Introduce GIT_MERGE_CONFIG_* for merge.ff settings

git_merge_analysis will now return GIT_MERGE_CONFIG_NO_FASTFORWARD
when merge.ff=false and GIT_MERGE_CONFIG_FASTFORWARD_ONLY when
merge.ff=true

include/git2/merge.h

@@ -266,6 +266,18 @@ typedef enum {
 	 * to simply set HEAD to the target commit(s).
 	 */
 	GIT_MERGE_ANALYSIS_UNBORN = (1 << 3),
+
+	/**
+	 * There is a `merge.ff=false` configuration setting, suggesting that
+	 * the user does not want to allow a fast-forward merge.
+	 */
+	GIT_MERGE_CONFIG_NO_FASTFORWARD = (1 << 4),
+
+	/**
+	 * There is a `merge.ff=only` configuration setting, suggesting that
+	 * the user only wants fast-forward merges.
+	 */
+	GIT_MERGE_CONFIG_FASTFORWARD_ONLY = (1 << 5),
 } git_merge_analysis_t;
 
 /**

src/merge.c

@@ -2564,6 +2564,37 @@ done:
 	return error;
 }
 
+int analysis_config(git_merge_analysis_t *out, git_repository *repo)
+{
+	git_config *config;
+	const char *value;
+	int bool_value, error = 0;
+
+	if ((error = git_repository_config(&config, repo)) < 0)
+		goto done;
+
+	if ((error = git_config_get_string(&value, config, "merge.ff")) < 0) {
+		if (error == GIT_ENOTFOUND) {
+			giterr_clear();
+			error = 0;
+		}
+
+		goto done;
+	}
+
+	if (git_config_parse_bool(&bool_value, value) == 0) {
+		if (!bool_value)
+			*out |= GIT_MERGE_CONFIG_NO_FASTFORWARD;
+	} else {
+		if (strcasecmp(value, "only") == 0)
+			*out |= GIT_MERGE_CONFIG_FASTFORWARD_ONLY;
+	}
+
+done:
+	git_config_free(config);
+	return error;
+}
+
 int git_merge_analysis(
 	git_merge_analysis_t *out,
 	git_repository *repo,
@@ -2575,16 +2606,19 @@ int git_merge_analysis(
 
 	assert(out && repo && their_heads);
 
+	if (their_heads_len != 1) {
+		giterr_set(GITERR_MERGE, "Can only merge a single branch");
+		error = -1;
+		goto done;
+	}
+
 	*out = GIT_MERGE_ANALYSIS_NONE;
 
-	if (git_repository_head_unborn(repo)) {
-		*out = GIT_MERGE_ANALYSIS_FASTFORWARD | GIT_MERGE_ANALYSIS_UNBORN;
+	if ((error = analysis_config(out, repo)) < 0)
 		goto done;
-	}
 
-	if (their_heads_len != 1) {
-		giterr_set(GITERR_MERGE, "Can only merge a single branch");
-		error = -1;
+	if (git_repository_head_unborn(repo)) {
+		*out |= GIT_MERGE_ANALYSIS_FASTFORWARD | GIT_MERGE_ANALYSIS_UNBORN;
 		goto done;
 	}
 
@@ -2593,15 +2627,15 @@ int git_merge_analysis(
 
 	/* We're up-to-date if we're trying to merge our own common ancestor. */
 	if (ancestor_head && git_oid_equal(&ancestor_head->oid, &their_heads[0]->oid))
-		*out = GIT_MERGE_ANALYSIS_UP_TO_DATE;
+		*out |= GIT_MERGE_ANALYSIS_UP_TO_DATE;
 
 	/* We're fastforwardable if we're our own common ancestor. */
 	else if (ancestor_head && git_oid_equal(&ancestor_head->oid, &our_head->oid))
-		*out = GIT_MERGE_ANALYSIS_FASTFORWARD | GIT_MERGE_ANALYSIS_NORMAL;
+		*out |= GIT_MERGE_ANALYSIS_FASTFORWARD | GIT_MERGE_ANALYSIS_NORMAL;
 
 	/* Otherwise, just a normal merge is possible. */
 	else
-		*out = GIT_MERGE_ANALYSIS_NORMAL;
+		*out |= GIT_MERGE_ANALYSIS_NORMAL;
 
 done:
 	git_merge_head_free(ancestor_head);

tests/merge/workdir/analysis.c

@@ -105,3 +105,29 @@ void test_merge_workdir_analysis__unborn(void)
 	git_buf_free(&master);
 }
 
+void test_merge_workdir_analysis__fastforward_with_config_noff(void)
+{
+	git_config *config;
+	git_merge_analysis_t analysis;
+
+	git_repository_config(&config, repo);
+	git_config_set_string(config, "merge.ff", "false");
+
+	analysis = analysis_from_branch(FASTFORWARD_BRANCH);
+	cl_assert_equal_i(GIT_MERGE_ANALYSIS_FASTFORWARD, (analysis & GIT_MERGE_ANALYSIS_FASTFORWARD));
+	cl_assert_equal_i(GIT_MERGE_ANALYSIS_NORMAL, (analysis & GIT_MERGE_ANALYSIS_NORMAL));
+	cl_assert_equal_i(GIT_MERGE_CONFIG_NO_FASTFORWARD, (analysis & GIT_MERGE_CONFIG_NO_FASTFORWARD));
+}
+
+void test_merge_workdir_analysis__no_fastforward_with_config_ffonly(void)
+{
+	git_config *config;
+	git_merge_analysis_t analysis;
+
+	git_repository_config(&config, repo);
+	git_config_set_string(config, "merge.ff", "only");
+
+	analysis = analysis_from_branch(NOFASTFORWARD_BRANCH);
+	cl_assert_equal_i(GIT_MERGE_ANALYSIS_NORMAL, (analysis & GIT_MERGE_ANALYSIS_NORMAL));
+	cl_assert_equal_i(GIT_MERGE_CONFIG_FASTFORWARD_ONLY, (analysis & GIT_MERGE_CONFIG_FASTFORWARD_ONLY));
+}