Weird fix in tuple-pattern

[csmoe]

When dealing with Reduce unused variable span, the fix keeps failing.

src:

let (mut var, unused_var) = (1, 2);

suggestion:

warning: unused variable: `var`
 --> src/lib.rs:2:10
  |
2 |     let (mut var, unused_var) = (1, 2);
  |          ^^^^^^^ help: consider using `_var` instead
  |
  = note: #[warn(unused_variables)] on by default

warning: unused variable: `unused_var`
 --> src/lib.rs:2:19
  |
2 |     let (mut var, unused_var) = (1, 2);
  |                   ^^^^^^^^^^ help: consider using `_unused_var` instead

warning: variable does not need to be mutable
 --> src/lib.rs:2:10
  |
2 |     let (mut var, unused_var) = (1, 2);
  |          ----^^^
  |          |
  |          help: remove this `mut`
  |
  = note: #[warn(unused_mut)] on by default

warning: function is never used: `main`
 --> src/lib.rs:1:1
  |
1 | fn main() {
  | ^^^^^^^^^
  |
  = note: #[warn(dead_code)] on by default

fixed:

let (_varus_unused_var(1, 2);

NOTE: the failed fix occurs both in current unreduce_var_span and reduced_var_span after the PR.

[killercup]

Oh, wow, that is… horrible. Rustfix seems to mess up the byte indices for some reason. Can you quote the json output from rustc? Oh, no need, I saw the log contains it. I'll also build your PR branch locally to try and debug this.

[csmoe]

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@killercup
To save your time, you don't need to build my branch, just cargo new a local crate with the src above in src/lib.rs, then build and fix it, the error will be reproduced.

[csmoe]

@killercup
Another crazy fix with the tuple-pattern is in the same line of fn main().
source:

fn main() {let (mut var, unused_var) = (1, 2);}

fix:

_var
_unused_var
fn main() {let (var, unused_var) = (1, 2);}

meta:

cargo 1.27.0-nightly (9e53ac6e6 2018-05-07)
rustc 1.27.0-nightly (acd3871ba 2018-05-10)

[killercup]

@csmoe are you using rustfix master? Or the released version that's used in rustc's compiletest?

I just built rust-lang/rust#50675 locally, linked it with rustup as s1 and inside the rustfix repo added a small example to apply fixes from json (see #101).

$ cd ~/Projekte/rustfix
$ git status
On branch json-tool
Your branch is up to date with 'killercup/json-tool'.
…
$ cd examples
$ echo "fn main() {let (mut var, unused_var) = (1, 2);}" > foo.rs
$ rustc +s1 foo.rs --error-format=pretty-json -Zunstable-options --emit=metadata 2> foo.json
$ code foo.json # looks okay
$ cargo run --example fix-json foo.json foo.rs
    Finished dev [unoptimized + debuginfo] target(s) in 0.14s
     Running `/Users/pascal/Projekte/rustfix/target/debug/examples/fix-json foo.json foo.rs`
fn main() {let (_var, _unused_var) = (1, 2);}

It works! :O Same for this:

fn main() {
    let (mut var, unused_var) = (1, 2);
}

which becomes

fn main() {
    let (_var, _unused_var) = (1, 2);
}

Feel free to ping me on gitter or irc or discord, too!

[killercup]

Oh, and using rustc nightly from 2018-05-09 fails with Error: ErrorMessage { msg: "Could not replace range 21...27 in file -- maybe parts of it were already replaced?" } -- which is correct because the (broken) fixes for unused mut and unused var overlap.

[killercup]

This should be fixed in rustfix master. Let's close this issue in a follow-up PR to rust-lang/rust#50675 that adds the appropriate rustfix tests to rustc.