thodg/libgit2

diff --git a/include/git2/merge.h b/include/git2/merge.h
index 7915050..9eb14cc 100644
--- a/include/git2/merge.h
+++ b/include/git2/merge.h
@@ -268,6 +268,26 @@ typedef enum {
 	GIT_MERGE_ANALYSIS_UNBORN = (1 << 3),
 } git_merge_analysis_t;
 
+typedef enum {
+	/*
+	 * No configuration was found that suggests a preferred behavior for
+	 * merge.
+	 */
+	GIT_MERGE_PREFERENCE_NONE = 0,
+
+	/**
+	 * There is a `merge.ff=false` configuration setting, suggesting that
+	 * the user does not want to allow a fast-forward merge.
+	 */
+	GIT_MERGE_PREFERENCE_NO_FASTFORWARD = (1 << 0),
+
+	/**
+	 * There is a `merge.ff=only` configuration setting, suggesting that
+	 * the user only wants fast-forward merges.
+	 */
+	GIT_MERGE_PREFERENCE_FASTFORWARD_ONLY = (1 << 1),
+} git_merge_preference_t;
+
 /**
  * Analyzes the given branch(es) and determines the opportunities for
  * merging them into the HEAD of the repository.
@@ -280,6 +300,7 @@ typedef enum {
  */
 GIT_EXTERN(int) git_merge_analysis(
 	git_merge_analysis_t *analysis_out,
+	git_merge_preference_t *preference_out,
 	git_repository *repo,
 	const git_merge_head **their_heads,
 	size_t their_heads_len);
diff --git a/src/merge.c b/src/merge.c
index 6a8e587..a279d31 100644
--- a/src/merge.c
+++ b/src/merge.c
@@ -2564,8 +2564,42 @@ done:
 	return error;
 }
 
+static int merge_preference(git_merge_preference_t *out, git_repository *repo)
+{
+	git_config *config;
+	const char *value;
+	int bool_value, error = 0;
+
+	*out = GIT_MERGE_PREFERENCE_NONE;
+
+	if ((error = git_repository_config_snapshot(&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_PREFERENCE_NO_FASTFORWARD;
+	} else {
+		if (strcasecmp(value, "only") == 0)
+			*out |= GIT_MERGE_PREFERENCE_FASTFORWARD_ONLY;
+	}
+
+done:
+	git_config_free(config);
+	return error;
+}
+
 int git_merge_analysis(
-	git_merge_analysis_t *out,
+	git_merge_analysis_t *analysis_out,
+	git_merge_preference_t *preference_out,
 	git_repository *repo,
 	const git_merge_head **their_heads,
 	size_t their_heads_len)
@@ -2573,14 +2607,7 @@ int git_merge_analysis(
 	git_merge_head *ancestor_head = NULL, *our_head = NULL;
 	int error = 0;
 
-	assert(out && repo && their_heads);
-
-	*out = GIT_MERGE_ANALYSIS_NONE;
-
-	if (git_repository_head_unborn(repo)) {
-		*out = GIT_MERGE_ANALYSIS_FASTFORWARD | GIT_MERGE_ANALYSIS_UNBORN;
-		goto done;
-	}
+	assert(analysis_out && preference_out && repo && their_heads);
 
 	if (their_heads_len != 1) {
 		giterr_set(GITERR_MERGE, "Can only merge a single branch");
@@ -2588,20 +2615,30 @@ int git_merge_analysis(
 		goto done;
 	}
 
+	*analysis_out = GIT_MERGE_ANALYSIS_NONE;
+
+	if ((error = merge_preference(preference_out, repo)) < 0)
+		goto done;
+
+	if (git_repository_head_unborn(repo)) {
+		*analysis_out |= GIT_MERGE_ANALYSIS_FASTFORWARD | GIT_MERGE_ANALYSIS_UNBORN;
+		goto done;
+	}
+
 	if ((error = merge_heads(&ancestor_head, &our_head, repo, their_heads, their_heads_len)) < 0)
 		goto done;
 
