[dev.typeparams] cmd/compile: keep export format unchanged if no type params are exported

Added new export tags 'G' and 'U' to export parameterized
functions/methods and parameterized types respectively. This has the
advantage that the Go 1.18 format remains backward-compatible with the
Go 1.17 format if no type parameters are exported.

Change-Id: I9dba8faaa65609eb3f9c693bd0c79daee98bd865
Reviewed-on: https://go-review.googlesource.com/c/go/+/340989
Trust: Dan Scales <danscales@google.com>
Run-TryBot: Dan Scales <danscales@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

1 files changed, 5 insertions, 5 deletions

diff --git a/src/cmd/compile/internal/typecheck/iimport.go b/src/cmd/compile/internal/typecheck/iimport.go
index d5f4bba98b..83974b6d56 100644
--- a/src/cmd/compile/internal/typecheck/iimport.go
+++ b/src/cmd/compile/internal/typecheck/iimport.go
@@ -305,9 +305,9 @@ func (r *importReader) doDecl(sym *types.Sym) *ir.Name {
 		r.constExt(n)
 		return n
 
-	case 'F':
+	case 'F', 'G':
 		var tparams []*types.Field
-		if r.p.exportVersion >= iexportVersionGenerics {
+		if tag == 'G' {
 			tparams = r.tparamList()
 		}
 		typ := r.signature(nil, tparams)
@@ -316,9 +316,9 @@ func (r *importReader) doDecl(sym *types.Sym) *ir.Name {
 		r.funcExt(n)
 		return n
 
-	case 'T':
+	case 'T', 'U':
 		var rparams []*types.Type
-		if r.p.exportVersion >= iexportVersionGenerics {
+		if tag == 'U' {
 			rparams = r.typeList()
 		}
 
@@ -326,7 +326,7 @@ func (r *importReader) doDecl(sym *types.Sym) *ir.Name {
 		// declaration before recursing.
 		n := importtype(pos, sym)
 		t := n.Type()
-		if rparams != nil {
+		if tag == 'U' {
 			t.SetRParams(rparams)
 		}