llvm-project/clang-tools-extra/clang-tidy/readability/FunctionCognitiveComplexity...

572 lines
20 KiB
C++

//===--- FunctionCognitiveComplexityCheck.cpp - clang-tidy ------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#include "FunctionCognitiveComplexityCheck.h"
#include "../ClangTidyDiagnosticConsumer.h"
#include "clang/AST/Decl.h"
#include "clang/AST/DeclBase.h"
#include "clang/AST/Expr.h"
#include "clang/AST/RecursiveASTVisitor.h"
#include "clang/AST/Stmt.h"
#include "clang/ASTMatchers/ASTMatchFinder.h"
#include "clang/ASTMatchers/ASTMatchers.h"
#include "clang/ASTMatchers/ASTMatchersInternal.h"
#include "clang/Basic/Diagnostic.h"
#include "clang/Basic/DiagnosticIDs.h"
#include "clang/Basic/LLVM.h"
#include "clang/Basic/SourceLocation.h"
#include "llvm/ADT/Optional.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/ErrorHandling.h"
#include <array>
#include <cassert>
#include <stack>
#include <tuple>
#include <type_traits>
#include <utility>
using namespace clang::ast_matchers;
namespace clang {
namespace tidy {
namespace readability {
namespace {
struct CognitiveComplexity final {
// Any increment is based on some combination of reasons.
// For details you can look at the Specification at
// https://www.sonarsource.com/docs/CognitiveComplexity.pdf
// or user-facing docs at
// http://clang.llvm.org/extra/clang-tidy/checks/readability-function-cognitive-complexity.html
// Here are all the possible reasons:
enum Criteria : uint8_t {
None = 0U,
// B1, increases cognitive complexity (by 1)
// What causes it:
// * if, else if, else, ConditionalOperator (not BinaryConditionalOperator)
// * SwitchStmt
// * ForStmt, CXXForRangeStmt
// * WhileStmt, DoStmt
// * CXXCatchStmt
// * GotoStmt, IndirectGotoStmt (but not BreakStmt, ContinueStmt)
// * sequences of binary logical operators (BinOpLAnd, BinOpLOr)
// * each method in a recursion cycle (not implemented)
Increment = 1U << 0,
// B2, increases current nesting level (by 1)
// What causes it:
// * if, else if, else, ConditionalOperator (not BinaryConditionalOperator)
// * SwitchStmt
// * ForStmt, CXXForRangeStmt
// * WhileStmt, DoStmt
// * CXXCatchStmt
// * nested CXXConstructor, CXXDestructor, CXXMethod (incl. C++11 Lambda)
// * GNU Statement Expression
// * Apple Block declaration
IncrementNesting = 1U << 1,
// B3, increases cognitive complexity by the current nesting level
// Applied before IncrementNesting
// What causes it:
// * IfStmt, ConditionalOperator (not BinaryConditionalOperator)
// * SwitchStmt
// * ForStmt, CXXForRangeStmt
// * WhileStmt, DoStmt
// * CXXCatchStmt
PenalizeNesting = 1U << 2,
All = Increment | PenalizeNesting | IncrementNesting,
};
// The helper struct used to record one increment occurrence, with all the
// details nessesary.
struct Detail {
const SourceLocation Loc; // What caused the increment?
const unsigned short Nesting; // How deeply nested is Loc located?
const Criteria C; // The criteria of the increment
Detail(SourceLocation SLoc, unsigned short CurrentNesting, Criteria Crit)
: Loc(SLoc), Nesting(CurrentNesting), C(Crit) {}
// To minimize the sizeof(Detail), we only store the minimal info there.
// This function is used to convert from the stored info into the usable
// information - what message to output, how much of an increment did this
// occurrence actually result in.
std::pair<unsigned, unsigned short> process() const {
assert(C != Criteria::None && "invalid criteria");
unsigned MsgId; // The id of the message to output.
unsigned short Increment; // How much of an increment?
if (C == Criteria::All) {
Increment = 1 + Nesting;
MsgId = 0;
} else if (C == (Criteria::Increment | Criteria::IncrementNesting)) {
Increment = 1;
MsgId = 1;
} else if (C == Criteria::Increment) {
Increment = 1;
MsgId = 2;
} else if (C == Criteria::IncrementNesting) {
Increment = 0; // Unused in this message.
