go/types, types2: implement adjCoreType using TypeParam.is

TypeParam.is also provides ~ (tilde) information which is needed
to fix #51229. Delete all code related to singleType as it's not
used anymore.

Also, remove TypeParam.hasTerms as it was not used.

For #51229.

Change-Id: Ie49b19d157230beecb17a444d1f17cf24aa4f6ba
Reviewed-on: https://go-review.googlesource.com/c/go/+/387774
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>

src/cmd/compile/internal/types2/infer.go

@@ -591,15 +591,24 @@ func (check *Checker) inferB(pos syntax.Pos, tparams []*TypeParam, targs []Type)
 	return
 }
 
+// adjCoreType returns the core type of tpar unless the
+// type parameter embeds a single, possibly named type,
+// in which case it returns that single type instead.
+// (The core type is always the underlying type of that
+// single type.)
 func adjCoreType(tpar *TypeParam) Type {
-	// If the type parameter embeds a single, possibly named
-	// type, use that one instead of the core type (which is
-	// always the underlying type of that single type).
-	if single := tpar.singleType(); single != nil {
-		if debug {
-			assert(under(single) == coreType(tpar))
+	var single *term
+	if tpar.is(func(t *term) bool {
+		if single == nil && t != nil {
+			single = t
+			return true
 		}
-		return single
+		return false // zero or more than one terms
+	}) {
+		if debug {
+			assert(under(single.typ) == coreType(tpar))
+		}
+		return single.typ
 	}
 	return coreType(tpar)
 }

src/cmd/compile/internal/types2/termlist.go

@@ -92,15 +92,6 @@ func (xl termlist) norm() termlist {
 	return rl
 }
 
-// If the type set represented by xl is specified by a single (non-𝓤) term,
-// singleType returns that type. Otherwise it returns nil.
-func (xl termlist) singleType() Type {
-	if nl := xl.norm(); len(nl) == 1 {
-		return nl[0].typ // if nl.isAll() then typ is nil, which is ok
-	}
-	return nil
-}
-
 // union returns the union xl ∪ yl.
 func (xl termlist) union(yl termlist) termlist {
 	return append(xl, yl...).norm()

src/cmd/compile/internal/types2/termlist_test.go

@@ -106,35 +106,6 @@ func TestTermlistNorm(t *testing.T) {
 	}
 }
 
-func TestTermlistSingleType(t *testing.T) {
-	// helper to deal with nil types
-	tstring := func(typ Type) string {
-		if typ == nil {
-			return "nil"
-		}
-		return typ.String()
-	}
-
-	for test, want := range map[string]string{
-		"∅":                 "nil",
-		"𝓤":                 "nil",
-		"int":               "int",
-		"myInt":             "myInt",
-		"~int":              "int",
-		"~int ∪ string":     "nil",
-		"~int ∪ myInt":      "int",
-		"∅ ∪ int":           "int",
-		"∅ ∪ ~int":          "int",
-		"∅ ∪ ~int ∪ string": "nil",
-	} {
-		xl := maketl(test)
-		got := tstring(xl.singleType())
-		if got != want {
-			t.Errorf("(%v).singleType() == %v; want %v", test, got, want)
-		}
-	}
-}
-
 func TestTermlistUnion(t *testing.T) {
 	for _, test := range []struct {
 		xl, yl, want string

src/cmd/compile/internal/types2/typeparam.go

@@ -138,16 +138,6 @@ func (t *TypeParam) iface() *Interface {
 	return ityp
 }
 
-// singleType returns the single type of the type parameter constraint; or nil.
-func (t *TypeParam) singleType() Type {
-	return t.iface().typeSet().singleType()
-}
-
-// hasTerms reports whether the type parameter constraint has specific type terms.
-func (t *TypeParam) hasTerms() bool {
-	return t.iface().typeSet().hasTerms()
-}
-
 // is calls f with the specific type terms of t's constraint and reports whether
 // all calls to f returned true. If there are no specific terms, is
 // returns the result of f(nil).

src/cmd/compile/internal/types2/typeset.go

@@ -103,9 +103,6 @@ func (s *_TypeSet) String() string {
 // hasTerms reports whether the type set has specific type terms.
 func (s *_TypeSet) hasTerms() bool { return !s.terms.isEmpty() && !s.terms.isAll() }
 
