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rustc: Disallow modules and macros in expansions #50820

Merged
merged 1 commit into from
May 20, 2018
Merged

rustc: Disallow modules and macros in expansions #50820

merged 1 commit into from
May 20, 2018

Commits on May 18, 2018

  1. rustc: Disallow modules and macros in expansions 

    This commit feature gates generating modules and macro definitions in procedural
macro expansions. Custom derive is exempt from this check as it would be a large
retroactive breaking change (rust-lang#50587). It's hoped that we can hopefully stem the
bleeding to figure out a better solution here before opening up the floodgates.

The restriction here is specifically targeted at surprising hygiene results [1]
that result in non-"copy/paste" behavior. Hygiene and procedural macros is
intended to be avoided as much as possible for Macros 1.2 by saying everything
is "as if you copy/pasted the code", but modules and macros are sort of weird
exceptions to this rule that aren't fully fleshed out.

[1]: rust-lang#50504 (comment)

cc rust-lang#50504
    @alexcrichton
    alexcrichton committed May 18, 2018
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