Diagnostic suggestions sometimes incorrectly point to external crates #88514
Description
In some situations, rustc may provide a diagnostic suggestion in an external crate, which in general it shouldn't do. These external crates may be in cargo's registry cache, which the user should not be modifying. For example, cargo fix may stomp on changes outside of the package (which is a separate issue rust-lang/cargo#9857). Usually rustc is good about avoiding this, so I'm not sure what is wrong in these situations.
In general, I expect rustc to not provide suggestions to modify dependencies.
The crater run found several instances of this, each for different underlying reasons (all dealing with macros).
Example 1 — unused tt
Example dependency:
// bar.rs
#[macro_export]
macro_rules! m {
($i:tt) => {
$crate::m!(foo $i);
};
(foo $i:tt) => {
let $i = 1;
}
}Example local crate:
// foo.rs
pub fn foo() {
bar::m!(abc);
}Resulting suggestion:
warning: unused variable: `abc`
--> /Users/eric/Temp/crater-2021/foo/bar/src/lib.rs:7:13
|
7 | let $i = 1;
| ^^ help: if this is intentional, prefix it with an underscore: `_abc`
|
= note: `#[warn(unused_variables)]` on by default
A key point of this example is that the macro uses tt instead of ident. ident will not issue an unused warning.
Found in the 2021 crater run for:
Example 2 — Weird $body suggestion
The following makes a suggestion to remove unnecessary braces, but the suggestion doesn't actually remove any braces.
// Using cpython 0.2.1
use cpython::*;
fn hello(py: Python) -> PyResult<PyString> {
Ok(PyString::new(py, "Rust says: Hello world"))
}
py_module_initializer!(example, initexample, PyInit_example, |py, m| {
m.add(py, "hello", py_fn!(py, hello()))?;
Ok(())
});Suggestion:
warning: unnecessary braces around block return value
--> /Users/eric/.cargo/registry/src/github.com-1ecc6299db9ec823/cpython-0.2.1/src/argparse.rs:386:52
|
386 | ( $py:expr, $iter:expr, $body:block, [] ) => { $body };
| ^^^^^ help: remove these braces
|
= note: `#[warn(unused_braces)]` on by default
warning: `foo` (lib) generated 1 warning
Finished dev [unoptimized + debuginfo] target(s) in 0.01s
Found in the 2021 crater run for:
- https://tiny.cc/oaaiuz/gh/AustinHaugerud.mb_ext_script/log.txt
- https://tiny.cc/oaaiuz/gh/expobrain.python-rust-library-example/log.txt
- https://tiny.cc/oaaiuz/gh/mazurwiktor.aoaddons-python/log.txt
Example 3 — Hidden JSON suggestion
In this example, the human-readable text doesn't mention the dependency, but the JSON includes a MachineApplicable suggestion.
// diesel 1.4.7
#[macro_use]
extern crate diesel;
use diesel::table;
table! {
use diesel::sql_types::*;
use std::fs;
users {
id -> Integer,
name -> VarChar,
favorite_color -> Nullable<VarChar>,
}
}This emits two duplicate diagnostics in human form:
warning: unused import: `std::fs`
--> src/lib.rs:7:9
|
7 | use std::fs;
| ^^^^^^^
|
= note: `#[warn(unused_imports)]` on by default
warning: unused import: `std::fs`
--> src/lib.rs:7:9
|
7 | use std::fs;
| ^^^^^^^
warning: `foo` (lib) generated 2 warnings
Buried in the JSON output is a machine-applicable change which modifies diesel:
{
"byte_end": 9126,
"byte_start": 9108,
"column_end": 55,
"column_start": 37,
"expansion":
{},
"file_name": "/Users/eric/.cargo/registry/src/github.com-1ecc6299db9ec823/diesel-1.4.7/src/macros/mod.rs",
"is_primary": true,
"label": null,
"line_end": 299,
"line_start": 299,
"suggested_replacement": "",
"suggestion_applicability": "MachineApplicable",
"text":
[
{
"highlight_end": 55,
"highlight_start": 37,
"text": " imports = [$($imports)* use $($import)::+;],"
}
]
}Found in the 2021 crater run for:
Meta
rustc --version --verbose:
rustc 1.56.0-nightly (5eacec9ec 2021-08-28)
binary: rustc
commit-hash: 5eacec9ec7e112a0de1011519a57c45586d58414
commit-date: 2021-08-28
host: x86_64-apple-darwin
release: 1.56.0-nightly
LLVM version: 13.0.0
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cargo fixmay attempt to write to the registry cache rust-lang/cargo#9857weihanglo commentedon Sep 25, 2021
The regression of "Example 1" was introduced between 1.51.0 and 1.52.0. The bisect report gave me three rollup PRs. The bug can be reproduced after this rollup and the suspect may be #82655.
