Auto merge of #15223 - lowr:patch/no-unresolved-field-for-missing, r=HKalbasi

Don't show `unresolved-field` diagnostic for missing names

I don't think reporting ``"no field `[missing name]` on type `SomeType`"`` makes much sense because it's a syntax error rather than a semantic error. We already report a syntax error for it and I find it sufficient.

crates/hir-expand/src/name.rs

@@ -96,6 +96,15 @@ pub const fn missing() -> Name {
         Name::new_inline("[missing name]")
     }
 
+    /// Returns true if this is a fake name for things missing in the source code. See
+    /// [`missing()`][Self::missing] for details.
+    ///
+    /// Use this method instead of comparing with `Self::missing()` as missing names
+    /// (ideally should) have a `gensym` semantics.
+    pub fn is_missing(&self) -> bool {
+        self == &Name::missing()
+    }
+
     /// Generates a new name which is only equal to itself, by incrementing a counter. Due
     /// its implementation, it should not be used in things that salsa considers, like
     /// type names or field names, and it should be only used in names of local variables

crates/hir-ty/src/infer/expr.rs

@@ -1449,6 +1449,13 @@ fn lookup_field(
 
     fn infer_field_access(&mut self, tgt_expr: ExprId, receiver: ExprId, name: &Name) -> Ty {
         let receiver_ty = self.infer_expr_inner(receiver, &Expectation::none());
+
+        if name.is_missing() {
+            // Bail out early, don't even try to look up field. Also, we don't issue an unresolved
+            // field diagnostic because this is a syntax error rather than a semantic error.
+            return self.err_ty();
+        }
+
         match self.lookup_field(&receiver_ty, name) {
             Some((ty, field_id, adjustments, is_public)) => {
                 self.write_expr_adj(receiver, adjustments);

crates/ide-diagnostics/src/handlers/unresolved_field.rs

@@ -68,7 +68,10 @@ fn method_fix(
 }
 #[cfg(test)]
 mod tests {
-    use crate::tests::check_diagnostics;
+    use crate::{
+        tests::{check_diagnostics, check_diagnostics_with_config},
+        DiagnosticsConfig,
+    };
 
     #[test]
     fn smoke_test() {
@@ -146,4 +149,11 @@ fn foo() {
 "#,
         );
     }
+
+    #[test]
+    fn no_diagnostic_for_missing_name() {
+        let mut config = DiagnosticsConfig::test_sample();
+        config.disabled.insert("syntax-error".to_owned());
+        check_diagnostics_with_config(config, "fn foo() { (). }");
+    }
 }