From: Tom Jones <thj@freebsd.org>
Subject: diff: Function names appearing inside diff context
To: gameoftrees@openbsd.org
Date: Wed, 21 Sep 2022 16:58:15 +0100

Hi,

There is an issue that if a function name appears within the context it
isn't discovered correctly and we instead get the previously declared
function in the file.

I am not sure how to fix this. I can't quite grasp why the range for the
left side contains the context already. I have included a patch that
resolves a single case, but I think I am missing how to discover the
correct offset.

The patch also includes tests that exercise this case. gdiff exhibits
this error, but openbsd diff doesn't seem to.

I'd love some advice on how to construct the start of the search
correctly.

- Tom
diff --git a/lib/diff_output.c b/lib/diff_output.c
index 3047221..4fa8900 100644
--- a/lib/diff_output.c
+++ b/lib/diff_output.c
@@ -280,7 +280,7 @@ diff_output_match_function_prototype(char *prototype, size_t prototype_size,
 
 	if (result->left->atoms.len > 0 && cc->left.start > 0) {
 		data = result->left;
-		start_atom = &data->atoms.head[cc->left.start - 1];
+		start_atom = &data->atoms.head[cc->left.start + 3];
 	} else
 		return DIFF_RC_OK;
 
diff --git a/test/expect124.diff b/test/expect124.diff
new file mode 100644
index 0000000..2ae051a
--- /dev/null
+++ b/test/expect124.diff
@@ -0,0 +1,9 @@
+--- test124.left-p.txt
++++ test124.right-p.txt
+@@ -11,5 +11,5 @@ return_test(int test) {
+ 
+ struct testfile *
+ return_test(int test) {
+-	return NULL;
++	return test*2;
+ }
diff --git a/test/test124.left-p.txt b/test/test124.left-p.txt
new file mode 100644
index 0000000..2c57789
--- /dev/null
+++ b/test/test124.left-p.txt
@@ -0,0 +1,15 @@
+static void
+doSomethingThenPrintHello(int test)
+{
+	test = test << 4;
+	if (test % 8 == 6) {
+		return;
+	}
+
+	print("goodbye\n");
+}
+
+struct testfile *
+return_test(int test) {
+	return NULL;
+}
diff --git a/test/test124.right-p.txt b/test/test124.right-p.txt
new file mode 100644
index 0000000..9f2252e
--- /dev/null
+++ b/test/test124.right-p.txt
@@ -0,0 +1,15 @@
+static void
+doSomethingThenPrintHello(int test)
+{
+	test = test << 4;
+	if (test % 8 == 6) {
+		return;
+	}
+
+	print("goodbye\n");
+}
+
+struct testfile *
+return_test(int test) {
+	return test*2;
+}