[cxx-importer] Import more C++ source locations into Swift

Occasionally, when the Swift compiler emits a diagnostic for a construct
that was imported from C++ we get a diagnostic with unknown location.
This is a bad user experience. It is particularly bad with the
borrow-checker related diagnostics. This patch extends the source
location importing to declarations in ClangImporter. There are some
invariants enforced by the Swift compile, e.g., a source range is
comprised of two valid source locations or two invalid ones. As a
result, this patch adds approximate source locations to some separators
like braces or parens that are not maintained by Clang. Having slightly
incorrect ranges in this case is better than emitting unknown source
locations.

Author: Gabor Horvath

lib/ClangImporter/ClangImporter.cpp

@@ -42,6 +42,7 @@
 #include "swift/Basic/Defer.h"
 #include "swift/Basic/Platform.h"
 #include "swift/Basic/Range.h"
+#include "swift/Basic/SourceLoc.h"
 #include "swift/Basic/StringExtras.h"
 #include "swift/Basic/Version.h"
 #include "swift/ClangImporter/ClangImporterRequests.h"
@@ -2854,14 +2855,12 @@ ClangImporter::Implementation::exportSourceLoc(SourceLoc loc) {
 
 SourceLoc
 ClangImporter::Implementation::importSourceLoc(clang::SourceLocation loc) {
-  // FIXME: Implement!
-  return SourceLoc();
+  return BuffersForDiagnostics.resolveSourceLocation(Instance->getSourceManager(), loc);
 }
 
 SourceRange
-ClangImporter::Implementation::importSourceRange(clang::SourceRange loc) {
-  // FIXME: Implement!
-  return SourceRange();
+ClangImporter::Implementation::importSourceRange(clang::SourceRange range) {
+  return SourceRange(importSourceLoc(range.getBegin()), importSourceLoc(range.getEnd()));
 }
 
 #pragma mark Importing names
@@ -5975,9 +5974,10 @@ cloneBaseMemberDecl(ValueDecl *decl, DeclContext *newContext) {
   if (auto typeAlias = dyn_cast<TypeAliasDecl>(decl)) {
     auto rawMemory = allocateMemoryForDecl<TypeAliasDecl>(
         typeAlias->getASTContext(), sizeof(TypeAliasDecl), false);
-    auto out = new (rawMemory) TypeAliasDecl(
-        typeAlias->getLoc(), typeAlias->getEqualLoc(), typeAlias->getName(),
-        typeAlias->getNameLoc(), typeAlias->getGenericParams(), newContext);
+    auto out = new (rawMemory)
+        TypeAliasDecl(typeAlias->getStartLoc(), typeAlias->getEqualLoc(),
+                      typeAlias->getName(), typeAlias->getNameLoc(),
+                      typeAlias->getGenericParams(), newContext);
     out->setUnderlyingType(typeAlias->getUnderlyingType());
     out->copyFormalAccessFrom(typeAlias);
     return out;

lib/ClangImporter/ImportDecl.cpp

@@ -43,6 +43,7 @@
 #include "swift/Basic/Assertions.h"
 #include "swift/Basic/Defer.h"
 #include "swift/Basic/PrettyStackTrace.h"
+#include "swift/Basic/SourceLoc.h"
 #include "swift/Basic/Statistic.h"
 #include "swift/Basic/StringExtras.h"
 #include "swift/Basic/Version.h"
@@ -1680,6 +1681,8 @@ namespace {
           // Create the wrapper struct.
           errorWrapper =
               new (C) StructDecl(loc, name, loc, std::nullopt, nullptr, dc);
+          SourceLoc end = Impl.importSourceLoc(decl->getEndLoc());
+          errorWrapper->setBraces(SourceRange(loc, end));
           errorWrapper->setAccess(AccessLevel::Public);
           errorWrapper->getAttrs().add(
             new (Impl.SwiftContext) FrozenAttr(/*IsImplicit*/true));
@@ -6491,7 +6494,8 @@ Decl *SwiftDeclConverter::importGlobalAsInitializer(
   }
 
