decl.go

     1  // Copyright 2014 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/token"
    12  )
    13  
    14  func (check *Checker) reportAltDecl(obj Object) {
    15  	if pos := obj.Pos(); pos.IsValid() {
    16  		// We use "other" rather than "previous" here because
    17  		// the first declaration seen may not be textually
    18  		// earlier in the source.
    19  		check.errorf(obj, _DuplicateDecl, "\tother declaration of %s", obj.Name()) // secondary error, \t indented
    20  	}
    21  }
    22  
    23  func (check *Checker) declare(scope *Scope, id *ast.Ident, obj Object, pos token.Pos) {
    24  	// spec: "The blank identifier, represented by the underscore
    25  	// character _, may be used in a declaration like any other
    26  	// identifier but the declaration does not introduce a new
    27  	// binding."
    28  	if obj.Name() != "_" {
    29  		if alt := scope.Insert(obj); alt != nil {
    30  			check.errorf(obj, _DuplicateDecl, "%s redeclared in this block", obj.Name())
    31  			check.reportAltDecl(alt)
    32  			return
    33  		}
    34  		obj.setScopePos(pos)
    35  	}
    36  	if id != nil {
    37  		check.recordDef(id, obj)
    38  	}
    39  }
    40  
    41  // pathString returns a string of the form a->b-> ... ->g for a path [a, b, ... g].
    42  func pathString(path []Object) string {
    43  	var s string
    44  	for i, p := range path {
    45  		if i > 0 {
    46  			s += "->"
    47  		}
    48  		s += p.Name()
    49  	}
    50  	return s
    51  }
    52  
    53  // objDecl type-checks the declaration of obj in its respective (file) environment.
    54  // For the meaning of def, see Checker.definedType, in typexpr.go.
    55  func (check *Checker) objDecl(obj Object, def *Named) {
    56  	if trace && obj.Type() == nil {
    57  		if check.indent == 0 {
    58  			fmt.Println() // empty line between top-level objects for readability
    59  		}
    60  		check.trace(obj.Pos(), "-- checking %s (%s, objPath = %s)", obj, obj.color(), pathString(check.objPath))
    61  		check.indent++
    62  		defer func() {
    63  			check.indent--
    64  			check.trace(obj.Pos(), "=> %s (%s)", obj, obj.color())
    65  		}()
    66  	}
    67  
    68  	// Checking the declaration of obj means inferring its type
    69  	// (and possibly its value, for constants).
    70  	// An object's type (and thus the object) may be in one of
    71  	// three states which are expressed by colors:
    72  	//
    73  	// - an object whose type is not yet known is painted white (initial color)
    74  	// - an object whose type is in the process of being inferred is painted grey
    75  	// - an object whose type is fully inferred is painted black
    76  	//
    77  	// During type inference, an object's color changes from white to grey
    78  	// to black (pre-declared objects are painted black from the start).
    79  	// A black object (i.e., its type) can only depend on (refer to) other black
    80  	// ones. White and grey objects may depend on white and black objects.
    81  	// A dependency on a grey object indicates a cycle which may or may not be
    82  	// valid.
    83  	//
    84  	// When objects turn grey, they are pushed on the object path (a stack);
    85  	// they are popped again when they turn black. Thus, if a grey object (a
    86  	// cycle) is encountered, it is on the object path, and all the objects
    87  	// it depends on are the remaining objects on that path. Color encoding
    88  	// is such that the color value of a grey object indicates the index of
    89  	// that object in the object path.
    90  
    91  	// During type-checking, white objects may be assigned a type without
    92  	// traversing through objDecl; e.g., when initializing constants and
    93  	// variables. Update the colors of those objects here (rather than
    94  	// everywhere where we set the type) to satisfy the color invariants.
    95  	if obj.color() == white && obj.Type() != nil {
    96  		obj.setColor(black)
    97  		return
    98  	}
    99  
   100  	switch obj.color() {
   101  	case white:
   102  		assert(obj.Type() == nil)
   103  		// All color values other than white and black are considered grey.
   104  		// Because black and white are < grey, all values >= grey are grey.
   105  		// Use those values to encode the object's index into the object path.
   106  		obj.setColor(grey + color(check.push(obj)))
   107  		defer func() {
   108  			check.pop().setColor(black)
   109  		}()
   110  
   111  	case black:
   112  		assert(obj.Type() != nil)
   113  		return
   114  
   115  	default:
   116  		// Color values other than white or black are considered grey.
   117  		fallthrough
   118  
   119  	case grey:
   120  		// We have a (possibly invalid) cycle.
