new loplugin:emptyif

Change-Id: I1092115a0ceb3a5e6680a4b724b129f98a892c42
Reviewed-on: https://gerrit.libreoffice.org/48128
Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>

compilerplugins/clang/emptyif.cxx

@@ -0,0 +1,95 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/*
+ * 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 <cassert>
+#include <string>
+#include <iostream>
+#include <fstream>
+#include <set>
+#include "plugin.hxx"
+
+/**
+  Check for places where we do
+   if (xxx) ;
+  or
+   if (xxx) {}
+ */
+namespace
+{
+class EmptyIf : public RecursiveASTVisitor<EmptyIf>, public loplugin::RewritePlugin
+{
+public:
+    explicit EmptyIf(loplugin::InstantiationData const& data)
+        : RewritePlugin(data)
+    {
+    }
+
+    virtual void run() override
+    {
+        StringRef fn(compiler.getSourceManager()
+                         .getFileEntryForID(compiler.getSourceManager().getMainFileID())
+                         ->getName());
+        TraverseDecl(compiler.getASTContext().getTranslationUnitDecl());
+    }
+
+    bool VisitIfStmt(IfStmt const*);
+
+private:
+    bool ContainsComment(Stmt const*);
+};
+
+static bool empty(Stmt const* stmt)
+{
+    if (isa<NullStmt>(stmt))
+        return true;
+    auto compoundStmt = dyn_cast<CompoundStmt>(stmt);
+    if (!compoundStmt)
+        return false;
+    return compoundStmt->size() == 0;
+}
+
+bool EmptyIf::ContainsComment(Stmt const* stmt)
+{
+    auto range = stmt->getSourceRange();
+    SourceManager& SM = compiler.getSourceManager();
+    SourceLocation startLoc = range.getBegin();
+    SourceLocation endLoc = range.getEnd();
+    char const* p1 = SM.getCharacterData(startLoc);
+    char const* p2 = SM.getCharacterData(endLoc);
+    p2 += Lexer::MeasureTokenLength(endLoc, SM, compiler.getLangOpts());
+    auto s = llvm::StringRef(p1, p2 - p1);
+    return s.find("//") != llvm::StringRef::npos || s.find("/*") != llvm::StringRef::npos
+           || s.find("#if") != llvm::StringRef::npos;
+}
+
+bool EmptyIf::VisitIfStmt(IfStmt const* ifStmt)
+{
+    if (ignoreLocation(ifStmt))
+        return true;
+
+    if (ifStmt->getElse() && empty(ifStmt->getElse()) && !ContainsComment(ifStmt->getElse()))
+    {
+        report(DiagnosticsEngine::Warning, "empty else body", ifStmt->getElse()->getLocStart())
+            << ifStmt->getElse()->getSourceRange();
+        return true;
+    }
+
+    if (!ifStmt->getElse() && empty(ifStmt->getThen()) && !ContainsComment(ifStmt->getThen()))
+    {
+        report(DiagnosticsEngine::Warning, "empty if body", ifStmt->getLocStart())
+            << ifStmt->getSourceRange();
+    }
+
+    return true;
+}
+
+loplugin::Plugin::Registration<EmptyIf> X("emptyif", true);
+}
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab: */