compilerplugins/clang/collapseif.cxx

   1 /* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
   2 /*
   3  * This file is part of the LibreOffice project.
   4  *
   5  * This Source Code Form is subject to the terms of the Mozilla Public
   6  * License, v. 2.0. If a copy of the MPL was not distributed with this
   7  * file, You can obtain one at http://mozilla.org/MPL/2.0/.
   8  */
   9
  10 #include <cassert>
  11 #include <string>
  12 #include <iostream>
  13 #include <unordered_map>
  14 #include <unordered_set>
  15
  16 #include "plugin.hxx"
  17 #include "check.hxx"
  18 #include "clang/AST/CXXInheritance.h"
  19 #include "clang/AST/StmtVisitor.h"
  20
  21 /**
  22     Look for nested if statements with relatively small conditions, where they can be collapsed into
  23     one if statement.
  24 */
  25 namespace
  26 {
  27 class CollapseIf : public loplugin::FilteringPlugin<CollapseIf>
  28 {
  29 public:
  30     explicit CollapseIf(loplugin::InstantiationData const& data)
  31         : FilteringPlugin(data)
  32     {
  33     }
  34
  35     virtual void run() override { TraverseDecl(compiler.getASTContext().getTranslationUnitDecl()); }
  36
  37     bool VisitIfStmt(IfStmt const*);
  38
  39 private:
  40     int getNoCharsInSourceCodeOfExpr(IfStmt const*);
  41     bool containsComment(Stmt const* stmt);
  42 };
  43
  44 bool CollapseIf::VisitIfStmt(IfStmt const* ifStmt)
  45 {
  46     if (ignoreLocation(ifStmt))
  47         return true;
  48     if (ifStmt->getElse())
  49         return true;
  50
  51     IfStmt const* secondIfStmt = nullptr;
  52     if (auto compoundStmt = dyn_cast<CompoundStmt>(ifStmt->getThen()))
  53     {
  54         if (compoundStmt->size() != 1)
  55             return true;
  56         secondIfStmt = dyn_cast<IfStmt>(*compoundStmt->body_begin());
  57         if (!secondIfStmt)
  58             return true;
  59         if (secondIfStmt->getElse())
  60             return true;
  61     }
  62     else
  63     {
  64         secondIfStmt = dyn_cast<IfStmt>(ifStmt->getThen());
  65         if (!secondIfStmt)
  66             return true;
  67     }
  68
  69     int noChars1 = getNoCharsInSourceCodeOfExpr(ifStmt);
  70     int noChars2 = getNoCharsInSourceCodeOfExpr(secondIfStmt);
  71     if (noChars1 + noChars2 > 40)
  72         return true;
  73
  74     // Sometimes there is a comment between the first and second if, so
  75     // merging them would make the comment more awkward to write.
  76     if (containsComment(ifStmt))
  77         return true;
  78
  79     report(DiagnosticsEngine::Warning, "nested if should be collapsed into one statement %0 %1",
  80            compat::getBeginLoc(ifStmt))
  81         << noChars1 << noChars2 << ifStmt->getSourceRange();
  82     return true;
  83 }
  84
  85 int CollapseIf::getNoCharsInSourceCodeOfExpr(IfStmt const* ifStmt)
  86 {
  87     // Measure the space between the "if" the beginning of the "then" block because
  88     // measuring the size of the condition expression is unreliable, because clang
  89     // does not report the location of the last token accurately.
  90     SourceManager& SM = compiler.getSourceManager();
  91     SourceLocation startLoc = compat::getBeginLoc(ifStmt);
  92     SourceLocation endLoc = compat::getBeginLoc(ifStmt->getThen());
  93     char const* p1 = SM.getCharacterData(startLoc);
  94     char const* p2 = SM.getCharacterData(endLoc);
  95
  96     int count = 0;
  97     for (auto p = p1; p < p2; ++p)
  98         if (*p != ' ')
  99             ++count;
 100
 101     return count;
 102 }
 103
 104 bool CollapseIf::containsComment(Stmt const* stmt)
 105 {
 106     SourceManager& SM = compiler.getSourceManager();
 107     auto range = stmt->getSourceRange();
 108     SourceLocation startLoc = range.getBegin();
 109     SourceLocation endLoc = range.getEnd();
 110     char const* p1 = SM.getCharacterData(startLoc);
 111     char const* p2 = SM.getCharacterData(endLoc);
 112     p2 += Lexer::MeasureTokenLength(endLoc, SM, compiler.getLangOpts());
 113
 114     // check for comments
 115     constexpr char const comment1[] = "/*";
 116     constexpr char const comment2[] = "//";
 117     if (std::search(p1, p2, comment1, comment1 + strlen(comment1)) != p2)
 118         return true;
 119     if (std::search(p1, p2, comment2, comment2 + strlen(comment2)) != p2)
 120         return true;
 121
 122     return false;
 123 }
 124
 125 /** Off by default because some places are a judgement call if it should be collapsed or not. */
 126 loplugin::Plugin::Registration<CollapseIf> X("collapseif", false);
 127 }
 128
 129 /* vim:set shiftwidth=4 softtabstop=4 expandtab: */