[dev.typeparams] cmd/compile/internal/types2: implement package height

This CL extends types2 with package height information, styled after
the way it works already in cmd/compile:

- A new NewPackageHeight entry point for constructing packages with
  explicit height information, and a corresponding Height accessor
  method.

- The types2 importer is updated to provide package height for
  imported packages.

- The types2 type checker sets height based on imported packages.

- Adds an assertion to irgen to verify that types1 and types2
  calculated the same height for the source package.

- Func.less's ordering incorporates package height to match
  types.Sym.less and is generalized to object.less.

- sortTypes (used for sorting embedded types) now sorts defined types
  using object.less as well.

Change-Id: Id4dbbb627aef405cc7438d611cbdd5a5bd97fc96
Reviewed-on: https://go-review.googlesource.com/c/go/+/321231
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Trust: Matthew Dempsky <mdempsky@google.com>
Trust: Robert Griesemer <gri@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

src/cmd/compile/internal/importer/iimport.go

@@ -118,17 +118,22 @@ func iImportData(imports map[string]*types2.Package, data []byte, path string) (
 		pkgPathOff := r.uint64()
 		pkgPath := p.stringAt(pkgPathOff)
 		pkgName := p.stringAt(r.uint64())
-		_ = r.uint64() // package height; unused by go/types
+		pkgHeight := int(r.uint64())
 
 		if pkgPath == "" {
 			pkgPath = path
 		}
 		pkg := imports[pkgPath]
 		if pkg == nil {
-			pkg = types2.NewPackage(pkgPath, pkgName)
+			pkg = types2.NewPackageHeight(pkgPath, pkgName, pkgHeight)
 			imports[pkgPath] = pkg
-		} else if pkg.Name() != pkgName {
-			errorf("conflicting names %s and %s for package %q", pkg.Name(), pkgName, path)
+		} else {
+			if pkg.Name() != pkgName {
+				errorf("conflicting names %s and %s for package %q", pkg.Name(), pkgName, path)
+			}
+			if pkg.Height() != pkgHeight {
+				errorf("conflicting heights %v and %v for package %q", pkg.Height(), pkgHeight, path)
+			}
 		}
 
 		p.pkgCache[pkgPathOff] = pkg

src/cmd/compile/internal/noder/irgen.go

@@ -132,6 +132,7 @@ Outer:
 			}
 		}
 	}
+	assert(myheight == g.self.Height())
 	types.LocalPkg.Height = myheight
 
 	// 2. Process all package-block type declarations. As with imports,

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

@@ -186,6 +186,45 @@ func (obj *object) sameId(pkg *Package, name string) bool {
 	return pkg.path == obj.pkg.path
 }
 
+// less reports whether object a is ordered before object b.
+//
+// Objects are ordered nil before non-nil, exported before
+// non-exported, then by name, and finally (for non-exported
+// functions) by package height and path.
+func (a *object) less(b *object) bool {
+	if a == b {
+		return false
+	}
+
+	// Nil before non-nil.
+	if a == nil {
+		return true
+	}
+	if b == nil {
+		return false
+	}
+
+	// Exported functions before non-exported.
+	ea := isExported(a.name)
+	eb := isExported(b.name)
+	if ea != eb {
+		return ea
+	}
+
+	// Order by name and then (for non-exported names) by package.
+	if a.name != b.name {
+		return a.name < b.name
+	}
+	if !ea {
+		if a.pkg.height != b.pkg.height {
+			return a.pkg.height < b.pkg.height
+		}
+		return a.pkg.path < b.pkg.path
+	}
+
+	return false
+}
+
 // A PkgName represents an imported Go package.
 // PkgNames don't have a type.
 type PkgName struct {
@@ -329,36 +368,6 @@ func (obj *Func) FullName() string {
 // Scope returns the scope of the function's body block.
 func (obj *Func) Scope() *Scope { return obj.typ.(*Signature).scope }
 
-// Less reports whether function a is ordered before function b.
-//
-// Functions are ordered exported before non-exported, then by name,
-// and finally (for non-exported functions) by package path.
-//
-// TODO(gri) The compiler also sorts by package height before package
-//           path for non-exported names.
-func (a *Func) less(b *Func) bool {
-	if a == b {
-		return false
-	}
-
-	// Exported functions before non-exported.
-	ea := isExported(a.name)
-	eb := isExported(b.name)
-	if ea != eb {
-		return ea
-	}
-
-	// Order by name and then (for non-exported names) by package.
-	if a.name != b.name {
-		return a.name < b.name
-	}
-	if !ea {
-		return a.pkg.path < b.pkg.path
-	}
-
-	return false
-}
-
 func (*Func) isDependency() {} // a function may be a dependency of an initialization expression
 
 // A Label represents a declared label.