 	/* 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;
+		*analysis_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;
+		*analysis_out |= GIT_MERGE_ANALYSIS_FASTFORWARD | GIT_MERGE_ANALYSIS_NORMAL;
 
 	/* Otherwise, just a normal merge is possible. */
 	else
-		*out = GIT_MERGE_ANALYSIS_NORMAL;
+		*analysis_out |= GIT_MERGE_ANALYSIS_NORMAL;
 
 done:
 	git_merge_head_free(ancestor_head);
diff --git a/tests/merge/workdir/analysis.c b/tests/merge/workdir/analysis.c
index 0e93785..85918ab 100644
--- a/tests/merge/workdir/analysis.c
+++ b/tests/merge/workdir/analysis.c
@@ -36,72 +36,105 @@ void test_merge_workdir_analysis__cleanup(void)
 	cl_git_sandbox_cleanup();
 }
 
-static git_merge_analysis_t analysis_from_branch(const char *branchname)
+static void analysis_from_branch(
+	git_merge_analysis_t *merge_analysis,
+	git_merge_preference_t *merge_pref,
+	const char *branchname)
 {
 	git_buf refname = GIT_BUF_INIT;
 	git_reference *their_ref;
 	git_merge_head *their_head;
-	git_merge_analysis_t analysis;
 
 	git_buf_printf(&refname, "%s%s", GIT_REFS_HEADS_DIR, branchname);
 
 	cl_git_pass(git_reference_lookup(&their_ref, repo, git_buf_cstr(&refname)));
 	cl_git_pass(git_merge_head_from_ref(&their_head, repo, their_ref));
 
-	cl_git_pass(git_merge_analysis(&analysis, repo, (const git_merge_head **)&their_head, 1));
+	cl_git_pass(git_merge_analysis(merge_analysis, merge_pref, repo, (const git_merge_head **)&their_head, 1));
 
 	git_buf_free(&refname);
 	git_merge_head_free(their_head);
 	git_reference_free(their_ref);
-
-	return analysis;
 }
 
 void test_merge_workdir_analysis__fastforward(void)
 {
-	git_merge_analysis_t analysis;
+	git_merge_analysis_t merge_analysis;
+	git_merge_preference_t merge_pref;
 
-	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));
+	analysis_from_branch(&merge_analysis, &merge_pref, FASTFORWARD_BRANCH);
+	cl_assert_equal_i(GIT_MERGE_ANALYSIS_FASTFORWARD, (merge_analysis & GIT_MERGE_ANALYSIS_FASTFORWARD));
+	cl_assert_equal_i(GIT_MERGE_ANALYSIS_NORMAL, (merge_analysis & GIT_MERGE_ANALYSIS_NORMAL));
 }
 
 void test_merge_workdir_analysis__no_fastforward(void)
 {
-	git_merge_analysis_t analysis;
+	git_merge_analysis_t merge_analysis;
+	git_merge_preference_t merge_pref;
 
-	analysis = analysis_from_branch(NOFASTFORWARD_BRANCH);
-	cl_assert_equal_i(GIT_MERGE_ANALYSIS_NORMAL, analysis);
+	analysis_from_branch(&merge_analysis, &merge_pref, NOFASTFORWARD_BRANCH);
+	cl_assert_equal_i(GIT_MERGE_ANALYSIS_NORMAL, merge_analysis);
 }
 
 void test_merge_workdir_analysis__uptodate(void)
 {
-	git_merge_analysis_t analysis;
+	git_merge_analysis_t merge_analysis;
+	git_merge_preference_t merge_pref;
 
