Find places where OUString and OString are passed by value.

It's not very efficient, because we generally end up copying it twice -
once into the parameter and again into the destination OUString.

So I create a clang plugin that finds such places and generates a
warning so that we can convert them to pass-by-reference.

Change-Id: I5341a6ea9e3190f4b4c05c42c85595e3dcd83361

1 files changed, 71 insertions, 0 deletions

diff --git a/compilerplugins/clang/passstringbyref.cxx b/compilerplugins/clang/passstringbyref.cxx
new file mode 100644
index 000000000000..610796936493
--- /dev/null
+++ b/compilerplugins/clang/passstringbyref.cxx
@@ -0,0 +1,71 @@
+/* -*- 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 "plugin.hxx"
+
+// Find places where OUString and OString are passed by value.
+// It's not very efficient, because we generally end up copying it twice - once into the parameter and
+// again into the destination OUString.
+// They should rather be passed by reference.
+
+namespace {
+
+class PassStringByRef:
+    public RecursiveASTVisitor<PassStringByRef>, public loplugin::Plugin
+{
+public:
+    explicit PassStringByRef(InstantiationData const & data): Plugin(data) {}
+
+    virtual void run() override { TraverseDecl(compiler.getASTContext().getTranslationUnitDecl()); }
+
+    bool VisitFunctionDecl(const FunctionDecl * decl);
+};
+
+bool PassStringByRef::VisitFunctionDecl(const FunctionDecl * functionDecl) {
+    if (ignoreLocation(functionDecl)) {
+        return true;
+    }
+    // only warn on the definition/prototype of the function,
+    // not on the function implementation
+    if (functionDecl->isThisDeclarationADefinition() && functionDecl->getPreviousDecl() != nullptr) {
+        return true;
+    }
+    unsigned n = functionDecl->getNumParams();
+    for (unsigned i = 0; i != n; ++i) {
+        const ParmVarDecl * pvDecl = functionDecl->getParamDecl(i);
+        QualType t1 { pvDecl->getType() };
+        if (!t1->isClassType()) {
+            continue;
+        }
+        string typeName = t1.getUnqualifiedType().getCanonicalType().getAsString();
+        if (typeName == "class rtl::OUString") {
+            report(
+                DiagnosticsEngine::Warning,
+                "passing OUString by value, rather pass by reference",
+                pvDecl->getSourceRange().getBegin())
+              << pvDecl->getSourceRange();
+        }
+        else if (typeName == "class rtl::OString") {
+            report(
+                DiagnosticsEngine::Warning,
+                "passing OString by value, rather pass by reference",
+                pvDecl->getSourceRange().getBegin())
+              << pvDecl->getSourceRange();
+        }
+    }
+    return true;
+}
+
+loplugin::Plugin::Registration< PassStringByRef > X("passstringbyref");
+
+}
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab: */