Auto merge of #6294 - giraffate:fix_suggestion_to_add_space_in_manual_async, r=Manishearth

Fix suggestion to add unneeded space in `manual_async`

Fix a same case as https://github.com/rust-lang/rust-clippy/pull/6247

changelog: Fix suggestion to add unneeded space in `manual_async`

6 files changed, 140 insertions, 32 deletions

diff --git a/clippy_lints/src/manual_async_fn.rs b/clippy_lints/src/manual_async_fn.rs
index 864d1ea87f5..7b3b450ef93 100644
--- a/clippy_lints/src/manual_async_fn.rs
+++ b/clippy_lints/src/manual_async_fn.rs
@@ -1,5 +1,5 @@
 use crate::utils::paths::FUTURE_FROM_GENERATOR;
-use crate::utils::{match_function_call, snippet_block, snippet_opt, span_lint_and_then};
+use crate::utils::{match_function_call, position_before_rarrow, snippet_block, snippet_opt, span_lint_and_then};
 use if_chain::if_chain;
 use rustc_errors::Applicability;
 use rustc_hir::intravisit::FnKind;
@@ -69,7 +69,7 @@ impl<'tcx> LateLintPass<'tcx> for ManualAsyncFn {
                     |diag| {
                         if_chain! {
                             if let Some(header_snip) = snippet_opt(cx, header_span);
-                            if let Some(ret_pos) = header_snip.rfind("->");
+                            if let Some(ret_pos) = position_before_rarrow(header_snip.clone());
                             if let Some((ret_sugg, ret_snip)) = suggested_ret(cx, output);
                             then {
                                 let help = format!("make the function `async` and {}", ret_sugg);
@@ -194,7 +194,7 @@ fn suggested_ret(cx: &LateContext<'_>, output: &Ty<'_>) -> Option<(&'static str,
         },
         _ => {
             let sugg = "return the output of the future directly";
-            snippet_opt(cx, output.span).map(|snip| (sugg, format!("-> {}", snip)))
+            snippet_opt(cx, output.span).map(|snip| (sugg, format!(" -> {}", snip)))
         },
     }
 }
diff --git a/clippy_lints/src/unused_unit.rs b/clippy_lints/src/unused_unit.rs
index b1339c3d639..f61fd2ecd73 100644
--- a/clippy_lints/src/unused_unit.rs
+++ b/clippy_lints/src/unused_unit.rs
@@ -7,7 +7,7 @@ use rustc_session::{declare_lint_pass, declare_tool_lint};
 use rustc_span::source_map::Span;
 use rustc_span::BytePos;
 
-use crate::utils::span_lint_and_sugg;
+use crate::utils::{position_before_rarrow, span_lint_and_sugg};
 
 declare_clippy_lint! {
     /// **What it does:** Checks for unit (`()`) expressions that can be removed.
@@ -120,26 +120,13 @@ fn is_unit_expr(expr: &ast::Expr) -> bool {
 
 fn lint_unneeded_unit_return(cx: &EarlyContext<'_>, ty: &ast::Ty, span: Span) {
     let (ret_span, appl) = if let Ok(fn_source) = cx.sess().source_map().span_to_snippet(span.with_hi(ty.span.hi())) {
-        fn_source
-            .rfind("->")
-            .map_or((ty.span, Applicability::MaybeIncorrect), |rpos| {
-                let mut rpos = rpos;
-                let chars: Vec<char> = fn_source.chars().collect();
-                while rpos > 1 {
-                    if let Some(c) = chars.get(rpos - 1) {
-                        if c.is_whitespace() {
-                            rpos -= 1;
-                            continue;
-                        }
-                    }
-                    break;
-                }
-                (
-                    #[allow(clippy::cast_possible_truncation)]
-                    ty.span.with_lo(BytePos(span.lo().0 + rpos as u32)),
-                    Applicability::MachineApplicable,
-                )
-            })
+        position_before_rarrow(fn_source).map_or((ty.span, Applicability::MaybeIncorrect), |rpos| {
+            (
+                #[allow(clippy::cast_possible_truncation)]
+                ty.span.with_lo(BytePos(span.lo().0 + rpos as u32)),
+                Applicability::MachineApplicable,
+            )
+        })
     } else {
         (ty.span, Applicability::MaybeIncorrect)
     };
diff --git a/clippy_lints/src/utils/mod.rs b/clippy_lints/src/utils/mod.rs
index 85e7f055e79..8e4149df032 100644
--- a/clippy_lints/src/utils/mod.rs
+++ b/clippy_lints/src/utils/mod.rs
@@ -659,6 +659,35 @@ pub fn indent_of<T: LintContext>(cx: &T, span: Span) -> Option<usize> {
     snippet_opt(cx, line_span(cx, span)).and_then(|snip| snip.find(|c: char| !c.is_whitespace()))
 }
 