MsgId = 3;
} else
llvm_unreachable("should not get to here.");
return std::make_pair(MsgId, Increment);
}
};
// Limit of 25 is the "upstream"'s default.
static constexpr unsigned DefaultLimit = 25U;
// Based on the publicly-avaliable numbers for some big open-source projects
// https://sonarcloud.io/projects?languages=c%2Ccpp&size=5 we can estimate:
// value ~20 would result in no allocs for 98% of functions, ~12 for 96%, ~10
// for 91%, ~8 for 88%, ~6 for 84%, ~4 for 77%, ~2 for 64%, and ~1 for 37%.
static_assert(sizeof(Detail) <= 8,
"Since we use SmallVector to minimize the amount of "
"allocations, we also need to consider the price we pay for "
"that in terms of stack usage. "
"Thus, it is good to minimize the size of the Detail struct.");
SmallVector<Detail, DefaultLimit> Details; // 25 elements is 200 bytes.
// Yes, 25 is a magic number. This is the seemingly-sane default for the
// upper limit for function cognitive complexity. Thus it would make sense
// to avoid allocations for any function that does not violate the limit.
// The grand total Cognitive Complexity of the function.
unsigned Total = 0;
// The function used to store new increment, calculate the total complexity.
void account(SourceLocation Loc, unsigned short Nesting, Criteria C);
};
// All the possible messages that can be output. The choice of the message
// to use is based of the combination of the CognitiveComplexity::Criteria.
// It would be nice to have it in CognitiveComplexity struct, but then it is
// not static.
static const std::array<const StringRef, 4> Msgs = {{
// B1 + B2 + B3
"+%0, including nesting penalty of %1, nesting level increased to %2",
// B1 + B2
"+%0, nesting level increased to %2",
// B1
"+%0",
// B2
"nesting level increased to %2",
}};
// Criteria is a bitset, thus a few helpers are needed.
CognitiveComplexity::Criteria operator|(CognitiveComplexity::Criteria LHS,
CognitiveComplexity::Criteria RHS) {
return static_cast<CognitiveComplexity::Criteria>(
static_cast<std::underlying_type<CognitiveComplexity::Criteria>::type>(
LHS) |
static_cast<std::underlying_type<CognitiveComplexity::Criteria>::type>(
RHS));
}
CognitiveComplexity::Criteria operator&(CognitiveComplexity::Criteria LHS,
CognitiveComplexity::Criteria RHS) {
return static_cast<CognitiveComplexity::Criteria>(
static_cast<std::underlying_type<CognitiveComplexity::Criteria>::type>(
LHS) &
static_cast<std::underlying_type<CognitiveComplexity::Criteria>::type>(
RHS));
}
CognitiveComplexity::Criteria &operator|=(CognitiveComplexity::Criteria &LHS,
CognitiveComplexity::Criteria RHS) {
LHS = operator|(LHS, RHS);
return LHS;
}
CognitiveComplexity::Criteria &operator&=(CognitiveComplexity::Criteria &LHS,
CognitiveComplexity::Criteria RHS) {
LHS = operator&(LHS, RHS);
return LHS;
}
void CognitiveComplexity::account(SourceLocation Loc, unsigned short Nesting,
Criteria C) {
C &= Criteria::All;
assert(C != Criteria::None && "invalid criteria");
Details.emplace_back(Loc, Nesting, C);
const Detail &D = Details.back();
unsigned MsgId;
unsigned short Increase;
std::tie(MsgId, Increase) = D.process();
Total += Increase;
}
class FunctionASTVisitor final
: public RecursiveASTVisitor<FunctionASTVisitor> {
using Base = RecursiveASTVisitor<FunctionASTVisitor>;
// If set to true, macros are ignored during analysis.
const bool IgnoreMacros;
// The current nesting level (increased by Criteria::IncrementNesting).
unsigned short CurrentNestingLevel = 0;
// Used to efficiently know the last type of the binary sequence operator
// that was encountered. It would make sense for the function call to start
// the new sequence, thus it is a stack.
