711683 - Use Clang's feature-detection macros for feature testing, not its "marketing" version numbers

Status: RESOLVED FIXED

(Core :: MFBT, defect)

Description

[Jeff Walden [:Waldo]]

Attachment: Patch

Skimming Clang mailing list traffic tonight, I discovered that vendors are seemingly intent on muddying the waters by disconnecting Clang version numbers from feature sets -- good times.  So relying on version checks for features is a bit dodgy.  Conveniently Clang provides feature detection macros which will do the same work, arguably more clearly.  Whee, kinda-make-work.

The warning about version checking is here, for the major/minor macros:

http://clang.llvm.org/docs/LanguageExtensions.html#builtinmacros

The patch uses the __has_extension macro because we want to use the relevant language features even if we're not compiling plain old C++98 -- no reason to hold back use of these features for a full transition over.  __has_extension is documented here:

http://clang.llvm.org/docs/LanguageExtensions.html#__has_feature_extension

The arguments passed to __has_extension are documented here:

http://clang.llvm.org/docs/LanguageExtensions.html#cxx_deleted_functions
http://clang.llvm.org/docs/LanguageExtensions.html#cxx_override_control

I checked some .i files with this patch, and things translate as expected in a Clang compile.

Comment 1

[Jeff Walden [:Waldo]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/87be07cf8c10

Comment 2

[Marco Bonardo [:mak]]

https://hg.mozilla.org/mozilla-central/rev/87be07cf8c10