go/internal/gcimporter: add support for importing parameterized types

Port the necessary logic to go/internal/gcimporter from
cmd/compile/internal/importer/iimport.go to support type parameters.

This is a partial port of several compiler CLs: at least CL 319930,
CL 322609, CL 323029, CL 338192, CL 340251, and CL 340989. Because these
ports were not interleaved with the corresponding go/types API changes,
it is easier to just take the latest importer logic.

Notably, the equivalent of types2.AsTypeParam is not used. It should be
unnecessary.

Updates #48101

Change-Id: I938bd8debc3f6a68a3ad8d44c61ef9c5038be7e5
Reviewed-on: https://go-review.googlesource.com/c/go/+/347069
Trust: Robert Findley <rfindley@google.com>
Trust: Dan Scales <danscales@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Dan Scales <danscales@google.com>
Reviewed-by: Robert Griesemer <gri@golang.org>

src/go/internal/gcimporter/gcimporter_test.go

@@ -138,7 +138,6 @@ func TestVersionHandling(t *testing.T) {
 	skipSpecialPlatforms(t)
 
 	// This package only handles gc export data.
-	// Disable test until we put in the new export version.
 	if runtime.Compiler != "gc" {
 		t.Skipf("gc-built packages not available (compiler = %s)", runtime.Compiler)
 	}

src/go/internal/gcimporter/iimport.go

@@ -51,6 +51,11 @@ const (
 	iexportVersionCurrent = iexportVersionGenerics
 )
 
+type ident struct {
+	pkg  string
+	name string
+}
+
 const predeclReserved = 32
 
 type itag uint64
@@ -68,6 +73,7 @@ const (
 	interfaceType
 	typeParamType
 	instType
+	unionType
 )
 
 // iImportData imports a package from the serialized package data
@@ -122,6 +128,9 @@ func iImportData(fset *token.FileSet, imports map[string]*types.Package, dataRea
 		declData: declData,
 		pkgIndex: make(map[*types.Package]map[string]uint64),
 		typCache: make(map[uint64]types.Type),
+		// Separate map for typeparams, keyed by their package and unique
+		// name (name with subscript).
+		tparamIndex: make(map[ident]types.Type),
 
 		fake: fakeFileSet{
 			fset:  fset,
@@ -197,9 +206,10 @@ type iimporter struct {
 	stringCache map[uint64]string
 	pkgCache    map[uint64]*types.Package
 
-	declData []byte
-	pkgIndex map[*types.Package]map[string]uint64
-	typCache map[uint64]types.Type
+	declData    []byte
+	pkgIndex    map[*types.Package]map[string]uint64
+	typCache    map[uint64]types.Type
+	tparamIndex map[ident]types.Type
 
 	fake          fakeFileSet
 	interfaceList []*types.Interface
@@ -289,19 +299,28 @@ func (r *importReader) obj(name string) {
 
 		r.declare(types.NewConst(pos, r.currPkg, name, typ, val))
 
-	case 'F':
+	case 'F', 'G':
+		var tparams []*types.TypeParam
+		if tag == 'G' {
+			tparams = r.tparamList()
+		}
 		sig := r.signature(nil)
-
+		sig.SetTParams(tparams)
 		r.declare(types.NewFunc(pos, r.currPkg, name, sig))
 
-	case 'G':
-		errorf("unexpected parameterized function/method")
-
-	case 'T':
+	case 'T', 'U':
+		var tparams []*types.TypeParam
+		if tag == 'U' {
+			tparams = r.tparamList()
+		}
 		// Types can be recursive. We need to setup a stub
 		// declaration before recursing.
 		obj := types.NewTypeName(pos, r.currPkg, name, nil)
 		named := types.NewNamed(obj, nil, nil)
+		// TODO(rfindley): guarding on tag == 'U' should not be necessary here.
+		if tag == 'U' {
+			named.SetTParams(tparams)
+		}
 		r.declare(obj)
 
 		underlying := r.p.typAt(r.uint64(), named).Underlying()
@@ -314,12 +333,45 @@ func (r *importReader) obj(name string) {
 				recv := r.param()
 				msig := r.signature(recv)
 
+				// If the receiver has any targs, set those as the
+				// rparams of the method (since those are the
+				// typeparams being used in the method sig/body).
+				targs := baseType(msig.Recv().Type()).TArgs()
+				if targs.Len() > 0 {
+					rparams := make([]*types.TypeParam, targs.Len())
+					for i := range rparams {
+						rparams[i], _ = targs.At(i).(*types.TypeParam)
+					}
+					msig.SetRParams(rparams)
+				}
+
 				named.AddMethod(types.NewFunc(mpos, r.currPkg, mname, msig))
 			}
 		}
 
