Add clang-tidy check readability-math-missing-parentheses

[11happy]

Overview: This pull request fixes #80850 where author suggests adding a readability check to detect missing parentheses around mathematical expressions when operators of different priorities are used.

Testing:

• Tested the updated code.
• Verified that other functionalities remain unaffected.

Dependencies:

• No dependencies on other pull requests.

CC:

• @PiotrZSL

[llvmbot]

@llvm/pr-subscribers-clang-tools-extra

@llvm/pr-subscribers-clang-tidy

Author: Bhuminjay Soni (11happy)

Changes

Overview: This pull request fixes #80850 where author suggests adding a readability check to detect missing parentheses around mathematical expressions when operators of different priorities are used.

Testing:

• Tested the updated code.
• Verified that other functionalities remain unaffected.

Dependencies:

• No dependencies on other pull requests.

CC:

• @PiotrZSL

---

Full diff: https://github.com/llvm/llvm-project/pull/84481.diff

8 Files Affected:

• (modified) clang-tools-extra/clang-tidy/readability/CMakeLists.txt (+1)
• (added) clang-tools-extra/clang-tidy/readability/MathMissingParenthesesCheck.cpp (+167)
• (added) clang-tools-extra/clang-tidy/readability/MathMissingParenthesesCheck.h (+31)
• (modified) clang-tools-extra/clang-tidy/readability/ReadabilityTidyModule.cpp (+3)
• (modified) clang-tools-extra/docs/ReleaseNotes.rst (+6)
• (modified) clang-tools-extra/docs/clang-tidy/checks/list.rst (+1)
• (added) clang-tools-extra/docs/clang-tidy/checks/readability/math-missing-parentheses.rst (+19)
• (added) clang-tools-extra/test/clang-tidy/checkers/readability/math-missing-parentheses.cpp (+42)

