Source file src/go/types/resolver.go

Documentation: go/types

		 1  // Copyright 2013 The Go Authors. All rights reserved.
		 2  // Use of this source code is governed by a BSD-style
		 3  // license that can be found in the LICENSE file.
		 4  
		 5  package types
		 6  
		 7  import (
		 8  	"fmt"
		 9  	"go/ast"
		10  	"go/constant"
		11  	"go/internal/typeparams"
		12  	"go/token"
		13  	"sort"
		14  	"strconv"
		15  	"strings"
		16  	"unicode"
		17  )
		18  
		19  // A declInfo describes a package-level const, type, var, or func declaration.
		20  type declInfo struct {
		21  	file			*Scope				// scope of file containing this declaration
		22  	lhs			 []*Var				// lhs of n:1 variable declarations, or nil
		23  	vtyp			ast.Expr			// type, or nil (for const and var declarations only)
		24  	init			ast.Expr			// init/orig expression, or nil (for const and var declarations only)
		25  	inherited bool					// if set, the init expression is inherited from a previous constant declaration
		26  	tdecl		 *ast.TypeSpec // type declaration, or nil
		27  	fdecl		 *ast.FuncDecl // func declaration, or nil
		28  
		29  	// The deps field tracks initialization expression dependencies.
		30  	deps map[Object]bool // lazily initialized
		31  }
		32  
		33  // hasInitializer reports whether the declared object has an initialization
		34  // expression or function body.
		35  func (d *declInfo) hasInitializer() bool {
		36  	return d.init != nil || d.fdecl != nil && d.fdecl.Body != nil
		37  }
		38  
		39  // addDep adds obj to the set of objects d's init expression depends on.
		40  func (d *declInfo) addDep(obj Object) {
		41  	m := d.deps
		42  	if m == nil {
		43  		m = make(map[Object]bool)
		44  		d.deps = m
		45  	}
		46  	m[obj] = true
		47  }
		48  
		49  // arityMatch checks that the lhs and rhs of a const or var decl
		50  // have the appropriate number of names and init exprs. For const
		51  // decls, init is the value spec providing the init exprs; for
		52  // var decls, init is nil (the init exprs are in s in this case).
		53  func (check *Checker) arityMatch(s, init *ast.ValueSpec) {
		54  	l := len(s.Names)
		55  	r := len(s.Values)
		56  	if init != nil {
		57  		r = len(init.Values)
		58  	}
		59  
		60  	const code = _WrongAssignCount
		61  	switch {
		62  	case init == nil && r == 0:
		63  		// var decl w/o init expr
		64  		if s.Type == nil {
		65  			check.errorf(s, code, "missing type or init expr")
		66  		}
		67  	case l < r:
		68  		if l < len(s.Values) {
		69  			// init exprs from s
		70  			n := s.Values[l]
		71  			check.errorf(n, code, "extra init expr %s", n)
		72  			// TODO(gri) avoid declared but not used error here
		73  		} else {
		74  			// init exprs "inherited"
		75  			check.errorf(s, code, "extra init expr at %s", check.fset.Position(init.Pos()))
		76  			// TODO(gri) avoid declared but not used error here
		77  		}
		78  	case l > r && (init != nil || r != 1):
		79  		n := s.Names[r]
		80  		check.errorf(n, code, "missing init expr for %s", n)
		81  	}
		82  }
		83  
		84  func validatedImportPath(path string) (string, error) {
		85  	s, err := strconv.Unquote(path)
		86  	if err != nil {
		87  		return "", err
		88  	}
		89  	if s == "" {
		90  		return "", fmt.Errorf("empty string")
		91  	}
		92  	const illegalChars = `!"#$%&'()*,:;<=>?[\]^{|}` + "`\uFFFD"
		93  	for _, r := range s {
		94  		if !unicode.IsGraphic(r) || unicode.IsSpace(r) || strings.ContainsRune(illegalChars, r) {
		95  			return s, fmt.Errorf("invalid character %#U", r)
		96  		}
		97  	}
		98  	return s, nil
		99  }
	 100  
	 101  // declarePkgObj declares obj in the package scope, records its ident -> obj mapping,
	 102  // and updates check.objMap. The object must not be a function or method.
