Fix loplugin:conststringvar

...after abc0344a234567aee0edcb4523036758d966481d "convert conststringvar plugin
to shared infrastructre", causing errors like

> [C  ] cppuhelper/source/findsofficepath.c
> Assertion failed: (Ctx.getLangOpts().CPlusPlus), function isCXX11ConstantExpr, file llvm/llvm-project/clang/lib/AST/ExprConstant.cpp, line 14567.
> Stack dump:
[...]
> 6  libsystem_c.dylib        0x00007fff7266ca1c abort + 120
> 7  libsystem_c.dylib        0x00007fff7266bcd6 err + 0
> 8  clang                    0x000000010b857ca3 clang::Expr::isCXX11ConstantExpr(clang::ASTContext const&, clang::APValue*, clang::SourceLocation*) const (.cold.2) + 35
> 9  clang                    0x0000000109f7497e clang::Expr::isCXX11ConstantExpr(clang::ASTContext const&, clang::APValue*, clang::SourceLocation*) const + 1022
> 10 plugin.so                0x00000001182741ab loplugin::SharedRecursiveASTVisitorBasic::VisitVarDecl(clang::VarDecl*) + 1051
[...]
> clang-11: error: clang frontend command failed due to signal (use -v to see invocation)

Change-Id: I18c37dba294b0effd85bead8aa6e5679f77502d9
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/88777
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

1 files changed, 17 insertions, 10 deletions

diff --git a/compilerplugins/clang/conststringvar.cxx b/compilerplugins/clang/conststringvar.cxx
index c5e83722ac47..99cfb01c06f7 100644
--- a/compilerplugins/clang/conststringvar.cxx
+++ b/compilerplugins/clang/conststringvar.cxx
@@ -27,17 +27,24 @@ public:
     explicit ConstStringVar(loplugin::InstantiationData const & data):
         FilteringPlugin(data) {}
 
+    bool preRun() override {
+        return compiler.getLangOpts().CPlusPlus;
+            // clang::Expr::isCXX11ConstantExpr only works for C++
+    }
+
+    void postRun() override {
+        for (auto v: vars_) {
+            report(
+                DiagnosticsEngine::Warning,
+                "variable is only used as rvalue, should be const",
+                v->getLocation())
+                << v->getSourceRange();
+        }
+    }
+
     void run() override {
-        if (compiler.getLangOpts().CPlusPlus) {
-                // clang::Expr::isCXX11ConstantExpr only works for C++
-            TraverseDecl(compiler.getASTContext().getTranslationUnitDecl());
-            for (auto v: vars_) {
-                report(
-                    DiagnosticsEngine::Warning,
-                    "variable is only used as rvalue, should be const",
-                    v->getLocation())
-                    << v->getSourceRange();
-            }
+        if (preRun() && TraverseDecl(compiler.getASTContext().getTranslationUnitDecl())) {
+            postRun();
         }
     }