Add extern crate core to diagnostic tests

tests/ui-fulldeps/session-diagnostic/diagnostic-derive-doc-comment-field.rs

@@ -18,6 +18,7 @@ extern crate rustc_fluent_macro;
 extern crate rustc_macros;
 extern crate rustc_session;
 extern crate rustc_span;
+extern crate core;
 
 use rustc_errors::{Applicability, DiagMessage, SubdiagMessage};
 use rustc_macros::{Diagnostic, Subdiagnostic};

tests/ui-fulldeps/session-diagnostic/diagnostic-derive-doc-comment-field.stderr

@@ -1,5 +1,5 @@
 error[E0277]: the trait bound `NotIntoDiagArg: IntoDiagArg` is not satisfied
-  --> $DIR/diagnostic-derive-doc-comment-field.rs:36:10
+  --> $DIR/diagnostic-derive-doc-comment-field.rs:37:10
    |
 LL | #[derive(Diagnostic)]
    |          ---------- required by a bound introduced by this call
@@ -8,7 +8,7 @@ LL |     arg: NotIntoDiagArg,
    |          ^^^^^^^^^^^^^^ unsatisfied trait bound
    |
 help: the nightly-only, unstable trait `IntoDiagArg` is not implemented for `NotIntoDiagArg`
-  --> $DIR/diagnostic-derive-doc-comment-field.rs:28:1
+  --> $DIR/diagnostic-derive-doc-comment-field.rs:29:1
    |
 LL | struct NotIntoDiagArg;
    | ^^^^^^^^^^^^^^^^^^^^^
@@ -21,7 +21,7 @@ note: required by a bound in `Diag::<'a, G>::arg`
    = note: this error originates in the macro `with_fn` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error[E0277]: the trait bound `NotIntoDiagArg: IntoDiagArg` is not satisfied
-  --> $DIR/diagnostic-derive-doc-comment-field.rs:46:10
+  --> $DIR/diagnostic-derive-doc-comment-field.rs:47:10
    |
 LL | #[derive(Subdiagnostic)]
    |          ------------- required by a bound introduced by this call
@@ -30,7 +30,7 @@ LL |     arg: NotIntoDiagArg,
    |          ^^^^^^^^^^^^^^ unsatisfied trait bound
    |
 help: the nightly-only, unstable trait `IntoDiagArg` is not implemented for `NotIntoDiagArg`
-  --> $DIR/diagnostic-derive-doc-comment-field.rs:28:1
+  --> $DIR/diagnostic-derive-doc-comment-field.rs:29:1
    |
 LL | struct NotIntoDiagArg;
    | ^^^^^^^^^^^^^^^^^^^^^

tests/ui-fulldeps/session-diagnostic/diagnostic-derive.rs

@@ -29,6 +29,8 @@ use rustc_errors::{Applicability, DiagMessage, ErrCode, MultiSpan, SubdiagMessag
 
 extern crate rustc_session;
 
+extern crate core;
+
 rustc_fluent_macro::fluent_messages! { "./example.ftl" }
 
 // E0123 and E0456 are no longer used, so we define our own constants here just for this test.
@@ -56,7 +58,7 @@ enum DiagnosticOnEnum {
 #[derive(Diagnostic)]
 #[diag(no_crate_example, code = E0123)]
 #[diag = "E0123"]
-//~^ ERROR failed to resolve: you might be missing crate `core`
+//~^ ERROR expected parentheses: #[diag(...)]
 struct WrongStructAttrStyle {}
 
 #[derive(Diagnostic)]
@@ -801,15 +803,15 @@ struct SuggestionsNoItem {
 struct SuggestionsInvalidItem {
     #[suggestion(code(foo))]
     //~^ ERROR `code(...)` must contain only string literals
-    //~| ERROR failed to resolve: you might be missing crate `core`
+    //~| ERROR unexpected token, expected `)`
     sub: Span,
 }
 
 #[derive(Diagnostic)] //~ ERROR cannot find value `__code_34` in this scope
 #[diag(no_crate_example)]
 struct SuggestionsInvalidLiteral {
     #[suggestion(code = 3)]
-    //~^ ERROR failed to resolve: you might be missing crate `core`
+    //~^ ERROR expected string literal
     sub: Span,
 }