Find places where uno::Sequence is passed by value.

Implement a clang plugin to find them, and clean up existing code
to pass them by reference.

Change-Id: If642d87407c73346d9c0164b9fc77c5c3c4354b8
Reviewed-on: https://gerrit.libreoffice.org/9351
Reviewed-by: Noel Grandin <noelgrandin@gmail.com>
Tested-by: Noel Grandin <noelgrandin@gmail.com>

compilerplugins/clang/passsequencebyref.cxx

@@ -0,0 +1,63 @@
+/* -*- 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 com::sun::star::uno::Sequence is passed by value.
+// It's not very efficient, because that copies a whole list
+// They should rather be passed by reference.
+
+namespace {
+
+class PassSequenceByRef:
+    public RecursiveASTVisitor<PassSequenceByRef>, public loplugin::Plugin
+{
+public:
+    explicit PassSequenceByRef(InstantiationData const & data): Plugin(data) {}
+
+    virtual void run() override { TraverseDecl(compiler.getASTContext().getTranslationUnitDecl()); }
+
+    bool VisitFunctionDecl(const FunctionDecl * decl);
+};
+
+bool PassSequenceByRef::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.find("class com::sun::star::uno::Sequence") == 0) {
+            report(
+                DiagnosticsEngine::Warning,
+                "passing css::uno::Sequence by value, rather pass by reference .e.g. 'const css::uno::Sequence&' " + typeName,
+                pvDecl->getSourceRange().getBegin())
+              << pvDecl->getSourceRange();
+        }
+    }
+    return true;
+}
+
+loplugin::Plugin::Registration< PassSequenceByRef > X("passsequencebyref");
+
+}
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab: */