From: Robert Griesemer <gri@golang.org>
Date: Mon, 1 Nov 2021 20:41:32 +0000 (-0700)
Subject: cmd/compile/internal/types2: adjust printing of type parameter in error
X-Git-Tag: go1.18beta1~620
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=599de4b2c348738a5d6d2f5d475c74ac835e091a;p=gostls13.git

cmd/compile/internal/types2: adjust printing of type parameter in error

For constraint type inference failures where the type parameter doesn't
match the constraint, print the type parameter rather than its type name
object. This provides more flexibility for improving the error message
down the road.

Change-Id: I188871d6f26a16cd96e59770966a1ec65607b128
Reviewed-on: https://go-review.googlesource.com/c/go/+/360514
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>
---

diff --git a/src/cmd/compile/internal/types2/infer.go b/src/cmd/compile/internal/types2/infer.go
index 494e896ee9..24c461f1c3 100644
--- a/src/cmd/compile/internal/types2/infer.go
+++ b/src/cmd/compile/internal/types2/infer.go
@@ -378,7 +378,6 @@ func (check *Checker) inferB(tparams []*TypeParam, targs []Type) (types []Type,
 
 	// If a constraint has a structural type, unify the corresponding type parameter with it.
 	for _, tpar := range tparams {
-		typ := tpar
 		sbound := structure(tpar)
 		if sbound != nil {
 			// If the structural type is the underlying type of a single
@@ -386,8 +385,10 @@ func (check *Checker) inferB(tparams []*TypeParam, targs []Type) (types []Type,
 			if named, _ := tpar.singleType().(*Named); named != nil {
 				sbound = named
 			}
-			if !u.unify(typ, sbound) {
-				check.errorf(tpar.obj, "%s does not match %s", tpar.obj, sbound)
+			if !u.unify(tpar, sbound) {
+				// TODO(gri) improve error message by providing the type arguments
+				//           which we know already
+				check.errorf(tpar.obj, "%s does not match %s", tpar, sbound)
 				return nil, 0
 			}
 		}
diff --git a/src/cmd/compile/internal/types2/testdata/fixedbugs/issue45985.go2 b/src/cmd/compile/internal/types2/testdata/fixedbugs/issue45985.go2
index ee5282d6ef..9963d2ee00 100644
--- a/src/cmd/compile/internal/types2/testdata/fixedbugs/issue45985.go2
+++ b/src/cmd/compile/internal/types2/testdata/fixedbugs/issue45985.go2
@@ -5,7 +5,7 @@
 package issue45985
 
 // TODO(gri): this error should be on app[int] below.
-func app[S /* ERROR "type S S does not match" */ interface{ ~[]T }, T any](s S, e T) S {
+func app[S /* ERROR "S does not match" */ interface{ ~[]T }, T any](s S, e T) S {
     return append(s, e)
 }