<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/100909>100909</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [clang-tidy 20] `warning: argument unused during compilation: '-c'` when using compilation database
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Assignees</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Reporter</th>
      <td>
          zufuliu
      </td>
    </tr>
</table>

<pre>
    This is regression from clang-tidy 18 and 19, with clang-tidy build from today's main (at bbc457a4f40328452f0c8c8f9b0b5fcb8d286a7b).

test.cpp:
```cpp
#include <stdio.h>
int main() {
        return printf("Hello, world!\n");
}
```

compile_commands.json:
```json
[
        {
                "directory": "D:\\test",
                "command": "clang++.exe -c D:\\test\\test.cpp",
                "file": "D:\\test\\test.cpp"
        }
]
```

output:
```
D:\test>clang-tidy test.cpp
1 warning generated.
warning: argument unused during compilation: '-c' [clang-diagnostic-unused-command-line-argument]

D:\test>clang-tidy -checks=* test.cpp
9508 warnings generated.
warning: argument unused during compilation: '-c' [clang-diagnostic-unused-command-line-argument]
D:\test\test.cpp:1:1: warning: system include stdio.h not allowed [llvmlibc-restrict-system-libc-headers]
    1 | #include <stdio.h>
 | ^~~~~~~~~~~~~~~~~~
    2 | int main() {
D:\test\test.cpp:1:10: warning: inclusion of deprecated C++ header 'stdio.h'; consider using 'cstdio' instead [hicpp-deprecated-headers,modernize-deprecated-headers]
 1 | #include <stdio.h>
      |          ^
note: this fix will not be applied because it overlaps with another fix
D:\test\test.cpp:2:5: warning: declaration must be enclosed within the 'LIBC_NAMESPACE_DECL' namespace [llvmlibc-implementation-in-namespace]
    2 | int main() {
 |     ^
D:\test\test.cpp:2:5: warning: use a trailing return type for this function [modernize-use-trailing-return-type]
    2 | int main() {
      | ~~~ ^
      | auto       -> int
D:\test\test.cpp:3:9: warning: do not call c-style vararg functions [cppcoreguidelines-pro-type-vararg,hicpp-vararg]
    3 |         return printf("Hello, world!\n");
      |                ^
Suppressed 9500 warnings (9500 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.

D:\test>
```

