Fix #10498

clippy_lints/src/let_with_type_underscore.rs

@@ -1,4 +1,4 @@
-use clippy_utils::diagnostics::span_lint_and_help;
+use clippy_utils::{diagnostics::span_lint_and_help, is_from_proc_macro};
 use rustc_hir::{Local, TyKind};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_middle::lint::in_external_macro;
@@ -32,7 +32,12 @@ fn check_local<'tcx>(&mut self, cx: &LateContext<'tcx>, local: &'tcx Local<'tcx>
             if let TyKind::Infer = &ty.kind; // that type is '_'
             if local.span.ctxt() == ty.span.ctxt();
             then {
-                span_lint_and_help(cx,
+                if let Some(init) = local.init && is_from_proc_macro(cx, init) {
+                    return;
+                }
+
+                span_lint_and_help(
+                    cx,
                     LET_WITH_TYPE_UNDERSCORE,
                     local.span,
                     "variable declared with type underscore",

tests/ui/let_with_type_underscore.rs

@@ -1,7 +1,10 @@
+//@aux-build: proc_macros.rs
 #![allow(unused)]
 #![warn(clippy::let_with_type_underscore)]
 #![allow(clippy::let_unit_value)]
 
+extern crate proc_macros;
+
 fn func() -> &'static str {
     ""
 }
@@ -16,4 +19,10 @@ fn main() {
     let x = func();
     let x: Vec<_> = Vec::<u32>::new();
     let x: [_; 1] = [1];
+
+    // do not lint from procedural macros
+    proc_macros::with_span! {
+        span
+        let x: _ = ();
+    };
 }

tests/ui/let_with_type_underscore.stderr

@@ -1,36 +1,36 @@
 error: variable declared with type underscore
-  --> $DIR/let_with_type_underscore.rs:11:5
+  --> $DIR/let_with_type_underscore.rs:14:5
    |
 LL |     let x: _ = 1;
    |     ^^^^^^^^^^^^^
    |
 help: remove the explicit type `_` declaration
-  --> $DIR/let_with_type_underscore.rs:11:10
+  --> $DIR/let_with_type_underscore.rs:14:10
    |
 LL |     let x: _ = 1;
    |          ^^^
    = note: `-D clippy::let-with-type-underscore` implied by `-D warnings`
 
 error: variable declared with type underscore
-  --> $DIR/let_with_type_underscore.rs:12:5
+  --> $DIR/let_with_type_underscore.rs:15:5
    |
 LL |     let _: _ = 2;
    |     ^^^^^^^^^^^^^
    |
 help: remove the explicit type `_` declaration
-  --> $DIR/let_with_type_underscore.rs:12:10
+  --> $DIR/let_with_type_underscore.rs:15:10
    |
 LL |     let _: _ = 2;
    |          ^^^
 
 error: variable declared with type underscore
-  --> $DIR/let_with_type_underscore.rs:13:5
+  --> $DIR/let_with_type_underscore.rs:16:5
    |
 LL |     let x: _ = func();
    |     ^^^^^^^^^^^^^^^^^^
    |
 help: remove the explicit type `_` declaration
-  --> $DIR/let_with_type_underscore.rs:13:10
+  --> $DIR/let_with_type_underscore.rs:16:10
    |
 LL |     let x: _ = func();
    |          ^^^