diff: consolidate diff algorithm option parsing

A subsequent commit will need the ability to tell if the diff algorithm
was set through the command line through setting a new member of
diff_options. While this logic can be added to the
diff_opt_diff_algorithm() callback, the `--minimal` and `--histogram`
options are handled via OPT_BIT without a callback.

Remedy this by consolidating the options parsing logic for --minimal and
--histogram into one callback. This way we can modify `diff_options` in
that function.

As an additional refactor, the logic that sets the diff algorithm in
diff_opt_diff_algorithm() can be refactored into a helper that will
allow multiple callsites to set the diff algorithm.

Signed-off-by: John Cai <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: john-cai

diff.c

@@ -3437,6 +3437,22 @@ static int diff_filepair_is_phoney(struct diff_filespec *one,
 	return !DIFF_FILE_VALID(one) && !DIFF_FILE_VALID(two);
 }
 
+static int set_diff_algorithm(struct diff_options *opts,
+			      const char *alg)
+{
+	long value = parse_algorithm_value(alg);
+
+	if (value < 0)
+		return -1;
+
+	/* clear out previous settings */
+	DIFF_XDL_CLR(opts, NEED_MINIMAL);
+	opts->xdl_opts &= ~XDF_DIFF_ALGORITHM_MASK;
+	opts->xdl_opts |= value;
+
+	return 0;
+}
+
 static void builtin_diff(const char *name_a,
 			 const char *name_b,
 			 struct diff_filespec *one,
@@ -5117,17 +5133,28 @@ static int diff_opt_diff_algorithm(const struct option *opt,
 				   const char *arg, int unset)
 {
 	struct diff_options *options = opt->value;
-	long value = parse_algorithm_value(arg);
 
 	BUG_ON_OPT_NEG(unset);
-	if (value < 0)
+
+	if (set_diff_algorithm(options, arg))
 		return error(_("option diff-algorithm accepts \"myers\", "
 			       "\"minimal\", \"patience\" and \"histogram\""));
 
-	/* clear out previous settings */
-	DIFF_XDL_CLR(options, NEED_MINIMAL);
-	options->xdl_opts &= ~XDF_DIFF_ALGORITHM_MASK;
-	options->xdl_opts |= value;
+	return 0;
+}
+
+static int diff_opt_diff_algorithm_no_arg(const struct option *opt,
+				   const char *arg, int unset)
+{
+	struct diff_options *options = opt->value;
+
+	BUG_ON_OPT_NEG(unset);
+	BUG_ON_OPT_ARG(arg);
+
+	if (set_diff_algorithm(options, opt->long_name))
+		BUG("available diff algorithms include \"myers\", "
+			       "\"minimal\", \"patience\" and \"histogram\"");
+
 	return 0;
 }
 
@@ -5260,7 +5287,6 @@ static int diff_opt_patience(const struct option *opt,
 
 	BUG_ON_OPT_NEG(unset);
 	BUG_ON_OPT_ARG(arg);
-	options->xdl_opts = DIFF_WITH_ALG(options, PATIENCE_DIFF);
 	/*
 	 * Both --patience and --anchored use PATIENCE_DIFF
 	 * internally, so remove any anchors previously
@@ -5269,7 +5295,8 @@ static int diff_opt_patience(const struct option *opt,
 	for (i = 0; i < options->anchors_nr; i++)
 		free(options->anchors[i]);
 	options->anchors_nr = 0;
-	return 0;
+
+	return set_diff_algorithm(options, "patience");
 }
 
 static int diff_opt_ignore_regex(const struct option *opt,
@@ -5571,9 +5598,10 @@ static void prep_parse_options(struct diff_options *options)
 			    N_("prevent rename/copy detection if the number of rename/copy targets exceeds given limit")),
 
 		OPT_GROUP(N_("Diff algorithm options")),
-		OPT_BIT(0, "minimal", &options->xdl_opts,
-			N_("produce the smallest possible diff"),
-			XDF_NEED_MINIMAL),
+		OPT_CALLBACK_F(0, "minimal", options, NULL,
+			       N_("produce the smallest possible diff"),
+			       PARSE_OPT_NONEG | PARSE_OPT_NOARG,
+			       diff_opt_diff_algorithm_no_arg),
 		OPT_BIT_F('w', "ignore-all-space", &options->xdl_opts,
 			  N_("ignore whitespace when comparing lines"),
 			  XDF_IGNORE_WHITESPACE, PARSE_OPT_NONEG),
@@ -5599,9 +5627,10 @@ static void prep_parse_options(struct diff_options *options)
 			       N_("generate diff using the \"patience diff\" algorithm"),
 			       PARSE_OPT_NONEG | PARSE_OPT_NOARG,
 			       diff_opt_patience),
-		OPT_BITOP(0, "histogram", &options->xdl_opts,
-			  N_("generate diff using the \"histogram diff\" algorithm"),
-			  XDF_HISTOGRAM_DIFF, XDF_DIFF_ALGORITHM_MASK),
+		OPT_CALLBACK_F(0, "histogram", options, NULL,
+			       N_("generate diff using the \"histogram diff\" algorithm"),
+			       PARSE_OPT_NONEG | PARSE_OPT_NOARG,
+			       diff_opt_diff_algorithm_no_arg),
 		OPT_CALLBACK_F(0, "diff-algorithm", options, N_("<algorithm>"),
 			       N_("choose a diff algorithm"),
 			       PARSE_OPT_NONEG, diff_opt_diff_algorithm),