Fix #117284, Skip unused variables lint for args in macro

Author: chenyukang

compiler/rustc_passes/src/liveness.rs

@@ -1579,8 +1579,16 @@ impl<'tcx> Liveness<'_, 'tcx> {
         pat: &hir::Pat<'_>,
         opt_body: Option<&hir::Body<'_>>,
     ) {
-        let first_hir_id = hir_ids_and_spans[0].0;
+        // #117284, when `pat_span` and `ident_span` have different contexts
+        // we can't provide a good suggestion.
+        if hir_ids_and_spans
+            .iter()
+            .any(|(_, pat_span, ident_span)| pat_span.ctxt() != ident_span.ctxt())
+        {
+            return;
+        }
 
+        let first_hir_id = hir_ids_and_spans[0].0;
         if let Some(name) = self.should_warn(var).filter(|name| name != "self") {
             // annoying: for parameters in funcs like `fn(x: i32)
             // {ret}`, there is only one node, so asking about

tests/ui/lint/unused/issue-117284-arg-in-macro.rs

@@ -0,0 +1,17 @@
+// check-pass
+#![deny(unused_variables)]
+macro_rules! make_var {
+    ($struct:ident, $var:ident) => {
+        let $var = $struct.$var;
+    };
+}
+
+#[allow(unused)]
+struct MyStruct {
+    var: i32,
+}
+
+fn main() {
+    let s = MyStruct { var: 42 };
+    make_var!(s, var);
+}