go/types: first steps towards collecting/recognizing type constraints

Change-Id: Ic0d70db24ad9fb76a5bb128df654c131f173247e

src/go/types/contracts.go

@@ -29,13 +29,13 @@ func (check *Checker) contractType(contr *Contract, e *ast.ContractType) {
 	// each type parameter's constraints are represented by an interface
 	ifaces := make(map[*TypeName]*Interface)
 
-	addMethod := func(tpar *TypeName, m *Func) {
+	ifaceFor := func(tpar *TypeName) *Interface {
 		iface := ifaces[tpar]
 		if iface == nil {
 			iface = new(Interface)
 			ifaces[tpar] = iface
 		}
-		iface.methods = append(iface.methods, m)
+		return iface
 	}
 
 	// collect constraints
@@ -75,6 +75,7 @@ func (check *Checker) contractType(contr *Contract, e *ast.ContractType) {
 			}
 
 			tpar := obj.(*TypeName)
+			iface := ifaceFor(tpar)
 			switch nmethods {
 			case 0:
 				// type constraints
@@ -92,7 +93,9 @@ func (check *Checker) contractType(contr *Contract, e *ast.ContractType) {
 						check.errorf(texpr.Pos(), "invalid type constraint %s (%s)", typ, why)
 						continue
 					}
-					// TODO(gri) add type
+					// add type
+					iface.types = append(iface.types, typ)
+
 				}
 
 			case 1:
@@ -115,7 +118,7 @@ func (check *Checker) contractType(contr *Contract, e *ast.ContractType) {
 				// add the method
 				mname := c.MNames[0]
 				m := NewFunc(mname.Pos(), check.pkg, mname.Name, sig)
-				addMethod(tpar, m)
+				iface.methods = append(iface.methods, m)
 
 			default:
 				// ignore (error was reported earlier)
@@ -243,6 +246,7 @@ func (check *Checker) satisfyContract(contr *Contract, targs []Type) bool {
 		iface := contr.ifaceAt(i)
 		// If iface is parameterized, we need to replace the type parameters
 		// with the respective type arguments.
+		// TODO(gri) fix this
 		if IsParameterized(iface) {
 			panic("unimplemented")
 		}
@@ -252,6 +256,24 @@ func (check *Checker) satisfyContract(contr *Contract, targs []Type) bool {
 			// check.dump("missing %s (%s, %s)", m, targ, iface)
 			return false
 		}
+		// targ's underlying type must also be one of the interface types listed, if any
+		if len(iface.types) > 0 {
+			utyp := targ.Underlying()
+			// TODO(gri) Cannot handle a type argument that is itself parameterized for now
+			switch utyp.(type) {
+			case *Interface, *Contract:
+				panic("unimplemented")
+			}
+			ok := false
+			for _, t := range iface.types {
+				// if we find one matching type, we're ok
+				if Identical(utyp, t) {
+					ok = true
+					break
+				}
+			}
+			return ok
+		}
 	}
 
 	return true

src/go/types/testdata/contracts.go2

@@ -101,3 +101,18 @@ var _ List /* ERROR not satisfied */ (int)
 type MyData string
 
 func (s MyData) String() string { return string(s) }
+
+// Contracts that mention types can only be satisfied by similar types.
+
+contract C3(T) {
+        T int16, int32, int, struct{x int}
+}
+
+type T2 (type _ C3) struct{}
+
+var _ T2 /* ERROR not satisfied */ (int8)
+var _ T2(int16)
+var _ T2(int32)
+var _ T2 /* ERROR not satisfied */ (int64)
+var _ T2(int)
+var _ T2(struct{x int})

src/go/types/type.go

@@ -249,6 +249,9 @@ type Interface struct {
 	embeddeds []Type  // ordered list of explicitly embedded types
 
 	allMethods []*Func // ordered list of methods declared with or embedded in this interface (TODO(gri): replace with mset)
+
+	// for contracts
+	types []Type // for contracts
 }
 
 // emptyInterface represents the empty (completed) interface