[flang] Add contextualizing interfaces to ExpressionAnalyzer and ContextualMessages

Original-commit: flang-compiler/f18@30a004d7b1
Reviewed-on: https://github.com/flang-compiler/f18/pull/790

flang/lib/parser/message.h

@@ -285,6 +285,7 @@ public:
 
   CharBlock at() const { return at_; }
   Messages *messages() const { return messages_; }
+  bool empty() const { return !messages_ || messages_->empty(); }
 
   // Set CharBlock for messages; restore when the returned value is deleted
   common::Restorer<CharBlock> SetLocation(CharBlock at) {
@@ -294,6 +295,12 @@ public:
     return common::ScopedSet(at_, std::move(at));
   }
 
+  // Diverts messages to another buffer; restored when the returned
+  // value is deleted.
+  common::Restorer<Messages *> SetMessages(Messages &buffer) {
+    return common::ScopedSet(messages_, &buffer);
+  }
+
   template<typename... A> Message *Say(CharBlock at, A &&... args) {
     if (messages_ != nullptr) {
       return &messages_->Say(at, std::forward<A>(args)...);

flang/lib/semantics/expression.cc

@@ -885,7 +885,7 @@ MaybeExpr ExpressionAnalyzer::Analyze(const parser::StructureComponent &sc) {
             "a designator"_err_en_US);
       }
     } else if (dtSpec == nullptr || dtSpec->scope() == nullptr) {
-      CHECK(context_.AnyFatalError());
+      CHECK(context_.AnyFatalError() || !foldingContext_.messages().empty());
       return std::nullopt;
     } else if (std::optional<DataRef> dataRef{
                    ExtractDataRef(std::move(*dtExpr))}) {
@@ -1534,7 +1534,7 @@ auto ExpressionAnalyzer::AnalyzeProcedureComponentRef(
       }
     }
   }
-  CHECK(context_.messages().AnyFatalError());
+  CHECK(!GetContextualMessages().empty());
   return std::nullopt;
 }
 

flang/lib/semantics/expression.h

@@ -121,16 +121,16 @@ public:
   using MaybeExpr = std::optional<Expr<SomeType>>;
 
   explicit ExpressionAnalyzer(semantics::SemanticsContext &sc) : context_{sc} {}
+  ExpressionAnalyzer(semantics::SemanticsContext &sc, FoldingContext &fc)
+    : context_{sc}, foldingContext_{fc} {}
   ExpressionAnalyzer(ExpressionAnalyzer &) = default;
 
   semantics::SemanticsContext &context() const { return context_; }
 
-  FoldingContext &GetFoldingContext() const {
-    return context_.foldingContext();
-  }
+  FoldingContext &GetFoldingContext() const { return foldingContext_; }
 
   parser::ContextualMessages &GetContextualMessages() {
-    return GetFoldingContext().messages();
+    return foldingContext_.messages();
   }
 
   template<typename... A> parser::Message *Say(A &&... args) {
@@ -341,6 +341,7 @@ private:
   MaybeExpr MakeFunctionRef(parser::CharBlock intrinsic, ActualArguments &&);
 
   semantics::SemanticsContext &context_;
+  FoldingContext &foldingContext_{context_.foldingContext()};
   std::map<parser::CharBlock, int> acImpliedDos_;  // values are INTEGER kinds
   bool fatalErrors_{false};
 };