   auto result = Impl.createDeclWithClangNode<ConstructorDecl>(
-      decl, AccessLevel::Public, name, /*NameLoc=*/SourceLoc(), failable,
+      decl, AccessLevel::Public, name,
+      Impl.importSourceLoc(decl->getLocation()), failable,
       /*FailabilityLoc=*/SourceLoc(),
       /*Async=*/false, /*AsyncLoc=*/SourceLoc(),
       /*Throws=*/false, /*ThrowsLoc=*/SourceLoc(), /*ThrownType=*/TypeLoc(),
@@ -7006,7 +7010,8 @@ ConstructorDecl *SwiftDeclConverter::importConstructor(
   assert(!importedName.getAsyncInfo());
   auto result = Impl.createDeclWithClangNode<ConstructorDecl>(
       objcMethod, AccessLevel::Public, importedName.getDeclName(),
-      /*NameLoc=*/SourceLoc(), failability, /*FailabilityLoc=*/SourceLoc(),
+      /*NameLoc=*/Impl.importSourceLoc(objcMethod->getLocation()), failability,
+      /*FailabilityLoc=*/SourceLoc(),
       /*Async=*/false, /*AsyncLoc=*/SourceLoc(),
       /*Throws=*/importedName.getErrorInfo().has_value(),
       /*ThrowsLoc=*/SourceLoc(), /*ThrownType=*/TypeLoc(), bodyParams,

lib/ClangImporter/ImportType.cpp

@@ -2788,7 +2788,15 @@ ParameterList *ClangImporter::Implementation::importFunctionParameterList(
   }
 
   // Form the parameter list.
-  return ParameterList::create(SwiftContext, parameters);
+  // Estimate locations for the begin and end of parameter list.
+  auto begin = clangDecl->getLocation();
+  auto end = begin;
+  if (!params.empty()) {
+    begin = params.front()->getBeginLoc();
+    end = params.back()->getEndLoc();
+  }
+  return ParameterList::create(SwiftContext, importSourceLoc(begin), parameters,
+                               importSourceLoc(end));
 }
 
 static bool isObjCMethodResultAudited(const clang::Decl *decl) {

lib/ClangImporter/ImporterImpl.h

@@ -23,12 +23,14 @@
 #include "ImportName.h"
 #include "SwiftLookupTable.h"
 #include "swift/AST/ASTContext.h"
+#include "swift/AST/Decl.h"
 #include "swift/AST/ForeignErrorConvention.h"
 #include "swift/AST/LazyResolver.h"
 #include "swift/AST/Module.h"
 #include "swift/AST/RequirementSignature.h"
 #include "swift/AST/Type.h"
 #include "swift/Basic/FileTypes.h"
+#include "swift/Basic/SourceLoc.h"
 #include "swift/Basic/StringExtras.h"
 #include "swift/ClangImporter/ClangImporter.h"
 #include "swift/ClangImporter/ClangModule.h"
@@ -1719,6 +1721,20 @@ class LLVM_LIBRARY_VISIBILITY ClangImporter::Implementation
     if (!isa<ParamDecl>(D))
       importSwiftAttrAttributes(D);
 
+    if constexpr (std::is_base_of_v<NominalTypeDecl, DeclTy>) {
+      // Estimate brace locations.
+      auto begin = ClangN.getAsDecl()->getBeginLoc();
+      auto end = ClangN.getAsDecl()->getEndLoc();
+      SourceRange range;
+      if (begin.isValid() && end.isValid() && D->getNameLoc().isValid())
+        range = SourceRange(importSourceLoc(begin), importSourceLoc(end));
+      else {
+        range = SourceRange(D->getNameLoc(), D->getNameLoc());
+      }
+      assert(range.isValid() == D->getNameLoc().isValid());
+      D->setBraces(range);
+    }
+
     return D;
   }