diff --git a/clang-tools-extra/clang-tidy/readability/CMakeLists.txt b/clang-tools-extra/clang-tidy/readability/CMakeLists.txt
index a6c8cbd8eb448a..0d4fa095501dfb 100644
--- a/clang-tools-extra/clang-tidy/readability/CMakeLists.txt
+++ b/clang-tools-extra/clang-tidy/readability/CMakeLists.txt
@@ -27,6 +27,7 @@ add_clang_library(clangTidyReadabilityModule
   IsolateDeclarationCheck.cpp
   MagicNumbersCheck.cpp
   MakeMemberFunctionConstCheck.cpp
+  MathMissingParenthesesCheck.cpp
   MisleadingIndentationCheck.cpp
   MisplacedArrayIndexCheck.cpp
   NamedParameterCheck.cpp
diff --git a/clang-tools-extra/clang-tidy/readability/MathMissingParenthesesCheck.cpp b/clang-tools-extra/clang-tidy/readability/MathMissingParenthesesCheck.cpp
new file mode 100644
index 00000000000000..d9574a9fb7a476
--- /dev/null
+++ b/clang-tools-extra/clang-tidy/readability/MathMissingParenthesesCheck.cpp
@@ -0,0 +1,167 @@
+//===--- MathMissingParenthesesCheck.cpp - clang-tidy ---------------------===//
+//
+// 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 "MathMissingParenthesesCheck.h"
+#include "../utils/ASTUtils.h"
+#include "clang/AST/ASTContext.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "clang/Lex/Preprocessor.h"
+#include <set>
+#include <stack>
+
+using namespace clang::ast_matchers;
+
+namespace clang::tidy::readability {
+
+void MathMissingParenthesesCheck::registerMatchers(MatchFinder *Finder) {
+  Finder->addMatcher(binaryOperator(unless(hasParent(binaryOperator())),
+                                    hasDescendant(binaryOperator()))
+                         .bind("binOp"),
+                     this);
+}
+static int precedenceCheck(const char op) {
+  if (op == '/' || op == '*' || op == '%')
+    return 5;
+
+  else if (op == '+' || op == '-')
+    return 4;
+
+  else if (op == '&')
+    return 3;
+  else if (op == '^')
+    return 2;
+
+  else if (op == '|')
+    return 1;
+
+  else
+    return 0;
+}
+static bool isOperand(const char c) {
+  if (c >= 'a' && c <= 'z')
+    return true;
+  else if (c >= 'A' && c <= 'Z')
+    return true;
+  else if (c >= '0' && c <= '9')
+    return true;
+  else if (c == '$')
+    return true;
+  else
+    return false;
+}
+static bool conditionForNegative(const std::string s, int i,
+                                 const std::string CurStr) {
+  if (CurStr[0] == '-') {
+    if (i == 0) {
+      return true;
+    } else {
+      while (s[i - 1] == ' ') {
+        i--;
+      }
+      if (!isOperand(s[i - 1])) {
+        return true;
+      } else {
+        return false;
+      }
+    }
+  } else {
+    return false;
+  }
+}
+static std::string getOperationOrder(std::string s, std::set<char> &Operators) {
+  std::stack<std::string> StackOne;
+  std::string TempStr = "";
+  for (int i = 0; i < s.length(); i++) {
+    std::string CurStr = "";
+    CurStr += s[i];
+    if (CurStr == " ")
+      continue;
+    else {
+      if (isOperand(CurStr[0]) || conditionForNegative(s, i, CurStr)) {
+        while (i < s.length() && (isOperand(s[i]) || s[i] == '-')) {
+          if (s[i] == '-') {
+            TempStr += "$";
+          } else {
+            TempStr += CurStr;
+          }
+          i++;
+          CurStr = s[i];
+        }
+        TempStr += " ";
+      } else if (CurStr == "(") {
+        StackOne.push("(");
+      } else if (CurStr == ")") {
+        while (StackOne.top() != "(") {
+          TempStr += StackOne.top();
+          StackOne.pop();
+        }
+        StackOne.pop();
+      } else {
+        while (!StackOne.empty() && precedenceCheck(CurStr[0]) <=
+                                        precedenceCheck((StackOne.top())[0])) {
+          TempStr += StackOne.top();
+          StackOne.pop();
+        }
+        StackOne.push(CurStr);
+      }
+    }
+  }
+  while (!StackOne.empty()) {
+    TempStr += StackOne.top();
+    StackOne.pop();
+  }
+  std::stack<std::string> StackTwo;
+  for (int i = 0; i < TempStr.length(); i++) {
+    if (TempStr[i] == ' ')
+      continue;
+    else if (isOperand(TempStr[i])) {
+      std::string CurStr = "";
+      while (i < TempStr.length() && isOperand(TempStr[i])) {
+        if (TempStr[i] == '$') {
+          CurStr += "-";
+        } else {