using OBO = Optional<BinaryOperator::Opcode>;
std::stack<OBO, SmallVector<OBO, 4>> BinaryOperatorsStack;
public:
explicit FunctionASTVisitor(const bool IgnoreMacros)
: IgnoreMacros(IgnoreMacros) {}
bool traverseStmtWithIncreasedNestingLevel(Stmt *Node) {
++CurrentNestingLevel;
bool ShouldContinue = Base::TraverseStmt(Node);
--CurrentNestingLevel;
return ShouldContinue;
}
bool traverseDeclWithIncreasedNestingLevel(Decl *Node) {
++CurrentNestingLevel;
bool ShouldContinue = Base::TraverseDecl(Node);
--CurrentNestingLevel;
return ShouldContinue;
}
bool TraverseIfStmt(IfStmt *Node, bool InElseIf = false) {
if (!Node)
return Base::TraverseIfStmt(Node);
{
CognitiveComplexity::Criteria Reasons;
Reasons = CognitiveComplexity::Criteria::None;
// "If" increases cognitive complexity.
Reasons |= CognitiveComplexity::Criteria::Increment;
// "If" increases nesting level.
Reasons |= CognitiveComplexity::Criteria::IncrementNesting;
if (!InElseIf) {
// "If" receives a nesting increment commensurate with it's nested
// depth, if it is not part of "else if".
Reasons |= CognitiveComplexity::Criteria::PenalizeNesting;
}
CC.account(Node->getIfLoc(), CurrentNestingLevel, Reasons);
}
// If this IfStmt is *NOT* "else if", then only the body (i.e. "Then" and
// "Else") is traversed with increased Nesting level.
// However if this IfStmt *IS* "else if", then Nesting level is increased
// for the whole IfStmt (i.e. for "Init", "Cond", "Then" and "Else").
if (!InElseIf) {
if (!TraverseStmt(Node->getInit()))
return false;
if (!TraverseStmt(Node->getCond()))
return false;
} else {
if (!traverseStmtWithIncreasedNestingLevel(Node->getInit()))
return false;
if (!traverseStmtWithIncreasedNestingLevel(Node->getCond()))
return false;
}
// "Then" always increases nesting level.
if (!traverseStmtWithIncreasedNestingLevel(Node->getThen()))
return false;
if (!Node->getElse())
return true;
if (auto *E = dyn_cast<IfStmt>(Node->getElse()))
return TraverseIfStmt(E, true);
{
CognitiveComplexity::Criteria Reasons;
Reasons = CognitiveComplexity::Criteria::None;
// "Else" increases cognitive complexity.
Reasons |= CognitiveComplexity::Criteria::Increment;
// "Else" increases nesting level.
Reasons |= CognitiveComplexity::Criteria::IncrementNesting;
// "Else" DOES NOT receive a nesting increment commensurate with it's
// nested depth.
CC.account(Node->getElseLoc(), CurrentNestingLevel, Reasons);
}
// "Else" always increases nesting level.
return traverseStmtWithIncreasedNestingLevel(Node->getElse());
}
// The currently-being-processed stack entry, which is always the top.
#define CurrentBinaryOperator BinaryOperatorsStack.top()
// In a sequence of binary logical operators, if the new operator is different
// from the previous one, then the cognitive complexity is increased.
bool TraverseBinaryOperator(BinaryOperator *Op) {
if (!Op || !Op->isLogicalOp())
return Base::TraverseBinaryOperator(Op);
// Make sure that there is always at least one frame in the stack.
if (BinaryOperatorsStack.empty())
BinaryOperatorsStack.emplace();
// If this is the first binary operator that we are processing, or the
// previous binary operator was different, there is an increment.
if (!CurrentBinaryOperator || Op->getOpcode() != CurrentBinaryOperator)
CC.account(Op->getOperatorLoc(), CurrentNestingLevel,
CognitiveComplexity::Criteria::Increment);
// We might encounter a function call, which starts a new sequence, thus
// we need to save the current previous binary operator.
const Optional<BinaryOperator::Opcode> BinOpCopy(CurrentBinaryOperator);
// Record the operator that we are currently processing and traverse it.
CurrentBinaryOperator = Op->getOpcode();
bool ShouldContinue = Base::TraverseBinaryOperator(Op);
// And restore the previous binary operator, which might be nonexistent.