Same behavior after change `command` to `clang-cl.exe /c D:\\test\\test.cpp`:
```
D:\test>clang-tidy test.cpp
1 warning generated.
warning: argument unused during compilation: '/c' [clang-diagnostic-unused-command-line-argument]

D:\test>clang-tidy -checks=* test.cpp
9508 warnings generated.
warning: argument unused during compilation: '/c' [clang-diagnostic-unused-command-line-argument]
D:\test\test.cpp:1:1: warning: system include stdio.h not allowed [llvmlibc-restrict-system-libc-headers]
    1 | #include <stdio.h>
 | ^~~~~~~~~~~~~~~~~~
    2 | int main() {
D:\test\test.cpp:1:10: warning: inclusion of deprecated C++ header 'stdio.h'; consider using 'cstdio' instead [hicpp-deprecated-headers,modernize-deprecated-headers]
 1 | #include <stdio.h>
      |          ^
note: this fix will not be applied because it overlaps with another fix
D:\test\test.cpp:2:5: warning: declaration must be enclosed within the 'LIBC_NAMESPACE_DECL' namespace [llvmlibc-implementation-in-namespace]
    2 | int main() {
 |     ^
D:\test\test.cpp:2:5: warning: use a trailing return type for this function [modernize-use-trailing-return-type]
    2 | int main() {
      | ~~~ ^
      | auto       -> int
D:\test\test.cpp:3:9: warning: do not call c-style vararg functions [cppcoreguidelines-pro-type-vararg,hicpp-vararg]
    3 |         return printf("Hello, world!\n");
      |                ^
Suppressed 9500 warnings (9500 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.

D:\test>
```
</pre>
<img width="1px" height="1px" alt="" src="http://email.email.llvm.org/o/eJzsWEuP27YT_zT0ZSBDoixbOviwfiz-fyAtCqQ9BxQ5sphSpEBSu3EO-9kLUvJjneymSS9Bu4L34SFn-PvNkzZzTh404poUG1LsZmzwrbHrz0MzKDnMaiOO699b6UA6sHiw6Jw0GhprOuCK6UPipThCVgLTArKK0C08St9eL9aDVGJU8UawI6ErBx2TGggtmYe65otixRbNIs1puShok_KSl01Vp3XR8LoUtFyyVU1oNSfpjqR342-Pzs9535N8EpBlOr6CcJTQXGquBoFA8q3zQpp5S_L9uCq1jzgILQmtgKw2J_OVRT9YDb2V2jdxnf4PlTKRn7FKEJqRYqsJpYRWJD9prnY3UK4Bc9P1UuEHbrqOaeHmH53RX6KP0lFUXBBdowsvSoW0yL2xxwAivwNC6S5YK7ak2AbnRHDbG63p8ItOjBShG0I3c_yEkHC4MXP-L3r7a0YbqfBFFF-oXyidvFW85jYz-H7wX_ppfDsdFk_K91dpdz4xbsvgkVkt9QEOqNEyj2JKpkkesDN7GDrUHgY9OBQgBhs0xrgxL2O0gNBVwgldASk243lCsoM2zkuejJrJ5OVESY3JyeyF5uvIE94i_9ORfEfo3Q2PqkjLExX3M3C5ZnEV5vwum37gCpQ7Oo8dnGpyKkjQxgNTyjyiCECUeuiUrHli0XkruU9GvSQKW2QCrTsDAADIgKy28Hq1j1uK_dPtczFD456X2sLrTNMbqhFJbJamAYG9RR4CBdux1GCkEQJwAkpXJN8AN9rJsDK4EC9CVzxuCEGS2nlk0Uet5H2fXOye3UK3nRFotfyMX1s-e-1vuSw-Yd_5IcW0po3HwNOH6dDIT_AolYqRrBFY3yuJAmrkbHAI0oN5QKtY78bxwLTxLdqg-A3nhqZS3PhWIFfMxiSGbnDxSNRcmZDowb7U4FsMznv3_832w693v-zf_3a33X_Y7bfvgic169D1jOOzfJNdrzBkdzSdSJ2c9z1Lt9fz5Oyws6--i1zwFwNvmVQhAaZJ5I89QmPs5O9B88ieFJtLuAeHyUkvGfWSoPc92M8Rf3p6uhC4iNngzZQKCcn3wdA3OOYkv6tuA2hipnCmFPDE-aNCeGCW2cOZmostqe-5sXgYpMDQflzSWxM5JeN2QrdjJUxvr5nmzzL3Byf6V0rgphDeD30f7kUooCrS9NKcCS2jQGrQRofoWOBG4OUe84dDmCozaaTyaEm-m8emb0BI1yt2BLTWWDfen1gsMT31w6mHuDlEQ1OTnIQvmXiuCszBIyo1f3kwvTKZ37MOocaWPUhjgTU-MGyZPiCEW9h001imAUsQxAHDVbxmEHr_jYvGMv2pZn4A_O-Z-v-Yzdvcf5v7b3P_be6_zf3_xtyfiXUuqrxiM1xnK0ozWmVLOmvXGS9wuayXqyUraFFyJrDMalbiosnEsqlnck1TukhXtEyzjC7oHPOSFXW2TMslLsRySRYpdkyqeSjIubGHmXRuwHWWplVazRSrUbnTN1R2HXYl9XBwZJEq6by76HnpVfwu62qu0pQUu3D9-OEPx-EG89iinlrz1S4QzLOaOZwNVq1b73sXfEjvCb0_SN8O9ZybjtD7gHD6E1L5I3JP6H2k6Qi9n5g-rOlfAQAA__-RAwKO">