   121  		// In the existing code, this is marked by a non-nil type
   122  		// for the object except for constants and variables whose
   123  		// type may be non-nil (known), or nil if it depends on the
   124  		// not-yet known initialization value.
   125  		// In the former case, set the type to Typ[Invalid] because
   126  		// we have an initialization cycle. The cycle error will be
   127  		// reported later, when determining initialization order.
   128  		// TODO(gri) Report cycle here and simplify initialization
   129  		// order code.
   130  		switch obj := obj.(type) {
   131  		case *Const:
   132  			if !check.validCycle(obj) || obj.typ == nil {
   133  				obj.typ = Typ[Invalid]
   134  			}
   135  
   136  		case *Var:
   137  			if !check.validCycle(obj) || obj.typ == nil {
   138  				obj.typ = Typ[Invalid]
   139  			}
   140  
   141  		case *TypeName:
   142  			if !check.validCycle(obj) {
   143  				// break cycle
   144  				// (without this, calling underlying()
   145  				// below may lead to an endless loop
   146  				// if we have a cycle for a defined
   147  				// (*Named) type)
   148  				obj.typ = Typ[Invalid]
   149  			}
   150  
   151  		case *Func:
   152  			if !check.validCycle(obj) {
   153  				// Don't set obj.typ to Typ[Invalid] here
   154  				// because plenty of code type-asserts that
   155  				// functions have a *Signature type. Grey
   156  				// functions have their type set to an empty
   157  				// signature which makes it impossible to
   158  				// initialize a variable with the function.
   159  			}
   160  
   161  		default:
   162  			unreachable()
   163  		}
   164  		assert(obj.Type() != nil)
   165  		return
   166  	}
   167  
   168  	d := check.objMap[obj]
   169  	if d == nil {
   170  		check.dump("%v: %s should have been declared", obj.Pos(), obj)
   171  		unreachable()
   172  	}
   173  
   174  	// save/restore current environment and set up object environment
   175  	defer func(env environment) {
   176  		check.environment = env
   177  	}(check.environment)
   178  	check.environment = environment{
   179  		scope: d.file,
   180  	}
   181  
   182  	// Const and var declarations must not have initialization
   183  	// cycles. We track them by remembering the current declaration
   184  	// in check.decl. Initialization expressions depending on other
   185  	// consts, vars, or functions, add dependencies to the current
   186  	// check.decl.
   187  	switch obj := obj.(type) {
   188  	case *Const:
   189  		check.decl = d // new package-level const decl
   190  		check.constDecl(obj, d.vtyp, d.init, d.inherited)
   191  	case *Var:
   192  		check.decl = d // new package-level var decl
   193  		check.varDecl(obj, d.lhs, d.vtyp, d.init)
   194  	case *TypeName:
   195  		// invalid recursive types are detected via path
   196  		check.typeDecl(obj, d.tdecl, def)
   197  		check.collectMethods(obj) // methods can only be added to top-level types
   198  	case *Func:
   199  		// functions may be recursive - no need to track dependencies
   200  		check.funcDecl(obj, d)
   201  	default:
   202  		unreachable()
   203  	}
   204  }
   205  
   206  // validCycle checks if the cycle starting with obj is valid and
   207  // reports an error if it is not.
   208  func (check *Checker) validCycle(obj Object) (valid bool) {
   209  	// The object map contains the package scope objects and the non-interface methods.
   210  	if debug {
   211  		info := check.objMap[obj]
   212  		inObjMap := info != nil && (info.fdecl == nil || info.fdecl.Recv == nil) // exclude methods
   213  		isPkgObj := obj.Parent() == check.pkg.scope
   214  		if isPkgObj != inObjMap {
   215  			check.dump("%v: inconsistent object map for %s (isPkgObj = %v, inObjMap = %v)", obj.Pos(), obj, isPkgObj, inObjMap)
   216  			unreachable()
   217  		}
   218  	}
   219  
   220  	// Count cycle objects.
   221  	assert(obj.color() >= grey)
   222  	start := obj.color() - grey // index of obj in objPath
   223  	cycle := check.objPath[start:]
   224  	tparCycle := false // if set, the cycle is through a type parameter list
   225  	nval := 0          // number of (constant or variable) values in the cycle; valid if !generic
   226  	ndef := 0          // number of type definitions in the cycle; valid if !generic
   227  loop:
   228  	for _, obj := range cycle {
   229  		switch obj := obj.(type) {
   230  		case *Const, *Var:
   231  			nval++
   232  		case *TypeName:
   233  			// If we reach a generic type that is part of a cycle
   234  			// and we are in a type parameter list, we have a cycle
   235  			// through a type parameter list, which is invalid.