CurrentBinaryOperator = BinOpCopy;
return ShouldContinue;
}
// It would make sense for the function call to start the new binary
// operator sequence, thus let's make sure that it creates a new stack frame.
bool TraverseCallExpr(CallExpr *Node) {
// If we are not currently processing any binary operator sequence, then
// no Node-handling is needed.
if (!Node || BinaryOperatorsStack.empty() || !CurrentBinaryOperator)
return Base::TraverseCallExpr(Node);
// Else, do add [uninitialized] frame to the stack, and traverse call.
BinaryOperatorsStack.emplace();
bool ShouldContinue = Base::TraverseCallExpr(Node);
// And remove the top frame.
BinaryOperatorsStack.pop();
return ShouldContinue;
}
#undef CurrentBinaryOperator
bool TraverseStmt(Stmt *Node) {
if (!Node)
return Base::TraverseStmt(Node);
if (IgnoreMacros && Node->getBeginLoc().isMacroID())
return true;
// Three following switch()'es have huge duplication, but it is better to
// keep them separate, to simplify comparing them with the Specification.
CognitiveComplexity::Criteria Reasons = CognitiveComplexity::Criteria::None;
SourceLocation Location = Node->getBeginLoc();
// B1. Increments
// There is an increment for each of the following:
switch (Node->getStmtClass()) {
// if, else if, else are handled in TraverseIfStmt(),
// FIXME: "each method in a recursion cycle" Increment is not implemented.
case Stmt::ConditionalOperatorClass:
case Stmt::SwitchStmtClass:
case Stmt::ForStmtClass:
case Stmt::CXXForRangeStmtClass:
case Stmt::WhileStmtClass:
case Stmt::DoStmtClass:
case Stmt::CXXCatchStmtClass:
case Stmt::GotoStmtClass:
case Stmt::IndirectGotoStmtClass:
Reasons |= CognitiveComplexity::Criteria::Increment;
break;
default:
// break LABEL, continue LABEL increase cognitive complexity,
// but they are not supported in C++ or C.
// Regular break/continue do not increase cognitive complexity.
break;
}
// B2. Nesting level
// The following structures increment the nesting level:
switch (Node->getStmtClass()) {
// if, else if, else are handled in TraverseIfStmt(),
// Nested methods and such are handled in TraverseDecl.
case Stmt::ConditionalOperatorClass:
case Stmt::SwitchStmtClass:
case Stmt::ForStmtClass:
case Stmt::CXXForRangeStmtClass:
case Stmt::WhileStmtClass:
case Stmt::DoStmtClass:
case Stmt::CXXCatchStmtClass:
case Stmt::LambdaExprClass:
case Stmt::StmtExprClass:
Reasons |= CognitiveComplexity::Criteria::IncrementNesting;
break;
default:
break;
}
// B3. Nesting increments
// The following structures receive a nesting increment
// commensurate with their nested depth inside B2 structures:
switch (Node->getStmtClass()) {
// if, else if, else are handled in TraverseIfStmt().
case Stmt::ConditionalOperatorClass:
case Stmt::SwitchStmtClass:
case Stmt::ForStmtClass:
case Stmt::CXXForRangeStmtClass:
case Stmt::WhileStmtClass:
case Stmt::DoStmtClass:
case Stmt::CXXCatchStmtClass:
Reasons |= CognitiveComplexity::Criteria::PenalizeNesting;
break;
default:
break;
}
if (Node->getStmtClass() == Stmt::ConditionalOperatorClass) {
// A little beautification.
// For conditional operator "cond ? true : false" point at the "?"
// symbol.
