cargo fix: Adjusting a path in a turbofish doesn't work when also adjusting the outer path

[jtgeibel]

The following example code is not automatically fixed on the most recent nightly (cargo 1.29.0-nightly (506eea76e 2018-07-17)).

The issue only occurs when both the outer path and the path inside the turbofish need to be adjusted.

Code

#![feature(rust_2018_preview)]

fn generic_return<T>() {
}

pub struct B{}

pub mod submod {
    pub fn test() {
        ::generic_return::<::B>();
    }
}

Output

$ cargo fix --prepare-for 2018 --allow-dirty
    Checking cargo-fix-test v0.1.0 (file:///home/jtgeibel/repos/localhost/tmp/cargo-fix-test)                                                                                                                                                                                  
warning: error applying suggestions to `src/lib.rs`

The full error message was:

> Could not replace range 140...162 in file -- maybe parts of it were already replaced?This likely indicates a bug in either rustc or cargo itself,
and we would appreciate a bug report! You're likely to see 
a number of compiler warnings after this message which cargo
attempted to fix but failed. If you could open an issue at
https://github.com/rust-lang/cargo/issues
quoting the full output of this command we'd be very appreciative!

warning: absolute paths must start with `self`, `super`, `crate`, or an external crate name in the 2018 edition
  --> src/lib.rs:11:9
   |
11 |         ::generic_return::<::B>();
   |         ^^^^^^^^^^^^^^^^^^^^^^^ help: use `crate`: `crate::generic_return::<::B>`
   |
   = note: `-W absolute-paths-not-starting-with-crate` implied by `-W rust-2018-compatibility`
   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in the 2018 edition!
   = note: for more information, see issue TBD

warning: absolute paths must start with `self`, `super`, `crate`, or an external crate name in the 2018 edition
  --> src/lib.rs:11:28
   |
11 |         ::generic_return::<::B>();
   |                            ^^^ help: use `crate`: `crate::B`
   |
   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in the 2018 edition!
   = note: for more information, see issue TBD

    Finished dev [unoptimized + debuginfo] target(s) in 0.18s

Manual patches

Either of the following patches allows cargo fix to prefix both (now decoupled) paths with crate and exit succesfully.

@@ -7,7 +7,9 @@ fn generic_return<T>() {
 pub struct B{}
 
 pub mod submod {
+    use generic_return;
+
     pub fn test() {
-        ::generic_return::<::B>();
+        generic_return::<::B>();
     }
 }

@@ -7,7 +7,9 @@ fn generic_return<T>() {
 pub struct B{}
 
 pub mod submod {
+    use B;
+
     pub fn test() {
-        ::generic_return::<::B>();
+        ::generic_return::<B>();
     }
 }

[alexcrichton]

Thanks for the report! I've split this into rust-lang/rust#52754 and #5813, so I'm going to close this in favor of those issues.

[jtgeibel]

Thanks! It looks to me like those 2 issues would cover this upstream and as a workaround.