Make namespace checks look through LinkageSpecs

My clang-cl --with-visual-studio=2022preview build against VS 2022 Preview
17.5.0 Preview 2.0 had started to fail with

> [build CPT] compilerplugins/clang/test/getstr.cxx
> error: 'error' diagnostics expected but not seen:
>   File compilerplugins/clang/test/getstr.cxx Line 42: directly use object of type '{{(rtl::)?}}OString' in a call of 'operator <<', instead of calling 'getStr' first [loplugin:getstr]
>   File compilerplugins/clang/test/getstr.cxx Line 48: directly use object of type 'S' (aka 'rtl::OString') in a call of 'operator <<', instead of calling 'getStr' first [loplugin:getstr]
>   File compilerplugins/clang/test/getstr.cxx Line 49: directly use object of type 'rtl::OString' in a call of 'operator <<', instead of calling 'getStr' first [loplugin:getstr]
>   File compilerplugins/clang/test/getstr.cxx Line 55: directly use object of type 'rtl::OString' in a call of 'operator <<', instead of calling 'getStr' first [loplugin:getstr]
>   File compilerplugins/clang/test/getstr.cxx Line 57: directly use object of type '{{(rtl::)?}}OString' in a call of 'operator <<', instead of calling 'getStr' first [loplugin:getstr]
> 5 errors generated.

apparently because
C:/Program Files/Microsoft Visual Studio/2022/Preview/VC/Tools/MSVC/14.35.32124/include/ostream
now contains

[...]
> _EXPORT_STD extern "C++" template <class _Elem, class _Traits>
> class basic_ostream : virtual public basic_ios<_Elem, _Traits> { // control insertions into a stream buffer
[...]

with a wrapping extern "C++", so the call to StdNamespace() in

>         if (!loplugin::TypeCheck(expr->getArg(0)->getType())
>                  .ClassOrStruct("basic_ostream")
>                  .StdNamespace()) //TODO: check template args

in compilerplugins/clang/getstr.cxx no longer matched

Change-Id: Iaeb461d5aa855a8602c5c6f791407c08a1c5d309
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/144735
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

2 files changed, 13 insertions, 4 deletions

diff --git a/compilerplugins/clang/check.cxx b/compilerplugins/clang/check.cxx
index 93fd7c7f7307..7be98bf97d5c 100644
--- a/compilerplugins/clang/check.cxx
+++ b/compilerplugins/clang/check.cxx
@@ -202,7 +202,7 @@ TerminalCheck ContextCheck::GlobalNamespace() const {
 
 TerminalCheck ContextCheck::StdNamespace() const {
     return TerminalCheck(
-        context_ != nullptr && context_->isStdNamespace());
+        context_ != nullptr && lookThroughLinkageSpec()->isStdNamespace());
 }
 
 namespace {
@@ -224,15 +224,22 @@ bool isStdOrNestedNamespace(clang::DeclContext const * context) {
 }
 
 TerminalCheck ContextCheck::StdOrNestedNamespace() const {
-    return TerminalCheck(context_ != nullptr && isStdOrNestedNamespace(context_));
+    return TerminalCheck(context_ != nullptr && isStdOrNestedNamespace(lookThroughLinkageSpec()));
 }
 
 ContextCheck ContextCheck::AnonymousNamespace() const {
-    auto n = llvm::dyn_cast_or_null<clang::NamespaceDecl>(context_);
+    auto n = llvm::dyn_cast_or_null<clang::NamespaceDecl>(lookThroughLinkageSpec());
     return ContextCheck(
         n != nullptr && n->isAnonymousNamespace() ? n->getParent() : nullptr);
 }
 
+clang::DeclContext const * ContextCheck::lookThroughLinkageSpec() const {
+    if (context_ != nullptr && context_->getDeclKind() == clang::Decl::LinkageSpec) {
+        return context_->getParent();
+    }
+    return context_;
+}
+
 namespace {
 
 bool BaseCheckNotSomethingInterestingSubclass(const clang::CXXRecordDecl *BaseDefinition) {
diff --git a/compilerplugins/clang/check.hxx b/compilerplugins/clang/check.hxx
index 9c35acff7b5e..4ac311759832 100644
--- a/compilerplugins/clang/check.hxx
+++ b/compilerplugins/clang/check.hxx
@@ -140,6 +140,8 @@ public:
     explicit ContextCheck(const clang::NamespaceDecl * decl ) : context_( decl ) {}
 
 private:
+    clang::DeclContext const * lookThroughLinkageSpec() const;
+
     clang::DeclContext const * const context_;
 };
 
@@ -277,7 +279,7 @@ ContextCheck DeclCheck::Var(llvm::StringRef id) const
 ContextCheck ContextCheck::Namespace(llvm::StringRef id) const
 {
     if (context_) {
-        auto n = llvm::dyn_cast<clang::NamespaceDecl>(context_);
+        auto n = llvm::dyn_cast<clang::NamespaceDecl>(lookThroughLinkageSpec());
         if (n != nullptr) {
             auto const i = n->getIdentifier();
             if (i != nullptr && i->getName() == id) {