[PATCH v2 1/3] range-diff/format-patch: refactor check for commit range

["Johannes Schindelin via GitGitGadget" <gitgitgadget@xxxxxxxxx>]

From: Johannes Schindelin <johannes.schindelin@xxxxxx>

Currently, when called with exactly two arguments, `git range-diff`
tests for a literal `..` in each of the two. Likewise, the argument
provided via `--range-diff` to `git format-patch` is checked in the same
manner.

However, `<commit>^!` is a perfectly valid commit range, equivalent to
`<commit>^..<commit>` according to the `SPECIFYING RANGES` section of
gitrevisions[7].

In preparation for allowing more sophisticated ways to specify commit
ranges, let's refactor the check into its own function.

Signed-off-by: Johannes Schindelin <johannes.schindelin@xxxxxx>
---
 builtin/log.c        | 2 +-
 builtin/range-diff.c | 9 +++++----
 revision.c           | 5 +++++
 revision.h           | 7 +++++++
 4 files changed, 18 insertions(+), 5 deletions(-)

diff --git a/builtin/log.c b/builtin/log.c
index bd6ff4f9f95..099abdfb7e6 100644
--- a/builtin/log.c
+++ b/builtin/log.c
@@ -1680,7 +1680,7 @@ static void infer_range_diff_ranges(struct strbuf *r1,
 				    struct commit *head)
 {
 	const char *head_oid = oid_to_hex(&head->object.oid);
-	int prev_is_range = !!strstr(prev, "..");
+	int prev_is_range = specifies_commit_range(prev);
 
 	if (prev_is_range)
 		strbuf_addstr(r1, prev);
diff --git a/builtin/range-diff.c b/builtin/range-diff.c
index 24c4162f744..89d54158011 100644
--- a/builtin/range-diff.c
+++ b/builtin/range-diff.c
@@ -3,6 +3,7 @@
 #include "parse-options.h"
 #include "range-diff.h"
 #include "config.h"
+#include "revision.h"
 
 static const char * const builtin_range_diff_usage[] = {
 N_("git range-diff [<options>] <old-base>..<old-tip> <new-base>..<new-tip>"),
@@ -46,12 +47,12 @@ int cmd_range_diff(int argc, const char **argv, const char *prefix)
 		diffopt.use_color = 1;
 
 	if (argc == 2) {
-		if (!strstr(argv[0], ".."))
-			die(_("no .. in range: '%s'"), argv[0]);
+		if (!specifies_commit_range(argv[0]))
+			die(_("not a commit range: '%s'"), argv[0]);
 		strbuf_addstr(&range1, argv[0]);
 
-		if (!strstr(argv[1], ".."))
-			die(_("no .. in range: '%s'"), argv[1]);
+		if (!specifies_commit_range(argv[1]))
+			die(_("not a commit range: '%s'"), argv[1]);
 		strbuf_addstr(&range2, argv[1]);
 	} else if (argc == 3) {
 		strbuf_addf(&range1, "%s..%s", argv[0], argv[1]);
diff --git a/revision.c b/revision.c
index 9dff845bed6..00675f598a3 100644
--- a/revision.c
+++ b/revision.c
@@ -4206,3 +4206,8 @@ void put_revision_mark(const struct rev_info *revs, const struct commit *commit)
 	fputs(mark, stdout);
 	putchar(' ');
 }
+
+int specifies_commit_range(const char *range)
+{
+	return !!strstr(range, "..");
+}
diff --git a/revision.h b/revision.h
index 086ff10280d..66777c8e60f 100644
--- a/revision.h
+++ b/revision.h
@@ -457,4 +457,11 @@ int rewrite_parents(struct rev_info *revs,
  */
 struct commit_list *get_saved_parents(struct rev_info *revs, const struct commit *commit);
 
+/*
+ * Determine whether the given argument defines a commit range, e.g. A..B.
+ * Note that this only validates the format but does _not_ parse it, i.e.
+ * it does _not_ look up the specified commits in the local repository.
+ */
+int specifies_commit_range(const char *range);
+
 #endif
-- 
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