+          CurStr += TempStr[i];
+        }
+        i++;
+      }
+      StackTwo.push(CurStr);
+    } else {
+      std::string OperandOne = StackTwo.top();
+      StackTwo.pop();
+      std::string OperandTwo = StackTwo.top();
+      StackTwo.pop();
+      Operators.insert(TempStr[i]);
+      StackTwo.push("(" + OperandTwo + " " + TempStr[i] + " " + OperandOne +
+                    ")");
+    }
+  }
+  return StackTwo.top();
+}
+void MathMissingParenthesesCheck::check(
+    const MatchFinder::MatchResult &Result) {
+  const auto *BinOp = Result.Nodes.getNodeAs<BinaryOperator>("binOp");
+  if (!BinOp)
+    return;
+  clang::SourceManager &SM = *Result.SourceManager;
+  clang::LangOptions LO = Result.Context->getLangOpts();
+  clang::CharSourceRange Range =
+      clang::CharSourceRange::getTokenRange(BinOp->getSourceRange());
+  std::string Expression = clang::Lexer::getSourceText(Range, SM, LO).str();
+  std::set<char> Operators;
+  std::string FinalExpression = getOperationOrder(Expression, Operators);
+  if (Operators.size() > 1) {
+    if (FinalExpression.length() > 2) {
+      FinalExpression = FinalExpression.substr(1, FinalExpression.length() - 2);
+    }
+    diag(BinOp->getBeginLoc(),
+         "add parantheses to clarify the precedence of operations")
+        << FixItHint::CreateReplacement(Range, FinalExpression);
+  }
+}
+
+} // namespace clang::tidy::readability
diff --git a/clang-tools-extra/clang-tidy/readability/MathMissingParenthesesCheck.h b/clang-tools-extra/clang-tidy/readability/MathMissingParenthesesCheck.h
new file mode 100644
index 00000000000000..60b402831b45e0
--- /dev/null
+++ b/clang-tools-extra/clang-tidy/readability/MathMissingParenthesesCheck.h
@@ -0,0 +1,31 @@
+//===--- MathMissingParenthesesCheck.h - 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_READABILITY_MATHMISSINGPARENTHESESCHECK_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_READABILITY_MATHMISSINGPARENTHESESCHECK_H
+
+#include "../ClangTidyCheck.h"
+
+namespace clang::tidy::readability {
+
+/// Checks for mathematical expressions that involve operators of different
+/// priorities.
+///
+/// For the user-facing documentation see:
+/// http://clang.llvm.org/extra/clang-tidy/checks/readability/math-missing-parentheses.html
+class MathMissingParenthesesCheck : public ClangTidyCheck {
+public:
+  MathMissingParenthesesCheck(StringRef Name, ClangTidyContext *Context)
+      : ClangTidyCheck(Name, Context) {}
+  void registerMatchers(ast_matchers::MatchFinder *Finder) override;
+  void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
+};
+
+} // namespace clang::tidy::readability
+
+#endif // LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_READABILITY_MATHMISSINGPARENTHESESCHECK_H
diff --git a/clang-tools-extra/clang-tidy/readability/ReadabilityTidyModule.cpp b/clang-tools-extra/clang-tidy/readability/ReadabilityTidyModule.cpp
index 87b299bf1ef1c5..b198153d27ee49 100644
--- a/clang-tools-extra/clang-tidy/readability/ReadabilityTidyModule.cpp
+++ b/clang-tools-extra/clang-tidy/readability/ReadabilityTidyModule.cpp
@@ -31,6 +31,7 @@
 #include "IsolateDeclarationCheck.h"
 #include "MagicNumbersCheck.h"
 #include "MakeMemberFunctionConstCheck.h"
+#include "MathMissingParenthesesCheck.h"
 #include "MisleadingIndentationCheck.h"
 #include "MisplacedArrayIndexCheck.h"
 #include "NamedParameterCheck.h"
@@ -101,6 +102,8 @@ class ReadabilityModule : public ClangTidyModule {
         "readability-identifier-naming");
     CheckFactories.registerCheck<ImplicitBoolConversionCheck>(
         "readability-implicit-bool-conversion");
+    CheckFactories.registerCheck<MathMissingParenthesesCheck>(
+        "readability-math-missing-parentheses");
     CheckFactories.registerCheck<RedundantInlineSpecifierCheck>(
         "readability-redundant-inline-specifier");
     CheckFactories.registerCheck<InconsistentDeclarationParameterNameCheck>(
diff --git a/clang-tools-extra/docs/ReleaseNotes.rst b/clang-tools-extra/docs/ReleaseNotes.rst
index fd2cba4e4f463b..61b9665ffe73ed 100644
--- a/clang-tools-extra/docs/ReleaseNotes.rst
+++ b/clang-tools-extra/docs/ReleaseNotes.rst
@@ -100,6 +100,12 @@ Improvements to clang-tidy
 New checks
 ^^^^^^^^^^
 
