From: Robert Griesemer <gri@golang.org>
Date: Tue, 6 Jun 2023 21:30:31 +0000 (-0700)
Subject: go/types, types2: use inexact unification when unifying against core types
X-Git-Tag: go1.21rc1~34
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=f35d2dae74d12b06df061d909cb9721f27208a15;p=gostls13.git

go/types, types2: use inexact unification when unifying against core types

Follow-up on CL 498955 which introduced a unification mode, to be used
to control the precision of unification of element types (CL 498895):
When unifying against core types of unbound type parameters, we must
use inexact unification at the top (irrespective of the unification mode),
otherwise it may fail when unifying against a defined type (core types
are always underlying types).

No specific test case (I have not been able to create one yet).

Change-Id: Ie15e98f4b9e9fb60d6857d34b03d350ebbf0375e
Reviewed-on: https://go-review.googlesource.com/c/go/+/501302
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
Run-TryBot: Robert Griesemer <gri@google.com>
---

diff --git a/src/cmd/compile/internal/types2/unify.go b/src/cmd/compile/internal/types2/unify.go
index 10c4ec7632..48adc185c3 100644
--- a/src/cmd/compile/internal/types2/unify.go
+++ b/src/cmd/compile/internal/types2/unify.go
@@ -700,7 +700,11 @@ func (u *unifier) nify(x, y Type, mode unifyMode, p *ifacePair) (result bool) {
 				if traceInference {
 					u.tracef("core %s ≡ %s", x, y)
 				}
-				return u.nify(cx, y, mode, p)
+				// If y is a defined type, it may not match against cx which
+				// is an underlying type (incl. int, string, etc.). Use assign
+				// mode here so that the unifier automatically takes under(y)
+				// if necessary.
+				return u.nify(cx, y, assign, p)
 			}
 		}
 		// x != y and there's nothing to do
diff --git a/src/go/types/unify.go b/src/go/types/unify.go
index d704a27f7c..3ecc80f161 100644
--- a/src/go/types/unify.go
+++ b/src/go/types/unify.go
@@ -702,7 +702,11 @@ func (u *unifier) nify(x, y Type, mode unifyMode, p *ifacePair) (result bool) {
 				if traceInference {
 					u.tracef("core %s ≡ %s", x, y)
 				}
-				return u.nify(cx, y, mode, p)
+				// If y is a defined type, it may not match against cx which
+				// is an underlying type (incl. int, string, etc.). Use assign
+				// mode here so that the unifier automatically takes under(y)
+				// if necessary.
+				return u.nify(cx, y, assign, p)
 			}
 		}
 		// x != y and there's nothing to do