cmake: correctly detect if system provides regcomp
#5063
Merged
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
We assume that if we are on Win32, Amiga OS, Solaris or SunOS, that the regcomp(3P) function cannot be provided by the system. Thus we will in these cases always include our own, bundled regex sources to make a regcomp implementation available. This test is obviously very fragile, and we have seen it fail on MSYS2/MinGW systems, which do in fact provide the regcomp symbol. The effect is that during compilation, we will use the "regex.h" header provided by MinGW, but use symbols provided by ourselves. This in fact may cause subtle memory layout issues, as the structure made available via MinGW doesn't match what our bundled code expects. There's one more problem with our regex detection: on the listed platforms, we will incorrectly include the bundled regex code even in case where the system provides regcomp_l(3), but it will never be used for anything. Fix the issue by improving our regcomp detection code. Instead of relying on a fragile listing of platforms, we can just use `CHECK_FUNCTION_EXISTS` instead. This will not in fact avoid the header-ordering problem. But we can assume that as soon as a system-provided "regex.h" header is provided, that `CHECK_FUNCTION_EXISTS` will now correctly find the desired symbol and thus not include our bundled regex code.
When linking against bundled libraries, we include their header directories by using "-isystem". The reason for that is that we want to handle our vendored library headers specially, most importantly to ignore warnings generated by including them. By using "-isystem", though, we screw up the order of searched include directories by moving those bundled dependencies towards the end of the lookup order. Like this, chances are high that any other specified include directory contains a file that collides with the actual desired include file. Fix this by not treating the bundled dependencies' include directories as system includes. This will move them to the front of the lookup order and thus cause them to override system-provided headers. While this may cause the compiler to generate additional warnings when processing bundled headers, this is a tradeoff we should make regardless to fix builds on systems hitting this issue.
This was referenced May 2, 2019
Merged
azuredevopsexamples
approved these changes
May 2, 2019
ethomson
approved these changes
May 2, 2019
|
Thanks, @ethomson! |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Same as #5007 but with master branch as target.