cmd/compile: revert package typecheck part of CL 422914

This code path is unreachable anyway, and it adds new uses of
Type.Pkg, which shouldn't be used anymore.

Mark Type.Pkg as deprecated while here.

Updates #57410.

Change-Id: I1eec1c8ed99207d58d0ba0c44822bbad29dc64f3
Reviewed-on: https://go-review.googlesource.com/c/go/+/458575
Reviewed-by: David Chase <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Run-TryBot: Matthew Dempsky <[email protected]>
Reviewed-by: Cherry Mui <[email protected]>

Author: mdempsky

src/cmd/compile/internal/typecheck/expr.go

@@ -516,18 +516,6 @@ func tcDot(n *ir.SelectorExpr, top int) ir.Node {
 	return n
 }
 
-func wrongTypeFor(haveSym *types.Sym, haveType *types.Type, wantSym *types.Sym, wantType *types.Type) string {
-	haveT := fmt.Sprintf("%S", haveType)
-	wantT := fmt.Sprintf("%S", wantType)
-	if haveT == wantT {
-		// Add packages instead of reporting "got Foo but wanted Foo", see #54258.
-		haveT = haveType.Pkg().Path + "." + haveT
-		wantT = wantType.Pkg().Path + "." + wantT
-	}
-	return fmt.Sprintf("(wrong type for %v method)\n"+
-		"\t\thave %v%s\n\t\twant %v%s", wantSym, haveSym, haveT, wantSym, wantT)
-}
-
 // tcDotType typechecks an ODOTTYPE node.
 func tcDotType(n *ir.TypeAssertExpr) ir.Node {
 	n.X = Expr(n.X)
@@ -551,8 +539,8 @@ func tcDotType(n *ir.TypeAssertExpr) ir.Node {
 		var ptr int
 		if !implements(n.Type(), t, &missing, &have, &ptr) {
 			if have != nil && have.Sym == missing.Sym {
-				base.Errorf("impossible type assertion:\n\t%v does not implement %v %s", n.Type(), t,
-					wrongTypeFor(have.Sym, have.Type, missing.Sym, missing.Type))
+				base.Errorf("impossible type assertion:\n\t%v does not implement %v (wrong type for %v method)\n"+
+					"\t\thave %v%S\n\t\twant %v%S", n.Type(), t, missing.Sym, have.Sym, have.Type, missing.Sym, missing.Type)
 			} else if ptr != 0 {
 				base.Errorf("impossible type assertion:\n\t%v does not implement %v (%v method has pointer receiver)", n.Type(), t, missing.Sym)
 			} else if have != nil {

src/cmd/compile/internal/typecheck/stmt.go

@@ -604,8 +604,8 @@ func tcSwitchType(n *ir.SwitchStmt) {
 			}
 			if !n1.Type().IsInterface() && !implements(n1.Type(), t, &missing, &have, &ptr) {
 				if have != nil {
-					base.ErrorfAt(ncase.Pos(), "impossible type switch case: %L cannot have dynamic type %v %s", guard.X, n1.Type(),
-						wrongTypeFor(have.Sym, have.Type, missing.Sym, missing.Type))
+					base.ErrorfAt(ncase.Pos(), "impossible type switch case: %L cannot have dynamic type %v"+
+						" (wrong type for %v method)\n\thave %v%S\n\twant %v%S", guard.X, n1.Type(), missing.Sym, have.Sym, have.Type, missing.Sym, missing.Type)
 				} else if ptr != 0 {
 					base.ErrorfAt(ncase.Pos(), "impossible type switch case: %L cannot have dynamic type %v"+
 						" (%v method has pointer receiver)", guard.X, n1.Type(), missing.Sym)

src/cmd/compile/internal/typecheck/subr.go

@@ -397,7 +397,8 @@ func Assignop1(src, dst *types.Type) (ir.Op, string) {
 		} else if have != nil && have.Sym == missing.Sym && have.Nointerface() {
 			why = fmt.Sprintf(":\n\t%v does not implement %v (%v method is marked 'nointerface')", src, dst, missing.Sym)
 		} else if have != nil && have.Sym == missing.Sym {
-			why = fmt.Sprintf(":\n\t%v does not implement %v %s", src, dst, wrongTypeFor(have.Sym, have.Type, missing.Sym, missing.Type))
+			why = fmt.Sprintf(":\n\t%v does not implement %v (wrong type for %v method)\n"+
+				"\t\thave %v%S\n\t\twant %v%S", src, dst, missing.Sym, have.Sym, have.Type, missing.Sym, missing.Type)
 		} else if ptr != 0 {
 			why = fmt.Sprintf(":\n\t%v does not implement %v (%v method has pointer receiver)", src, dst, missing.Sym)
 		} else if have != nil {

src/cmd/compile/internal/types/type.go

@@ -319,6 +319,9 @@ var NoPkg *Pkg = nil
 // (i.e., types with named elements). This information isn't used by
 // cmd/compile itself, but we need to track it because it's exposed by
 // the go/types API.
+//
+// Deprecated: Pkg exists only for iexport, which will go away after
+// Go 1.20. It should not be used by other code.
 func (t *Type) Pkg() *Pkg {
 	switch t.kind {
 	case TFUNC: