Add check if span is from macro expansion

compiler/rustc_lint/src/shadowed_into_iter.rs

@@ -134,6 +134,8 @@ impl<'tcx> LateLintPass<'tcx> for ShadowedIntoIter {
             && let hir::ExprKind::Call(path, [_]) = &arg.kind
             && let hir::ExprKind::Path(hir::QPath::LangItem(hir::LangItem::IntoIterIntoIter, ..)) =
                 &path.kind
+            && !receiver_arg.span.from_expansion()
+            && !expr.span.from_expansion()
         {
             Some(ShadowedIntoIterDiagSub::RemoveIntoIter {
                 span: receiver_arg.span.shrink_to_hi().to(expr.span.shrink_to_hi()),

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

@@ -0,0 +1,23 @@
+//@ check-pass
+
+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]) {} //~ WARN for loop over an
+}

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

@@ -0,0 +1,58 @@
+ WARN rustc_errors::emitter Invalid span $SRC_DIR/std/src/macros.rs:LL:COL (#11), error=SourceNotAvailable { filename: Real(Remapped { local_path: None, virtual_name: "$SRC_DIR/std/src/macros.rs" }) }
+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:18:27
+   |
+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: `#[warn(array_into_iter)]` (part of `#[warn(rust_2021_compatibility)]`) on by default
+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() {}
+   |
+
+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:9:16
+   |
+LL |             $e.into_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)
+help: use `.iter()` instead of `.into_iter()` to avoid ambiguity
+   |
+LL -             $e.into_iter()
+LL +             $e.iter()
+   |
+help: or use `IntoIterator::into_iter(..)` instead of `.into_iter()` to explicitly iterate by value
+   |
+LL |             IntoIterator::into_iter($e.into_iter())
+   |             ++++++++++++++++++++++++              +
+
+warning: for loop over an `Option`. This is more readably written as an `if let` statement
+  --> $DIR/macro-expansion-empty-span-147408.rs:22:14
+   |
+LL |     for _ in mac!(next [1, 2]) {}
+   |              ^^^^^^^^^^^^^^^^^
+   |
+   = note: `#[warn(for_loops_over_fallibles)]` on by default
+help: to iterate over `$e.iter()` remove the call to `next`
+   |
+LL -             $e.iter().next()
+LL +             .by_ref().next()
+   |
+help: consider using `if let` to clear intent
+   |
+LL -     for _ in mac!(next [1, 2]) {}
+LL +     if let Some(_) = mac!(next [1, 2]) {}
+   |
+
+warning: 3 warnings emitted
+