	 103  func (check *Checker) declarePkgObj(ident *ast.Ident, obj Object, d *declInfo) {
	 104  	assert(ident.Name == obj.Name())
	 105  
	 106  	// spec: "A package-scope or file-scope identifier with name init
	 107  	// may only be declared to be a function with this (func()) signature."
	 108  	if ident.Name == "init" {
	 109  		check.errorf(ident, _InvalidInitDecl, "cannot declare init - must be func")
	 110  		return
	 111  	}
	 112  
	 113  	// spec: "The main package must have package name main and declare
	 114  	// a function main that takes no arguments and returns no value."
	 115  	if ident.Name == "main" && check.pkg.name == "main" {
	 116  		check.errorf(ident, _InvalidMainDecl, "cannot declare main - must be func")
	 117  		return
	 118  	}
	 119  
	 120  	check.declare(check.pkg.scope, ident, obj, token.NoPos)
	 121  	check.objMap[obj] = d
	 122  	obj.setOrder(uint32(len(check.objMap)))
	 123  }
	 124  
	 125  // filename returns a filename suitable for debugging output.
	 126  func (check *Checker) filename(fileNo int) string {
	 127  	file := check.files[fileNo]
	 128  	if pos := file.Pos(); pos.IsValid() {
	 129  		return check.fset.File(pos).Name()
	 130  	}
	 131  	return fmt.Sprintf("file[%d]", fileNo)
	 132  }
	 133  
	 134  func (check *Checker) importPackage(at positioner, path, dir string) *Package {
	 135  	// If we already have a package for the given (path, dir)
	 136  	// pair, use it instead of doing a full import.
	 137  	// Checker.impMap only caches packages that are marked Complete
	 138  	// or fake (dummy packages for failed imports). Incomplete but
	 139  	// non-fake packages do require an import to complete them.
	 140  	key := importKey{path, dir}
	 141  	imp := check.impMap[key]
	 142  	if imp != nil {
	 143  		return imp
	 144  	}
	 145  
	 146  	// no package yet => import it
	 147  	if path == "C" && (check.conf.FakeImportC || check.conf.go115UsesCgo) {
	 148  		imp = NewPackage("C", "C")
	 149  		imp.fake = true // package scope is not populated
	 150  		imp.cgo = check.conf.go115UsesCgo
	 151  	} else {
	 152  		// ordinary import
	 153  		var err error
	 154  		if importer := check.conf.Importer; importer == nil {
	 155  			err = fmt.Errorf("Config.Importer not installed")
	 156  		} else if importerFrom, ok := importer.(ImporterFrom); ok {
	 157  			imp, err = importerFrom.ImportFrom(path, dir, 0)
	 158  			if imp == nil && err == nil {
	 159  				err = fmt.Errorf("Config.Importer.ImportFrom(%s, %s, 0) returned nil but no error", path, dir)
	 160  			}
	 161  		} else {
	 162  			imp, err = importer.Import(path)
	 163  			if imp == nil && err == nil {
	 164  				err = fmt.Errorf("Config.Importer.Import(%s) returned nil but no error", path)
	 165  			}
	 166  		}
	 167  		// make sure we have a valid package name
	 168  		// (errors here can only happen through manipulation of packages after creation)
	 169  		if err == nil && imp != nil && (imp.name == "_" || imp.name == "") {
	 170  			err = fmt.Errorf("invalid package name: %q", imp.name)
	 171  			imp = nil // create fake package below
	 172  		}
	 173  		if err != nil {
	 174  			check.errorf(at, _BrokenImport, "could not import %s (%s)", path, err)
	 175  			if imp == nil {
	 176  				// create a new fake package
	 177  				// come up with a sensible package name (heuristic)
	 178  				name := path
	 179  				if i := len(name); i > 0 && name[i-1] == '/' {
	 180  					name = name[:i-1]
	 181  				}
	 182  				if i := strings.LastIndex(name, "/"); i >= 0 {
	 183  					name = name[i+1:]
	 184  				}
	 185  				imp = NewPackage(path, name)
	 186  			}
	 187  			// continue to use the package as best as we can
	 188  			imp.fake = true // avoid follow-up lookup failures
	 189  		}
	 190  	}
	 191  
	 192  	// package should be complete or marked fake, but be cautious
	 193  	if imp.complete || imp.fake {
	 194  		check.impMap[key] = imp
	 195  		// Once we've formatted an error message once, keep the pkgPathMap
	 196  		// up-to-date on subsequent imports.