   236  			if check.inTParamList && isGeneric(obj.typ) {
   237  				tparCycle = true
   238  				break loop
   239  			}
   240  
   241  			// Determine if the type name is an alias or not. For
   242  			// package-level objects, use the object map which
   243  			// provides syntactic information (which doesn't rely
   244  			// on the order in which the objects are set up). For
   245  			// local objects, we can rely on the order, so use
   246  			// the object's predicate.
   247  			// TODO(gri) It would be less fragile to always access
   248  			// the syntactic information. We should consider storing
   249  			// this information explicitly in the object.
   250  			var alias bool
   251  			if d := check.objMap[obj]; d != nil {
   252  				alias = d.tdecl.Assign.IsValid() // package-level object
   253  			} else {
   254  				alias = obj.IsAlias() // function local object
   255  			}
   256  			if !alias {
   257  				ndef++
   258  			}
   259  		case *Func:
   260  			// ignored for now
   261  		default:
   262  			unreachable()
   263  		}
   264  	}
   265  
   266  	if trace {
   267  		check.trace(obj.Pos(), "## cycle detected: objPath = %s->%s (len = %d)", pathString(cycle), obj.Name(), len(cycle))
   268  		if tparCycle {
   269  			check.trace(obj.Pos(), "## cycle contains: generic type in a type parameter list")
   270  		} else {
   271  			check.trace(obj.Pos(), "## cycle contains: %d values, %d type definitions", nval, ndef)
   272  		}
   273  		defer func() {
   274  			if valid {
   275  				check.trace(obj.Pos(), "=> cycle is valid")
   276  			} else {
   277  				check.trace(obj.Pos(), "=> error: cycle is invalid")
   278  			}
   279  		}()
   280  	}
   281  
   282  	if !tparCycle {
   283  		// A cycle involving only constants and variables is invalid but we
   284  		// ignore them here because they are reported via the initialization
   285  		// cycle check.
   286  		if nval == len(cycle) {
   287  			return true
   288  		}
   289  
   290  		// A cycle involving only types (and possibly functions) must have at least
   291  		// one type definition to be permitted: If there is no type definition, we
   292  		// have a sequence of alias type names which will expand ad infinitum.
   293  		if nval == 0 && ndef > 0 {
   294  			return true
   295  		}
   296  	}
   297  
   298  	check.cycleError(cycle)
   299  	return false
   300  }
   301  
   302  // cycleError reports a declaration cycle starting with
   303  // the object in cycle that is "first" in the source.
   304  func (check *Checker) cycleError(cycle []Object) {
   305  	// TODO(gri) Should we start with the last (rather than the first) object in the cycle
   306  	//           since that is the earliest point in the source where we start seeing the
   307  	//           cycle? That would be more consistent with other error messages.
   308  	i := firstInSrc(cycle)
   309  	obj := cycle[i]
   310  	// If obj is a type alias, mark it as valid (not broken) in order to avoid follow-on errors.
   311  	tname, _ := obj.(*TypeName)
   312  	if tname != nil && tname.IsAlias() {
   313  		check.validAlias(tname, Typ[Invalid])
   314  	}
   315  	if tname != nil && compilerErrorMessages {
   316  		check.errorf(obj, _InvalidDeclCycle, "invalid recursive type %s", obj.Name())
   317  	} else {
   318  		check.errorf(obj, _InvalidDeclCycle, "illegal cycle in declaration of %s", obj.Name())
   319  	}
   320  	for range cycle {
   321  		check.errorf(obj, _InvalidDeclCycle, "\t%s refers to", obj.Name()) // secondary error, \t indented
   322  		i++
   323  		if i >= len(cycle) {
   324  			i = 0
   325  		}
   326  		obj = cycle[i]
   327  	}
   328  	check.errorf(obj, _InvalidDeclCycle, "\t%s", obj.Name())
   329  }
   330  
   331  // firstInSrc reports the index of the object with the "smallest"
   332  // source position in path. path must not be empty.
