hex));
+	cl_git_pass(git_oid_fromstrn(&oid, hex, strlen(hex)));
+	cl_git_pass(git_odb_read_prefix(&obj, _odb, &oid, strlen(hex)));
+	git_odb_object_free(obj);
+
+	/* ambiguous in different pack files */
+
+	strncpy(hex, "81b5bff5", sizeof(hex));
+	cl_git_pass(git_oid_fromstrn(&oid, hex, strlen(hex)));
+	cl_assert_equal_i(
+		GIT_EAMBIGUOUS, git_odb_read_prefix(&obj, _odb, &oid, strlen(hex)));
+
+	strncpy(hex, "81b5bff5b", sizeof(hex));
+	cl_git_pass(git_oid_fromstrn(&oid, hex, strlen(hex)));
+	cl_git_pass(git_odb_read_prefix(&obj, _odb, &oid, strlen(hex)));
+	git_odb_object_free(obj);
+
+	strncpy(hex, "81b5bff5f", sizeof(hex));
+	cl_git_pass(git_oid_fromstrn(&oid, hex, strlen(hex)));
+	cl_git_pass(git_odb_read_prefix(&obj, _odb, &oid, strlen(hex)));
+	git_odb_object_free(obj);
+
+	/* ambiguous in pack file and loose */
+
+	strncpy(hex, "0ddeaded", sizeof(hex));
+	cl_git_pass(git_oid_fromstrn(&oid, hex, strlen(hex)));
+	cl_assert_equal_i(
+		GIT_EAMBIGUOUS, git_odb_read_prefix(&obj, _odb, &oid, strlen(hex)));
+
+	strncpy(hex, "0ddeaded9", sizeof(hex));
+	cl_git_pass(git_oid_fromstrn(&oid, hex, strlen(hex)));
+	cl_git_pass(git_odb_read_prefix(&obj, _odb, &oid, strlen(hex)));
+	git_odb_object_free(obj);
+
+	strncpy(hex, "0ddeadede", sizeof(hex));
+	cl_git_pass(git_oid_fromstrn(&oid, hex, strlen(hex)));
+	cl_git_pass(git_odb_read_prefix(&obj, _odb, &oid, strlen(hex)));
+	git_odb_object_free(obj);
+}

tests-clar/resources/duplicate.git/config

 [core]
 	repositoryformatversion = 0
 	filemode = true
-	bare = false
+	bare = true
 	logallrefupdates = true

tests-clar/resources/duplicate.git/refs/heads/dummy-marker.txt

+dummy