-// singleType returns the single type in s if there is exactly one; otherwise the result is nil.
-func (s *_TypeSet) singleType() Type { return s.terms.singleType() }
-
 // subsetOf reports whether s1 ⊆ s2.
 func (s1 *_TypeSet) subsetOf(s2 *_TypeSet) bool { return s1.terms.subsetOf(s2.terms) }
 

src/go/types/infer.go

@@ -590,15 +590,24 @@ func (check *Checker) inferB(posn positioner, tparams []*TypeParam, targs []Type
 	return
 }
 
+// adjCoreType returns the core type of tpar unless the
+// type parameter embeds a single, possibly named type,
+// in which case it returns that single type instead.
+// (The core type is always the underlying type of that
+// single type.)
 func adjCoreType(tpar *TypeParam) Type {
-	// If the type parameter embeds a single, possibly named
-	// type, use that one instead of the core type (which is
-	// always the underlying type of that single type).
-	if single := tpar.singleType(); single != nil {
-		if debug {
-			assert(under(single) == coreType(tpar))
+	var single *term
+	if tpar.is(func(t *term) bool {
+		if single == nil && t != nil {
+			single = t
+			return true
 		}
-		return single
+		return false // zero or more than one terms
+	}) {
+		if debug {
+			assert(under(single.typ) == coreType(tpar))
+		}
+		return single.typ
 	}
 	return coreType(tpar)
 }

src/go/types/termlist.go

@@ -92,15 +92,6 @@ func (xl termlist) norm() termlist {
 	return rl
 }
 
-// If the type set represented by xl is specified by a single (non-𝓤) term,
-// singleType returns that type. Otherwise it returns nil.
-func (xl termlist) singleType() Type {
-	if nl := xl.norm(); len(nl) == 1 {
-		return nl[0].typ // if nl.isAll() then typ is nil, which is ok
-	}
-	return nil
-}
-
 // union returns the union xl ∪ yl.
 func (xl termlist) union(yl termlist) termlist {
 	return append(xl, yl...).norm()

src/go/types/termlist_test.go

@@ -106,35 +106,6 @@ func TestTermlistNorm(t *testing.T) {
 	}
 }
 
-func TestTermlistSingleType(t *testing.T) {
-	// helper to deal with nil types
-	tstring := func(typ Type) string {
-		if typ == nil {
-			return "nil"
-		}
-		return typ.String()
-	}
-
-	for test, want := range map[string]string{
-		"∅":                 "nil",
-		"𝓤":                 "nil",
-		"int":               "int",
-		"myInt":             "myInt",
-		"~int":              "int",
-		"~int ∪ string":     "nil",
-		"~int ∪ myInt":      "int",
-		"∅ ∪ int":           "int",
-		"∅ ∪ ~int":          "int",
-		"∅ ∪ ~int ∪ string": "nil",
-	} {
-		xl := maketl(test)
-		got := tstring(xl.singleType())
-		if got != want {
-			t.Errorf("(%v).singleType() == %v; want %v", test, got, want)
-		}
-	}
-}
-
 func TestTermlistUnion(t *testing.T) {
 	for _, test := range []struct {
 		xl, yl, want string

src/go/types/typeparam.go

@@ -140,16 +140,6 @@ func (t *TypeParam) iface() *Interface {
 	return ityp
 }
 
-// singleType returns the single type of the type parameter constraint; or nil.
-func (t *TypeParam) singleType() Type {
-	return t.iface().typeSet().singleType()
-}
-
-// hasTerms reports whether the type parameter constraint has specific type terms.
-func (t *TypeParam) hasTerms() bool {
-	return t.iface().typeSet().hasTerms()
-}
-
 // is calls f with the specific type terms of t's constraint and reports whether
 // all calls to f returned true. If there are no specific terms, is
 // returns the result of f(nil).

src/go/types/typeset.go

@@ -101,9 +101,6 @@ func (s *_TypeSet) String() string {
 // hasTerms reports whether the type set has specific type terms.
 func (s *_TypeSet) hasTerms() bool { return !s.terms.isEmpty() && !s.terms.isAll() }
 
-// singleType returns the single type in s if there is exactly one; otherwise the result is nil.
-func (s *_TypeSet) singleType() Type { return s.terms.singleType() }
-
 // subsetOf reports whether s1 ⊆ s2.
 func (s1 *_TypeSet) subsetOf(s2 *_TypeSet) bool { return s1.terms.subsetOf(s2.terms) }