+- New :doc:`readability-math-missing-parentheses
+  <clang-tidy/checks/readability/math-missing-parentheses>` check.
+
+  Checks for mathematical expressions that involve operators
+  of different priorities.
+
 New check aliases
 ^^^^^^^^^^^^^^^^^
 
diff --git a/clang-tools-extra/docs/clang-tidy/checks/list.rst b/clang-tools-extra/docs/clang-tidy/checks/list.rst
index f773e80b562e4f..0cc5c217899d4d 100644
--- a/clang-tools-extra/docs/clang-tidy/checks/list.rst
+++ b/clang-tools-extra/docs/clang-tidy/checks/list.rst
@@ -359,6 +359,7 @@ Clang-Tidy Checks
    :doc:`readability-isolate-declaration <readability/isolate-declaration>`, "Yes"
    :doc:`readability-magic-numbers <readability/magic-numbers>`,
    :doc:`readability-make-member-function-const <readability/make-member-function-const>`, "Yes"
+   :doc:`readability-math-missing-parentheses <readability/math-missing-parentheses>`, "Yes"
    :doc:`readability-misleading-indentation <readability/misleading-indentation>`,
    :doc:`readability-misplaced-array-index <readability/misplaced-array-index>`, "Yes"
    :doc:`readability-named-parameter <readability/named-parameter>`, "Yes"
diff --git a/clang-tools-extra/docs/clang-tidy/checks/readability/math-missing-parentheses.rst b/clang-tools-extra/docs/clang-tidy/checks/readability/math-missing-parentheses.rst
new file mode 100644
index 00000000000000..fb3167e8e0f8f1
--- /dev/null
+++ b/clang-tools-extra/docs/clang-tidy/checks/readability/math-missing-parentheses.rst
@@ -0,0 +1,19 @@
+.. title:: clang-tidy - readability-math-missing-parentheses
+
+readability-math-missing-parentheses
+====================================
+
+Checks for mathematical expressions that involve operators of different priorities.
+
+Before:
+
+.. code-block:: c++
+
+  int x = 1 + 2 * 3 - 4 / 5;
+
+
+After:
+
+.. code-block:: c++
+
+  int x = (1 + (2 * 3)) - (4 / 5);
\ No newline at end of file
diff --git a/clang-tools-extra/test/clang-tidy/checkers/readability/math-missing-parentheses.cpp b/clang-tools-extra/test/clang-tidy/checkers/readability/math-missing-parentheses.cpp
new file mode 100644
index 00000000000000..54cc0d4dabbdee
--- /dev/null
+++ b/clang-tools-extra/test/clang-tidy/checkers/readability/math-missing-parentheses.cpp
@@ -0,0 +1,42 @@
+// RUN: %check_clang_tidy %s readability-math-missing-parentheses %t
+
+// FIXME: Add something that triggers the check here.
+void f(){
+    //CHECK-MESSAGES: :[[@LINE+2]]:13: warning: add parantheses to clarify the precedence of operations [readability-math-missing-parentheses]
+    //CHECK-FIXES: int a = 1 + (2 * 3);
+    int a = 1 + 2 * 3; 
+
+    int b = 1 + 2 + 3; // No warning
+
+    int c = 1 * 2 * 3; // No warning
+
+    //CHECK-MESSAGES: :[[@LINE+2]]:13: warning: add parantheses to clarify the precedence of operations [readability-math-missing-parentheses]
+    //CHECK-FIXES: int d = (1 + (2 * 3)) - (4 / 5);
+    int d = 1 + 2 * 3 - 4 / 5;
+
+    //CHECK-MESSAGES: :[[@LINE+2]]:13: warning: add parantheses to clarify the precedence of operations [readability-math-missing-parentheses]
+    //CHECK-FIXES: int e = (1 & (2 + 3)) | (4 * 5);
+    int e = 1 & 2 + 3 | 4 * 5;
+
+    //CHECK-MESSAGES: :[[@LINE+2]]:13: warning: add parantheses to clarify the precedence of operations [readability-math-missing-parentheses]
+    //CHECK-FIXES: int f = (1 * -2) + 4;
+    int f = 1 * -2 + 4;
+
+    //CHECK-MESSAGES: :[[@LINE+2]]:13: warning: add parantheses to clarify the precedence of operations [readability-math-missing-parentheses]
+    //CHECK-FIXES: int g = (((1 * 2) * 3) + 4) + 5;
+    int g = 1 * 2 * 3 + 4 + 5;
+
+    // CHECK-MESSAGES: :[[@LINE+2]]:13: warning: add parantheses to clarify the precedence of operations [readability-math-missing-parentheses]
+    // CHECK-FIXES: int h = (120 & (2 + 3)) | (22 * 5);
+    int h = 120 & 2 + 3 | 22 * 5;
+
+    int i = 1 & 2 & 3; // No warning
+
+    int j = 1 | 2 | 3; // No warning
+
+    int k = 1 ^ 2 ^ 3; // No warning
+
+    // CHECK-MESSAGES: :[[@LINE+2]]:13: warning: add parantheses to clarify the precedence of operations [readability-math-missing-parentheses]
+    // CHECK-FIXES: int l = (1 + 2) ^ 3;
+    int l = 1 + 2 ^ 3;
+}