+/// Returns the positon just before rarrow
+///
+/// ```rust,ignore
+/// fn into(self) -> () {}
+///              ^
+/// // in case of unformatted code
+/// fn into2(self)-> () {}
+///               ^
+/// fn into3(self)   -> () {}
+///               ^
+/// ```
+#[allow(clippy::needless_pass_by_value)]
+pub fn position_before_rarrow(s: String) -> Option<usize> {
+    s.rfind("->").map(|rpos| {
+        let mut rpos = rpos;
+        let chars: Vec<char> = s.chars().collect();
+        while rpos > 1 {
+            if let Some(c) = chars.get(rpos - 1) {
+                if c.is_whitespace() {
+                    rpos -= 1;
+                    continue;
+                }
+            }
+            break;
+        }
+        rpos
+    })
+}
+
 /// Extends the span to the beginning of the spans line, incl. whitespaces.
 ///
 /// ```rust,ignore
diff --git a/tests/ui/manual_async_fn.fixed b/tests/ui/manual_async_fn.fixed
index 4f551690c43..5184f6fdb88 100644
--- a/tests/ui/manual_async_fn.fixed
+++ b/tests/ui/manual_async_fn.fixed
@@ -7,7 +7,19 @@ use std::future::Future;
 
 async fn fut() -> i32 { 42 }
 
-async fn empty_fut()  {}
+#[rustfmt::skip]
+async fn fut2() -> i32 { 42 }
+
+#[rustfmt::skip]
+async fn fut3() -> i32 { 42 }
+
+async fn empty_fut() {}
+
+#[rustfmt::skip]
+async fn empty_fut2() {}
+
+#[rustfmt::skip]
+async fn empty_fut3() {}
 
 async fn core_fut() -> i32 { 42 }
 
diff --git a/tests/ui/manual_async_fn.rs b/tests/ui/manual_async_fn.rs
index 6ed60309947..68c0e591f0b 100644
--- a/tests/ui/manual_async_fn.rs
+++ b/tests/ui/manual_async_fn.rs
@@ -9,10 +9,30 @@ fn fut() -> impl Future<Output = i32> {
     async { 42 }
 }
 
+#[rustfmt::skip]
+fn fut2() ->impl Future<Output = i32> {
+    async { 42 }
+}
+
+#[rustfmt::skip]
+fn fut3()-> impl Future<Output = i32> {
+    async { 42 }
+}
+
 fn empty_fut() -> impl Future<Output = ()> {
     async {}
 }
 
+#[rustfmt::skip]
+fn empty_fut2() ->impl Future<Output = ()> {
+    async {}
+}
+
+#[rustfmt::skip]
+fn empty_fut3()-> impl Future<Output = ()> {
+    async {}
+}
+
 fn core_fut() -> impl core::future::Future<Output = i32> {
     async move { 42 }
 }
diff --git a/tests/ui/manual_async_fn.stderr b/tests/ui/manual_async_fn.stderr
index ccd82867427..fdd43db3255 100644
--- a/tests/ui/manual_async_fn.stderr
+++ b/tests/ui/manual_async_fn.stderr
@@ -15,14 +15,44 @@ LL | fn fut() -> impl Future<Output = i32> { 42 }
    |                                       ^^^^^^
 
