Add suggestion on type signatures

Author: hkmatsumoto

clippy_lints/src/unnecessary_wrap.rs

@@ -7,7 +7,7 @@ use rustc_errors::Applicability;
 use rustc_hir::intravisit::{FnKind, NestedVisitorMap, Visitor};
 use rustc_hir::*;
 use rustc_lint::{LateContext, LateLintPass};
-use rustc_middle::hir::map::Map;
+use rustc_middle::{hir::map::Map, ty::subst::GenericArgKind};
 use rustc_session::{declare_lint_pass, declare_tool_lint};
 use rustc_span::Span;
 
@@ -100,14 +100,27 @@ impl<'tcx> LateLintPass<'tcx> for UnnecessaryWrap {
                 return;
             }
 
-            let suggs = result.iter().filter_map(|expr| {
-                let snippet = if let ExprKind::Call(_, ref args) = expr.kind {
-                    Some(snippet(cx, args[0].span, "..").to_string())
-                } else {
-                    None
-                };
-                snippet.map(|snip| (expr.span, snip))
-            });
+            let suggs = result
+                .iter()
+                .filter_map(|expr| {
+                    let snippet = if let ExprKind::Call(_, ref args) = expr.kind {
+                        Some(snippet(cx, args[0].span, "..").to_string())
+                    } else {
+                        None
+                    };
+                    snippet.map(|snip| (expr.span, snip))
+                })
+                .chain({
+                    let inner_ty = return_ty(cx, hir_id)
+                        .walk()
+                        .skip(1) // skip `std::option::Option` or `std::result::Result`
+                        .take(1) // first outermost inner type is needed
+                        .filter_map(|inner| match inner.unpack() {
+                            GenericArgKind::Type(inner_ty) => Some(inner_ty.to_string()),
+                            _ => None,
+                        });
+                    inner_ty.map(|inner_ty| (fn_decl.output.span(), inner_ty))
+                });
 
             span_lint_and_then(
                 cx,

tests/ui/unnecessary_wrap.fixed

@@ -1,8 +1,10 @@
 // run-rustfix
+
 #![warn(clippy::unnecessary_wrap)]
 #![allow(clippy::no_effect)]
 #![allow(clippy::needless_return)]
 #![allow(clippy::if_same_then_else)]
+#![allow(dead_code)]
 
 // should be linted
 fn func1(a: bool, b: bool) -> Option<i32> {
@@ -37,7 +39,21 @@ fn func3(a: bool) -> Option<i32> {
 
 // should be linted
 fn func4() -> Option<i32> {
-    1
+    Some(1)
+}
+
+// should be linted
+fn func5() -> Result<i32, ()> {
+    Ok(1)
+}
+
+// should not be linted
+fn func6(a: bool) -> Result<i32, ()> {
+    if a {
+        Ok(1)
+    } else {
+        Err(())
+    }
 }
 
 fn main() {

tests/ui/unnecessary_wrap.rs

@@ -1,8 +1,10 @@
 // run-rustfix
+
 #![warn(clippy::unnecessary_wrap)]
 #![allow(clippy::no_effect)]
 #![allow(clippy::needless_return)]
 #![allow(clippy::if_same_then_else)]
+#![allow(dead_code)]
 
 // should be linted
 fn func1(a: bool, b: bool) -> Option<i32> {
@@ -40,6 +42,20 @@ fn func4() -> Option<i32> {
     Some(1)
 }
 
+// should be linted
+fn func5() -> Result<i32, ()> {
+    Ok(1)
+}
+
+// should not be linted
+fn func6(a: bool) -> Result<i32, ()> {
+    if a {
+        Ok(1)
+    } else {
+        Err(())
+    }
+}
+
 fn main() {
     // method calls are not linted
     func1(true, true);

tests/ui/unnecessary_wrap.stderr

@@ -1,5 +1,5 @@
-error: this function unnecessarily wrapping data
-  --> $DIR/unnecessary_wrap.rs:8:1
+error: this function returns unnecessarily wrapping data
+  --> $DIR/unnecessary_wrap.rs:10:1
    |
 LL | / fn func1(a: bool, b: bool) -> Option<i32> {
 LL | |     if a && b {
@@ -13,22 +13,41 @@ LL | | }
    = note: `-D clippy::unnecessary-wrap` implied by `-D warnings`
 help: factor this out to
    |
+LL | fn func1(a: bool, b: bool) -> i32 {
+LL |     if a && b {
 LL |         return 42;
 LL |     }
 LL |     if a {
 LL |         Some(-1);
-LL |         2
-LL |     } else {
  ...
 
-error: this function unnecessarily wrapping data
-  --> $DIR/unnecessary_wrap.rs:39:1
+error: this function returns unnecessarily wrapping data
+  --> $DIR/unnecessary_wrap.rs:41:1
    |
 LL | / fn func4() -> Option<i32> {
 LL | |     Some(1)
-   | |     ------- help: factor this out to: `1`
 LL | | }
    | |_^
+   |
+help: factor this out to
+   |
+LL | fn func4() -> i32 {
+LL |     1
+   |
+
+error: this function returns unnecessarily wrapping data
+  --> $DIR/unnecessary_wrap.rs:46:1
+   |
+LL | / fn func5() -> Result<i32, ()> {
+LL | |     Ok(1)
+LL | | }
+   | |_^
+   |
+help: factor this out to
+   |
+LL | fn func5() -> i32 {
+LL |     1
+   |
 
-error: aborting due to 2 previous errors
+error: aborting due to 3 previous errors