Commit my clang plugin and fix up documentation.

tools/clang/plugins/FindBadConstructs.cpp

Index: tools/clang/plugins/FindBadConstructs.cpp
diff --git a/tools/clang/plugins/FindBadConstructs.cpp b/tools/clang/plugins/FindBadConstructs.cpp
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+++ b/tools/clang/plugins/FindBadConstructs.cpp
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+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// This file defines a bunch of recurring problems in the Chromium C++ code.
+//
+// Checks that are implemented:
+// - Constructors/Destructors should not be inlined if they are of a complex
+//   class type.
+// - Missing "virtual" keywords on methods that should be virtual.
+// - Virtual methods with nonempty implementations in their headers.
+//
+// Things that are still TODO:
+// - Deriving from base::RefCounted and friends should mandate non-public
+//   destructors.
+
+#include "clang/Frontend/FrontendPluginRegistry.h"
+#include "clang/AST/ASTConsumer.h"
+#include "clang/AST/AST.h"
+#include "clang/AST/TypeLoc.h"
+#include "clang/Basic/SourceManager.h"
+#include "clang/Frontend/CompilerInstance.h"
+#include "llvm/Support/raw_ostream.h"
+
+#include "ChromeClassTester.h"
+
+using namespace clang;
+
+namespace {
+
+bool TypeHasNonTrivialDtor(const Type* type) {
+  if (const CXXRecordDecl* cxx_r = type->getCXXRecordDeclForPointerType())
+    return cxx_r->hasTrivialDestructor();
+
+  return false;
+}
+
+// Searches for constructs that we know we don't want in the Chromium code base.
+class FindBadConstructsConsumer : public ChromeClassTester {
+ public:
+  FindBadConstructsConsumer(CompilerInstance& instance)
+      : ChromeClassTester(instance) {}
+
+  virtual void CheckChromeClass(const SourceLocation& record_location,
+                                CXXRecordDecl* record) {
+    CheckCtorDtorWeight(record_location, record);
+    CheckVirtualMethods(record_location, record);
+  }
+
+  // Prints errors if the constructor/destructor weight it too heavy.
+  void CheckCtorDtorWeight(const SourceLocation& record_location,
+                           CXXRecordDecl* record) {
+    // We don't handle anonymous structs. If this record doesn't have a
+    // name, it's of the form:
+    //
+    // struct {
+    //   ...
+    // } name_;
+    if (record->getIdentifier() == NULL)
+      return;
+
+    // Count the number of templated base classes as a feature of whether the
+    // destructor can be inlined.
+    int templated_base_classes = 0;
+    for (CXXRecordDecl::base_class_const_iterator it = record->bases_begin();
+         it != record->bases_end(); ++it) {
+      if (it->getTypeSourceInfo()->getTypeLoc().getTypeLocClass() ==
+          TypeLoc::TemplateSpecialization) {
+        ++templated_base_classes;
+      }
+    }
+
+    // Count the number of trivial and non-trivial member variables.
+    int trivial_member = 0;
+    int non_trivial_member = 0;
+    int templated_non_trivial_member = 0;
+    for (RecordDecl::field_iterator it = record->field_begin();
+         it != record->field_end(); ++it) {
+      CountType(it->getType().getTypePtr(),
+                &trivial_member,
+                &non_trivial_member,
+                &templated_non_trivial_member);
+    }
+
+    // Check to see if we need to ban inlined/synthesized constructors. Note
+    // that the cutoffs here are kind of arbitrary. Scores over 10 break.
+    int dtor_score = 0;
+    // Deriving from a templated base class shouldn't be enough to trigger
+    // the ctor warning, but if you do *anything* else, it should.
+    //
+    // TODO(erg): This is motivated by templated base classes that don't have
+    // any data members. Somehow detect when templated base classes have data
+    // members and treat them differently.
+    dtor_score += templated_base_classes * 9;
+    // Instantiating a template is an insta-hit.
+    dtor_score += templated_non_trivial_member * 10;
+    // The fourth normal class member should trigger the warning.
+    dtor_score += non_trivial_member * 3;
+
+    int ctor_score = dtor_score;
+    // You should be able to have 9 ints before we warn you.
+    ctor_score += trivial_member;
+
+    if (ctor_score >= 10) {
+      if (!record->hasUserDeclaredConstructor()) {
+        emitWarning(record_location,
+                    "Complex class/struct needs a declared constructor.");
+      } else {
+        // Iterate across all the constructors in this file and yell if we
+        // find one that tries to be inline.
+        for (CXXRecordDecl::ctor_iterator it = record->ctor_begin();
+             it != record->ctor_end(); ++it) {
+          if (it->hasInlineBody()) {
+            emitWarning(it->getInnerLocStart(),
+                        "Complex constructor has an inlined body.");
+          }
+        }
+      }
+    }
+
+    // The destructor side is equivalent except that we don't check for
+    // trivial members; 20 ints don't need a destructor.