   333  func firstInSrc(path []Object) int {
   334  	fst, pos := 0, path[0].Pos()
   335  	for i, t := range path[1:] {
   336  		if t.Pos() < pos {
   337  			fst, pos = i+1, t.Pos()
   338  		}
   339  	}
   340  	return fst
   341  }
   342  
   343  type (
   344  	decl interface {
   345  		node() ast.Node
   346  	}
   347  
   348  	importDecl struct{ spec *ast.ImportSpec }
   349  	constDecl  struct {
   350  		spec      *ast.ValueSpec
   351  		iota      int
   352  		typ       ast.Expr
   353  		init      []ast.Expr
   354  		inherited bool
   355  	}
   356  	varDecl  struct{ spec *ast.ValueSpec }
   357  	typeDecl struct{ spec *ast.TypeSpec }
   358  	funcDecl struct{ decl *ast.FuncDecl }
   359  )
   360  
   361  func (d importDecl) node() ast.Node { return d.spec }
   362  func (d constDecl) node() ast.Node  { return d.spec }
   363  func (d varDecl) node() ast.Node    { return d.spec }
   364  func (d typeDecl) node() ast.Node   { return d.spec }
   365  func (d funcDecl) node() ast.Node   { return d.decl }
   366  
   367  func (check *Checker) walkDecls(decls []ast.Decl, f func(decl)) {
   368  	for _, d := range decls {
   369  		check.walkDecl(d, f)
   370  	}
   371  }
   372  
   373  func (check *Checker) walkDecl(d ast.Decl, f func(decl)) {
   374  	switch d := d.(type) {
   375  	case *ast.BadDecl:
   376  		// ignore
   377  	case *ast.GenDecl:
   378  		var last *ast.ValueSpec // last ValueSpec with type or init exprs seen
   379  		for iota, s := range d.Specs {
   380  			switch s := s.(type) {
   381  			case *ast.ImportSpec:
   382  				f(importDecl{s})
   383  			case *ast.ValueSpec:
   384  				switch d.Tok {
   385  				case token.CONST:
   386  					// determine which initialization expressions to use
   387  					inherited := true
   388  					switch {
   389  					case s.Type != nil || len(s.Values) > 0:
   390  						last = s
   391  						inherited = false
   392  					case last == nil:
   393  						last = new(ast.ValueSpec) // make sure last exists
   394  						inherited = false
   395  					}
   396  					check.arityMatch(s, last)
   397  					f(constDecl{spec: s, iota: iota, typ: last.Type, init: last.Values, inherited: inherited})
   398  				case token.VAR:
   399  					check.arityMatch(s, nil)
   400  					f(varDecl{s})
   401  				default:
   402  					check.invalidAST(s, "invalid token %s", d.Tok)
   403  				}
   404  			case *ast.TypeSpec:
   405  				f(typeDecl{s})
   406  			default:
   407  				check.invalidAST(s, "unknown ast.Spec node %T", s)
   408  			}
   409  		}
   410  	case *ast.FuncDecl:
   411  		f(funcDecl{d})
   412  	default:
   413  		check.invalidAST(d, "unknown ast.Decl node %T", d)
   414  	}
   415  }
   416  
   417  func (check *Checker) constDecl(obj *Const, typ, init ast.Expr, inherited bool) {
   418  	assert(obj.typ == nil)
   419  
   420  	// use the correct value of iota
   421  	defer func(iota constant.Value, errpos positioner) {
   422  		check.iota = iota
   423  		check.errpos = errpos
   424  	}(check.iota, check.errpos)
   425  	check.iota = obj.val
   426  	check.errpos = nil
   427  
   428  	// provide valid constant value under all circumstances
   429  	obj.val = constant.MakeUnknown()
   430  
   431  	// determine type, if any
   432  	if typ != nil {
   433  		t := check.typ(typ)
   434  		if !isConstType(t) {
   435  			// don't report an error if the type is an invalid C (defined) type
   436  			// (issue #22090)
   437  			if under(t) != Typ[Invalid] {
   438  				check.errorf(typ, _InvalidConstType, "invalid constant type %s", t)
   439  			}
   440  			obj.typ = Typ[Invalid]
   441  			return
   442  		}
   443  		obj.typ = t
   444  	}
   445  
   446  	// check initialization
   447  	var x operand
   448  	if init != nil {
   449  		if inherited {
   450  			// The initialization expression is inherited from a previous
   451  			// constant declaration, and (error) positions refer to that
   452  			// expression and not the current constant declaration. Use
   453  			// the constant identifier position for any errors during
   454  			// init expression evaluation since that is all we have
   455  			// (see issues #42991, #42992).
   456  			check.errpos = atPos(obj.pos)
   457  		}
   458  		check.expr(&x, init)
   459  	}
   460  	check.initConst(obj, &x)
   461  }
   462  
   463  func (check *Checker) varDecl(obj *Var, lhs []*Var, typ, init ast.Expr) {
   464  	assert(obj.typ == nil)
   465  
   466  	// determine type, if any
   467  	if typ != nil {
   468  		obj.typ = check.varType(typ)
   469  		// We cannot spread the type to all lhs variables if there
   470  		// are more than one since that would mark them as checked
   471  		// (see Checker.objDecl) and the assignment of init exprs,
   472  		// if any, would not be checked.
