Rollup merge of rust-lang#55980 - csmoe:issue-55891, r=estebank

Suggest on closure args count mismatching with pipe span

Closes rust-lang#55891
r? @estebank

Author: GuillaumeGomez

src/librustc/traits/error_reporting.rs

@@ -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 {

src/test/ui/mismatched_types/closure-arg-count.rs

@@ -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

src/test/ui/mismatched_types/closure-arg-count.stderr

@@ -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
@@ -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
@@ -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
@@ -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
@@ -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
@@ -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`.