I am not familiar with this part, so if anyone want to address it, just take it. (Or even better mentor me 😆, thanks)
Report from cargo-bisect-rustc
Script for cargo-bisect-rustc
Report from cargo-bisect-rustc
Rollup merge of rust-lang#109082 - estebank:macro-spans, r=oli-obk
Rollup merge of rust-lang#109082 - estebank:macro-spans, r=oli-obk
ehuss commentedon Apr 8, 2024
This example attempts to make modifications to the standard library (if you have the source component installed).
JSON:
SEE JSON
{ "$message_type": "diagnostic", "message": "mismatched types", "code": { "code": "E0308", "explanation": "Expected type did not match the received type.\n\nErroneous code examples:\n\n```compile_fail,E0308\nfn plus_one(x: i32) -> i32 {\n x + 1\n}\n\nplus_one(\"Not a number\");\n// ^^^^^^^^^^^^^^ expected `i32`, found `&str`\n\nif \"Not a bool\" {\n// ^^^^^^^^^^^^ expected `bool`, found `&str`\n}\n\nlet x: f32 = \"Not a float\";\n// --- ^^^^^^^^^^^^^ expected `f32`, found `&str`\n// |\n// expected due to this\n```\n\nThis error occurs when an expression was used in a place where the compiler\nexpected an expression of a different type. It can occur in several cases, the\nmost common being when calling a function and passing an argument which has a\ndifferent type than the matching type in the function declaration.\n" }, "level": "error", "spans": [ { "file_name": "/Users/eric/.rustup/toolchains/nightly-aarch64-apple-darwin/lib/rustlib/src/rust/library/core/src/macros/mod.rs", "byte_start": 23568, "byte_end": 23617, "line_start": 670, "line_end": 670, "column_start": 9, "column_end": 58, "is_primary": true, "text": [ { "text": " $dst.write_fmt($crate::format_args_nl!($($arg)*))", "highlight_start": 9, "highlight_end": 58 } ], "label": "expected `()`, found `Result<(), Error>`", "suggested_replacement": null, "suggestion_applicability": null, "expansion": { "span": { "file_name": "lib.rs", "byte_start": 144, "byte_end": 171, "line_start": 5, "line_end": 5, "column_start": 9, "column_end": 36, "is_primary": false, "text": [ { "text": " writeln!(w, \"but not here\")", "highlight_start": 9, "highlight_end": 36 } ], "label": null, "suggested_replacement": null, "suggestion_applicability": null, "expansion": null }, "macro_decl_name": "writeln!", "def_site_span": { "file_name": "/Users/eric/.rustup/toolchains/nightly-aarch64-apple-darwin/lib/rustlib/src/rust/library/core/src/macros/mod.rs", "byte_start": 23434, "byte_end": 23454, "line_start": 665, "line_end": 665, "column_start": 1, "column_end": 21, "is_primary": false, "text": [ { "text": "macro_rules! writeln {", "highlight_start": 1, "highlight_end": 21 } ], "label": null, "suggested_replacement": null, "suggestion_applicability": null, "expansion": null } } }, { "file_name": "lib.rs", "byte_start": 75, "byte_end": 177, "line_start": 2, "line_end": 6, "column_start": 5, "column_end": 6, "is_primary": false, "text": [ { "text": " if true {", "highlight_start": 5, "highlight_end": 14 }, { "text": " writeln!(w, \"`;?` here ->\")?;", "highlight_start": 1, "highlight_end": 38 }, { "text": " } else {", "highlight_start": 1, "highlight_end": 13 }, { "text": " writeln!(w, \"but not here\")", "highlight_start": 1, "highlight_end": 36 }, { "text": " }", "highlight_start": 1, "highlight_end": 6 } ], "label": "expected this to be `()`", "suggested_replacement": null, "suggestion_applicability": null, "expansion": null } ], "children": [ { "message": "expected unit type `()`\n found enum `Result<(), std::fmt::Error>`", "code": null, "level": "note", "spans": [], "children": [], "rendered": null }, { "message": "consider using a semicolon here", "code": null, "level": "help", "spans": [ { "file_name": "lib.rs", "byte_start": 177, "byte_end": 177, "line_start": 6, "line_end": 6, "column_start": 6, "column_end": 6, "is_primary": true, "text": [ { "text": " }", "highlight_start": 6, "highlight_end": 6 } ], "label": null, "suggested_replacement": ";", "suggestion_applicability": "MaybeIncorrect", "expansion": null } ], "children": [], "rendered": null }, { "message": "you might have meant to return this value", "code": null, "level": "help", "spans": [ { "file_name": "lib.rs", "byte_start": 144, "byte_end": 144, "line_start": 5, "line_end": 5, "column_start": 9, "column_end": 9, "is_primary": true, "text": [ { "text": " writeln!