Fix 13018: self should be T

with `Option::unwrap_or(self, T) -> T`.

Author: tesuji

clippy_lints/src/matches/manual_unwrap_or.rs

@@ -35,6 +35,17 @@ pub(super) fn check_if_let<'tcx>(
     else_expr: &'tcx Expr<'_>,
 ) {
     let ty = cx.typeck_results().expr_ty(let_expr);
+    let then_ty = cx.typeck_results().expr_ty(then_expr);
+    // The signature is `fn unwrap_or<T>(self: Option<T>, default: T) -> T`.
+    // When `expr_adjustments(then_expr).is_empty()`, `T` should equate to `default`'s type.
+    // Otherwise, type error will occur.
+    if cx.typeck_results().expr_adjustments(then_expr).is_empty()
+        && let rustc_middle::ty::Adt(_did, args) = ty.kind()
+        && let Some(some_ty) = args.first().and_then(|arg| arg.as_type())
+        && some_ty != then_ty
+    {
+        return;
+    }
     check_and_lint(cx, expr, let_pat, let_expr, then_expr, peel_blocks(else_expr), ty);
 }
 

tests/ui/manual_unwrap_or.fixed

@@ -239,7 +239,14 @@ mod issue_13018 {
 
     type RefName = i32;
     pub fn get(index: &HashMap<usize, Vec<RefName>>, id: usize) -> &[RefName] {
-        index.get(&id).unwrap_or(&[])
+        if let Some(names) = index.get(&id) { names } else { &[] }
+    }
+
+    pub fn get_match(index: &HashMap<usize, Vec<RefName>>, id: usize) -> &[RefName] {
+        match index.get(&id) {
+            Some(names) => names,
+            None => &[],
+        }
     }
 }
 

tests/ui/manual_unwrap_or.rs

@@ -289,10 +289,13 @@ mod issue_13018 {
 
     type RefName = i32;
     pub fn get(index: &HashMap<usize, Vec<RefName>>, id: usize) -> &[RefName] {
-        if let Some(names) = index.get(&id) {
-            names
-        } else {
-            &[]
+        if let Some(names) = index.get(&id) { names } else { &[] }
+    }
+
+    pub fn get_match(index: &HashMap<usize, Vec<RefName>>, id: usize) -> &[RefName] {
+        match index.get(&id) {
+            Some(names) => names,
+            None => &[],
         }
     }
 }

tests/ui/manual_unwrap_or.stderr

@@ -172,15 +172,5 @@ LL | |             None => 0,
 LL | |         };
    | |_________^ help: replace with: `some_macro!().unwrap_or(0)`
 
-error: this pattern reimplements `Option::unwrap_or`
-  --> tests/ui/manual_unwrap_or.rs:292:9
-   |
-LL | /         if let Some(names) = index.get(&id) {
-LL | |             names
-LL | |         } else {
-LL | |             &[]
-LL | |         }
-   | |_________^ help: replace with: `index.get(&id).unwrap_or(&[])`
-
-error: aborting due to 17 previous errors
+error: aborting due to 16 previous errors