   473  		//
   474  		// TODO(gri) If we have no init expr, we should distribute
   475  		// a given type otherwise we need to re-evalate the type
   476  		// expr for each lhs variable, leading to duplicate work.
   477  	}
   478  
   479  	// check initialization
   480  	if init == nil {
   481  		if typ == nil {
   482  			// error reported before by arityMatch
   483  			obj.typ = Typ[Invalid]
   484  		}
   485  		return
   486  	}
   487  
   488  	if lhs == nil || len(lhs) == 1 {
   489  		assert(lhs == nil || lhs[0] == obj)
   490  		var x operand
   491  		check.expr(&x, init)
   492  		check.initVar(obj, &x, "variable declaration")
   493  		return
   494  	}
   495  
   496  	if debug {
   497  		// obj must be one of lhs
   498  		found := false
   499  		for _, lhs := range lhs {
   500  			if obj == lhs {
   501  				found = true
   502  				break
   503  			}
   504  		}
   505  		if !found {
   506  			panic("inconsistent lhs")
   507  		}
   508  	}
   509  
   510  	// We have multiple variables on the lhs and one init expr.
   511  	// Make sure all variables have been given the same type if
   512  	// one was specified, otherwise they assume the type of the
   513  	// init expression values (was issue #15755).
   514  	if typ != nil {
   515  		for _, lhs := range lhs {
   516  			lhs.typ = obj.typ
   517  		}
   518  	}
   519  
   520  	check.initVars(lhs, []ast.Expr{init}, nil)
   521  }
   522  
   523  // isImportedConstraint reports whether typ is an imported type constraint.
   524  func (check *Checker) isImportedConstraint(typ Type) bool {
   525  	named, _ := typ.(*Named)
   526  	if named == nil || named.obj.pkg == check.pkg || named.obj.pkg == nil {
   527  		return false
   528  	}
   529  	u, _ := named.under().(*Interface)
   530  	return u != nil && !u.IsMethodSet()
   531  }
   532  
   533  func (check *Checker) typeDecl(obj *TypeName, tdecl *ast.TypeSpec, def *Named) {
   534  	assert(obj.typ == nil)
   535  
   536  	var rhs Type
   537  	check.later(func() {
   538  		if t, _ := obj.typ.(*Named); t != nil { // type may be invalid
   539  			check.validType(t)
   540  		}
   541  		// If typ is local, an error was already reported where typ is specified/defined.
   542  		if check.isImportedConstraint(rhs) && !check.allowVersion(check.pkg, 1, 18) {
   543  			check.errorf(tdecl.Type, _UnsupportedFeature, "using type constraint %s requires go1.18 or later", rhs)
   544  		}
   545  	}).describef(obj, "validType(%s)", obj.Name())
   546  
   547  	alias := tdecl.Assign.IsValid()
   548  	if alias && tdecl.TypeParams.NumFields() != 0 {
   549  		// The parser will ensure this but we may still get an invalid AST.
   550  		// Complain and continue as regular type definition.
   551  		check.error(atPos(tdecl.Assign), _BadDecl, "generic type cannot be alias")
   552  		alias = false
   553  	}
   554  
   555  	// alias declaration
   556  	if alias {
   557  		if !check.allowVersion(check.pkg, 1, 9) {
   558  			check.errorf(atPos(tdecl.Assign), _BadDecl, "type aliases requires go1.9 or later")
   559  		}
   560  
   561  		check.brokenAlias(obj)
   562  		rhs = check.varType(tdecl.Type)
   563  		check.validAlias(obj, rhs)
   564  		return
   565  	}
   566  
   567  	// type definition or generic type declaration
   568  	named := check.newNamed(obj, nil, nil, nil, nil)
   569  	def.setUnderlying(named)
   570  
   571  	if tdecl.TypeParams != nil {
   572  		check.openScope(tdecl, "type parameters")
   573  		defer check.closeScope()
   574  		check.collectTypeParams(&named.tparams, tdecl.TypeParams)
   575  	}
   576  
   577  	// determine underlying type of named
   578  	rhs = check.definedType(tdecl.Type, named)
   579  	assert(rhs != nil)
   580  	named.fromRHS = rhs
   581  
   582  	// If the underlying was not set while type-checking the right-hand side, it
   583  	// is invalid and an error should have been reported elsewhere.
   584  	if named.underlying == nil {
   585  		named.underlying = Typ[Invalid]
   586  	}
   587  
   588  	// Disallow a lone type parameter as the RHS of a type declaration (issue #45639).