	 197  		if check.pkgPathMap != nil {
	 198  			check.markImports(imp)
	 199  		}
	 200  		return imp
	 201  	}
	 202  
	 203  	// something went wrong (importer may have returned incomplete package without error)
	 204  	return nil
	 205  }
	 206  
	 207  // collectObjects collects all file and package objects and inserts them
	 208  // into their respective scopes. It also performs imports and associates
	 209  // methods with receiver base type names.
	 210  func (check *Checker) collectObjects() {
	 211  	pkg := check.pkg
	 212  
	 213  	// pkgImports is the set of packages already imported by any package file seen
	 214  	// so far. Used to avoid duplicate entries in pkg.imports. Allocate and populate
	 215  	// it (pkg.imports may not be empty if we are checking test files incrementally).
	 216  	// Note that pkgImports is keyed by package (and thus package path), not by an
	 217  	// importKey value. Two different importKey values may map to the same package
	 218  	// which is why we cannot use the check.impMap here.
	 219  	var pkgImports = make(map[*Package]bool)
	 220  	for _, imp := range pkg.imports {
	 221  		pkgImports[imp] = true
	 222  	}
	 223  
	 224  	type methodInfo struct {
	 225  		obj	*Func			// method
	 226  		ptr	bool			 // true if pointer receiver
	 227  		recv *ast.Ident // receiver type name
	 228  	}
	 229  	var methods []methodInfo // collected methods with valid receivers and non-blank _ names
	 230  	var fileScopes []*Scope
	 231  	for fileNo, file := range check.files {
	 232  		// The package identifier denotes the current package,
	 233  		// but there is no corresponding package object.
	 234  		check.recordDef(file.Name, nil)
	 235  
	 236  		// Use the actual source file extent rather than *ast.File extent since the
	 237  		// latter doesn't include comments which appear at the start or end of the file.
	 238  		// Be conservative and use the *ast.File extent if we don't have a *token.File.
	 239  		pos, end := file.Pos(), file.End()
	 240  		if f := check.fset.File(file.Pos()); f != nil {
	 241  			pos, end = token.Pos(f.Base()), token.Pos(f.Base()+f.Size())
	 242  		}
	 243  		fileScope := NewScope(check.pkg.scope, pos, end, check.filename(fileNo))
	 244  		fileScopes = append(fileScopes, fileScope)
	 245  		check.recordScope(file, fileScope)
	 246  
	 247  		// determine file directory, necessary to resolve imports
	 248  		// FileName may be "" (typically for tests) in which case
	 249  		// we get "." as the directory which is what we would want.