[11happy]

Not bad, still few issues left, mainly with getOpcode.

Thanks for your review! Update: I will update the PR with the requested changes after 24 as I have mid semester exams from 21-24.

[github-actions[bot]]

:white_check_mark: With the latest revision this PR passed the Python code formatter.

[github-actions[bot]]

:white_check_mark: With the latest revision this PR passed the C/C++ code formatter.

[11happy]

Humble reminder! @PiotrZSL

[11happy]

Hello @PiotrZSL , I ran it on simple codebases & it looks good. I havent tried it on llvm codebase. it was taking a lot of time on my pc.

[5chmidti]

I let it run for a few minutes and didn't observe any crashes (on a release build though). However, I did find an issue with macros:

int sink(int);
#define FUN(ARG) (sink(ARG))
#define FUN2(ARG) sink((ARG))
#define FUN3(ARG) sink(ARG)

void f() {
    ...

    //CHECK-MESSAGES: :[[@LINE+4]]:17: warning: '*' has higher precedence than '+'; add parentheses to explicitly specify the order of operations [readability-math-missing-parentheses]
    //CHECK-FIXES: int r = FUN(0 + (1 * 2));
    int r = FUN(0 + 1 * 2);

    //CHECK-MESSAGES: :[[@LINE+4]]:17: warning: '*' has higher precedence than '+'; add parentheses to explicitly specify the order of operations [readability-math-missing-parentheses]
    //CHECK-FIXES: int s = FUN2(0 + (1 * 2));
    int s = FUN2(0 + 1 * 2);

    //CHECK-MESSAGES: :[[@LINE+4]]:17: warning: '*' has higher precedence than '+'; add parentheses to explicitly specify the order of operations [readability-math-missing-parentheses]
    //CHECK-FIXES: int s = FUN3(0 + (1 * 2));
    int t = FUN3(0 + 1 * 2);
}

All three of these fail, because the closing parentheses is not added.

Files with issues:

• polly/lib/External/isl/isl_map.c
• /home/julian/dev/llvm/llvm-tmp/llvm/unittests/DebugInfo/MSF/MSFBuilderTest.cpp
• unittest files will generally have issues with this, because of the test macros
  • found by invoking this inside the build dir: run-clang-tidy -clang-tidy-binary /path/to/clang-tidy -checks="-*,readability-math-missing*" -quiet unittests

Checking EndLoc.isValid() reveals that the location is invalid for all of these cases (llvm::errs() << "EndLoc: " << EndLoc.isValid() << "\n";).

The documentation for getLocForEndOfToken also explicitly mentions this case for macros:

/// token where it expected something different that it received. If
/// the returned source location would not be meaningful (e.g., if
/// it points into a macro), this routine returns an invalid
/// source location.

[11happy]

hello @5chmidti I am sorry for my delayed response, was quite busy with my academic work last week, I have added this change

if (EndLoc.isInvalid())
      return;

this works fine for those macros. Thank you