clang-tidy-21 FIX-ITs include <algorithm> header twice (readability-use-std-min-max and modernize-use-ranges)

Reproduce Steps

Setup

Create a directory with three files (test.cpp, test.h, and compile_commands.json), with the following content. (You may need to change the directory in compile_commands.json to use an absolute path.)

test.cpp

#include "test.h"

int main() {
    std::vector<int> nums {1, 3, 2, 4};
    std::sort(nums.begin(), nums.end());

    int largest = nums.front();
    for (auto n : nums) {
        if (n > largest) {
            largest = n;
        }
    }
}

test.h

#include <vector>
#include <algorithm>

compile_commands.json

[
  {
    "directory": ".",
    "command": "clang++-21 -std=c++20 -Wall -Wextra -c test.cpp",
    "file": "test.cpp"
  }
]

Invoke clang-tidy

$ clang-tidy-21 -p . --fix --warnings-as-errors='*' --checks='readability-use-std-min-max,modernize-use-ranges,readability-duplicate-include' test.cpp

Command output:

3 warnings generated.
test.cpp:5:5: error: use a ranges version of this algorithm [modernize-use-ranges,-warnings-as-errors]
    2 |
    3 | int main() {
    4 |     std::vector<int> nums {1, 3, 2, 4};
    5 |     std::sort(nums.begin(), nums.end());
      |     ^~~~~~~~~ ~~~~~~~~~~~~  ~~~~~~~~~~
      |     std::ranges::sort nums
test.cpp:2:1: note: FIX-IT applied suggested code changes
    2 |
      | ^
test.cpp:5:5: note: FIX-IT applied suggested code changes
    5 |     std::sort(nums.begin(), nums.end());
      |     ^
test.cpp:5:15: note: FIX-IT applied suggested code changes
    5 |     std::sort(nums.begin(), nums.end());
      |               ^
test.cpp:5:28: note: FIX-IT applied suggested code changes
    5 |     std::sort(nums.begin(), nums.end());
      |                            ^
test.cpp:9:9: error: use `std::max` instead of `>` [readability-use-std-min-max,-warnings-as-errors]
    2 |
    3 | int main() {
    4 |     std::vector<int> nums {1, 3, 2, 4};
    5 |     std::sort(nums.begin(), nums.end());
    6 |
    7 |     int largest = nums.front();
    8 |     for (auto n : nums) {
    9 |         if (n > largest) {
      |         ^~~~~~~~~~~~~~~~~~
      |         largest = std::max(n, largest);
   10 |             largest = n;
      |             ~~~~~~~~~~~~
   11 |         }
      |         ~
test.cpp:2:1: note: FIX-IT applied suggested code changes
    2 |
      | ^
test.cpp:9:9: note: FIX-IT applied suggested code changes
    9 |         if (n > largest) {
      |         ^
clang-tidy applied 6 of 6 suggested fixes.
Suppressed 1 warnings (1 in non-user code).
Use -header-filter=.* to display errors from all non-system headers. Use -system-headers to display errors from system headers as well.
2 warnings treated as errors

test.cpp after fix-its:

#include "test.h"

#include <algorithm>

#include <algorithm>

int main() {
    std::vector<int> nums {1, 3, 2, 4};
    std::ranges::sort(nums);

    int largest = nums.front();
    for (auto n : nums) {
        largest = std::max(n, largest);
    }
}

The algorithm header was included twice by the different checks. If you run clang-tidy again, this fails due to the readability-duplicate-include rule. It can be fixed again, but it requires 2 passes.

In my case, my build script does a first pass with -fix and a second pass without it, and this triggers an error which was not introduced by the user.

Environment

$ clang-tidy-21 --version
Ubuntu LLVM version 21.1.8
  Optimized build.

$ uname -a
Linux alternating-bike 5.15.167.4-microsoft-standard-WSL2 #1 SMP Tue Nov 5 00:21:55 UTC 2024 x86_64 x86_64 x86_64 GNU/Linux

$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 24.04.3 LTS
Release:        24.04
Codename:       noble

I installed LLVM via ./llvm.sh 21 all downloaded from https://apt.llvm.org/llvm.sh.

Start with the test.cpp, test.h, and compile_commands.json reproducer and run the stated clang-tidy command with readability-use-std-min-max, modernize-use-ranges, and readability-duplicate-include. Read the fix-it behavior of the two checks and their interaction with include insertion. Done means one fix pass does not introduce a duplicate include or cause the subsequent duplicate-include check to fail.