go/internal/gcimporter: write export data for go/types

Add an iexport.go (and corresponding iexport_test.go) file, which is an
adapted version of $GOROOT/src/cmd/compile/internal/gc/iexport.go. This
code writes exportdata for a *go/types.Package.

A majority of this code is directly copied from iexport.go, with a
change of types, while some of it had to be modified slightly.

Updates golang/go#28260

Change-Id: Ic7e8e99f0c6b886839280b410afffb037da8a79b
Reviewed-on: https://go-review.googlesource.com/c/156901
Run-TryBot: Rebecca Stambler <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>
Reviewed-by: Robert Griesemer <[email protected]>

Author: stamblerre

go/internal/gcimporter/bexport.go

@@ -127,10 +127,10 @@ func BExportData(fset *token.FileSet, pkg *types.Package) (b []byte, err error)
 	// --- generic export data ---
 
 	// populate type map with predeclared "known" types
-	for index, typ := range predeclared {
+	for index, typ := range predeclared() {
 		p.typIndex[typ] = index
 	}
-	if len(p.typIndex) != len(predeclared) {
+	if len(p.typIndex) != len(predeclared()) {
 		return nil, internalError("duplicate entries in type map?")
 	}
 

go/internal/gcimporter/bimport.go

@@ -126,7 +126,7 @@ func BImportData(fset *token.FileSet, imports map[string]*types.Package, data []
 	// --- generic export data ---
 
 	// populate typList with predeclared "known" types
-	p.typList = append(p.typList, predeclared...)
+	p.typList = append(p.typList, predeclared()...)
 
 	// read package data
 	pkg = p.pkg()
@@ -976,50 +976,58 @@ const (
 	aliasTag
 )
 
-var predeclared = []types.Type{
-	// basic types
-	types.Typ[types.Bool],
-	types.Typ[types.Int],
-	types.Typ[types.Int8],
-	types.Typ[types.Int16],
-	types.Typ[types.Int32],
-	types.Typ[types.Int64],
-	types.Typ[types.Uint],
-	types.Typ[types.Uint8],
-	types.Typ[types.Uint16],
-	types.Typ[types.Uint32],
-	types.Typ[types.Uint64],
-	types.Typ[types.Uintptr],
-	types.Typ[types.Float32],
-	types.Typ[types.Float64],
-	types.Typ[types.Complex64],
-	types.Typ[types.Complex128],
-	types.Typ[types.String],
-
-	// basic type aliases
-	types.Universe.Lookup("byte").Type(),
-	types.Universe.Lookup("rune").Type(),
-
-	// error
-	types.Universe.Lookup("error").Type(),
-
-	// untyped types
-	types.Typ[types.UntypedBool],
-	types.Typ[types.UntypedInt],
-	types.Typ[types.UntypedRune],
-	types.Typ[types.UntypedFloat],
-	types.Typ[types.UntypedComplex],
-	types.Typ[types.UntypedString],
-	types.Typ[types.UntypedNil],
-
-	// package unsafe
-	types.Typ[types.UnsafePointer],
-
-	// invalid type
-	types.Typ[types.Invalid], // only appears in packages with errors
-
-	// used internally by gc; never used by this package or in .a files
-	anyType{},
+var predecl []types.Type // initialized lazily
+
+func predeclared() []types.Type {
+	if predecl == nil {
+		// initialize lazily to be sure that all
+		// elements have been initialized before
+		predecl = []types.Type{ // basic types
+			types.Typ[types.Bool],
+			types.Typ[types.Int],
+			types.Typ[types.Int8],
+			types.Typ[types.Int16],
+			types.Typ[types.Int32],
+			types.Typ[types.Int64],
+			types.Typ[types.Uint],
+			types.Typ[types.Uint8],
+			types.Typ[types.Uint16],
+			types.Typ[types.Uint32],
+			types.Typ[types.Uint64],
+			types.Typ[types.Uintptr],
+			types.Typ[types.Float32],
+			types.Typ[types.Float64],
+			types.Typ[types.Complex64],
+			types.Typ[types.Complex128],
+			types.Typ[types.String],
+
+			// basic type aliases
+			types.Universe.Lookup("byte").Type(),
+			types.Universe.Lookup("rune").Type(),
+
+			// error
+			types.Universe.Lookup("error").Type(),
+
+			// untyped types
+			types.Typ[types.UntypedBool],
+			types.Typ[types.UntypedInt],
+			types.Typ[types.UntypedRune],
+			types.Typ[types.UntypedFloat],
+			types.Typ[types.UntypedComplex],
+			types.Typ[types.UntypedString],
+			types.Typ[types.UntypedNil],
+
+			// package unsafe
+			types.Typ[types.UnsafePointer],
+
+			// invalid type
+			types.Typ[types.Invalid], // only appears in packages with errors
+
+			// used internally by gc; never used by this package or in .a files
+			anyType{},
+		}
+	}
+	return predecl
 }
 
 type anyType struct{}