Auto merge of rust-lang#5290 - polybuildr:map-message, r=phansch

Improve error messages for {option,result}_map_unit_fn

Instead of saying "unit function", use the phrase the description uses: "function that returns the unit type".

Fixes rust-lang#5180.

changelog: Improve error messages for {option,result}_map_unit_fn

Author: bors

clippy_lints/src/map_unit_fn.rs

@@ -198,7 +198,7 @@ fn let_binding_name(cx: &LateContext<'_, '_>, var_arg: &hir::Expr<'_>) -> String
 #[must_use]
 fn suggestion_msg(function_type: &str, map_type: &str) -> String {
     format!(
-        "called `map(f)` on an `{0}` value where `f` is a unit {1}",
+        "called `map(f)` on an `{0}` value where `f` is a {1} that returns the unit type",
         map_type, function_type
     )
 }

tests/ui/option_map_unit_fn_fixable.stderr

@@ -1,4 +1,4 @@
-error: called `map(f)` on an `Option` value where `f` is a unit function
+error: called `map(f)` on an `Option` value where `f` is a function that returns the unit type
   --> $DIR/option_map_unit_fn_fixable.rs:34:5
    |
 LL |     x.field.map(do_nothing);
@@ -8,127 +8,127 @@ LL |     x.field.map(do_nothing);
    |
    = note: `-D clippy::option-map-unit-fn` implied by `-D warnings`
 
-error: called `map(f)` on an `Option` value where `f` is a unit function
+error: called `map(f)` on an `Option` value where `f` is a function that returns the unit type
   --> $DIR/option_map_unit_fn_fixable.rs:36:5
    |
 LL |     x.field.map(do_nothing);
    |     ^^^^^^^^^^^^^^^^^^^^^^^-
    |     |
    |     help: try this: `if let Some(x_field) = x.field { do_nothing(x_field) }`
 
-error: called `map(f)` on an `Option` value where `f` is a unit function
+error: called `map(f)` on an `Option` value where `f` is a function that returns the unit type
   --> $DIR/option_map_unit_fn_fixable.rs:38:5
    |
 LL |     x.field.map(diverge);
    |     ^^^^^^^^^^^^^^^^^^^^-
    |     |
    |     help: try this: `if let Some(x_field) = x.field { diverge(x_field) }`
 
-error: called `map(f)` on an `Option` value where `f` is a unit closure
+error: called `map(f)` on an `Option` value where `f` is a closure that returns the unit type
   --> $DIR/option_map_unit_fn_fixable.rs:44:5
    |
 LL |     x.field.map(|value| x.do_option_nothing(value + captured));
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^-
    |     |
    |     help: try this: `if let Some(value) = x.field { x.do_option_nothing(value + captured) }`
 
-error: called `map(f)` on an `Option` value where `f` is a unit closure
+error: called `map(f)` on an `Option` value where `f` is a closure that returns the unit type
   --> $DIR/option_map_unit_fn_fixable.rs:46:5
    |
 LL |     x.field.map(|value| { x.do_option_plus_one(value + captured); });
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^-
    |     |
    |     help: try this: `if let Some(value) = x.field { x.do_option_plus_one(value + captured); }`
 
-error: called `map(f)` on an `Option` value where `f` is a unit closure
+error: called `map(f)` on an `Option` value where `f` is a closure that returns the unit type
   --> $DIR/option_map_unit_fn_fixable.rs:49:5
    |
 LL |     x.field.map(|value| do_nothing(value + captured));
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^-
    |     |
    |     help: try this: `if let Some(value) = x.field { do_nothing(value + captured) }`
 
-error: called `map(f)` on an `Option` value where `f` is a unit closure
+error: called `map(f)` on an `Option` value where `f` is a closure that returns the unit type
   --> $DIR/option_map_unit_fn_fixable.rs:51:5
    |
 LL |     x.field.map(|value| { do_nothing(value + captured) });
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^-
    |     |
    |     help: try this: `if let Some(value) = x.field { do_nothing(value + captured) }`
 
-error: called `map(f)` on an `Option` value where `f` is a unit closure
+error: called `map(f)` on an `Option` value where `f` is a closure that returns the unit type
   --> $DIR/option_map_unit_fn_fixable.rs:53:5
    |
 LL |     x.field.map(|value| { do_nothing(value + captured); });
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^-
    |     |
    |     help: try this: `if let Some(value) = x.field { do_nothing(value + captured); }`
 
-error: called `map(f)` on an `Option` value where `f` is a unit closure
+error: called `map(f)` on an `Option` value where `f` is a closure that returns the unit type
   --> $DIR/option_map_unit_fn_fixable.rs:55:5
    |
 LL |     x.field.map(|value| { { do_nothing(value + captured); } });
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^-
    |     |
    |     help: try this: `if let Some(value) = x.field { do_nothing(value + captured); }`
 
-error: called `map(f)` on an `Option` value where `f` is a unit closure
+error: called `map(f)` on an `Option` value where `f` is a closure that returns the unit type
   --> $DIR/option_map_unit_fn_fixable.rs:58:5
    |
 LL |     x.field.map(|value| diverge(value + captured));
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^-
    |     |
    |     help: try this: `if let Some(value) = x.field { diverge(value + captured) }`
 
