new loplugin:constfields

look for fields which are only assigned to in the constructor, so they
can be made const

Change-Id: I0b76817c2181227b04f6a29d6a808f5e31999765
Reviewed-on: https://gerrit.libreoffice.org/60393
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>

compilerplugins/clang/constfieldsrewrite.cxx

@@ -0,0 +1,143 @@
+/* -*- 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/.
+ */
+
+#if !defined _WIN32 //TODO, #include <sys/mman.h>
+
+#include <cassert>
+#include <string>
+#include <iostream>
+#include "plugin.hxx"
+#include "check.hxx"
+#include <sys/mman.h>
+#include <sys/types.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <sys/stat.h>
+#include <assert.h>
+#include <cstring>
+
+/**
+  This is intended to be run as the second stage of the "constfields" clang plugin.
+*/
+
+namespace
+{
+class ConstFieldsRewrite : public RecursiveASTVisitor<ConstFieldsRewrite>,
+                           public loplugin::RewritePlugin
+{
+public:
+    explicit ConstFieldsRewrite(loplugin::InstantiationData const& data);
+    ~ConstFieldsRewrite();
+
+    virtual void run() override
+    {
+        if (rewriter)
+        {
+            TraverseDecl(compiler.getASTContext().getTranslationUnitDecl());
+        }
+    }
+
+    bool VisitFieldDecl(const FieldDecl* var);
+
+private:
+    // I use a brute-force approach - mmap the results file and do a linear search on it
+    // It works surprisingly well, because the file is small enough to fit into L2 cache on modern CPU's
+    size_t mmapFilesize;
+    int mmapFD;
+    char* mmappedData;
+};
+
+size_t getFilesize(const char* filename)
+{
+    struct stat st;
+    stat(filename, &st);
+    return st.st_size;
+}
+
+ConstFieldsRewrite::ConstFieldsRewrite(loplugin::InstantiationData const& data)
+    : RewritePlugin(data)
+{
+    static const char sInputFile[] = SRCDIR "/compilerplugins/clang/constfields.results";
+    mmapFilesize = getFilesize(sInputFile);
+    //Open file
+    mmapFD = open(sInputFile, O_RDONLY, 0);
+    assert(mmapFD != -1);
+    //Execute mmap
+    mmappedData = static_cast<char*>(mmap(NULL, mmapFilesize, PROT_READ, MAP_PRIVATE, mmapFD, 0));
+    assert(mmappedData != NULL);
+}
+
+ConstFieldsRewrite::~ConstFieldsRewrite()
+{
+    //Cleanup
+    int rc = munmap(mmappedData, mmapFilesize);
+    assert(rc == 0);
+    close(mmapFD);
+}
+
+bool ConstFieldsRewrite::VisitFieldDecl(const FieldDecl* fieldDecl)
+{
+    if (ignoreLocation(fieldDecl))
+        return true;
+    // ignore stuff that forms part of the stable URE interface
+    if (isInUnoIncludeFile(compiler.getSourceManager().getSpellingLoc(
+            fieldDecl->getCanonicalDecl()->getLocation())))
+        return true;
+    // in case we've already processed this field
+    if (fieldDecl->getType().isConstQualified())
+        return true;
+    // in case we've already processed this field
+    if (fieldDecl->getType().isConstQualified())
+        return true;
+    // TODO rewriting T& is a bit trickier
+    if (loplugin::TypeCheck(fieldDecl->getType()).LvalueReference())
+        return true;
+
+    const RecordDecl* recordDecl = fieldDecl->getParent();
+    std::string parentClassName;
+    if (const CXXRecordDecl* cxxRecordDecl = dyn_cast<CXXRecordDecl>(recordDecl))
+    {
+        if (cxxRecordDecl->getTemplateInstantiationPattern())
+            cxxRecordDecl = cxxRecordDecl->getTemplateInstantiationPattern();
+        parentClassName = cxxRecordDecl->getQualifiedNameAsString();
+    }
+    else
+    {
+        parentClassName = recordDecl->getQualifiedNameAsString();
+    }
+    // the extra spaces match the formatting in the results file, and help avoid false+
+    std::string aNiceName = "    " + parentClassName + " " + fieldDecl->getNameAsString() + " "
+                            + fieldDecl->getType().getAsString() + "\n";
+
+    // search mmap'ed file for field
+    const char* aNiceNameStr = aNiceName.c_str();
+    char* found = std::search(mmappedData, mmappedData + mmapFilesize, aNiceNameStr,
+                              aNiceNameStr + aNiceName.size());
+    if (!(found < mmappedData + mmapFilesize))
+        return true;
+
+    auto endLoc = fieldDecl->getTypeSourceInfo()->getTypeLoc().getEndLoc();
+    endLoc = endLoc.getLocWithOffset(
+        Lexer::MeasureTokenLength(endLoc, compiler.getSourceManager(), compiler.getLangOpts()));
+
+    if (!insertText(endLoc, " const"))
+    {
+        report(DiagnosticsEngine::Warning, "Could not mark field as const",
+               compat::getBeginLoc(fieldDecl))
+            << fieldDecl->getSourceRange();
+    }
+    return true;
+}
+
+loplugin::Plugin::Registration<ConstFieldsRewrite> X("constfieldsrewrite", false);
+}
+
+#endif
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab: */