New loplugin:externvar

Change-Id: Ie5404f11cbc5b05bd18455ae81526eb2de01548c

1 files changed, 104 insertions, 0 deletions

diff --git a/compilerplugins/clang/externvar.cxx b/compilerplugins/clang/externvar.cxx
new file mode 100644
index 000000000000..9569a3de37d2
--- /dev/null
+++ b/compilerplugins/clang/externvar.cxx
@@ -0,0 +1,104 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4; fill-column: 100 -*- */
+/*
+ * This file is part of the LibreOffice project.
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+#include "check.hxx"
+#include "plugin.hxx"
+
+// Find variable declarations at namespace scope that need not have external
+// linkage.
+
+namespace {
+
+// It looks like Clang wrongly implements DR 4
+// (<http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#4>) and treats
+// a variable declared in an 'extern "..." {...}'-style linkage-specification as
+// if it contained the 'extern' specifier:
+bool hasExternalLinkage(VarDecl const * decl) {
+    if (decl->getLinkageAndVisibility().getLinkage() != ExternalLinkage) {
+        return false;
+    }
+    for (auto ctx = decl->getLexicalDeclContext();
+         ctx->getDeclKind() != Decl::TranslationUnit;
+         ctx = ctx->getLexicalParent())
+    {
+        if (auto ls = dyn_cast<LinkageSpecDecl>(ctx)) {
+            if (!ls->hasBraces()) {
+                return true;
+            }
+            if (auto prev = decl->getPreviousDecl()) {
+                return hasExternalLinkage(prev);
+            }
+            return !decl->isInAnonymousNamespace();
+        }
+    }
+    return true;
+}
+
+class ExternVar: public RecursiveASTVisitor<ExternVar>, public loplugin::Plugin
+{
+public:
+    explicit ExternVar(InstantiationData const & data): Plugin(data) {}
+
+    void run() override
+    { TraverseDecl(compiler.getASTContext().getTranslationUnitDecl()); }
+
+    bool VisitVarDecl(VarDecl const * decl) {
+        if (ignoreLocation(decl)) {
+            return true;
+        }
+        if (decl->isStaticDataMember()) {
+            return true;
+        }
+        if (!(decl->isFirstDecl()
+              && compiler.getSourceManager().isInMainFile(decl->getLocation())
+              && hasExternalLinkage(decl)))
+        {
+            return true;
+        }
+        auto def = decl->getDefinition();
+        if (def == nullptr) {
+            // Code like
+            //
+            //   namespace { extern int v; }
+            //   int f() { return sizeof(v); }
+            //
+            // is already handled by Clang itself with an error "variable 'v' is
+            // not needed and will not be emitted"
+            return true;
+        }
+        report(
+            DiagnosticsEngine::Warning,
+            "variable with external linkage not declared in an include file",
+            def->getLocation())
+            << def->getSourceRange();
+        report(
+            DiagnosticsEngine::Note,
+            ("should either have internal linkage or be declared in an include"
+             " file"),
+            def->getLocation())
+            << def->getSourceRange();
+        for (auto prev = def;;) {
+            prev = prev->getPreviousDecl();
+            if (prev == nullptr) {
+                break;
+            }
+            report(
+                DiagnosticsEngine::Note, "previously declared here",
+                prev->getLocation())
+                << prev->getSourceRange();
+        }
+        return true;
+    }
+};
+
+loplugin::Plugin::Registration<ExternVar> X("externvar");
+
+}
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab cinoptions=b1,g0,N-s cinkeys+=0=break: */