Add check if span is from macro expansion

compiler/rustc_lint/src/shadowed_into_iter.rs

@@ -124,6 +124,11 @@ impl<'tcx> LateLintPass<'tcx> for ShadowedIntoIter {
                 return;
             };
 
+        // This check needs to avoid ICE from when `receiver_arg` is from macro expansion
+        // Which leads to empty span in span arithmetic below
+        // cc: https://github.com/rust-lang/rust/issues/147408
+        let span = receiver_arg.span.find_ancestor_in_same_ctxt(expr.span);
+
         // If this expression comes from the `IntoIter::into_iter` inside of a for loop,
         // we should just suggest removing the `.into_iter()` or changing it to `.iter()`
         // to disambiguate if we want to iterate by-value or by-ref.
@@ -134,14 +139,15 @@ impl<'tcx> LateLintPass<'tcx> for ShadowedIntoIter {
             && let hir::ExprKind::Call(path, [_]) = &arg.kind
             && let hir::ExprKind::Path(qpath) = path.kind
             && cx.tcx.qpath_is_lang_item(qpath, LangItem::IntoIterIntoIter)
+            && let Some(span) = span
         {
             Some(ShadowedIntoIterDiagSub::RemoveIntoIter {
-                span: receiver_arg.span.shrink_to_hi().to(expr.span.shrink_to_hi()),
+                span: span.shrink_to_hi().to(expr.span.shrink_to_hi()),
             })
-        } else if can_suggest_ufcs {
+        } else if can_suggest_ufcs && let Some(span) = span {
             Some(ShadowedIntoIterDiagSub::UseExplicitIntoIter {
                 start_span: expr.span.shrink_to_lo(),
-                end_span: receiver_arg.span.shrink_to_hi().to(expr.span.shrink_to_hi()),
+                end_span: span.shrink_to_hi().to(expr.span.shrink_to_hi()),
             })
         } else {
             None

tests/ui/macros/macro-expansion-empty-span-147408.rs

@@ -0,0 +1,24 @@
+//@ check-pass
+//@ compile-flags: -Afor_loops_over_fallibles -Warray_into_iter
+
+fn main() {
+    macro_rules! mac {
+        (iter $e:expr) => {
+            $e.iter()
+        };
+        (into_iter $e:expr) => {
+            $e.into_iter() //~ WARN this method call resolves to
+            //~^ WARN this changes meaning in Rust 2021
+        };
+        (next $e:expr) => {
+            $e.iter().next()
+        };
+    }
+
+    for _ in dbg!([1, 2]).iter() {}
+    for _ in dbg!([1, 2]).into_iter() {} //~ WARN this method call resolves to
+    //~^ WARN this changes meaning in Rust 2021
+    for _ in mac!(iter [1, 2]) {}
+    for _ in mac!(into_iter [1, 2]) {}
+    for _ in mac!(next [1, 2]) {}
+}

tests/ui/macros/macro-expansion-empty-span-147408.stderr

@@ -0,0 +1,35 @@
+warning: this method call resolves to `<&[T; N] as IntoIterator>::into_iter` (due to backwards compatibility), but will resolve to `<[T; N] as IntoIterator>::into_iter` in Rust 2021
+  --> $DIR/macro-expansion-empty-span-147408.rs:19:27
+   |
+LL |     for _ in dbg!([1, 2]).into_iter() {}
+   |                           ^^^^^^^^^
+   |
+   = warning: this changes meaning in Rust 2021
+   = note: for more information, see <https://doc.rust-lang.org/edition-guide/rust-2021/IntoIterator-for-arrays.html>
+   = note: requested on the command line with `-W array-into-iter`
+help: use `.iter()` instead of `.into_iter()` to avoid ambiguity
+   |
+LL -     for _ in dbg!([1, 2]).into_iter() {}
+LL +     for _ in dbg!([1, 2]).iter() {}
+   |
+help: or remove `.into_iter()` to iterate by value
+   |
+LL -     for _ in dbg!([1, 2]).into_iter() {}
+LL +     for _ in dbg!([1, 2]) {}
+   |
+
+warning: this method call resolves to `<&[T; N] as IntoIterator>::into_iter` (due to backwards compatibility), but will resolve to `<[T; N] as IntoIterator>::into_iter` in Rust 2021
+  --> $DIR/macro-expansion-empty-span-147408.rs:10:16
+   |
+LL |             $e.into_iter()
+   |                ^^^^^^^^^ help: use `.iter()` instead of `.into_iter()` to avoid ambiguity: `iter`
+...
+LL |     for _ in mac!(into_iter [1, 2]) {}
+   |              ---------------------- in this macro invocation
+   |
+   = warning: this changes meaning in Rust 2021
+   = note: for more information, see <https://doc.rust-lang.org/edition-guide/rust-2021/IntoIterator-for-arrays.html>
+   = note: this warning originates in the macro `mac` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+warning: 2 warnings emitted
+