   589  	// We don't need this restriction anymore if we make the underlying type of a type
   590  	// parameter its constraint interface: if the RHS is a lone type parameter, we will
   591  	// use its underlying type (like we do for any RHS in a type declaration), and its
   592  	// underlying type is an interface and the type declaration is well defined.
   593  	if isTypeParam(rhs) {
   594  		check.error(tdecl.Type, _MisplacedTypeParam, "cannot use a type parameter as RHS in type declaration")
   595  		named.underlying = Typ[Invalid]
   596  	}
   597  }
   598  
   599  func (check *Checker) collectTypeParams(dst **TypeParamList, list *ast.FieldList) {
   600  	var tparams []*TypeParam
   601  	// Declare type parameters up-front, with empty interface as type bound.
   602  	// The scope of type parameters starts at the beginning of the type parameter
   603  	// list (so we can have mutually recursive parameterized interfaces).
   604  	for _, f := range list.List {
   605  		tparams = check.declareTypeParams(tparams, f.Names)
   606  	}
   607  
   608  	// Set the type parameters before collecting the type constraints because
   609  	// the parameterized type may be used by the constraints (issue #47887).
   610  	// Example: type T[P T[P]] interface{}
   611  	*dst = bindTParams(tparams)
   612  
   613  	// Signal to cycle detection that we are in a type parameter list.
   614  	// We can only be inside one type parameter list at any given time:
   615  	// function closures may appear inside a type parameter list but they
   616  	// cannot be generic, and their bodies are processed in delayed and
   617  	// sequential fashion. Note that with each new declaration, we save
   618  	// the existing environment and restore it when done; thus inTPList is
   619  	// true exactly only when we are in a specific type parameter list.
   620  	assert(!check.inTParamList)
   621  	check.inTParamList = true
   622  	defer func() {
   623  		check.inTParamList = false
   624  	}()
   625  
   626  	index := 0
   627  	for _, f := range list.List {
   628  		var bound Type
   629  		// NOTE: we may be able to assert that f.Type != nil here, but this is not
   630  		// an invariant of the AST, so we are cautious.
   631  		if f.Type != nil {
   632  			bound = check.bound(f.Type)
   633  			if isTypeParam(bound) {
   634  				// We may be able to allow this since it is now well-defined what
   635  				// the underlying type and thus type set of a type parameter is.
   636  				// But we may need some additional form of cycle detection within
   637  				// type parameter lists.
   638  				check.error(f.Type, _MisplacedTypeParam, "cannot use a type parameter as constraint")
   639  				bound = Typ[Invalid]
   640  			}
   641  		} else {
   642  			bound = Typ[Invalid]
   643  		}
   644  		for i := range f.Names {
   645  			tparams[index+i].bound = bound
   646  		}
   647  		index += len(f.Names)
   648  	}
   649  }
   650  
   651  func (check *Checker) bound(x ast.Expr) Type {
   652  	// A type set literal of the form ~T and A|B may only appear as constraint;
   653  	// embed it in an implicit interface so that only interface type-checking
   654  	// needs to take care of such type expressions.
   655  	wrap := false
   656  	switch op := x.(type) {
   657  	case *ast.UnaryExpr:
   658  		wrap = op.Op == token.TILDE
   659  	case *ast.BinaryExpr:
   660  		wrap = op.Op == token.OR
   661  	}
   662  	if wrap {
   663  		x = &ast.InterfaceType{Methods: &ast.FieldList{List: []*ast.Field{{Type: x}}}}
   664  		t := check.typ(x)
   665  		// mark t as implicit interface if all went well
   666  		if t, _ := t.(*Interface); t != nil {
   667  			t.implicit = true
   668  		}
   669  		return t
   670  	}
   671  	return check.typ(x)
   672  }
   673  
   674  func (check *Checker) declareTypeParams(tparams []*TypeParam, names []*ast.Ident) []*TypeParam {
   675  	// Use Typ[Invalid] for the type constraint to ensure that a type
   676  	// is present even if the actual constraint has not been assigned
   677  	// yet.
   678  	// TODO(gri) Need to systematically review all uses of type parameter
   679  	//           constraints to make sure we don't rely on them if they
   680  	//           are not properly set yet.
   681  	for _, name := range names {
   682  		tname := NewTypeName(name.Pos(), check.pkg, name.Name, nil)
   683  		tpar := check.newTypeParam(tname, Typ[Invalid])          // assigns type to tpar as a side-effect
   684  		check.declare(check.scope, name, tname, check.scope.pos) // TODO(gri) check scope position
   685  		tparams = append(tparams, tpar)
   686  	}
   687  
   688  	if trace && len(names) > 0 {
   689  		check.trace(names[0].Pos(), "type params = %v", tparams[len(tparams)-len(names):])
   690  	}
   691  
   692  	return tparams
   693  }
   694  
   695  func (check *Checker) collectMethods(obj *TypeName) {
   696  	// get associated methods
   697  	// (Checker.collectObjects only collects methods with non-blank names;
   698  	// Checker.resolveBaseTypeName ensures that obj is not an alias name
   699  	// if it has attached methods.)
