Ensure that we don't try to access fields on a non-struct pattern type

compiler/rustc_resolve/src/late/diagnostics.rs

@@ -1130,7 +1130,9 @@ impl<'ast, 'ra: 'ast, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
         let None = following_seg else { return };
         for rib in self.ribs[ValueNS].iter().rev() {
             for (def_id, spans) in &rib.patterns_with_skipped_bindings {
-                if let Some(fields) = self.r.field_idents(*def_id) {
+                if let DefKind::Struct | DefKind::Variant = self.r.tcx.def_kind(*def_id)
+                    && let Some(fields) = self.r.field_idents(*def_id)
+                {
                     for field in fields {
                         if field.name == segment.ident.name {
                             if spans.iter().all(|(_, had_error)| had_error.is_err()) {

tests/ui/pattern/struct-pattern-on-non-struct-resolve-error.rs

@@ -0,0 +1,10 @@
+// Regression test for #135209.
+// We ensure that we don't try to access fields on a non-struct pattern type.
+fn main() {
+    if let <Vec<()> as Iterator>::Item { .. } = 1 {
+        //~^ ERROR E0658
+        //~| ERROR E0071
+        //~| ERROR E0277
+        x //~ ERROR E0425
+    }
+}

tests/ui/pattern/struct-pattern-on-non-struct-resolve-error.stderr

@@ -0,0 +1,34 @@
+error[E0425]: cannot find value `x` in this scope
+  --> $DIR/struct-pattern-on-non-struct-resolve-error.rs:8:9
+   |
+LL |         x
+   |         ^ not found in this scope
+
+error[E0658]: usage of qualified paths in this context is experimental
+  --> $DIR/struct-pattern-on-non-struct-resolve-error.rs:4:12
+   |
+LL |     if let <Vec<()> as Iterator>::Item { .. } = 1 {
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #86935 <https://github.com/rust-lang/rust/issues/86935> for more information
+   = help: add `#![feature(more_qualified_paths)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0071]: expected struct, variant or union type, found inferred type
+  --> $DIR/struct-pattern-on-non-struct-resolve-error.rs:4:12
+   |
+LL |     if let <Vec<()> as Iterator>::Item { .. } = 1 {
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^ not a struct
+
+error[E0277]: `Vec<()>` is not an iterator
+  --> $DIR/struct-pattern-on-non-struct-resolve-error.rs:4:12
+   |
+LL |     if let <Vec<()> as Iterator>::Item { .. } = 1 {
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^ `Vec<()>` is not an iterator
+   |
+   = help: the trait `Iterator` is not implemented for `Vec<()>`
+
+error: aborting due to 4 previous errors
+
+Some errors have detailed explanations: E0071, E0277, E0425, E0658.
+For more information about an error, try `rustc --explain E0071`.

tests/ui/pattern/struct-pattern-with-missing-fields-resolve-error.rs

@@ -3,6 +3,10 @@ struct Website {
     title: Option<String>,
 }
 
+enum Foo {
+    Bar { a: i32 },
+}
+
 fn main() {
     let website = Website {
         url: "http://www.example.com".into(),
@@ -18,4 +22,9 @@ fn main() {
         println!("[{}]({})", title, url); //~ ERROR cannot find value `title` in this scope
         //~^ NOTE not found in this scope
     }
+
+    let x = Foo::Bar { a: 1 };
+    if let Foo::Bar { .. } = x { //~ NOTE this pattern
+        println!("{a}"); //~ ERROR cannot find value `a` in this scope
+    }
 }

tests/ui/pattern/struct-pattern-with-missing-fields-resolve-error.stderr

@@ -1,19 +1,27 @@
 error: expected `,`
-  --> $DIR/struct-pattern-with-missing-fields-resolve-error.rs:12:31
+  --> $DIR/struct-pattern-with-missing-fields-resolve-error.rs:16:31
    |
 LL |     if let Website { url, Some(title) } = website {
    |            -------            ^
    |            |
    |            while parsing the fields for this pattern
 
 error[E0425]: cannot find value `title` in this scope
-  --> $DIR/struct-pattern-with-missing-fields-resolve-error.rs:18:30
+  --> $DIR/struct-pattern-with-missing-fields-resolve-error.rs:22:30
    |
 LL |     if let Website { url, .. } = website {
    |            ------------------- this pattern doesn't include `title`, which is available in `Website`
 LL |         println!("[{}]({})", title, url);
    |                              ^^^^^ not found in this scope
 
-error: aborting due to 2 previous errors
+error[E0425]: cannot find value `a` in this scope
+  --> $DIR/struct-pattern-with-missing-fields-resolve-error.rs:28:20
+   |
+LL |     if let Foo::Bar { .. } = x {
+   |            --------------- this pattern doesn't include `a`, which is available in `Bar`
+LL |         println!("{a}");
+   |                    ^ help: a local variable with a similar name exists: `x`
+
+error: aborting due to 3 previous errors
 
 For more information about this error, try `rustc --explain E0425`.