Check arguments length in trivial diagnostic lint

Author: clubby789

compiler/rustc_lint/src/internal.rs

@@ -478,8 +478,10 @@ impl EarlyLintPass for Diagnostics {
         }
         if !segments.iter().all(|(name, args)| {
             let arg = match name.as_str() {
-                "struct_span_err" | "span_note" | "span_label" | "span_help" => &args[1],
-                "note" | "help" => &args[0],
+                "struct_span_err" | "span_note" | "span_label" | "span_help" if args.len() == 2 => {
+                    &args[1]
+                }
+                "note" | "help" if args.len() == 1 => &args[0],
                 _ => {
                     return false;
                 }

tests/ui/lint/internal/trivial-diagnostics.rs

@@ -0,0 +1,8 @@
+// compile-flags: -Zunstable-options
+
+pub fn issue_111280() {
+    struct_span_err(msg).emit(); //~ ERROR cannot find value `msg`
+    //~^ ERROR cannot find function `struct_span_err`
+}
+
+fn main() {}

tests/ui/lint/internal/trivial-diagnostics.stderr

@@ -0,0 +1,15 @@
+error[E0425]: cannot find value `msg` in this scope
+  --> $DIR/trivial-diagnostics.rs:4:21
+   |
+LL |     struct_span_err(msg).emit();
+   |                     ^^^ not found in this scope
+
+error[E0425]: cannot find function `struct_span_err` in this scope
+  --> $DIR/trivial-diagnostics.rs:4:5
+   |
+LL |     struct_span_err(msg).emit();
+   |     ^^^^^^^^^^^^^^^ not found in this scope
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0425`.