-error: called `map(f)` on an `Option` value where `f` is a unit closure
+error: called `map(f)` on an `Option` value where `f` is a closure that returns the unit type
   --> $DIR/option_map_unit_fn_fixable.rs:60:5
    |
 LL |     x.field.map(|value| { diverge(value + captured) });
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^-
    |     |
    |     help: try this: `if let Some(value) = x.field { diverge(value + captured) }`
 
-error: called `map(f)` on an `Option` value where `f` is a unit closure
+error: called `map(f)` on an `Option` value where `f` is a closure that returns the unit type
   --> $DIR/option_map_unit_fn_fixable.rs:62:5
    |
 LL |     x.field.map(|value| { diverge(value + captured); });
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^-
    |     |
    |     help: try this: `if let Some(value) = x.field { diverge(value + captured); }`
 
-error: called `map(f)` on an `Option` value where `f` is a unit closure
+error: called `map(f)` on an `Option` value where `f` is a closure that returns the unit type
   --> $DIR/option_map_unit_fn_fixable.rs:64:5
    |
 LL |     x.field.map(|value| { { diverge(value + captured); } });
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^-
    |     |
    |     help: try this: `if let Some(value) = x.field { diverge(value + captured); }`
 
-error: called `map(f)` on an `Option` value where `f` is a unit closure
+error: called `map(f)` on an `Option` value where `f` is a closure that returns the unit type
   --> $DIR/option_map_unit_fn_fixable.rs:69:5
    |
 LL |     x.field.map(|value| { let y = plus_one(value + captured); });
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^-
    |     |
    |     help: try this: `if let Some(value) = x.field { let y = plus_one(value + captured); }`
 
-error: called `map(f)` on an `Option` value where `f` is a unit closure
+error: called `map(f)` on an `Option` value where `f` is a closure that returns the unit type
   --> $DIR/option_map_unit_fn_fixable.rs:71:5
    |
 LL |     x.field.map(|value| { plus_one(value + captured); });
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^-
    |     |
    |     help: try this: `if let Some(value) = x.field { plus_one(value + captured); }`
 
-error: called `map(f)` on an `Option` value where `f` is a unit closure
+error: called `map(f)` on an `Option` value where `f` is a closure that returns the unit type
   --> $DIR/option_map_unit_fn_fixable.rs:73:5
    |
 LL |     x.field.map(|value| { { plus_one(value + captured); } });
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^-
    |     |
    |     help: try this: `if let Some(value) = x.field { plus_one(value + captured); }`
 
-error: called `map(f)` on an `Option` value where `f` is a unit closure
+error: called `map(f)` on an `Option` value where `f` is a closure that returns the unit type
   --> $DIR/option_map_unit_fn_fixable.rs:76:5
    |
 LL |     x.field.map(|ref value| { do_nothing(value + captured) });}

tests/ui/result_map_unit_fn_fixable.stderr

@@ -1,4 +1,4 @@
-error: called `map(f)` on an `Result` value where `f` is a unit function
+error: called `map(f)` on an `Result` value where `f` is a function that returns the unit type
   --> $DIR/result_map_unit_fn_fixable.rs:35:5
    |
 LL |     x.field.map(do_nothing);
@@ -8,127 +8,127 @@ LL |     x.field.map(do_nothing);
    |
    = note: `-D clippy::result-map-unit-fn` implied by `-D warnings`
 
-error: called `map(f)` on an `Result` value where `f` is a unit function
+error: called `map(f)` on an `Result` value where `f` is a function that returns the unit type
   --> $DIR/result_map_unit_fn_fixable.rs:37:5
    |
 LL |     x.field.map(do_nothing);
    |     ^^^^^^^^^^^^^^^^^^^^^^^-
    |     |
    |     help: try this: `if let Ok(x_field) = x.field { do_nothing(x_field) }`
 
-error: called `map(f)` on an `Result` value where `f` is a unit function
+error: called `map(f)` on an `Result` value where `f` is a function that returns the unit type
   --> $DIR/result_map_unit_fn_fixable.rs:39:5
    |
 LL |     x.field.map(diverge);
    |     ^^^^^^^^^^^^^^^^^^^^-
    |     |
    |     help: try this: `if let Ok(x_field) = x.field { diverge(x_field) }`
 
-error: called `map(f)` on an `Result` value where `f` is a unit closure
+error: called `map(f)` on an `Result` value where `f` is a closure that returns the unit type
   --> $DIR/result_map_unit_fn_fixable.rs:45:5
    |
 LL |     x.field.map(|value| x.do_result_nothing(value + captured));
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^-
    |     |
    |     help: try this: `if let Ok(value) = x.field { x.do_result_nothing(value + captured) }`
 
-error: called `map(f)` on an `Result` value where `f` is a unit closure
+error: called `map(f)` on an `Result` value where `f` is a closure that returns the unit type
   --> $DIR/result_map_unit_fn_fixable.rs:47:5
    |
 LL |     x.field.map(|value| { x.do_result_plus_one(value + captured); });
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^-
    |     |
    |     help: try this: `if let Ok(value) = x.field { x.do_result_plus_one(value + captured); }`
 
