fix issue 144074, having so many same diagnostics makes it hard to recognize the root cause

Author: lichuang

compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs

@@ -399,18 +399,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         };
 
         // Check the arguments.
-        // We do this in a pretty awful way: first we type-check any arguments
-        // that are not closures, then we type-check the closures. This is so
-        // that we have more information about the types of arguments when we
-        // type-check the functions. This isn't really the right way to do this.
+        // More awful hacks: before we check argument types, try to do
+        // an "opportunistic" trait resolution of any trait bounds on
+        // the call. This helps coercions.
+        self.select_obligations_where_possible(|_| {});
         for check_closures in [false, true] {
-            // More awful hacks: before we check argument types, try to do
-            // an "opportunistic" trait resolution of any trait bounds on
-            // the call. This helps coercions.
-            if check_closures {
-                self.select_obligations_where_possible(|_| {})
-            }
-
             // Check each argument, to satisfy the input it was provided for
             // Visually, we're traveling down the diagonal of the compatibility matrix
             for (idx, arg) in provided_args.iter().enumerate() {

tests/ui/suggestions/duplcate-diagnostics-issue-144074.rs

@@ -0,0 +1,10 @@
+struct Struct<T>(T);
+fn assert_sized(_x: impl Sized) {}
+fn f() {
+    assert_sized(Struct(*"")); //~ ERROR: the size for values of type `str` cannot be known at compilation time
+    //~^ ERROR: the size for values of type `str` cannot be known at compilation time
+}
+
+fn main() {
+    f();
+}

tests/ui/suggestions/duplcate-diagnostics-issue-144074.stderr

@@ -0,0 +1,43 @@
+error[E0277]: the size for values of type `str` cannot be known at compilation time
+  --> $DIR/issue-144074.rs:4:25
+   |
+LL |     assert_sized(Struct(*""));
+   |                  ------ ^^^ doesn't have a size known at compile-time
+   |                  |
+   |                  required by a bound introduced by this call
+   |
+   = help: the trait `Sized` is not implemented for `str`
+note: required by a bound in `Struct`
+  --> $DIR/issue-144074.rs:1:15
+   |
+LL | struct Struct<T>(T);
+   |               ^ required by this bound in `Struct`
+help: references are always `Sized`, even if they point to unsized data; consider not dereferencing the expression
+   |
+LL -     assert_sized(Struct(*""));
+LL +     assert_sized(Struct(""));
+   |
+
+error[E0277]: the size for values of type `str` cannot be known at compilation time
+  --> $DIR/issue-144074.rs:4:5
+   |
+LL |     assert_sized(Struct(*""));
+   |     ^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `str`
+note: required by an implicit `Sized` bound in `Struct`
+  --> $DIR/issue-144074.rs:1:15
+   |
+LL | struct Struct<T>(T);
+   |               ^ required by the implicit `Sized` requirement on this type parameter in `Struct`
+help: you could relax the implicit `Sized` bound on `T` if it were used through indirection like `&T` or `Box<T>`
+  --> $DIR/issue-144074.rs:1:15
+   |
+LL | struct Struct<T>(T);
+   |               ^  - ...if indirection were used here: `Box<T>`
+   |               |
+   |               this could be changed to `T: ?Sized`...
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0277`.