   700  	methods := check.methods[obj]
   701  	if methods == nil {
   702  		return
   703  	}
   704  	delete(check.methods, obj)
   705  	assert(!check.objMap[obj].tdecl.Assign.IsValid()) // don't use TypeName.IsAlias (requires fully set up object)
   706  
   707  	// use an objset to check for name conflicts
   708  	var mset objset
   709  
   710  	// spec: "If the base type is a struct type, the non-blank method
   711  	// and field names must be distinct."
   712  	base, _ := obj.typ.(*Named) // shouldn't fail but be conservative
   713  	if base != nil {
   714  		assert(base.targs.Len() == 0) // collectMethods should not be called on an instantiated type
   715  
   716  		// See issue #52529: we must delay the expansion of underlying here, as
   717  		// base may not be fully set-up.
   718  		check.later(func() {
   719  			check.checkFieldUniqueness(base)
   720  		}).describef(obj, "verifying field uniqueness for %v", base)
   721  
   722  		// Checker.Files may be called multiple times; additional package files
   723  		// may add methods to already type-checked types. Add pre-existing methods
   724  		// so that we can detect redeclarations.
   725  		for i := 0; i < base.methods.Len(); i++ {
   726  			m := base.methods.At(i, nil)
   727  			assert(m.name != "_")
   728  			assert(mset.insert(m) == nil)
   729  		}
   730  	}
   731  
   732  	// add valid methods
   733  	for _, m := range methods {
   734  		// spec: "For a base type, the non-blank names of methods bound
   735  		// to it must be unique."
   736  		assert(m.name != "_")
   737  		if alt := mset.insert(m); alt != nil {
   738  			check.errorf(m, _DuplicateMethod, "method %s already declared for %s", m.name, obj)
   739  			check.reportAltDecl(alt)
   740  			continue
   741  		}
   742  
   743  		if base != nil {
   744  			base.resolve(nil) // TODO(mdempsky): Probably unnecessary.
   745  			base.AddMethod(m)
   746  		}
   747  	}
   748  }
   749  
   750  func (check *Checker) checkFieldUniqueness(base *Named) {
   751  	if t, _ := base.under().(*Struct); t != nil {
   752  		var mset objset
   753  		for i := 0; i < base.methods.Len(); i++ {
   754  			m := base.methods.At(i, nil)
   755  			assert(m.name != "_")
   756  			assert(mset.insert(m) == nil)
   757  		}
   758  
   759  		// Check that any non-blank field names of base are distinct from its
   760  		// method names.
   761  		for _, fld := range t.fields {
   762  			if fld.name != "_" {
   763  				if alt := mset.insert(fld); alt != nil {
   764  					// Struct fields should already be unique, so we should only
   765  					// encounter an alternate via collision with a method name.
   766  					_ = alt.(*Func)
   767  
   768  					// For historical consistency, we report the primary error on the
   769  					// method, and the alt decl on the field.
   770  					check.errorf(alt, _DuplicateFieldAndMethod, "field and method with the same name %s", fld.name)
   771  					check.reportAltDecl(fld)
   772  				}
   773  			}
   774  		}
   775  	}
   776  }
   777  
   778  func (check *Checker) funcDecl(obj *Func, decl *declInfo) {
   779  	assert(obj.typ == nil)
   780  
   781  	// func declarations cannot use iota
   782  	assert(check.iota == nil)
   783  
   784  	sig := new(Signature)
   785  	obj.typ = sig // guard against cycles
   786  
   787  	// Avoid cycle error when referring to method while type-checking the signature.
   788  	// This avoids a nuisance in the best case (non-parameterized receiver type) and
   789  	// since the method is not a type, we get an error. If we have a parameterized
   790  	// receiver type, instantiating the receiver type leads to the instantiation of
   791  	// its methods, and we don't want a cycle error in that case.
   792  	// TODO(gri) review if this is correct and/or whether we still need this?