-	analysis = analysis_from_branch(UPTODATE_BRANCH);
-	cl_assert_equal_i(GIT_MERGE_ANALYSIS_UP_TO_DATE, analysis);
+	analysis_from_branch(&merge_analysis, &merge_pref, UPTODATE_BRANCH);
+	cl_assert_equal_i(GIT_MERGE_ANALYSIS_UP_TO_DATE, merge_analysis);
 }
 
 void test_merge_workdir_analysis__uptodate_merging_prev_commit(void)
 {
-	git_merge_analysis_t analysis;
+	git_merge_analysis_t merge_analysis;
+	git_merge_preference_t merge_pref;
 
-	analysis = analysis_from_branch(PREVIOUS_BRANCH);
-	cl_assert_equal_i(GIT_MERGE_ANALYSIS_UP_TO_DATE, analysis);
+	analysis_from_branch(&merge_analysis, &merge_pref, PREVIOUS_BRANCH);
+	cl_assert_equal_i(GIT_MERGE_ANALYSIS_UP_TO_DATE, merge_analysis);
 }
 
 void test_merge_workdir_analysis__unborn(void)
 {
-	git_merge_analysis_t analysis;
+	git_merge_analysis_t merge_analysis;
+	git_merge_preference_t merge_pref;
 	git_buf master = GIT_BUF_INIT;
 
 	git_buf_joinpath(&master, git_repository_path(repo), "refs/heads/master");
 	p_unlink(git_buf_cstr(&master));
 
-	analysis = analysis_from_branch(NOFASTFORWARD_BRANCH);
-	cl_assert_equal_i(GIT_MERGE_ANALYSIS_FASTFORWARD, (analysis & GIT_MERGE_ANALYSIS_FASTFORWARD));
-	cl_assert_equal_i(GIT_MERGE_ANALYSIS_UNBORN, (analysis & GIT_MERGE_ANALYSIS_UNBORN));
+	analysis_from_branch(&merge_analysis, &merge_pref, NOFASTFORWARD_BRANCH);
+	cl_assert_equal_i(GIT_MERGE_ANALYSIS_FASTFORWARD, (merge_analysis & GIT_MERGE_ANALYSIS_FASTFORWARD));
+	cl_assert_equal_i(GIT_MERGE_ANALYSIS_UNBORN, (merge_analysis & GIT_MERGE_ANALYSIS_UNBORN));
 
 	git_buf_free(&master);
 }
 
+void test_merge_workdir_analysis__fastforward_with_config_noff(void)
+{
+	git_config *config;
+	git_merge_analysis_t merge_analysis;
+	git_merge_preference_t merge_pref;
+
+	git_repository_config(&config, repo);
+	git_config_set_string(config, "merge.ff", "false");
+
+	analysis_from_branch(&merge_analysis, &merge_pref, FASTFORWARD_BRANCH);
+	cl_assert_equal_i(GIT_MERGE_ANALYSIS_FASTFORWARD, (merge_analysis & GIT_MERGE_ANALYSIS_FASTFORWARD));
+	cl_assert_equal_i(GIT_MERGE_ANALYSIS_NORMAL, (merge_analysis & GIT_MERGE_ANALYSIS_NORMAL));
+	cl_assert_equal_i(GIT_MERGE_PREFERENCE_NO_FASTFORWARD, (merge_pref & GIT_MERGE_PREFERENCE_NO_FASTFORWARD));
+}
+
+void test_merge_workdir_analysis__no_fastforward_with_config_ffonly(void)
+{
+	git_config *config;
+	git_merge_analysis_t merge_analysis;
+	git_merge_preference_t merge_pref;
+
+	git_repository_config(&config, repo);
+	git_config_set_string(config, "merge.ff", "only");
+
+	analysis_from_branch(&merge_analysis, &merge_pref, NOFASTFORWARD_BRANCH);
+	cl_assert_equal_i(GIT_MERGE_ANALYSIS_NORMAL, (merge_analysis & GIT_MERGE_ANALYSIS_NORMAL));
+	cl_assert_equal_i(GIT_MERGE_PREFERENCE_FASTFORWARD_ONLY, (merge_pref & GIT_MERGE_PREFERENCE_FASTFORWARD_ONLY));
+}