mozilla/rust — pull request #12419 by huonw (2014-02-20 12:30:20+00:00)
Title: rustc: avoid compiler generated `unsafe` blocks leaking.

Previously an `unsafe` block created by the compiler (like those in the
formatting macros) would be "ignored" if surrounded by `unsafe`, that
is, the internal unsafety would be being legitimised by the external
block:

unsafe { println!("...") } =(expansion)=> unsafe { ... unsafe { ... } }

And the code in the inner block would be using the outer block, making
it considered used (and the inner one considered unused).

This patch forces the compiler to create a new unsafe context for
compiler generated blocks, so that their internal unsafety doesn't
escape to external blocks.

Fixes #12418.