ConditionalOperator *COp = dyn_cast<ConditionalOperator>(Node);
Location = COp->getQuestionLoc();
}
// If we have found any reasons, let's account it.
if (Reasons & CognitiveComplexity::Criteria::All)
CC.account(Location, CurrentNestingLevel, Reasons);
// Did we decide that the nesting level should be increased?
if (!(Reasons & CognitiveComplexity::Criteria::IncrementNesting))
return Base::TraverseStmt(Node);
return traverseStmtWithIncreasedNestingLevel(Node);
}
// The parameter MainAnalyzedFunction is needed to differentiate between the
// cases where TraverseDecl() is the entry point from
// FunctionCognitiveComplexityCheck::check() and the cases where it was called
// from the FunctionASTVisitor itself. Explanation: if we get a function
// definition (e.g. constructor, destructor, method), the Cognitive Complexity
// specification states that the Nesting level shall be increased. But if this
// function is the entry point, then the Nesting level should not be
// increased. Thus that parameter is there and is used to fall-through
// directly to traversing if this is the main function that is being analyzed.
bool TraverseDecl(Decl *Node, bool MainAnalyzedFunction = false) {
if (!Node || MainAnalyzedFunction)
return Base::TraverseDecl(Node);
// B2. Nesting level
// The following structures increment the nesting level:
switch (Node->getKind()) {
case Decl::Function:
case Decl::CXXMethod:
case Decl::CXXConstructor:
case Decl::CXXDestructor:
case Decl::Block:
break;
default:
// If this is something else, we use early return!
return Base::TraverseDecl(Node);
break;
}
CC.account(Node->getBeginLoc(), CurrentNestingLevel,
CognitiveComplexity::Criteria::IncrementNesting);
return traverseDeclWithIncreasedNestingLevel(Node);
}
CognitiveComplexity CC;
};
} // namespace
FunctionCognitiveComplexityCheck::FunctionCognitiveComplexityCheck(
StringRef Name, ClangTidyContext *Context)
: ClangTidyCheck(Name, Context),
Threshold(Options.get("Threshold", CognitiveComplexity::DefaultLimit)),
DescribeBasicIncrements(Options.get("DescribeBasicIncrements", true)),
IgnoreMacros(Options.get("IgnoreMacros", false)) {}
void FunctionCognitiveComplexityCheck::storeOptions(
ClangTidyOptions::OptionMap &Opts) {
Options.store(Opts, "Threshold", Threshold);
Options.store(Opts, "DescribeBasicIncrements", DescribeBasicIncrements);
Options.store(Opts, "IgnoreMacros", IgnoreMacros);
}
void FunctionCognitiveComplexityCheck::registerMatchers(MatchFinder *Finder) {
Finder->addMatcher(
functionDecl(isDefinition(),
unless(anyOf(isDefaulted(), isDeleted(), isWeak())))
.bind("func"),
this);
Finder->addMatcher(lambdaExpr().bind("lambda"), this);
}
void FunctionCognitiveComplexityCheck::check(
const MatchFinder::MatchResult &Result) {
FunctionASTVisitor Visitor(IgnoreMacros);
SourceLocation Loc;
const auto *TheDecl = Result.Nodes.getNodeAs<FunctionDecl>("func");
const auto *TheLambdaExpr = Result.Nodes.getNodeAs<LambdaExpr>("lambda");
if (TheDecl) {
assert(TheDecl->hasBody() &&
"The matchers should only match the functions that "
"have user-provided body.");
Loc = TheDecl->getLocation();
Visitor.TraverseDecl(const_cast<FunctionDecl *>(TheDecl), true);
} else {
Loc = TheLambdaExpr->getBeginLoc();
Visitor.TraverseLambdaExpr(const_cast<LambdaExpr *>(TheLambdaExpr));
}
if (Visitor.CC.Total <= Threshold)
return;
if (TheDecl)
diag(Loc, "function %0 has cognitive complexity of %1 (threshold %2)")
<< TheDecl << Visitor.CC.Total << Threshold;
else
diag(Loc, "lambda has cognitive complexity of %0 (threshold %1)")
<< Visitor.CC.Total << Threshold;
if (!DescribeBasicIncrements)
return;
// Output all the basic increments of complexity.
for (const auto &Detail : Visitor.CC.Details) {
unsigned MsgId; // The id of the message to output.
unsigned short Increase; // How much of an increment?
std::tie(MsgId, Increase) = Detail.process();
assert(MsgId < Msgs.size() && "MsgId should always be valid");
// Increase, on the other hand, can be 0.
diag(Detail.Loc, Msgs[MsgId], DiagnosticIDs::Note)
<< (unsigned)Increase << (unsigned)Detail.Nesting << 1 + Detail.Nesting;
}
}
} // namespace readability
} // namespace tidy
} // namespace clang