Rollup merge of #127129 - compiler-errors:full-expr-span, r=jieyouxu

Use full expr span for return suggestion on type error/ambiguity

We sometimes use parts of an expression rather than the whole thing for an obligation span. For example, a method obligation will just point to the path segment corresponding to the `method` in `rcvr.method(args)`.

So let's not use that assuming it'll point to the *whole* expression span, which we can access from the expr hir id we store in `ObligationCauseCode::WhereClauseInExpr`.

Fixes #127109

compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs

@@ -2042,7 +2042,8 @@ pub(super) fn collect_unused_stmts_for_coerce_return_ty(
                     }
                     if block_num > 1 && found_semi {
                         err.span_suggestion_verbose(
-                            span.shrink_to_lo(),
+                            // use the span of the *whole* expr
+                            self.tcx.hir().span(binding_hir_id).shrink_to_lo(),
                             "you might have meant to return this to infer its type parameters",
                             "return ",
                             Applicability::MaybeIncorrect,

tests/ui/return/tail-expr-as-potential-return.rs

@@ -1,3 +1,5 @@
+//@ edition:2018
+
 // > Suggest returning tail expressions that match return type
 // >
 // > Some newcomers are confused by the behavior of tail expressions,
@@ -8,24 +10,24 @@
 //
 // This test was amended to also serve as a regression test for #92308, where
 // this suggestion would not trigger with async functions.
-//
-//@ edition:2018
 
 fn main() {
 }
 
 fn foo(x: bool) -> Result<f64, i32> {
     if x {
-        Err(42) //~ ERROR mismatched types
-                //| HELP you might have meant to return this value
+        Err(42)
+        //~^ ERROR mismatched types
+        //~| HELP you might have meant to return this value
     }
     Ok(42.0)
 }
 
 async fn bar(x: bool) -> Result<f64, i32> {
     if x {
-        Err(42) //~ ERROR mismatched types
-                //| HELP you might have meant to return this value
+        Err(42)
+        //~^ ERROR mismatched types
+        //~| HELP you might have meant to return this value
     }
     Ok(42.0)
 }
@@ -40,8 +42,26 @@ impl<T> Identity for T {
 
 async fn foo2() -> i32 {
     if true {
-        1i32 //~ ERROR mismatched types
-            //| HELP you might have meant to return this value
+        1i32
+        //~^ ERROR mismatched types
+        //~| HELP you might have meant to return this value
     }
     0
 }
+
+struct Receiver;
+impl Receiver {
+    fn generic<T>(self) -> Option<T> {
+        None
+    }
+}
+fn method() -> Option<i32> {
+    if true {
+        Receiver.generic();
+        //~^ ERROR type annotations needed
+        //~| HELP consider specifying the generic argument
+        //~| HELP you might have meant to return this to infer its type parameters
+    }
+
+    None
+}

tests/ui/return/tail-expr-as-potential-return.stderr

@@ -1,10 +1,11 @@
 error[E0308]: mismatched types
-  --> $DIR/tail-expr-as-potential-return.rs:27:9
+  --> $DIR/tail-expr-as-potential-return.rs:28:9
    |
 LL | /     if x {
 LL | |         Err(42)
    | |         ^^^^^^^ expected `()`, found `Result<_, {integer}>`
-LL | |                 //| HELP you might have meant to return this value
+LL | |
+LL | |
 LL | |     }
    | |_____- expected this to be `()`
    |
@@ -16,12 +17,13 @@ LL |         return Err(42);
    |         ++++++        +
 
 error[E0308]: mismatched types
-  --> $DIR/tail-expr-as-potential-return.rs:43:9
+  --> $DIR/tail-expr-as-potential-return.rs:45:9
    |
 LL | /     if true {
 LL | |         1i32
    | |         ^^^^ expected `()`, found `i32`
-LL | |             //| HELP you might have meant to return this value
+LL | |
+LL | |
 LL | |     }
    | |_____- expected this to be `()`
    |
@@ -36,7 +38,8 @@ error[E0308]: mismatched types
 LL | /     if x {
 LL | |         Err(42)
    | |         ^^^^^^^ expected `()`, found `Result<_, {integer}>`
-LL | |                 //| HELP you might have meant to return this value
+LL | |
+LL | |
 LL | |     }
    | |_____- expected this to be `()`
    |
@@ -47,6 +50,22 @@ help: you might have meant to return this value
 LL |         return Err(42);
    |         ++++++        +
 
-error: aborting due to 3 previous errors
+error[E0282]: type annotations needed
+  --> $DIR/tail-expr-as-potential-return.rs:60:18
+   |
+LL |         Receiver.generic();
+   |                  ^^^^^^^ cannot infer type of the type parameter `T` declared on the method `generic`
+   |
+help: consider specifying the generic argument
+   |
+LL |         Receiver.generic::<T>();
+   |                         +++++
+help: you might have meant to return this to infer its type parameters
+   |
+LL |         return Receiver.generic();
+   |         ++++++
 
-For more information about this error, try `rustc --explain E0308`.
+error: aborting due to 4 previous errors
+
+Some errors have detailed explanations: E0282, E0308.
+For more information about an error, try `rustc --explain E0282`.