   793  	saved := obj.color_
   794  	obj.color_ = black
   795  	fdecl := decl.fdecl
   796  	check.funcType(sig, fdecl.Recv, fdecl.Type)
   797  	obj.color_ = saved
   798  
   799  	if fdecl.Type.TypeParams.NumFields() > 0 && fdecl.Body == nil {
   800  		check.softErrorf(fdecl.Name, _BadDecl, "parameterized function is missing function body")
   801  	}
   802  
   803  	// function body must be type-checked after global declarations
   804  	// (functions implemented elsewhere have no body)
   805  	if !check.conf.IgnoreFuncBodies && fdecl.Body != nil {
   806  		check.later(func() {
   807  			check.funcBody(decl, obj.name, sig, fdecl.Body, nil)
   808  		})
   809  	}
   810  }
   811  
   812  func (check *Checker) declStmt(d ast.Decl) {
   813  	pkg := check.pkg
   814  
   815  	check.walkDecl(d, func(d decl) {
   816  		switch d := d.(type) {
   817  		case constDecl:
   818  			top := len(check.delayed)
   819  
   820  			// declare all constants
   821  			lhs := make([]*Const, len(d.spec.Names))
   822  			for i, name := range d.spec.Names {
   823  				obj := NewConst(name.Pos(), pkg, name.Name, nil, constant.MakeInt64(int64(d.iota)))
   824  				lhs[i] = obj
   825  
   826  				var init ast.Expr
   827  				if i < len(d.init) {
   828  					init = d.init[i]
   829  				}
   830  
   831  				check.constDecl(obj, d.typ, init, d.inherited)
   832  			}
   833  
   834  			// process function literals in init expressions before scope changes
   835  			check.processDelayed(top)
   836  
   837  			// spec: "The scope of a constant or variable identifier declared
   838  			// inside a function begins at the end of the ConstSpec or VarSpec
   839  			// (ShortVarDecl for short variable declarations) and ends at the
   840  			// end of the innermost containing block."
   841  			scopePos := d.spec.End()
   842  			for i, name := range d.spec.Names {
   843  				check.declare(check.scope, name, lhs[i], scopePos)
   844  			}
   845  
   846  		case varDecl:
   847  			top := len(check.delayed)
   848  
   849  			lhs0 := make([]*Var, len(d.spec.Names))
   850  			for i, name := range d.spec.Names {
   851  				lhs0[i] = NewVar(name.Pos(), pkg, name.Name, nil)
   852  			}
   853  
   854  			// initialize all variables
   855  			for i, obj := range lhs0 {
   856  				var lhs []*Var
   857  				var init ast.Expr
   858  				switch len(d.spec.Values) {
   859  				case len(d.spec.Names):
   860  					// lhs and rhs match
   861  					init = d.spec.Values[i]
   862  				case 1:
   863  					// rhs is expected to be a multi-valued expression
   864  					lhs = lhs0
   865  					init = d.spec.Values[0]
   866  				default:
   867  					if i < len(d.spec.Values) {
   868  						init = d.spec.Values[i]
   869  					}
   870  				}
   871  				check.varDecl(obj, lhs, d.spec.Type, init)
   872  				if len(d.spec.Values) == 1 {
   873  					// If we have a single lhs variable we are done either way.
   874  					// If we have a single rhs expression, it must be a multi-
   875  					// valued expression, in which case handling the first lhs
   876  					// variable will cause all lhs variables to have a type
   877  					// assigned, and we are done as well.
   878  					if debug {
   879  						for _, obj := range lhs0 {
   880  							assert(obj.typ != nil)
   881  						}
   882  					}
   883  					break
   884  				}
   885  			}
   886  
   887  			// process function literals in init expressions before scope changes
   888  			check.processDelayed(top)
   889  
   890  			// declare all variables
   891  			// (only at this point are the variable scopes (parents) set)
   892  			scopePos := d.spec.End() // see constant declarations
   893  			for i, name := range d.spec.Names {
   894  				// see constant declarations
   895  				check.declare(check.scope, name, lhs0[i], scopePos)
   896  			}
   897  
   898  		case typeDecl:
   899  			obj := NewTypeName(d.spec.Name.Pos(), pkg, d.spec.Name.Name, nil)
   900  			// spec: "The scope of a type identifier declared inside a function
   901  			// begins at the identifier in the TypeSpec and ends at the end of
   902  			// the innermost containing block."
   903  			scopePos := d.spec.Name.Pos()
   904  			check.declare(check.scope, d.spec.Name, obj, scopePos)
   905  			// mark and unmark type before calling typeDecl; its type is still nil (see Checker.objDecl)
   906  			obj.setColor(grey + color(check.push(obj)))
   907  			check.typeDecl(obj, d.spec, nil)
   908  			check.pop().setColor(black)
   909  		default:
   910  			check.invalidAST(d.node(), "unknown ast.Decl node %T", d.node())
   911  		}
   912  	})
   913  }
   914
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