(w, \"but not here\")", "highlight_start": 9, "highlight_end": 9 } ], "label": null, "suggested_replacement": "return ", "suggestion_applicability": "MaybeIncorrect", "expansion": null }, { "file_name": "lib.rs", "byte_start": 171, "byte_end": 171, "line_start": 5, "line_end": 5, "column_start": 36, "column_end": 36, "is_primary": true, "text": [ { "text": " writeln!(w, \"but not here\")", "highlight_start": 36, "highlight_end": 36 } ], "label": null, "suggested_replacement": ";", "suggestion_applicability": "MaybeIncorrect", "expansion": null } ], "children": [], "rendered": null }, { "message": "use the `?` operator to extract the `Result<(), std::fmt::Error>` value, propagating a `Result::Err` value to the caller", "code": null, "level": "help", "spans": [ { "file_name": "/Users/eric/.rustup/toolchains/nightly-aarch64-apple-darwin/lib/rustlib/src/rust/library/core/src/macros/mod.rs", "byte_start": 23617, "byte_end": 23617, "line_start": 670, "line_end": 670, "column_start": 58, "column_end": 58, "is_primary": true, "text": [ { "text": " $dst.write_fmt($crate::format_args_nl!($($arg)*))", "highlight_start": 58, "highlight_end": 58 } ], "label": null, "suggested_replacement": "?", "suggestion_applicability": "HasPlaceholders", "expansion": { "span": { "file_name": "lib.rs", "byte_start": 144, "byte_end": 171, "line_start": 5, "line_end": 5, "column_start": 9, "column_end": 36, "is_primary": false, "text": [ { "text": " writeln!(w, \"but not here\")", "highlight_start": 9, "highlight_end": 36 } ], "label": null, "suggested_replacement": null, "suggestion_applicability": null, "expansion": null }, "macro_decl_name": "writeln!", "def_site_span": { "file_name": "/Users/eric/.rustup/toolchains/nightly-aarch64-apple-darwin/lib/rustlib/src/rust/library/core/src/macros/mod.rs", "byte_start": 23434, "byte_end": 23454, "line_start": 665, "line_end": 665, "column_start": 1, "column_end": 21, "is_primary": false, "text": [ { "text": "macro_rules! writeln {", "highlight_start": 1, "highlight_end": 21 } ], "label": null, "suggested_replacement": null, "suggestion_applicability": null, "expansion": null } } } ], "children": [], "rendered": null } ], "rendered": "error[E0308]: mismatched types\n --> lib.rs:5:9\n |\n2 | / if true {\n3 | | writeln!(w, \"`;?` here ->\")?;\n4 | | } else {\n5 | | writeln!(w, \"but not here\")\n | | ^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `()`, found `Result<(), Error>`\n6 | | }\n | |_____- expected this to be `()`\n |\n = note: expected unit type `()`\n found enum `Result<(), std::fmt::Error>`\n = note: this error originates in the macro `writeln` (in Nightly builds, run with -Z macro-backtrace for more info)\nhelp: consider using a semicolon here\n |\n6 | };\n | +\nhelp: you might have meant to return this value\n |\n5 | return writeln!(w, \"but not here\");\n | ++++++ +\nhelp: use the `?` operator to extract the `Result<(), std::fmt::Error>` value, propagating a `Result::Err` value to the caller\n --> /Users/eric/.rustup/toolchains/nightly-aarch64-apple-darwin/lib/rustlib/src/rust/library/core/src/macros/mod.rs:670:58\n |\n67| $dst.write_fmt($crate::format_args_nl!($($arg)*))?\n | +\n\n" }Suggests to edit
lib/rustlib/src/rust/library/core/src/macros/mod.rstest(fix): verify cargo might fix into rust-src
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