	 250  		fileDir := dir(check.fset.Position(file.Name.Pos()).Filename)
	 251  
	 252  		check.walkDecls(file.Decls, func(d decl) {
	 253  			switch d := d.(type) {
	 254  			case importDecl:
	 255  				// import package
	 256  				path, err := validatedImportPath(d.spec.Path.Value)
	 257  				if err != nil {
	 258  					check.errorf(d.spec.Path, _BadImportPath, "invalid import path (%s)", err)
	 259  					return
	 260  				}
	 261  
	 262  				imp := check.importPackage(d.spec.Path, path, fileDir)
	 263  				if imp == nil {
	 264  					return
	 265  				}
	 266  
	 267  				// local name overrides imported package name
	 268  				name := imp.name
	 269  				if d.spec.Name != nil {
	 270  					name = d.spec.Name.Name
	 271  					if path == "C" {
	 272  						// match cmd/compile (not prescribed by spec)
	 273  						check.errorf(d.spec.Name, _ImportCRenamed, `cannot rename import "C"`)
	 274  						return
	 275  					}
	 276  				}
	 277  
	 278  				if name == "init" {
	 279  					check.errorf(d.spec, _InvalidInitDecl, "cannot import package as init - init must be a func")
	 280  					return
	 281  				}
	 282  
	 283  				// add package to list of explicit imports
	 284  				// (this functionality is provided as a convenience
	 285  				// for clients; it is not needed for type-checking)
	 286  				if !pkgImports[imp] {
	 287  					pkgImports[imp] = true
	 288  					pkg.imports = append(pkg.imports, imp)
	 289  				}
	 290  
	 291  				pkgName := NewPkgName(d.spec.Pos(), pkg, name, imp)
	 292  				if d.spec.Name != nil {
	 293  					// in a dot-import, the dot represents the package
	 294  					check.recordDef(d.spec.Name, pkgName)
	 295  				} else {
	 296  					check.recordImplicit(d.spec, pkgName)
	 297  				}
	 298  
	 299  				if path == "C" {
	 300  					// match cmd/compile (not prescribed by spec)
	 301  					pkgName.used = true
	 302  				}
	 303  
	 304  				// add import to file scope
	 305  				check.imports = append(check.imports, pkgName)
	 306  				if name == "." {
	 307  					// dot-import
	 308  					if check.dotImportMap == nil {
	 309  						check.dotImportMap = make(map[dotImportKey]*PkgName)
	 310  					}
	 311  					// merge imported scope with file scope
	 312  					for _, obj := range imp.scope.elems {
	 313  						// A package scope may contain non-exported objects,
	 314  						// do not import them!
	 315  						if obj.Exported() {
	 316  							// declare dot-imported object
	 317  							// (Do not use check.declare because it modifies the object
	 318  							// via Object.setScopePos, which leads to a race condition;
	 319  							// the object may be imported into more than one file scope
	 320  							// concurrently. See issue #32154.)
	 321  							if alt := fileScope.Insert(obj); alt != nil {
	 322  								check.errorf(d.spec.Name, _DuplicateDecl, "%s redeclared in this block", obj.Name())
	 323  								check.reportAltDecl(alt)
	 324  							} else {
	 325  								check.dotImportMap[dotImportKey{fileScope, obj}] = pkgName
	 326  							}
	 327  						}
	 328  					}
	 329  				} else {
	 330  					// declare imported package object in file scope
	 331  					// (no need to provide s.Name since we called check.recordDef earlier)
	 332  					check.declare(fileScope, nil, pkgName, token.NoPos)
	 333  				}
	 334  			case constDecl:
	 335  				// declare all constants
	 336  				for i, name := range d.spec.Names {
	 337  					obj := NewConst(name.Pos(), pkg, name.Name, nil, constant.MakeInt64(int64(d.iota)))
	 338  
	 339  					var init ast.Expr
	 340  					if i < len(d.init) {
	 341  						init = d.init[i]
	 342  					}
	 343  
	 344  					d := &declInfo{file: fileScope, vtyp: d.typ, init: init, inherited: d.inherited}
	 345  					check.declarePkgObj(name, obj, d)
	 346  				}
	 347  
	 348  			case varDecl:
	 349  				lhs := make([]*Var, len(d.spec.Names))
	 350  				// If there's exactly one rhs initializer, use
	 351  				// the same declInfo d1 for all lhs variables
	 352  				// so that each lhs variable depends on the same
	 353  				// rhs initializer (n:1 var declaration).
