Add regression test for source line numbers

tests/rustdoc/source-line-numbers.rs

@@ -0,0 +1,35 @@
+// This test ensures that we have the expected number of line generated.
+
+#![crate_name = "foo"]
+
+//@ has 'src/foo/source-line-numbers.rs.html'
+//@ count - '//a[@data-nosnippet]' 35
+//@ has - '//a[@id="35"]' '35'
+
+#[
+macro_export
+]
+macro_rules! bar {
+    ($x:ident) => {{
+        $x += 2;
+        $x *= 2;
+    }}
+}
+
+/*
+multi line
+comment
+*/
+fn x(_: u8, _: u8) {}
+
+fn foo() {
+    let mut y = 0;
+    bar!(y);
+    println!("
+    {y}
+    ");
+    x(
+      1,
+      2,
+    );
+}