[dev.typeparams] cmd/compile: adding union support in types1

Add union support in types1, and allow exporting of unions, and
importing unions back into types1 and types2.

Added new test mincheck.go/mincheck.dir that tests that type lists (type
sets) are correctly exported/imported, so that types2 gives correct
errors that an instantiation doesn't fit the type list in the type param
constraint.

Change-Id: I8041c6c79289c870a95ed5a1b10e4c1c16985b12
Reviewed-on: https://go-review.googlesource.com/c/go/+/322609
Trust: Dan Scales <danscales@google.com>
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Dan Scales <danscales@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

1 files changed, 39 insertions, 0 deletions

diff --git a/src/cmd/compile/internal/types/type.go b/src/cmd/compile/internal/types/type.go
index 3b0a9706f6..e7831121bf 100644
--- a/src/cmd/compile/internal/types/type.go
+++ b/src/cmd/compile/internal/types/type.go
@@ -73,6 +73,7 @@ const (
 	TSTRING
 	TUNSAFEPTR
 	TTYPEPARAM
+	TUNION
 
 	// pseudo-types for literals
 	TIDEAL // untyped numeric constants
@@ -392,6 +393,12 @@ type Typeparam struct {
 	bound *Type
 }
 
+// Union contains Type fields specific to union types.
+type Union struct {
+	terms  []*Type
+	tildes []bool // whether terms[i] is of form ~T
+}
+
 // Ptr contains Type fields specific to pointer types.
 type Ptr struct {
 	Elem *Type // element type
@@ -574,6 +581,8 @@ func New(et Kind) *Type {
 		t.Extra = new(Results)
 	case TTYPEPARAM:
 		t.Extra = new(Typeparam)
+	case TUNION:
+		t.Extra = new(Union)
 	}
 	return t
 }
@@ -1453,6 +1462,10 @@ func (t *Type) IsInterface() bool {
 	return t.kind == TINTER
 }
 
+func (t *Type) IsUnion() bool {
+	return t.kind == TUNION
+}
+
 // IsEmptyInterface reports whether t is an empty interface type.
 func (t *Type) IsEmptyInterface() bool {
 	return t.IsInterface() && t.AllMethods().Len() == 0
@@ -1811,6 +1824,32 @@ func (t *Type) Bound() *Type {
 	return t.Extra.(*Typeparam).bound
 }
 
+// NewUnion returns a new union with the specified set of terms (types). If
+// tildes[i] is true, then terms[i] represents ~T, rather than just T.
+func NewUnion(terms []*Type, tildes []bool) *Type {
+	t := New(TUNION)
+	if len(terms) != len(tildes) {
+		base.Fatalf("Mismatched terms and tildes for NewUnion")
+	}
+	t.Extra.(*Union).terms = terms
+	t.Extra.(*Union).tildes = tildes
+	return t
+}
+
+// NumTerms returns the number of terms in a union type.
+func (t *Type) NumTerms() int {
+	t.wantEtype(TUNION)
+	return len(t.Extra.(*Union).terms)
+}
+
+// Term returns ith term of a union type as (term, tilde). If tilde is true, term
+// represents ~T, rather than just T.
+func (t *Type) Term(i int) (*Type, bool) {
+	t.wantEtype(TUNION)
+	u := t.Extra.(*Union)
+	return u.terms[i], u.tildes[i]
+}
+
 const BOGUS_FUNARG_OFFSET = -1000000000
 
 func unzeroFieldOffsets(f []*Field) {