	 354  				var d1 *declInfo
	 355  				if len(d.spec.Values) == 1 {
	 356  					// The lhs elements are only set up after the for loop below,
	 357  					// but that's ok because declareVar only collects the declInfo
	 358  					// for a later phase.
	 359  					d1 = &declInfo{file: fileScope, lhs: lhs, vtyp: d.spec.Type, init: d.spec.Values[0]}
	 360  				}
	 361  
	 362  				// declare all variables
	 363  				for i, name := range d.spec.Names {
	 364  					obj := NewVar(name.Pos(), pkg, name.Name, nil)
	 365  					lhs[i] = obj
	 366  
	 367  					di := d1
	 368  					if di == nil {
	 369  						// individual assignments
	 370  						var init ast.Expr
	 371  						if i < len(d.spec.Values) {
	 372  							init = d.spec.Values[i]
	 373  						}
	 374  						di = &declInfo{file: fileScope, vtyp: d.spec.Type, init: init}
	 375  					}
	 376  
	 377  					check.declarePkgObj(name, obj, di)
	 378  				}
	 379  			case typeDecl:
	 380  				obj := NewTypeName(d.spec.Name.Pos(), pkg, d.spec.Name.Name, nil)
	 381  				check.declarePkgObj(d.spec.Name, obj, &declInfo{file: fileScope, tdecl: d.spec})
	 382  			case funcDecl:
	 383  				info := &declInfo{file: fileScope, fdecl: d.decl}
	 384  				name := d.decl.Name.Name
	 385  				obj := NewFunc(d.decl.Name.Pos(), pkg, name, nil)
	 386  				if d.decl.Recv.NumFields() == 0 {
	 387  					// regular function
	 388  					if d.decl.Recv != nil {
	 389  						check.error(d.decl.Recv, _BadRecv, "method is missing receiver")
	 390  						// treat as function
	 391  					}
	 392  					if name == "init" || (name == "main" && check.pkg.name == "main") {
	 393  						code := _InvalidInitDecl
	 394  						if name == "main" {
	 395  							code = _InvalidMainDecl
	 396  						}
	 397  						if tparams := typeparams.Get(d.decl.Type); tparams != nil {
	 398  							check.softErrorf(tparams, code, "func %s must have no type parameters", name)
	 399  						}
	 400  						if t := d.decl.Type; t.Params.NumFields() != 0 || t.Results != nil {
	 401  							// TODO(rFindley) Should this be a hard error?
	 402  							check.softErrorf(d.decl, code, "func %s must have no arguments and no return values", name)
	 403  						}
	 404  					}
	 405  					if name == "init" {
	 406  						// don't declare init functions in the package scope - they are invisible
	 407  						obj.parent = pkg.scope
	 408  						check.recordDef(d.decl.Name, obj)
	 409  						// init functions must have a body
	 410  						if d.decl.Body == nil {
	 411  							// TODO(gri) make this error message consistent with the others above
	 412  							check.softErrorf(obj, _MissingInitBody, "missing function body")
	 413  						}
	 414  					} else {
	 415  						check.declare(pkg.scope, d.decl.Name, obj, token.NoPos)
	 416  					}
	 417  				} else {
	 418  					// method
	 419  
	 420  					// TODO(rFindley) earlier versions of this code checked that methods
	 421  					//								have no type parameters, but this is checked later
	 422  					//								when type checking the function type. Confirm that
	 423  					//								we don't need to check tparams here.
	 424  
	 425  					ptr, recv, _ := check.unpackRecv(d.decl.Recv.List[0].Type, false)
	 426  					// (Methods with invalid receiver cannot be associated to a type, and
	 427  					// methods with blank _ names are never found; no need to collect any
	 428  					// of them. They will still be type-checked with all the other functions.)