-	case 'U':
-		errorf("unexpected parameterized type")
+	case 'P':
+		// We need to "declare" a typeparam in order to have a name that
+		// can be referenced recursively (if needed) in the type param's
+		// bound.
+		if r.p.exportVersion < iexportVersionGenerics {
+			errorf("unexpected type param type")
+		}
+		name0, sub := parseSubscript(name)
+		tn := types.NewTypeName(pos, r.currPkg, name0, nil)
+		t := (*types.Checker)(nil).NewTypeParam(tn, nil)
+		if sub == 0 {
+			errorf("missing subscript")
+		}
+
+		// TODO(rfindley): can we use a different, stable ID?
+		// t.SetId(sub)
+
+		// To handle recursive references to the typeparam within its
+		// bound, save the partial type in tparamIndex before reading the bounds.
+		id := ident{r.currPkg.Name(), name}
+		r.p.tparamIndex[id] = t
+
+		t.SetConstraint(r.typ())
 
 	case 'V':
 		typ := r.typ()
@@ -575,12 +627,47 @@ func (r *importReader) doType(base *types.Named) types.Type {
 		return typ
 
 	case typeParamType:
-		errorf("do not handle type param types yet")
-		return nil
+		if r.p.exportVersion < iexportVersionGenerics {
+			errorf("unexpected type param type")
+		}
+		pkg, name := r.qualifiedIdent()
+		id := ident{pkg.Name(), name}
+		if t, ok := r.p.tparamIndex[id]; ok {
+			// We're already in the process of importing this typeparam.
+			return t
+		}
+		// Otherwise, import the definition of the typeparam now.
+		r.p.doDecl(pkg, name)
+		return r.p.tparamIndex[id]
 
 	case instType:
-		errorf("do not handle instantiated types yet")
-		return nil
+		if r.p.exportVersion < iexportVersionGenerics {
+			errorf("unexpected instantiation type")
+		}
+		// pos does not matter for instances: they are positioned on the original
+		// type.
+		_ = r.pos()
+		len := r.uint64()
+		targs := make([]types.Type, len)
+		for i := range targs {
+			targs[i] = r.typ()
+		}
+		baseType := r.typ()
+		// The imported instantiated type doesn't include any methods, so
+		// we must always use the methods of the base (orig) type.
+		// TODO provide a non-nil *Checker
+		t, _ := types.Instantiate(nil, baseType, targs, false)
+		return t
+
+	case unionType:
+		if r.p.exportVersion < iexportVersionGenerics {
+			errorf("unexpected instantiation type")
+		}
+		terms := make([]*types.Term, r.uint64())
+		for i := range terms {
+			terms[i] = types.NewTerm(r.bool(), r.typ())
+		}
+		return types.NewUnion(terms)
 	}
 }
 
@@ -595,6 +682,18 @@ func (r *importReader) signature(recv *types.Var) *types.Signature {
 	return types.NewSignature(recv, params, results, variadic)
 }
 
+func (r *importReader) tparamList() []*types.TypeParam {
+	n := r.uint64()
+	if n == 0 {
+		return nil
+	}
+	xs := make([]*types.TypeParam, n)
+	for i := range xs {
+		xs[i], _ = r.typ().(*types.TypeParam)
+	}
+	return xs
+}
+
 func (r *importReader) paramList() *types.Tuple {
 	xs := make([]*types.Var, r.uint64())
 	for i := range xs {
@@ -637,3 +736,33 @@ func (r *importReader) byte() byte {
 	}
 	return x
 }
+
+func baseType(typ types.Type) *types.Named {
+	// pointer receivers are never types.Named types
+	if p, _ := typ.(*types.Pointer); p != nil {
+		typ = p.Elem()
+	}
+	// receiver base types are always (possibly generic) types.Named types
+	n, _ := typ.(*types.Named)
+	return n
+}
+
+func parseSubscript(name string) (string, uint64) {
+	// Extract the subscript value from the type param name. We export
+	// and import the subscript value, so that all type params have
+	// unique names.
+	sub := uint64(0)
+	startsub := -1
+	for i, r := range name {
+		if '₀' <= r && r < '₀'+10 {
+			if startsub == -1 {
+				startsub = i
+			}
+			sub = sub*10 + uint64(r-'₀')
+		}
+	}
+	if startsub >= 0 {
+		name = name[:startsub]
+	}
+	return name, sub
+}