[PATCH] D150966: [clang] Don't define predefined macros multiple times

[John Brawn via Phabricator via cfe-commits]

john.brawn added a comment.

In D150966#4356403 <https://reviews.llvm.org/D150966#4356403>, @barannikov88 wrote:

> Is it possible/worth to add an assertion to Builder.defineMacro to enforce this one definition rule?

It just appends a string to a raw_ostream, so it's not possible to check what's previously been written.

In D150966#4356470 <https://reviews.llvm.org/D150966#4356470>, @barannikov88 wrote:

> Q: What is it the -Wsystem-header can warn about? I mean, no system header is included by the test, what can go wrong?

The <built-in> buffer is treated as a system header. I've expanded on the comment to explain this more.


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