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

@@ -13,8 +13,9 @@ type Package struct {
 	path     string
 	name     string
 	scope    *Scope
-	complete bool
 	imports  []*Package
+	height   int
+	complete bool
 	fake     bool // scope lookup errors are silently dropped if package is fake (internal use only)
 	cgo      bool // uses of this package will be rewritten into uses of declarations from _cgo_gotypes.go
 }
@@ -22,8 +23,14 @@ type Package struct {
 // NewPackage returns a new Package for the given package path and name.
 // The package is not complete and contains no explicit imports.
 func NewPackage(path, name string) *Package {
+	return NewPackageHeight(path, name, 0)
+}
+
+// NewPackageHeight is like NewPackage, but allows specifying the
+// package's height.
+func NewPackageHeight(path, name string, height int) *Package {
 	scope := NewScope(Universe, nopos, nopos, fmt.Sprintf("package %q", path))
-	return &Package{path: path, name: name, scope: scope}
+	return &Package{path: path, name: name, scope: scope, height: height}
 }
 
 // Path returns the package path.
@@ -32,6 +39,9 @@ func (pkg *Package) Path() string { return pkg.path }
 // Name returns the package name.
 func (pkg *Package) Name() string { return pkg.name }
 
+// Height returns the package height.
+func (pkg *Package) Height() int { return pkg.height }
+
 // SetName sets the package name.
 func (pkg *Package) SetName(name string) { pkg.name = name }
 

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

@@ -196,6 +196,7 @@ func (check *Checker) importPackage(pos syntax.Pos, path, dir string) *Package {
 // methods with receiver base type names.
 func (check *Checker) collectObjects() {
 	pkg := check.pkg
+	pkg.height = 0
 
 	// pkgImports is the set of packages already imported by any package file seen
 	// so far. Used to avoid duplicate entries in pkg.imports. Allocate and populate
@@ -253,6 +254,15 @@ func (check *Checker) collectObjects() {
 					continue
 				}
 
+				if imp == Unsafe {
+					// typecheck ignores imports of package unsafe for
+					// calculating height.
+					// TODO(mdempsky): Revisit this. This seems fine, but I
+					// don't remember explicitly considering this case.
+				} else if h := imp.height + 1; h > pkg.height {
+					pkg.height = h
+				}
+
 				// local name overrides imported package name
 				name := imp.name
 				if s.LocalPkgName != nil {

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

@@ -1055,14 +1055,14 @@ func sortTypes(list []Type) {
 type byUniqueTypeName []Type
 
 func (a byUniqueTypeName) Len() int           { return len(a) }
-func (a byUniqueTypeName) Less(i, j int) bool { return sortName(a[i]) < sortName(a[j]) }
+func (a byUniqueTypeName) Less(i, j int) bool { return sortObj(a[i]).less(sortObj(a[j])) }
 func (a byUniqueTypeName) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }
 
-func sortName(t Type) string {
+func sortObj(t Type) *object {
 	if named := asNamed(t); named != nil {
-		return named.obj.Id()
+		return &named.obj.object
 	}
-	return ""
+	return nil
 }
 
 func sortMethods(list []*Func) {
@@ -1082,7 +1082,7 @@ func assertSortedMethods(list []*Func) {
 type byUniqueMethodName []*Func
 
 func (a byUniqueMethodName) Len() int           { return len(a) }
-func (a byUniqueMethodName) Less(i, j int) bool { return a[i].less(a[j]) }
+func (a byUniqueMethodName) Less(i, j int) bool { return a[i].less(&a[j].object) }
 func (a byUniqueMethodName) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }
 
 func (check *Checker) tag(t *syntax.BasicLit) string {