From: Robert Findley <rfindley@google.com>
Date: Mon, 16 Aug 2021 20:03:59 +0000 (-0400)
Subject: go/types: no need to validate substituted instances
X-Git-Tag: go1.18beta1~1695
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=30a423eb39;p=gostls13.git

go/types: no need to validate substituted instances

This is a straightforward port of CL 342150 to go/types.

Change-Id: I7363e4642ade7ab30ca822a2be71f4d2804cc4a9
Reviewed-on: https://go-review.googlesource.com/c/go/+/342669
Trust: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>
---

diff --git a/src/go/types/subst.go b/src/go/types/subst.go
index da0578ff5c..e47d20774f 100644
--- a/src/go/types/subst.go
+++ b/src/go/types/subst.go
@@ -228,10 +228,15 @@ func (subst *subster) typ(typ Type) Type {
 			return named
 		}
 
-		// create a new named type and populate typMap to avoid endless recursion
+		// Create a new named type and populate typMap to avoid endless recursion.
+		// The position used here is irrelevant because validation only occurs on t
+		// (we don't call validType on named), but we use subst.pos to help with
+		// debugging.
 		tname := NewTypeName(subst.pos, t.obj.pkg, t.obj.name, nil)
 		t.load()
-		named := subst.check.newNamed(tname, t.orig, t.underlying, t.TParams(), t.methods) // method signatures are updated lazily
+		// It's ok to provide a nil *Checker because the newly created type
+		// doesn't need to be (lazily) expanded; it's expanded below.
+		named := (*Checker)(nil).newNamed(tname, t.orig, nil, t.tparams, t.methods) // t is loaded, so tparams and methods are available
 		named.targs = newTArgs
 		subst.typMap[h] = named
 		t.expand(subst.typMap) // must happen after typMap update to avoid infinite recursion
@@ -241,7 +246,7 @@ func (subst *subster) typ(typ Type) Type {
 		named.underlying = subst.typOrNil(t.underlying)
 		dump(">>> underlying: %v", named.underlying)
 		assert(named.underlying != nil)
-		named.fromRHS = named.underlying // for cycle detection (Checker.validType)
+		named.fromRHS = named.underlying // for consistency, though no cycle detection is necessary
 
 		return named