https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91075
--- Comment #1 from joseph at codesourcery dot com <joseph at codesourcery dot com> --- This would definitely be invalid C (the prior declaration visible in the inner scope has no linkage, so the inner declaration has external linkage and "If, within a translation unit, the same identifier appears with both internal and external linkage, the behavior is undefined." applies). For C++, it appears the example in 3.5 paragraph 6 in the (old) document you linked to is the relevant one, explicitly saying the inner declaration refers to an entity with external linkage which is different from the static variable with internal linkage. In C++17, [basic.link] paragraph 6 says this example is ill-formed; no doubt one of our C++ experts can give details of when and why this changed and whether it was a defect fix.
