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Fix macro hygiene bug - #32923

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jseyfried:fix_hygiene
Apr 16, 2016
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Fix macro hygiene bug#32923
bors merged 4 commits into
rust-lang:masterfrom
jseyfried:fix_hygiene

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@jseyfried

@jseyfriedjseyfried commented Apr 13, 2016•
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This fixes#32922 (EDIT: also #31856, #10681, and #26223), macro hygiene bugs.
It is a [breaking-change]. For example, the following would break:

fnmain(){let x = true;macro_rules! foo {() => {let x = 0;
macro_rules! bar {() => {x}}let _:bool = bar!();//^ `bar!()` used to resolve the first `x` (a bool),//| but will now resolve to the second x (an i32).}}foo!{};}

r? @nrc

@jseyfriedjseyfried changed the title Fix hygieneFix macro hygiene bugApr 13, 2016
@jseyfriedjseyfried mentioned this pull request Apr 14, 2016
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@jseyfried

jseyfried commented Apr 14, 2016

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This could use a crater run (cf. discussion in #32922).

@alexcrichton

alexcrichton commented Apr 14, 2016

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Starting a crater run

@alexcrichtonalexcrichton added the S-waiting-on-crater Status: Waiting on a crater run to be completed. label Apr 14, 2016
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alexcrichton commented Apr 15, 2016

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Crater reports one regression, but it looks spurious, so essentially nothing from crater.

@jseyfried

jseyfried commented Apr 15, 2016

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Great, thanks!

@nrc

nrc commented Apr 15, 2016

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Could you add some of the tests from #31856 please? r+ with that

@jseyfried

jseyfried commented Apr 15, 2016

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@nrc I added another test from #31856.

@nrc

nrc commented Apr 15, 2016

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@bors: r+

@bors

bors commented Apr 15, 2016

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📌 Commit ca1d29c has been approved by nrc

Manishearth added a commit to Manishearth/rust that referenced this pull request Apr 15, 2016
@Manishearth
Rollup merge ofrust-lang#32923- jseyfried:fix_hygiene, r=nrc
6a0cfbc
Fix macro hygiene bug
This fixesrust-lang#32922 (EDIT: and fixesrust-lang#31856), macro hygiene bugs.
It is a [breaking-change]. For example, the following would break:
```rust
fn main() {
let x = true;
macro_rules! foo { () => {
let x = 0;
macro_rules! bar { () => {x} }
let _: bool = bar!();
//^ `bar!()` used to resolve the first `x` (a bool),
//| but will now resolve to the second x (an i32).
}}
foo! {};
}
```
r? @nrc
@ManishearthManishearth mentioned this pull request Apr 15, 2016
Merged
bors added a commit that referenced this pull request Apr 15, 2016
@bors
Auto merge of#33005- Manishearth:rollup, r=Manishearth
576229f
Rollup of 11 pull requests
- Successful merges: #32923, #32926, #32929, #32931, #32935, #32945, #32946, #32964, #32970, #32973, #32997
- Failed merges:
@bors
bors merged commit ca1d29c into rust-lang:masterApr 16, 2016
@jseyfriedjseyfried mentioned this pull request May 14, 2016
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@jseyfriedjseyfried mentioned this pull request Jun 2, 2016
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@jseyfried

jseyfried commented Jun 2, 2016

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Fixes #10681.

@sfacklersfackler mentioned this pull request Jun 2, 2016
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@jseyfriedjseyfried mentioned this pull request Jun 9, 2016
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@jseyfried

jseyfried commented Jun 9, 2016

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Fixes #26223.

@blussbluss added relnotes Marks issues that should be documented in the release notes of the next release. and removed S-waiting-on-crater Status: Waiting on a crater run to be completed. labels Jun 9, 2016
@jseyfriedjseyfried mentioned this pull request Jun 20, 2016
Merged
bors added a commit that referenced this pull request Jun 23, 2016
@bors
Auto merge of#34374- jseyfried:fix_hygiene_bug, r=nrc
4960f2f
Fix macro hygiene regression
The regression was caused by #32923, which is currently in beta.
The following is an example of regressed code:
```rust
fn main() {
let x = 0;
macro_rules! foo { () => {
println!("{}", x); // prints `0` on stable and after this PR, prints `1` on beta and nightly
} }
let x = 1;
foo!();
}
```
For code to regress, the following is necessary (but not sufficient):
- There must be a local variable before a macro in a block, and the macro must use the variable.
- There must be a second local variable with the same name after the macro.
- The macro must be invoked in a statement position after the second local variable.
For example, if the `let x = 0;` from the breaking example were commented out, it would (correctly) not compile on beta/nightly. If the semicolon were removed from `foo!();`, it would (correctly) print `0` on beta and nightly.
r? @nrc
@TimNNTimNN mentioned this pull request Sep 16, 2016
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@jseyfried
jseyfried deleted the fix_hygiene branch February 12, 2017 13:15
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Macro hygiene bug

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