new loplugin: defaultparams

find places where we do not need to be passing a parameter to a
function, because that function has a default value which matches the
value we are passing.

Change-Id: I04d1fd6275204dd4925e6563282464f461123632

compilerplugins/clang/defaultparams.cxx

@@ -0,0 +1,80 @@
+/* -*- 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 <string>
+#include <set>
+
+#include "plugin.hxx"
+
+// Find places where we call a method with values == the values specified in the parameter defaults.
+// i.e. where the code might as well not specify anything.
+
+namespace {
+
+class DefaultParams:
+    public RecursiveASTVisitor<DefaultParams>, public loplugin::Plugin
+{
+public:
+    explicit DefaultParams(InstantiationData const & data): Plugin(data) {}
+
+    virtual void run() override { TraverseDecl(compiler.getASTContext().getTranslationUnitDecl()); }
+
+    bool VisitCallExpr(const CallExpr * callExpr);
+};
+
+bool DefaultParams::VisitCallExpr(const CallExpr * callExpr) {
+    if (ignoreLocation(callExpr)) {
+        return true;
+    }
+    if (callExpr->getNumArgs() == 0) {
+        return true;
+    }
+    if (callExpr->getDirectCallee() == nullptr) {
+        return true;
+    }
+    const FunctionDecl* functionDecl = callExpr->getDirectCallee()->getCanonicalDecl();
+    unsigned i = callExpr->getNumArgs() - 1;
+    const Expr* arg = callExpr->getArg(i);
+    // variadic functions
+    if (i >= functionDecl->getNumParams()) {
+        return true;
+    }
+    const ParmVarDecl* parmVarDecl = functionDecl->getParamDecl(i);
+    const Expr* defaultArgExpr = parmVarDecl->getDefaultArg();
+    if (!arg->isDefaultArgument() &&
+        arg->isIntegerConstantExpr(compiler.getASTContext()) &&
+        parmVarDecl->hasDefaultArg() &&
+        !parmVarDecl->hasUninstantiatedDefaultArg() &&
+        defaultArgExpr->isIntegerConstantExpr(compiler.getASTContext()))
+    {
+        APSInt x1, x2;
+        if (arg->EvaluateAsInt(x1, compiler.getASTContext()) &&
+            defaultArgExpr->EvaluateAsInt(x2, compiler.getASTContext()) &&
+            x1 == x2)
+        {
+            report(
+                DiagnosticsEngine::Warning,
+                "not necessary to pass this argument, it defaults to the same value",
+                callExpr->getSourceRange().getBegin())
+              << callExpr->getSourceRange();
+            report(
+                DiagnosticsEngine::Warning,
+                "default method parameter declaration here",
+                parmVarDecl->getSourceRange().getBegin())
+              << parmVarDecl->getSourceRange();
+        }
+    }
+    return true;
+}
+
+loplugin::Plugin::Registration< DefaultParams > X("defaultparams", false);
+
+}
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab: */