Refactor to make getting position just before RArrow a common function

Author: giraffate

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;
@@ -69,20 +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("->").map(|rpos| {
-                                let mut rpos = rpos;
-                                let chars: Vec<char> = header_snip.chars().collect();
-                                while rpos > 1 {
-                                    if let Some(c) = chars.get(rpos - 1) {
-                                        if c.is_whitespace() {
-                                            rpos -= 1;
-                                            continue;
-                                        }
-                                    }
-                                    break;
-                                }
-                                rpos
-                            });
+                            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);

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)
     };

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