i found some ambiguous wording in the c89(/c90) standard, where gcc and clang disagree on the interpretation. it concerns the behavior of implicit function declarations, which were removed in c99, so this was never disambiguated.

for those unaware: c89 has a cool "feature" where, if you try to call a function which doesn't exist, rather than erroring out, the function is implicitly declared as a function with unspecified parameters returning int.

more specifically: if the function in a call expression is a non-parenthesized identifier which isn't in scope, it's inserted into scope as an extern int () .

(a funny thing about this is that it means that seemingly superfluous parentheses around expressions affect semantics: f() inserts f into scope, but (f)() doesn't)

anyways, i'm gonna show you a fun edge case with this feature. but to build up to it, let's start simple.…