[Diagnostics] Allow result build to detect ErrorExprs in the body

lib/Sema/BuilderTransform.cpp

@@ -1872,6 +1872,13 @@ class PreCheckResultBuilderApplication : public ASTWalker {
           E, DC, /*replaceInvalidRefsWithErrors=*/false);
       HasError |= transaction.hasErrors();
 
+      if (!HasError) {
+        E->forEachChildExpr([&](Expr *expr) {
+          HasError |= isa<ErrorExpr>(expr);
+          return HasError ? nullptr : expr;
+        });
+      }
+
       if (SuppressDiagnostics)
         transaction.abort();
 

lib/Sema/CSFix.cpp

@@ -1734,14 +1734,26 @@ bool IgnoreInvalidResultBuilderBody::diagnose(const Solution &solution,
   class PreCheckWalker : public ASTWalker {
     DeclContext *DC;
     DiagnosticTransaction Transaction;
+    // Check whether expression(s) in the body of the
+    // result builder had any `ErrorExpr`s before pre-check.
+    bool FoundErrorExpr = false;
 
   public:
     PreCheckWalker(DeclContext *dc)
         : DC(dc), Transaction(dc->getASTContext().Diags) {}
 
     std::pair<bool, Expr *> walkToExprPre(Expr *E) override {
+      // This has to be checked before `preCheckExpression`
+      // because pre-check would convert invalid references
+      // into `ErrorExpr`s.
+      E->forEachChildExpr([&](Expr *expr) {
+        FoundErrorExpr |= isa<ErrorExpr>(expr);
+        return FoundErrorExpr ? nullptr : expr;
+      });
+
       auto hasError = ConstraintSystem::preCheckExpression(
           E, DC, /*replaceInvalidRefsWithErrors=*/true);
+
       return std::make_pair(false, hasError ? nullptr : E);
     }
 
@@ -1755,7 +1767,18 @@ bool IgnoreInvalidResultBuilderBody::diagnose(const Solution &solution,
     }
 
     bool diagnosed() const {
-      return Transaction.hasErrors();
+      // pre-check produced an error.
+      if (Transaction.hasErrors())
+        return true;
+
+      // If there were `ErrorExpr`s before pre-check
+      // they should have been diagnosed already by parser.
+      if (FoundErrorExpr) {
+        auto &DE = DC->getASTContext().Diags;
+        return DE.hadAnyError();
+      }
+
+      return false;
     }
   };
 

test/Constraints/result_builder_diags.swift

@@ -712,4 +712,13 @@ struct TuplifiedStructWithInvalidClosure {
       0
     }
   }
+
+  @TupleBuilder var errorsDiagnosedByParser: some Any {
+    if let cond = condition {
+      tuplify { _ in
+        self. // expected-error {{expected member name following '.'}}
+      }
+      42
+    }
+  }
 }