-error: called `map(f)` on an `Result` value where `f` is a unit closure
+error: called `map(f)` on an `Result` value where `f` is a closure that returns the unit type
   --> $DIR/result_map_unit_fn_fixable.rs:50:5
    |
 LL |     x.field.map(|value| do_nothing(value + captured));
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^-
    |     |
    |     help: try this: `if let Ok(value) = x.field { do_nothing(value + captured) }`
 
-error: called `map(f)` on an `Result` value where `f` is a unit closure
+error: called `map(f)` on an `Result` value where `f` is a closure that returns the unit type
   --> $DIR/result_map_unit_fn_fixable.rs:52:5
    |
 LL |     x.field.map(|value| { do_nothing(value + captured) });
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^-
    |     |
    |     help: try this: `if let Ok(value) = x.field { do_nothing(value + captured) }`
 
-error: called `map(f)` on an `Result` value where `f` is a unit closure
+error: called `map(f)` on an `Result` value where `f` is a closure that returns the unit type
   --> $DIR/result_map_unit_fn_fixable.rs:54:5
    |
 LL |     x.field.map(|value| { do_nothing(value + captured); });
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^-
    |     |
    |     help: try this: `if let Ok(value) = x.field { do_nothing(value + captured); }`
 
-error: called `map(f)` on an `Result` value where `f` is a unit closure
+error: called `map(f)` on an `Result` value where `f` is a closure that returns the unit type
   --> $DIR/result_map_unit_fn_fixable.rs:56:5
    |
 LL |     x.field.map(|value| { { do_nothing(value + captured); } });
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^-
    |     |
    |     help: try this: `if let Ok(value) = x.field { do_nothing(value + captured); }`
 
-error: called `map(f)` on an `Result` value where `f` is a unit closure
+error: called `map(f)` on an `Result` value where `f` is a closure that returns the unit type
   --> $DIR/result_map_unit_fn_fixable.rs:59:5
    |
 LL |     x.field.map(|value| diverge(value + captured));
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^-
    |     |
    |     help: try this: `if let Ok(value) = x.field { diverge(value + captured) }`
 
-error: called `map(f)` on an `Result` value where `f` is a unit closure
+error: called `map(f)` on an `Result` value where `f` is a closure that returns the unit type
   --> $DIR/result_map_unit_fn_fixable.rs:61:5
    |
 LL |     x.field.map(|value| { diverge(value + captured) });
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^-
    |     |
    |     help: try this: `if let Ok(value) = x.field { diverge(value + captured) }`
 
-error: called `map(f)` on an `Result` value where `f` is a unit closure
+error: called `map(f)` on an `Result` value where `f` is a closure that returns the unit type
   --> $DIR/result_map_unit_fn_fixable.rs:63:5
    |
 LL |     x.field.map(|value| { diverge(value + captured); });
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^-
    |     |
    |     help: try this: `if let Ok(value) = x.field { diverge(value + captured); }`
 
-error: called `map(f)` on an `Result` value where `f` is a unit closure
+error: called `map(f)` on an `Result` value where `f` is a closure that returns the unit type
   --> $DIR/result_map_unit_fn_fixable.rs:65:5
    |
 LL |     x.field.map(|value| { { diverge(value + captured); } });
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^-
    |     |
    |     help: try this: `if let Ok(value) = x.field { diverge(value + captured); }`
 
-error: called `map(f)` on an `Result` value where `f` is a unit closure
+error: called `map(f)` on an `Result` value where `f` is a closure that returns the unit type
   --> $DIR/result_map_unit_fn_fixable.rs:70:5
    |
 LL |     x.field.map(|value| { let y = plus_one(value + captured); });
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^-
    |     |
    |     help: try this: `if let Ok(value) = x.field { let y = plus_one(value + captured); }`
 
-error: called `map(f)` on an `Result` value where `f` is a unit closure
+error: called `map(f)` on an `Result` value where `f` is a closure that returns the unit type
   --> $DIR/result_map_unit_fn_fixable.rs:72:5
    |
 LL |     x.field.map(|value| { plus_one(value + captured); });
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^-
    |     |
    |     help: try this: `if let Ok(value) = x.field { plus_one(value + captured); }`
 
-error: called `map(f)` on an `Result` value where `f` is a unit closure
+error: called `map(f)` on an `Result` value where `f` is a closure that returns the unit type
   --> $DIR/result_map_unit_fn_fixable.rs:74:5
    |
 LL |     x.field.map(|value| { { plus_one(value + captured); } });
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^-
    |     |
    |     help: try this: `if let Ok(value) = x.field { plus_one(value + captured); }`
 
-error: called `map(f)` on an `Result` value where `f` is a unit closure
+error: called `map(f)` on an `Result` value where `f` is a closure that returns the unit type
   --> $DIR/result_map_unit_fn_fixable.rs:77:5
    |
 LL |     x.field.map(|ref value| { do_nothing(value + captured) });