Error applying replacements from module files

[killercup]

It seems I have reintroduced a bug with regard to byte indices in module files.

Simple example: This change to rustfix itself

diff --git a/cargo-fix/src/cli.rs b/cargo-fix/src/cli.rs
index fbbdfe6..32a9bb4 100644
--- a/cargo-fix/src/cli.rs
+++ b/cargo-fix/src/cli.rs
@@ -107,6 +107,8 @@ fn log_for_human(kind: &str, msg: &str) -> Result<(), Error> {
     let mut stream = StandardStream::stderr(color_choice);
     stream.reset()?;
 
+    let mut i = 42;
+
     stream.set_color(ColorSpec::new().set_bold(true).set_fg(Some(Color::Cyan)))?;
     // Justify to 12 chars just like cargo
     write!(&mut stream, "{:>12}", kind)?;

leads to this output

Checking cargo-fix v0.2.0 (file:///Users/pascal/Projekte/rustfix/cargo-fix)
error: Could not find data slice that covers range 3823..3827
error: Could not compile `cargo-fix`.

That range looks an awful lot like the index in the whole crate's source, not in cli.rs. I'm pretty sure there is such a property in the compiler's json output, though, and I'm just not using it correctly.

[killercup]

Yes indeed, this was tracked in https://github.com/rust-lang/rust/issues/35164apparently fixed in rust-lang/rust#42973 a year ago, and this looks like it's still there.

Looks like byte indices are actually legit and something else is wrong here?

[killercup]

Yeah, I'm stupid. We get two suggestions for this specific case:

warning: unused variable: `i`
   --> cargo-fix/src/cli.rs:110:9
    |
110 |     let mut i = 42;
    |         ^^^^^ help: consider using `_i` instead
    |
    = note: #[warn(unused_variables)] on by default

warning: variable does not need to be mutable
   --> cargo-fix/src/cli.rs:110:9
    |
110 |     let mut i = 42;
    |         ----^
    |         |
    |         help: remove this `mut`
    |
    = note: #[warn(unused_mut)] on by default

This should of course not overlap! We can remove the mut and add the _ as two separate lints.

JSON

{
  "message": {
    "children": [
      {
        "children": [],
        "code": null,
        "level": "note",
        "message": "#[warn(unused_variables)] on by default",
        "rendered": null,
        "spans": []
      },
      {
        "children": [],
        "code": null,
        "level": "help",
        "message": "consider using `_i` instead",
        "rendered": null,
        "spans": [
          {
            "byte_end": 3828,
            "byte_start": 3823,
            "column_end": 14,
            "column_start": 9,
            "expansion": null,
            "file_name": "cargo-fix/src/cli.rs",
            "is_primary": true,
            "label": null,
            "line_end": 110,
            "line_start": 110,
            "suggested_replacement": "_i",
            "text": [
              {
                "highlight_end": 14,
                "highlight_start": 9,
                "text": "    let mut i = 42;"
              }
            ]
          }
        ]
      }
    ],
    "code": {
      "code": "unused_variables",
      "explanation": null
    },
    "level": "warning",
    "message": "unused variable: `i`",
    "rendered": "warning: unused variable: `i`\n   --> cargo-fix/src/cli.rs:110:9\n    |\n110 |     let mut i = 42;\n    |         ^^^^^ help: consider using `_i` instead\n    |\n    = note: #[warn(unused_variables)] on by default\n\n",
    "spans": [
      {
        "byte_end": 3828,
        "byte_start": 3823,
        "column_end": 14,
        "column_start": 9,
        "expansion": null,
        "file_name": "cargo-fix/src/cli.rs",
        "is_primary": true,
        "label": null,
        "line_end": 110,
        "line_start": 110,
        "suggested_replacement": null,
        "text": [
          {
            "highlight_end": 14,
            "highlight_start": 9,
            "text": "    let mut i = 42;"
          }
        ]
      }
    ]
  },
  "package_id": "cargo-fix 0.2.0 (path+file:///Users/pascal/Projekte/rustfix/cargo-fix)",
  "reason": "compiler-message",
  "target": {
    "crate_types": [
      "bin"
    ],
    "kind": [
      "bin"
    ],
    "name": "cargo-fix",
    "src_path": "/Users/pascal/Projekte/rustfix/cargo-fix/src/main.rs"
  }
}
{
  "message": {
    "children": [
      {
        "children": [],
        "code": null,
        "level": "note",
        "message": "#[warn(unused_mut)] on by default",
        "rendered": null,
        "spans": []
      },
      {
        "children": [],
        "code": null,
        "level": "help",
        "message": "remove this `mut`",
        "rendered": null,
        "spans": [
          {
            "byte_end": 3827,
            "byte_start": 3823,
            "column_end": 13,
            "column_start": 9,
            "expansion": null,
            "file_name": "cargo-fix/src/cli.rs",
            "is_primary": true,
            "label": null,
            "line_end": 110,
            "line_start": 110,
            "suggested_replacement": "",
            "text": [
              {
                "highlight_end": 13,
                "highlight_start": 9,
                "text": "    let mut i = 42;"
              }
            ]
          }
        ]
      }
    ],
    "code": {
      "code": "unused_mut",
      "explanation": null
    },
    "level": "warning",
    "message": "variable does not need to be mutable",
    "rendered": "warning: variable does not need to be mutable\n   --> cargo-fix/src/cli.rs:110:9\n |\n110 |     let mut i = 42;\n    |         ----^\n    |         |\n    |         help: remove this `mut`\n    |\n    = note: #[warn(unused_mut)] on by default\n\n",
    "spans": [
      {
        "byte_end": 3828,
        "byte_start": 3823,
        "column_end": 14,
        "column_start": 9,
        "expansion": null,
        "file_name": "cargo-fix/src/cli.rs",
        "is_primary": true,
        "label": null,
        "line_end": 110,
        "line_start": 110,
        "suggested_replacement": null,
        "text": [
          {
            "highlight_end": 14,
            "highlight_start": 9,
            "text": "    let mut i = 42;"
          }
        ]
      }
    ]
  },
  "package_id": "cargo-fix 0.2.0 (path+file:///Users/pascal/Projekte/rustfix/cargo-fix)",
  "reason": "compiler-message",
  "target": {
    "crate_types": [
      "bin"
    ],
    "kind": [
      "bin"
    ],
    "name": "cargo-fix",
    "src_path": "/Users/pascal/Projekte/rustfix/cargo-fix/src/main.rs"
  }
}

[killercup]

Long story short this is actually rust-lang/rust#50472 and I should get some sleep.