	 429  					if recv != nil && name != "_" {
	 430  						methods = append(methods, methodInfo{obj, ptr, recv})
	 431  					}
	 432  					check.recordDef(d.decl.Name, obj)
	 433  				}
	 434  				// Methods are not package-level objects but we still track them in the
	 435  				// object map so that we can handle them like regular functions (if the
	 436  				// receiver is invalid); also we need their fdecl info when associating
	 437  				// them with their receiver base type, below.
	 438  				check.objMap[obj] = info
	 439  				obj.setOrder(uint32(len(check.objMap)))
	 440  			}
	 441  		})
	 442  	}
	 443  
	 444  	// verify that objects in package and file scopes have different names
	 445  	for _, scope := range fileScopes {
	 446  		for _, obj := range scope.elems {
	 447  			if alt := pkg.scope.Lookup(obj.Name()); alt != nil {
	 448  				if pkg, ok := obj.(*PkgName); ok {
	 449  					check.errorf(alt, _DuplicateDecl, "%s already declared through import of %s", alt.Name(), pkg.Imported())
	 450  					check.reportAltDecl(pkg)
	 451  				} else {
	 452  					check.errorf(alt, _DuplicateDecl, "%s already declared through dot-import of %s", alt.Name(), obj.Pkg())
	 453  					// TODO(gri) dot-imported objects don't have a position; reportAltDecl won't print anything
	 454  					check.reportAltDecl(obj)
	 455  				}
	 456  			}
	 457  		}
	 458  	}
	 459  
	 460  	// Now that we have all package scope objects and all methods,
	 461  	// associate methods with receiver base type name where possible.
	 462  	// Ignore methods that have an invalid receiver. They will be
	 463  	// type-checked later, with regular functions.
	 464  	if methods == nil {
	 465  		return // nothing to do
	 466  	}
	 467  	check.methods = make(map[*TypeName][]*Func)
	 468  	for i := range methods {
	 469  		m := &methods[i]
	 470  		// Determine the receiver base type and associate m with it.
	 471  		ptr, base := check.resolveBaseTypeName(m.ptr, m.recv)
	 472  		if base != nil {
	 473  			m.obj.hasPtrRecv = ptr
	 474  			check.methods[base] = append(check.methods[base], m.obj)
	 475  		}
	 476  	}
	 477  }
	 478  
	 479  // unpackRecv unpacks a receiver type and returns its components: ptr indicates whether
	 480  // rtyp is a pointer receiver, rname is the receiver type name, and tparams are its
	 481  // type parameters, if any. The type parameters are only unpacked if unpackParams is
	 482  // set. If rname is nil, the receiver is unusable (i.e., the source has a bug which we
	 483  // cannot easily work around).
	 484  func (check *Checker) unpackRecv(rtyp ast.Expr, unpackParams bool) (ptr bool, rname *ast.Ident, tparams []*ast.Ident) {
	 485  L: // unpack receiver type
	 486  	// This accepts invalid receivers such as ***T and does not
	 487  	// work for other invalid receivers, but we don't care. The
	 488  	// validity of receiver expressions is checked elsewhere.
	 489  	for {
	 490  		switch t := rtyp.(type) {
	 491  		case *ast.ParenExpr:
	 492  			rtyp = t.X
	 493  		case *ast.StarExpr:
	 494  			ptr = true
	 495  			rtyp = t.X
	 496  		default:
	 497  			break L
	 498  		}
	 499  	}
	 500  
	 501  	// unpack type parameters, if any
	 502  	if ptyp, _ := rtyp.(*ast.IndexExpr); ptyp != nil {
	 503  		rtyp = ptyp.X
	 504  		if unpackParams {
	 505  			for _, arg := range typeparams.UnpackExpr(ptyp.Index) {
	 506  				var par *ast.Ident
	 507  				switch arg := arg.(type) {
	 508  				case *ast.Ident:
	 509  					par = arg
	 510  				case *ast.BadExpr:
	 511  					// ignore - error already reported by parser
	 512  				case nil:
	 513  					check.invalidAST(ptyp, "parameterized receiver contains nil parameters")
	 514  				default:
	 515  					check.errorf(arg, _Todo, "receiver type parameter %s must be an identifier", arg)
	 516  				}
	 517  				if par == nil {
	 518  					par = &ast.Ident{NamePos: arg.Pos(), Name: "_"}
	 519  				}
	 520  				tparams = append(tparams, par)
	 521  			}
	 522  		}
	 523  	}
	 524  
	 525  	// unpack receiver name
	 526  	if name, _ := rtyp.(*ast.Ident); name != nil {
	 527  		rname = name
	 528  	}
	 529  
	 530  	return
	 531  }
	 532  
	 533  // resolveBaseTypeName returns the non-alias base type name for typ, and whether
	 534  // there was a pointer indirection to get to it. The base type name must be declared
	 535  // in package scope, and there can be at most one pointer indirection. If no such type
	 536  // name exists, the returned base is nil.
