Auto merge of rust-lang#8584 - Alexendoo:map-unit-fn-context, r=Manishearth

Provide suggestion context in map_unit_fn

Fixes rust-lang#8569

changelog: Fix incorrect suggestion for `option_map_unit_fn` , `result_map_unit_fn`

Author: bors

clippy_lints/src/map_unit_fn.rs

@@ -1,5 +1,5 @@
 use clippy_utils::diagnostics::span_lint_and_then;
-use clippy_utils::source::snippet;
+use clippy_utils::source::{snippet, snippet_with_applicability, snippet_with_context};
 use clippy_utils::ty::is_type_diagnostic_item;
 use clippy_utils::{iter_input_pats, method_chain_args};
 use if_chain::if_chain;
@@ -217,36 +217,33 @@ fn lint_map_unit_fn(cx: &LateContext<'_>, stmt: &hir::Stmt<'_>, expr: &hir::Expr
     let fn_arg = &map_args[1];
 
     if is_unit_function(cx, fn_arg) {
+        let mut applicability = Applicability::MachineApplicable;
         let msg = suggestion_msg("function", map_type);
         let suggestion = format!(
             "if let {0}({binding}) = {1} {{ {2}({binding}) }}",
             variant,
-            snippet(cx, var_arg.span, "_"),
-            snippet(cx, fn_arg.span, "_"),
+            snippet_with_applicability(cx, var_arg.span, "_", &mut applicability),
+            snippet_with_applicability(cx, fn_arg.span, "_", &mut applicability),
             binding = let_binding_name(cx, var_arg)
         );
 
         span_lint_and_then(cx, lint, expr.span, &msg, |diag| {
-            diag.span_suggestion(stmt.span, "try this", suggestion, Applicability::MachineApplicable);
+            diag.span_suggestion(stmt.span, "try this", suggestion, applicability);
         });
     } else if let Some((binding, closure_expr)) = unit_closure(cx, fn_arg) {
         let msg = suggestion_msg("closure", map_type);
 
         span_lint_and_then(cx, lint, expr.span, &msg, |diag| {
             if let Some(reduced_expr_span) = reduce_unit_expression(cx, closure_expr) {
+                let mut applicability = Applicability::MachineApplicable;
                 let suggestion = format!(
                     "if let {0}({1}) = {2} {{ {3} }}",
                     variant,
-                    snippet(cx, binding.pat.span, "_"),
-                    snippet(cx, var_arg.span, "_"),
-                    snippet(cx, reduced_expr_span, "_")
-                );
-                diag.span_suggestion(
-                    stmt.span,
-                    "try this",
-                    suggestion,
-                    Applicability::MachineApplicable, // snippet
+                    snippet_with_applicability(cx, binding.pat.span, "_", &mut applicability),
+                    snippet_with_applicability(cx, var_arg.span, "_", &mut applicability),
+                    snippet_with_context(cx, reduced_expr_span, var_arg.span.ctxt(), "_", &mut applicability).0,
                 );
+                diag.span_suggestion(stmt.span, "try this", suggestion, applicability);
             } else {
                 let suggestion = format!(
                     "if let {0}({1}) = {2} {{ ... }}",

tests/ui/option_map_unit_fn_fixable.fixed

@@ -80,6 +80,9 @@ fn option_map_unit_fn() {
 
     if let Some(ref value) = x.field { do_nothing(value + captured) }
 
-    if let Some(a) = option() { do_nothing(a) }}
+    if let Some(a) = option() { do_nothing(a) }
+
+    if let Some(value) = option() { println!("{:?}", value) }
+}
 
 fn main() {}

tests/ui/option_map_unit_fn_fixable.rs

@@ -80,6 +80,9 @@ fn option_map_unit_fn() {
 
     x.field.map(|ref value| { do_nothing(value + captured) });
 
-    option().map(do_nothing);}
+    option().map(do_nothing);
+
+    option().map(|value| println!("{:?}", value));
+}
 
 fn main() {}

tests/ui/option_map_unit_fn_fixable.stderr

@@ -139,10 +139,18 @@ LL |     x.field.map(|ref value| { do_nothing(value + captured) });
 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:83:5
    |
-LL |     option().map(do_nothing);}
+LL |     option().map(do_nothing);
    |     ^^^^^^^^^^^^^^^^^^^^^^^^-
    |     |
    |     help: try this: `if let Some(a) = option() { do_nothing(a) }`
 
-error: aborting due to 18 previous errors
+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:85:5
+   |
+LL |     option().map(|value| println!("{:?}", value));
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^-
+   |     |
+   |     help: try this: `if let Some(value) = option() { println!("{:?}", value) }`
+
+error: aborting due to 19 previous errors
 

tests/ui/result_map_unit_fn_fixable.fixed

@@ -75,6 +75,8 @@ fn result_map_unit_fn() {
 
 
     if let Ok(ref value) = x.field { do_nothing(value + captured) }
+
+    if let Ok(value) = x.field { println!("{:?}", value) }
 }
 
 fn main() {}

tests/ui/result_map_unit_fn_fixable.rs

@@ -75,6 +75,8 @@ fn result_map_unit_fn() {
 
 
     x.field.map(|ref value| { do_nothing(value + captured) });
+
+    x.field.map(|value| println!("{:?}", value));
 }
 
 fn main() {}

tests/ui/result_map_unit_fn_fixable.stderr

@@ -136,5 +136,13 @@ LL |     x.field.map(|ref value| { do_nothing(value + captured) });
    |     |
    |     help: try this: `if let Ok(ref value) = x.field { do_nothing(value + captured) }`
 
-error: aborting due to 17 previous errors
+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:79:5
+   |
+LL |     x.field.map(|value| println!("{:?}", value));
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^-
+   |     |
+   |     help: try this: `if let Ok(value) = x.field { println!("{:?}", value) }`
+
+error: aborting due to 18 previous errors