Ignoring let_underscore_untyped warnings in code from proc macros

Author: lochetti

clippy_lints/src/let_underscore.rs

@@ -1,4 +1,5 @@
 use clippy_utils::diagnostics::span_lint_and_help;
+use clippy_utils::is_from_proc_macro;
 use clippy_utils::ty::{implements_trait, is_must_use_ty, match_type};
 use clippy_utils::{is_must_use_func_call, paths};
 use rustc_hir::{ExprKind, Local, PatKind};
@@ -138,7 +139,7 @@ const SYNC_GUARD_PATHS: [&[&str]; 3] = [
 ];
 
 impl<'tcx> LateLintPass<'tcx> for LetUnderscore {
-    fn check_local(&mut self, cx: &LateContext<'_>, local: &Local<'_>) {
+    fn check_local(&mut self, cx: &LateContext<'tcx>, local: &Local<'tcx>) {
         if !in_external_macro(cx.tcx.sess, local.span)
             && let PatKind::Wild = local.pat.kind
             && let Some(init) = local.init
@@ -191,15 +192,20 @@ impl<'tcx> LateLintPass<'tcx> for LetUnderscore {
             if local.pat.default_binding_modes && local.ty.is_none() {
                 // When `default_binding_modes` is true, the `let` keyword is present.
 
-				// Ignore function calls that return impl traits...
-				if let Some(init) = local.init &&
-				matches!(init.kind, ExprKind::Call(_, _) | ExprKind::MethodCall(_, _, _, _)) {
-					let expr_ty = cx.typeck_results().expr_ty(init);
-					if expr_ty.is_impl_trait() {
-						return;
-					}
-				}
-
+				if let Some(init) = local.init {
+                    // Ignore function calls that return impl traits...
+                    if matches!(init.kind, ExprKind::Call(_, _) | ExprKind::MethodCall(_, _, _, _)) {
+                        let expr_ty = cx.typeck_results().expr_ty(init);
+                        if expr_ty.is_impl_trait() {
+                            return;
+                        }
+                    }
+    
+                    // Ignore if it is from a procedural macro...
+                    if is_from_proc_macro(cx, init) {
+                        return;
+                    }
+                }
 
 				span_lint_and_help(
                     cx,

tests/ui/let_underscore_untyped.rs

@@ -1,6 +1,12 @@
+//@aux-build: proc_macros.rs
+
 #![allow(unused)]
 #![warn(clippy::let_underscore_untyped)]
 
+extern crate proc_macros;
+use proc_macros::with_span;
+
+use clippy_utils::is_from_proc_macro;
 use std::future::Future;
 use std::{boxed::Box, fmt::Display};
 
@@ -32,6 +38,14 @@ fn g() -> impl Fn() {
     || {}
 }
 
+with_span!(
+    span
+
+    fn dont_lint_proc_macro() {
+        let _ = a();
+    }
+);
+
 fn main() {
     let _ = a();
     let _ = b(1);

tests/ui/let_underscore_untyped.stderr

@@ -1,60 +1,60 @@
 error: non-binding `let` without a type annotation
-  --> $DIR/let_underscore_untyped.rs:36:5
+  --> $DIR/let_underscore_untyped.rs:50:5
    |
 LL |     let _ = a();
    |     ^^^^^^^^^^^^
    |
 help: consider adding a type annotation
-  --> $DIR/let_underscore_untyped.rs:36:10
+  --> $DIR/let_underscore_untyped.rs:50:10
    |
 LL |     let _ = a();
    |          ^
    = note: `-D clippy::let-underscore-untyped` implied by `-D warnings`
 
 error: non-binding `let` without a type annotation
-  --> $DIR/let_underscore_untyped.rs:37:5
+  --> $DIR/let_underscore_untyped.rs:51:5
    |
 LL |     let _ = b(1);
    |     ^^^^^^^^^^^^^
    |
 help: consider adding a type annotation
-  --> $DIR/let_underscore_untyped.rs:37:10
+  --> $DIR/let_underscore_untyped.rs:51:10
    |
 LL |     let _ = b(1);
    |          ^
 
 error: non-binding `let` without a type annotation
-  --> $DIR/let_underscore_untyped.rs:39:5
+  --> $DIR/let_underscore_untyped.rs:53:5
    |
 LL |     let _ = d(&1);
    |     ^^^^^^^^^^^^^^
    |
 help: consider adding a type annotation
-  --> $DIR/let_underscore_untyped.rs:39:10
+  --> $DIR/let_underscore_untyped.rs:53:10
    |
 LL |     let _ = d(&1);
    |          ^
 
 error: non-binding `let` without a type annotation
-  --> $DIR/let_underscore_untyped.rs:40:5
+  --> $DIR/let_underscore_untyped.rs:54:5
    |
 LL |     let _ = e();
    |     ^^^^^^^^^^^^
    |
 help: consider adding a type annotation
-  --> $DIR/let_underscore_untyped.rs:40:10
+  --> $DIR/let_underscore_untyped.rs:54:10
    |
 LL |     let _ = e();
    |          ^
 
 error: non-binding `let` without a type annotation
-  --> $DIR/let_underscore_untyped.rs:41:5
+  --> $DIR/let_underscore_untyped.rs:55:5
    |
 LL |     let _ = f();
    |     ^^^^^^^^^^^^
    |
 help: consider adding a type annotation
-  --> $DIR/let_underscore_untyped.rs:41:10
+  --> $DIR/let_underscore_untyped.rs:55:10
    |
 LL |     let _ = f();
    |          ^