Auto merge of #104920 - compiler-errors:avoid-infcx-build, r=jackh726

Avoid some `InferCtxt::build` calls

Either because we're inside of an `InferCtxt` already, or because we're not in a place where we'd ever see inference vars.

r? types

2 files changed, 34 insertions, 4 deletions

diff --git a/src/test/ui/return/tail-expr-as-potential-return.rs b/src/test/ui/return/tail-expr-as-potential-return.rs
index 2c3610fb24d..f46e088b85f 100644
--- a/src/test/ui/return/tail-expr-as-potential-return.rs
+++ b/src/test/ui/return/tail-expr-as-potential-return.rs
@@ -12,7 +12,6 @@
 // edition:2018
 
 fn main() {
-    let _ = foo(true);
 }
 
 fn foo(x: bool) -> Result<f64, i32> {
@@ -30,3 +29,19 @@ async fn bar(x: bool) -> Result<f64, i32> {
     }
     Ok(42.0)
 }
+
+trait Identity {
+    type Out;
+}
+
+impl<T> Identity for T {
+    type Out = T;
+}
+
+async fn foo2() -> i32 {
+    if true {
+        1i32 //~ ERROR mismatched types
+            //| HELP you might have meant to return this value
+    }
+    0
+}
diff --git a/src/test/ui/return/tail-expr-as-potential-return.stderr b/src/test/ui/return/tail-expr-as-potential-return.stderr
index dec1cbc4624..9183b4599ba 100644
--- a/src/test/ui/return/tail-expr-as-potential-return.stderr
+++ b/src/test/ui/return/tail-expr-as-potential-return.stderr
@@ -1,5 +1,5 @@
 error[E0308]: mismatched types
-  --> $DIR/tail-expr-as-potential-return.rs:28:9
+  --> $DIR/tail-expr-as-potential-return.rs:27:9
    |
 LL | /     if x {
 LL | |         Err(42)
@@ -16,7 +16,22 @@ LL |         return Err(42);
    |         ++++++        +
 
 error[E0308]: mismatched types
-  --> $DIR/tail-expr-as-potential-return.rs:20:9
+  --> $DIR/tail-expr-as-potential-return.rs:43:9
+   |
+LL | /     if true {
+LL | |         1i32
+   | |         ^^^^ expected `()`, found `i32`
+LL | |             //| HELP you might have meant to return this value
+LL | |     }
+   | |_____- expected this to be `()`
+   |
+help: you might have meant to return this value
+   |
+LL |         return 1i32;
+   |         ++++++     +
+
+error[E0308]: mismatched types
+  --> $DIR/tail-expr-as-potential-return.rs:19:9
    |
 LL | /     if x {
 LL | |         Err(42)
@@ -32,6 +47,6 @@ help: you might have meant to return this value
 LL |         return Err(42);
    |         ++++++        +
 
-error: aborting due to 2 previous errors
+error: aborting due to 3 previous errors
 
 For more information about this error, try `rustc --explain E0308`.