RFR: 8352645: Add tool support to check order of includes

[Magnus Ihse Bursie]

On Tue, 25 Mar 2025 12:06:42 GMT, Doug Simon <dnsimon at openjdk.org> wrote:

>> src/hotspot/cpu/aarch64/immediate_aarch64.cpp line 26:
>> 
>>> 24:  */
>>> 25: 
>>> 26: #include <stdlib.h>
>> 
>> Moving these sys includes causes a build failure: https://github.com/dougxc/jdk/actions/runs/14054959680/job/39352322113#step:12:537
>> 
>> In file included from /home/runner/work/jdk/jdk/src/hotspot/cpu/aarch64/immediate_aarch64.cpp:26:
>> /home/runner/work/jdk/jdk/src/hotspot/cpu/aarch64/immediate_aarch64.hpp:49:1: error: ‘uint64_t’ does not name a type; did you mean ‘u_int64_t’?
>>    49 | uint64_t logical_immediate_for_encoding(uint32_t encoding);
>>       | ^~~~~~~~
>>       | u_int64_t
>> 
>> The question is whether they should not be re-ordered or whether `immediate_aarch64.hpp` should add the sys includes it apparently needs.
>
> I pushed a commit that prevents the re-ordering: https://github.com/openjdk/jdk/pull/24180/commits/c0f202d2a7e7b8788719fe8cd2a4c7a095ecd3bb

My gut reaction is that header files should be self-sustaining, that is if they need some external header files, these should be included by the header file itself. But that is up to the hotspot folks to decide.

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PR Review Comment: https://git.openjdk.org/jdk/pull/24180#discussion_r2012289902