[clang-tidy] unexpected `readability-math-missing-parentheses` warnings for assignment

[zufuliu]

see https://godbolt.org/z/7nK7fG4Gs, reduced from https://github.com/zufuliu/notepad2/blob/main/scintilla/src/Document.cxx#L691

// clang-tidy -checks=readability-math-missing-parentheses test.cpp --
int LevelNumberPart(int level);
bool LevelIsHeader(int level);
bool LevelIsWhitespace(int level);
int GetFoldLevel(int line);
int GetFoldParent(int line);
int GetLastChild(int line);

int GetHighlightDelimiters(int line) {
    const int level = GetFoldLevel(line);
    int lookLine = line;
    int lookLineLevel = level;
    int lookLineLevelNum = 0;

    const int beginFoldBlock = LevelIsHeader(lookLineLevel) ? lookLine : GetFoldParent(lookLine);
    const int endFoldBlock = GetLastChild(beginFoldBlock);
    int firstChangeableLineBefore = -1;
    for (lookLine = line - 1, lookLineLevel = GetFoldLevel(lookLine), lookLineLevelNum = LevelNumberPart(lookLineLevel);
        lookLine >= beginFoldBlock;
        lookLineLevel = GetFoldLevel(--lookLine), lookLineLevelNum = LevelNumberPart(lookLineLevel)) {
        if (LevelIsWhitespace(lookLineLevel) || (lookLineLevelNum > LevelNumberPart(level))) {
            firstChangeableLineBefore = lookLine;
            break;
        }
    }

    int firstChangeableLineAfter = -1;
    for (lookLine = line + 1, lookLineLevel = GetFoldLevel(lookLine), lookLineLevelNum = LevelNumberPart(lookLineLevel);
        lookLine <= endFoldBlock;
        lookLineLevel = GetFoldLevel(++lookLine), lookLineLevelNum = LevelNumberPart(lookLineLevel)) {
        if (LevelIsHeader(lookLineLevel) && (lookLineLevelNum < LevelNumberPart(GetFoldLevel(lookLine + 1)))) {
            firstChangeableLineAfter = lookLine;
            break;
        }
    }
    return firstChangeableLineBefore + firstChangeableLineAfter;
}

[<source>:18:21: warning: '-' has higher precedence than '='; add parentheses to explicitly specify the order of operations [readability-math-missing-parentheses]](javascript:;)
   18 |     for (lookLine = line - 1, lookLineLevel = GetFoldLevel(lookLine), lookLineLevelNum = LevelNumberPart(lookLineLevel);
      |                     ^~~~~~~~~
      |                     (       )
[<source>:28:21: warning: '+' has higher precedence than '='; add parentheses to explicitly specify the order of operations [readability-math-missing-parentheses]](javascript:;)
   28 |     for (lookLine = line + 1, lookLineLevel = GetFoldLevel(lookLine), lookLineLevelNum = LevelNumberPart(lookLineLevel);
      |                     ^~~~~~~~~
      |                     (       )
2 warnings generated.

[chrchr-github]

Reduced:

void f(int i) {
    int j, k;
    for (j = i + 1, k = 0; j < 1; ++j) {}
}

[PiotrZSL]

Agree, check shouldn't warn for assignments, only for math operators.

[zufuliu]

Not sure why, but following code has no warnings:

void f(int i) {
    int j;
    for (j = i + 1; j < 1; ++j) {}
}

[zufuliu]

It seems somewhat related to the comma, following code has the warning too:

void f(int i) {
    int j;
    for (j = i + 1, 2; j < 1; ++j) {}
}