	 537  func (check *Checker) resolveBaseTypeName(seenPtr bool, name *ast.Ident) (ptr bool, base *TypeName) {
	 538  	// Algorithm: Starting from a type expression, which may be a name,
	 539  	// we follow that type through alias declarations until we reach a
	 540  	// non-alias type name. If we encounter anything but pointer types or
	 541  	// parentheses we're done. If we encounter more than one pointer type
	 542  	// we're done.
	 543  	ptr = seenPtr
	 544  	var seen map[*TypeName]bool
	 545  	var typ ast.Expr = name
	 546  	for {
	 547  		typ = unparen(typ)
	 548  
	 549  		// check if we have a pointer type
	 550  		if pexpr, _ := typ.(*ast.StarExpr); pexpr != nil {
	 551  			// if we've already seen a pointer, we're done
	 552  			if ptr {
	 553  				return false, nil
	 554  			}
	 555  			ptr = true
	 556  			typ = unparen(pexpr.X) // continue with pointer base type
	 557  		}
	 558  
	 559  		// typ must be a name
	 560  		name, _ := typ.(*ast.Ident)
	 561  		if name == nil {
	 562  			return false, nil
	 563  		}
	 564  
	 565  		// name must denote an object found in the current package scope
	 566  		// (note that dot-imported objects are not in the package scope!)
	 567  		obj := check.pkg.scope.Lookup(name.Name)
	 568  		if obj == nil {
	 569  			return false, nil
	 570  		}
	 571  
	 572  		// the object must be a type name...
	 573  		tname, _ := obj.(*TypeName)
	 574  		if tname == nil {
	 575  			return false, nil
	 576  		}
	 577  
	 578  		// ... which we have not seen before
	 579  		if seen[tname] {
	 580  			return false, nil
	 581  		}
	 582  
	 583  		// we're done if tdecl defined tname as a new type
	 584  		// (rather than an alias)
	 585  		tdecl := check.objMap[tname].tdecl // must exist for objects in package scope
	 586  		if !tdecl.Assign.IsValid() {
	 587  			return ptr, tname
	 588  		}
	 589  
	 590  		// otherwise, continue resolving
	 591  		typ = tdecl.Type
	 592  		if seen == nil {
	 593  			seen = make(map[*TypeName]bool)
	 594  		}
	 595  		seen[tname] = true
	 596  	}
	 597  }
	 598  
	 599  // packageObjects typechecks all package objects, but not function bodies.
	 600  func (check *Checker) packageObjects() {
	 601  	// process package objects in source order for reproducible results
	 602  	objList := make([]Object, len(check.objMap))
	 603  	i := 0
	 604  	for obj := range check.objMap {
	 605  		objList[i] = obj
	 606  		i++
	 607  	}
	 608  	sort.Sort(inSourceOrder(objList))
	 609  
	 610  	// add new methods to already type-checked types (from a prior Checker.Files call)
	 611  	for _, obj := range objList {
	 612  		if obj, _ := obj.(*TypeName); obj != nil && obj.typ != nil {
	 613  			check.collectMethods(obj)
	 614  		}
	 615  	}
	 616  
	 617  	// We process non-alias declarations first, in order to avoid situations where
	 618  	// the type of an alias declaration is needed before it is available. In general
	 619  	// this is still not enough, as it is possible to create sufficiently convoluted
	 620  	// recursive type definitions that will cause a type alias to be needed before it
	 621  	// is available (see issue #25838 for examples).