+    if (dtor_score >= 10 && !record->hasTrivialDestructor()) {
+      if (!record->hasUserDeclaredDestructor()) {
+        emitWarning(record_location,
+                    "Complex class/struct needs a declared destructor.");
+      } else if (CXXDestructorDecl* dtor = record->getDestructor()) {
+        if (dtor->hasInlineBody()) {
+          emitWarning(dtor->getInnerLocStart(),
+                      "Complex destructor has an inline body.");
+        }
+      }
+    }
+  }
+
+  // Makes sure there is a "virtual" keyword on virtual methods and that there
+  // are no inline function bodies on them (but "{}" is allowed).
+  void CheckVirtualMethods(const SourceLocation& record_location,
+                           CXXRecordDecl* record) {
+    for (CXXRecordDecl::method_iterator it = record->method_begin();
+         it != record->method_end(); ++it) {
+      if (it->isCopyAssignmentOperator() ||
+          dyn_cast<CXXConstructorDecl>(*it)) {
+        // Ignore constructors and assignment operators.
+      } else if (dyn_cast<CXXDestructorDecl>(*it)) {
+        // TODO: I'd love to handle this case, but
+        // CXXDestructorDecl::isImplicitlyDefined() asserts if I call it
+        // here, and against my better judgment, I don't want to *always*
+        // disallow implicit destructors.
+      } else {
+        if (it->isVirtual() && !it->isVirtualAsWritten()) {
+          emitWarning(it->getTypeSpecStartLoc(),
+                      "Overridden method must have \"virtual\" keyword.");
+        }
+
+        // Virtual methods should not have inline definitions beyond "{}".
+        if (it->isVirtual() && it->hasBody() && it->hasInlineBody()) {
+          if (CompoundStmt* cs = dyn_cast<CompoundStmt>(it->getBody())) {
+            if (cs->size()) {
+              emitWarning(
+                  cs->getLBracLoc(),
+                  "virtual methods with non-empty bodies shouldn't be "
+                  "declared inline.");
+            }
+          }
+        }
+      }
+    }
+  }
+
+  void CountType(const Type* type,
+                 int* trivial_member,
+                 int* non_trivial_member,
+                 int* templated_non_trivial_member) {
+    switch (type->getTypeClass()) {
+      case Type::Record: {
+        // Simplifying; the whole class isn't trivial if the dtor is, but
+        // we use this as a signal about complexity.
+        if (TypeHasNonTrivialDtor(type))
+          (*trivial_member)++;
+        else
+          (*non_trivial_member)++;
+        break;
+      }
+      case Type::TemplateSpecialization: {
+        TemplateName name =
+            dyn_cast<TemplateSpecializationType>(type)->getTemplateName();
+        bool whitelisted_template = false;
+
+        // HACK: I'm at a loss about how to get the syntax checker to get
+        // whether a template is exterened or not. For the first pass here,
+        // just do retarded string comparisons.
+        if (TemplateDecl* decl = name.getAsTemplateDecl()) {
+          std::string base_name = decl->getNameAsString();
+          if (base_name == "basic_string")
+            whitelisted_template = true;
+        }
+
+        if (whitelisted_template)
+          (*non_trivial_member)++;
+        else
+          (*templated_non_trivial_member)++;
+        break;
+      }
+      case Type::Elaborated: {
+        CountType(
+            dyn_cast<ElaboratedType>(type)->getNamedType().getTypePtr(),
+            trivial_member, non_trivial_member, templated_non_trivial_member);
+        break;
+      }
+      case Type::Typedef: {
+        while (const TypedefType *TT = dyn_cast<TypedefType>(type)) {
+          type = TT->getDecl()->getUnderlyingType().getTypePtr();
+        }
+        CountType(type, trivial_member, non_trivial_member,
+                  templated_non_trivial_member);
+        break;
+      }
+      default: {
+        // Stupid assumption: anything we see that isn't the above is one of
+        // the 20 integer types.
+        (*trivial_member)++;
+        break;
+      }
+    }
+  }
+};
+
+class FindBadConstructsAction : public PluginASTAction {
+ protected:
+  ASTConsumer* CreateASTConsumer(CompilerInstance &CI, llvm::StringRef ref) {
+    return new FindBadConstructsConsumer(CI);
+  }
+
+  bool ParseArgs(const CompilerInstance &CI,
+                 const std::vector<std::string>& args) {
+    // We don't take any additional arguments here.
+    return true;
+  }
+};
+
+}  // namespace
+
+static FrontendPluginRegistry::Add<FindBadConstructsAction>
+X("find-bad-constructs", "Finds bad C++ constructs");