 error: this function can be simplified using the `async fn` syntax
-  --> $DIR/manual_async_fn.rs:12:1
+  --> $DIR/manual_async_fn.rs:13:1
+   |
+LL | fn fut2() ->impl Future<Output = i32> {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+help: make the function `async` and return the output of the future directly
+   |
+LL | async fn fut2() -> i32 {
+   | ^^^^^^^^^^^^^^^^^^^^^^
+help: move the body of the async block to the enclosing function
+   |
+LL | fn fut2() ->impl Future<Output = i32> { 42 }
+   |                                       ^^^^^^
+
+error: this function can be simplified using the `async fn` syntax
+  --> $DIR/manual_async_fn.rs:18:1
+   |
+LL | fn fut3()-> impl Future<Output = i32> {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+help: make the function `async` and return the output of the future directly
+   |
+LL | async fn fut3() -> i32 {
+   | ^^^^^^^^^^^^^^^^^^^^^^
+help: move the body of the async block to the enclosing function
+   |
+LL | fn fut3()-> impl Future<Output = i32> { 42 }
+   |                                       ^^^^^^
+
+error: this function can be simplified using the `async fn` syntax
+  --> $DIR/manual_async_fn.rs:22:1
    |
 LL | fn empty_fut() -> impl Future<Output = ()> {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
 help: make the function `async` and remove the return type
    |
-LL | async fn empty_fut()  {
+LL | async fn empty_fut() {
    | ^^^^^^^^^^^^^^^^^^^^
 help: move the body of the async block to the enclosing function
    |
@@ -30,7 +60,37 @@ LL | fn empty_fut() -> impl Future<Output = ()> {}
    |                                            ^^
 
 error: this function can be simplified using the `async fn` syntax
-  --> $DIR/manual_async_fn.rs:16:1
+  --> $DIR/manual_async_fn.rs:27:1
+   |
+LL | fn empty_fut2() ->impl Future<Output = ()> {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+help: make the function `async` and remove the return type
+   |
+LL | async fn empty_fut2() {
+   | ^^^^^^^^^^^^^^^^^^^^^
+help: move the body of the async block to the enclosing function
+   |
+LL | fn empty_fut2() ->impl Future<Output = ()> {}
+   |                                            ^^
+
+error: this function can be simplified using the `async fn` syntax
+  --> $DIR/manual_async_fn.rs:32:1
+   |
+LL | fn empty_fut3()-> impl Future<Output = ()> {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+help: make the function `async` and remove the return type
+   |
+LL | async fn empty_fut3() {
+   | ^^^^^^^^^^^^^^^^^^^^^
+help: move the body of the async block to the enclosing function
+   |
+LL | fn empty_fut3()-> impl Future<Output = ()> {}
+   |                                            ^^
+
+error: this function can be simplified using the `async fn` syntax
+  --> $DIR/manual_async_fn.rs:36:1
    |
 LL | fn core_fut() -> impl core::future::Future<Output = i32> {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -45,7 +105,7 @@ LL | fn core_fut() -> impl core::future::Future<Output = i32> { 42 }
    |                                                          ^^^^^^
 
 error: this function can be simplified using the `async fn` syntax
-  --> $DIR/manual_async_fn.rs:38:5
+  --> $DIR/manual_async_fn.rs:58:5
    |
 LL |     fn inh_fut() -> impl Future<Output = i32> {
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -65,7 +125,7 @@ LL |             let c = 21;
  ...
 
 error: this function can be simplified using the `async fn` syntax
-  --> $DIR/manual_async_fn.rs:73:1
+  --> $DIR/manual_async_fn.rs:93:1
    |
 LL | fn elided(_: &i32) -> impl Future<Output = i32> + '_ {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -80,7 +140,7 @@ LL | fn elided(_: &i32) -> impl Future<Output = i32> + '_ { 42 }
    |                                                      ^^^^^^
 
 error: this function can be simplified using the `async fn` syntax
-  --> $DIR/manual_async_fn.rs:82:1
+  --> $DIR/manual_async_fn.rs:102:1
    |
 LL | fn explicit<'a, 'b>(_: &'a i32, _: &'b i32) -> impl Future<Output = i32> + 'a + 'b {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -94,5 +154,5 @@ help: move the body of the async block to the enclosing function
 LL | fn explicit<'a, 'b>(_: &'a i32, _: &'b i32) -> impl Future<Output = i32> + 'a + 'b { 42 }
    |                                                                                    ^^^^^^
 
-error: aborting due to 6 previous errors
+error: aborting due to 10 previous errors