	 622  	// As an aside, the cmd/compiler suffers from the same problem (#25838).
	 623  	var aliasList []*TypeName
	 624  	// phase 1
	 625  	for _, obj := range objList {
	 626  		// If we have a type alias, collect it for the 2nd phase.
	 627  		if tname, _ := obj.(*TypeName); tname != nil && check.objMap[tname].tdecl.Assign.IsValid() {
	 628  			aliasList = append(aliasList, tname)
	 629  			continue
	 630  		}
	 631  
	 632  		check.objDecl(obj, nil)
	 633  	}
	 634  	// phase 2
	 635  	for _, obj := range aliasList {
	 636  		check.objDecl(obj, nil)
	 637  	}
	 638  
	 639  	// At this point we may have a non-empty check.methods map; this means that not all
	 640  	// entries were deleted at the end of typeDecl because the respective receiver base
	 641  	// types were not found. In that case, an error was reported when declaring those
	 642  	// methods. We can now safely discard this map.
	 643  	check.methods = nil
	 644  }
	 645  
	 646  // inSourceOrder implements the sort.Sort interface.
	 647  type inSourceOrder []Object
	 648  
	 649  func (a inSourceOrder) Len() int					 { return len(a) }
	 650  func (a inSourceOrder) Less(i, j int) bool { return a[i].order() < a[j].order() }
	 651  func (a inSourceOrder) Swap(i, j int)			{ a[i], a[j] = a[j], a[i] }
	 652  
	 653  // unusedImports checks for unused imports.
	 654  func (check *Checker) unusedImports() {
	 655  	// if function bodies are not checked, packages' uses are likely missing - don't check
	 656  	if check.conf.IgnoreFuncBodies {
	 657  		return
	 658  	}
	 659  
	 660  	// spec: "It is illegal (...) to directly import a package without referring to
	 661  	// any of its exported identifiers. To import a package solely for its side-effects
	 662  	// (initialization), use the blank identifier as explicit package name."
	 663  
	 664  	for _, obj := range check.imports {
	 665  		if !obj.used && obj.name != "_" {
	 666  			check.errorUnusedPkg(obj)
	 667  		}
	 668  	}
	 669  }
	 670  
	 671  func (check *Checker) errorUnusedPkg(obj *PkgName) {
	 672  	// If the package was imported with a name other than the final
	 673  	// import path element, show it explicitly in the error message.
	 674  	// Note that this handles both renamed imports and imports of
	 675  	// packages containing unconventional package declarations.
	 676  	// Note that this uses / always, even on Windows, because Go import
	 677  	// paths always use forward slashes.
	 678  	path := obj.imported.path
	 679  	elem := path
	 680  	if i := strings.LastIndex(elem, "/"); i >= 0 {
	 681  		elem = elem[i+1:]
	 682  	}
	 683  	if obj.name == "" || obj.name == "." || obj.name == elem {
	 684  		check.softErrorf(obj, _UnusedImport, "%q imported but not used", path)
	 685  	} else {
	 686  		check.softErrorf(obj, _UnusedImport, "%q imported but not used as %s", path, obj.name)
	 687  	}
	 688  }
	 689  
	 690  // dir makes a good-faith attempt to return the directory
	 691  // portion of path. If path is empty, the result is ".".
	 692  // (Per the go/build package dependency tests, we cannot import
	 693  // path/filepath and simply use filepath.Dir.)
	 694  func dir(path string) string {
	 695  	if i := strings.LastIndexAny(path, `/\`); i > 0 {
	 696  		return path[:i]
	 697  	}
	 698  	// i <= 0
	 699  	return "."
	 700  }
	 701  

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