Remove 3 more unused ObligationCauseCodes

compiler/rustc_middle/src/traits/mod.rs

@@ -370,9 +370,6 @@ pub enum ObligationCauseCode<'tcx> {
         origin_expr: bool,
     },
 
-    /// Constants in patterns must have `Structural` type.
-    ConstPatternStructural,
-
     /// Computing common supertype in an if expression
     IfExpression(Box<IfExpressionCause<'tcx>>),
 
@@ -405,9 +402,6 @@ pub enum ObligationCauseCode<'tcx> {
     /// `return` with an expression
     ReturnValue(hir::HirId),
 
-    /// Return type of this function
-    ReturnType,
-
     /// Opaque return type of this function
     OpaqueReturnType(Option<(Ty<'tcx>, Span)>),
 
@@ -417,9 +411,6 @@ pub enum ObligationCauseCode<'tcx> {
     /// #[feature(trivial_bounds)] is not enabled
     TrivialBound,
 
-    /// If `X` is the concrete type of an opaque type `impl Y`, then `X` must implement `Y`
-    OpaqueType,
-
     AwaitableExpr(hir::HirId),
 
     ForLoopIterator,

compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs

@@ -2592,11 +2592,9 @@ fn note_obligation_cause_code<T>(
             | ObligationCauseCode::MethodReceiver
             | ObligationCauseCode::ReturnNoExpression
             | ObligationCauseCode::UnifyReceiver(..)
-            | ObligationCauseCode::OpaqueType
             | ObligationCauseCode::MiscObligation
             | ObligationCauseCode::WellFormed(..)
             | ObligationCauseCode::MatchImpl(..)
-            | ObligationCauseCode::ReturnType
             | ObligationCauseCode::ReturnValue(_)
             | ObligationCauseCode::BlockTailExpression(..)
             | ObligationCauseCode::AwaitableExpr(_)
@@ -2974,9 +2972,6 @@ fn note_obligation_cause_code<T>(
                     "all values live across `{what}` must have a statically known size"
                 ));
             }
-            ObligationCauseCode::ConstPatternStructural => {
-                err.note("constants used for pattern-matching must derive `PartialEq` and `Eq`");
-            }
             ObligationCauseCode::SharedStatic => {
                 err.note("shared static variables must have a type that implements `Sync`");
             }

compiler/rustc_trait_selection/src/traits/error_reporting/type_err_ctxt_ext.rs

@@ -1448,7 +1448,6 @@ fn report_projection_error(
                         | ObligationCauseCode::ExprItemObligation(..)
                         | ObligationCauseCode::ExprBindingObligation(..)
                         | ObligationCauseCode::Coercion { .. }
-                        | ObligationCauseCode::OpaqueType
                 );
 
                 // constrain inference variables a bit more to nested obligations from normalize so