WIP: Don't create self imports with merge_imports

[jrobsonchase]

Currently, rustfmt formats this:

use a::b;
use a::b::c;

into this:

use a::b::{self, c};

This changes the semantics of the imports since use a::b; could also be pulling in a function or macro named b, while use a::b::{self, c}; only imports the module named b.

Just have a failing test case for now, but I should have a fix before too long.

[scampi]

I was able to reproduce what you described, thanks. Below is what I used

$ tree src
src
├── main.rs
├── moda
│   └── modb.rs
└── moda.rs

1 directory, 3 files

$ cat src/**/*.rs
     File: src/main.rs
   1 pub mod moda;
   2
   3 //use moda::modb;
   4 use moda::modb::{self, fnc};
   5
   6 fn main() {
   7     modb();
   8     fnc();
   9 }

     File: src/moda/modb.rs
   1 pub fn fnc() {
   2     println!("in fnc");
   3 }

     File: src/moda.rs
   1 pub mod modb;
   2
   3 pub fn modb() {
   4     println!("in modb function");
   5 }

This fails to compile:

error[E0423]: expected function, found module `modb`
 --> src/main.rs:6:5
  |
6 |     modb();
  |     ^^^^ not a function
help: possible better candidate is found in another module, you can import it into scope
  |
3 | use crate::moda::modb;
  |

---

Your build is failing https://travis-ci.com/rust-lang/rustfmt/jobs/201273582:

Mismatch at tests/source/merge_imports.rs:1:
 // rustfmt-merge_imports: true
 
-use a::{a, b, c, d, e, f, g};
+use a::{
+    a, e, g, {b, b}, {c, c}, {d, d}, {f, f},
+};
 
 #[doc(hidden)]
 use a::b;
Mismatch at tests/source/merge_imports.rs:8:
 
 #[doc(hidden)]
 use a::b;
-use a::{c, d, e};
+use a::{
+    c, e, {d, d},
+};
 
 use foo::{a, b, c};
 pub use foo::{bar, foobar};
Mismatch at tests/source/merge_imports.rs:15:
 
 use a::b::c::{d, xxx, yyy, zzz, *};
 
-use a::b;
-use a::b::c;
+use a::{b, b::c};
 
Mismatch at tests/source/configs/imports_layout/merge_mixed.rs:4:
 
 use std::{
     fmt, io,
-    str::{self, FromStr},
+    {str, str::FromStr},
 };
 
Ran 367 system tests.
thread '<unnamed>' panicked at 'assertion failed: `(left == right)`
  left: `2`,
 right: `0`: 2 system tests failed', src/test/mod.rs:153:9
test test::system_tests ... FAILED
failures:
---- imports::test::test_use_tree_merge stdout ----
thread 'imports::test::test_use_tree_merge' panicked at 'assertion failed: `(left == right)`
  left: `[a::{b, b}]`,
 right: `[a::b]`', src/imports.rs:994:9
note: Run with `RUST_BACKTRACE=1` environment variable to display a backtrace.
---- test::idempotence_tests stdout ----
thread 'test::idempotence_tests' panicked at 'Failed to join a test thread: Any', src/libcore/result.rs:999:5
---- test::system_tests stdout ----
thread 'test::system_tests' panicked at 'Failed to join a test thread: Any', src/libcore/result.rs:999:5
failures:
    imports::test::test_use_tree_merge
    test::idempotence_tests
    test::system_tests

[jrobsonchase]

Yeah, my fix isn't quite there yet, and right now I fear that it might take a more extensive rewrite of the merging algorithm than I'm up for 😕

The last mismatch is a false positive, the second is actually the correct behavior and I just missed the test case. The others are all a result of my half-fix that leaves duplicate imports.

[topecongiro]

The issue seems to be fixed by #3753. As such, I am closing this. Thanks!