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Rollup merge of rust-lang#55980 - csmoe:issue-55891, r=estebank
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Suggest on closure args count mismatching with pipe span

Closes rust-lang#55891
r? @estebank
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@GuillaumeGomez
GuillaumeGomez authored Nov 22, 2018
2 parents fa3941c + d93e5b0 commit 636f0a9
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Showing 3 changed files with 45 additions and 11 deletions.
16 changes: 15 additions & 1 deletion src/librustc/traits/error_reporting.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1092,13 +1092,27 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
if let Some(found_span) = found_span {
err.span_label(found_span, format!("takes {}", found_str));

// move |_| { ... }
// ^^^^^^^^-- def_span
//
// move |_| { ... }
// ^^^^^-- prefix
let prefix_span = self.tcx.sess.source_map().span_until_non_whitespace(found_span);
// move |_| { ... }
// ^^^-- pipe_span
let pipe_span = if let Some(span) = found_span.trim_start(prefix_span) {
span
} else {
found_span
};

// Suggest to take and ignore the arguments with expected_args_length `_`s if
// found arguments is empty (assume the user just wants to ignore args in this case).
// For example, if `expected_args_length` is 2, suggest `|_, _|`.
if found_args.is_empty() && is_closure {
let underscores = vec!["_"; expected_args.len()].join(", ");
err.span_suggestion_with_applicability(
found_span,
pipe_span,
&format!(
"consider changing the closure to take and ignore the expected argument{}",
if expected_args.len() < 2 {
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2 changes: 2 additions & 0 deletions src/test/ui/mismatched_types/closure-arg-count.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -22,6 +22,8 @@ fn main() {
//~^ ERROR closure is expected to take
f(|| panic!());
//~^ ERROR closure is expected to take
f( move || panic!());
//~^ ERROR closure is expected to take

let _it = vec![1, 2, 3].into_iter().enumerate().map(|i, x| i);
//~^ ERROR closure is expected to take
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38 changes: 28 additions & 10 deletions src/test/ui/mismatched_types/closure-arg-count.stderr
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Original file line number Diff line number Diff line change
Expand Up @@ -60,8 +60,26 @@ help: consider changing the closure to take and ignore the expected argument
LL | f(|_| panic!());
| ^^^

error[E0593]: closure is expected to take 1 argument, but it takes 0 arguments
--> $DIR/closure-arg-count.rs:25:5
|
LL | f( move || panic!());
| ^ ---------- takes 0 arguments
| |
| expected closure that takes 1 argument
|
note: required by `f`
--> $DIR/closure-arg-count.rs:13:1
|
LL | fn f<F: Fn<usize>>(_: F) {}
| ^^^^^^^^^^^^^^^^^^^^^^^^
help: consider changing the closure to take and ignore the expected argument
|
LL | f( move |_| panic!());
| ^^^

error[E0593]: closure is expected to take a single 2-tuple as argument, but it takes 2 distinct arguments
--> $DIR/closure-arg-count.rs:26:53
--> $DIR/closure-arg-count.rs:28:53
|
LL | let _it = vec![1, 2, 3].into_iter().enumerate().map(|i, x| i);
| ^^^ ------ takes 2 distinct arguments
Expand All @@ -73,7 +91,7 @@ LL | let _it = vec![1, 2, 3].into_iter().enumerate().map(|(i, x)| i);
| ^^^^^^^^

error[E0593]: closure is expected to take a single 2-tuple as argument, but it takes 2 distinct arguments
--> $DIR/closure-arg-count.rs:28:53
--> $DIR/closure-arg-count.rs:30:53
|
LL | let _it = vec![1, 2, 3].into_iter().enumerate().map(|i: usize, x| i);
| ^^^ ------------- takes 2 distinct arguments
Expand All @@ -85,15 +103,15 @@ LL | let _it = vec![1, 2, 3].into_iter().enumerate().map(|(i, x)| i);
| ^^^^^^^^

error[E0593]: closure is expected to take a single 2-tuple as argument, but it takes 3 distinct arguments
--> $DIR/closure-arg-count.rs:30:53
--> $DIR/closure-arg-count.rs:32:53
|
LL | let _it = vec![1, 2, 3].into_iter().enumerate().map(|i, x, y| i);
| ^^^ --------- takes 3 distinct arguments
| |
| expected closure that takes a single 2-tuple as argument

error[E0593]: function is expected to take a single 2-tuple as argument, but it takes 0 arguments
--> $DIR/closure-arg-count.rs:32:53
--> $DIR/closure-arg-count.rs:34:53
|
LL | let _it = vec![1, 2, 3].into_iter().enumerate().map(foo);
| ^^^ expected function that takes a single 2-tuple as argument
Expand All @@ -102,15 +120,15 @@ LL | fn foo() {}
| -------- takes 0 arguments

error[E0593]: closure is expected to take a single 2-tuple as argument, but it takes 3 distinct arguments
--> $DIR/closure-arg-count.rs:35:53
--> $DIR/closure-arg-count.rs:37:53
|
LL | let bar = |i, x, y| i;
| --------- takes 3 distinct arguments
LL | let _it = vec![1, 2, 3].into_iter().enumerate().map(bar);
| ^^^ expected closure that takes a single 2-tuple as argument

error[E0593]: function is expected to take a single 2-tuple as argument, but it takes 2 distinct arguments
--> $DIR/closure-arg-count.rs:37:53
--> $DIR/closure-arg-count.rs:39:53
|
LL | let _it = vec![1, 2, 3].into_iter().enumerate().map(qux);
| ^^^ expected function that takes a single 2-tuple as argument
Expand All @@ -119,13 +137,13 @@ LL | fn qux(x: usize, y: usize) {}
| -------------------------- takes 2 distinct arguments

error[E0593]: function is expected to take 1 argument, but it takes 2 arguments
--> $DIR/closure-arg-count.rs:40:41
--> $DIR/closure-arg-count.rs:42:41
|
LL | let _it = vec![1, 2, 3].into_iter().map(usize::checked_add);
| ^^^ expected function that takes 1 argument

error[E0593]: function is expected to take 0 arguments, but it takes 1 argument
--> $DIR/closure-arg-count.rs:43:5
--> $DIR/closure-arg-count.rs:45:5
|
LL | call(Foo);
| ^^^^ expected function that takes 0 arguments
Expand All @@ -134,11 +152,11 @@ LL | struct Foo(u8);
| --------------- takes 1 argument
|
note: required by `call`
--> $DIR/closure-arg-count.rs:50:1
--> $DIR/closure-arg-count.rs:52:1
|
LL | fn call<F, R>(_: F) where F: FnOnce() -> R {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: aborting due to 13 previous errors
error: aborting due to 14 previous errors

For more information about this error, try `rustc --explain E0593`.

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