assignments.go

     1  // Code generated by "go test -run=Generate -write=all"; DO NOT EDIT.
     2  // Source: ../../cmd/compile/internal/types2/assignments.go
     3  
     4  // Copyright 2013 The Go Authors. All rights reserved.
     5  // Use of this source code is governed by a BSD-style
     6  // license that can be found in the LICENSE file.
     7  
     8  // This file implements initialization and assignment checks.
     9  
    10  package types
    11  
    12  import (
    13  	"fmt"
    14  	"go/ast"
    15  	. "internal/types/errors"
    16  	"strings"
    17  )
    18  
    19  // assignment reports whether x can be assigned to a variable of type T,
    20  // if necessary by attempting to convert untyped values to the appropriate
    21  // type. context describes the context in which the assignment takes place.
    22  // Use T == nil to indicate assignment to an untyped blank identifier.
    23  // If the assignment check fails, x.mode is set to invalid.
    24  func (check *Checker) assignment(x *operand, T Type, context string) {
    25  	check.singleValue(x)
    26  
    27  	switch x.mode {
    28  	case invalid:
    29  		return // error reported before
    30  	case nilvalue:
    31  		assert(isTypes2)
    32  		// ok
    33  	case constant_, variable, mapindex, value, commaok, commaerr:
    34  		// ok
    35  	default:
    36  		// we may get here because of other problems (go.dev/issue/39634, crash 12)
    37  		// TODO(gri) do we need a new "generic" error code here?
    38  		check.errorf(x, IncompatibleAssign, "cannot assign %s to %s in %s", x, T, context)
    39  		x.mode = invalid
    40  		return
    41  	}
    42  
    43  	if isUntyped(x.typ) {
    44  		target := T
    45  		// spec: "If an untyped constant is assigned to a variable of interface
    46  		// type or the blank identifier, the constant is first converted to type
    47  		// bool, rune, int, float64, complex128 or string respectively, depending
    48  		// on whether the value is a boolean, rune, integer, floating-point,
    49  		// complex, or string constant."
    50  		if isTypes2 {
    51  			if x.isNil() {
    52  				if T == nil {
    53  					check.errorf(x, UntypedNilUse, "use of untyped nil in %s", context)
    54  					x.mode = invalid
    55  					return
    56  				}
    57  			} else if T == nil || isNonTypeParamInterface(T) {
    58  				target = Default(x.typ)
    59  			}
    60  		} else { // go/types
    61  			if T == nil || isNonTypeParamInterface(T) {
    62  				if T == nil && x.typ == Typ[UntypedNil] {
    63  					check.errorf(x, UntypedNilUse, "use of untyped nil in %s", context)
    64  					x.mode = invalid
    65  					return
    66  				}
    67  				target = Default(x.typ)
    68  			}
    69  		}
    70  		newType, val, code := check.implicitTypeAndValue(x, target)
    71  		if code != 0 {
    72  			msg := check.sprintf("cannot use %s as %s value in %s", x, target, context)
    73  			switch code {
    74  			case TruncatedFloat:
    75  				msg += " (truncated)"
    76  			case NumericOverflow:
    77  				msg += " (overflows)"
    78  			default:
    79  				code = IncompatibleAssign
    80  			}
    81  			check.error(x, code, msg)
    82  			x.mode = invalid
    83  			return
    84  		}
    85  		if val != nil {
    86  			x.val = val
    87  			check.updateExprVal(x.expr, val)
    88  		}
    89  		if newType != x.typ {
    90  			x.typ = newType
    91  			check.updateExprType(x.expr, newType, false)
    92  		}
    93  	}
    94  	// x.typ is typed
    95  
    96  	// A generic (non-instantiated) function value cannot be assigned to a variable.
    97  	if sig, _ := under(x.typ).(*Signature); sig != nil && sig.TypeParams().Len() > 0 {
    98  		check.errorf(x, WrongTypeArgCount, "cannot use generic function %s without instantiation in %s", x, context)
    99  		x.mode = invalid
   100  		return
   101  	}
   102  
   103  	// spec: "If a left-hand side is the blank identifier, any typed or
   104  	// non-constant value except for the predeclared identifier nil may
   105  	// be assigned to it."
   106  	if T == nil {
   107  		return
   108  	}
   109  
   110  	cause := ""
   111  	if ok, code := x.assignableTo(check, T, &cause); !ok {
   112  		if cause != "" {
   113  			check.errorf(x, code, "cannot use %s as %s value in %s: %s", x, T, context, cause)
   114  		} else {
   115  			check.errorf(x, code, "cannot use %s as %s value in %s", x, T, context)
   116  		}
   117  		x.mode = invalid
   118  	}
   119  }
   120  
   121  func (check *Checker) initConst(lhs *Const, x *operand) {
   122  	if x.mode == invalid || !isValid(x.typ) || !isValid(lhs.typ) {
   123  		if lhs.typ == nil {
   124  			lhs.typ = Typ[Invalid]
   125  		}
   126  		return
   127  	}
   128  
   129  	// rhs must be a constant
   130  	if x.mode != constant_ {
   131  		check.errorf(x, InvalidConstInit, "%s is not constant", x)
   132  		if lhs.typ == nil {
   133  			lhs.typ = Typ[Invalid]
   134  		}
   135  		return
   136  	}
   137  	assert(isConstType(x.typ))
   138  
   139  	// If the lhs doesn't have a type yet, use the type of x.
   140  	if lhs.typ == nil {
   141  		lhs.typ = x.typ
   142  	}
   143  
   144  	check.assignment(x, lhs.typ, "constant declaration")
   145  	if x.mode == invalid {
   146  		return
   147  	}
   148  
   149  	lhs.val = x.val
   150  }
   151  
   152  // initVar checks the initialization lhs = x in a variable declaration.
   153  // If lhs doesn't have a type yet, it is given the type of x,
   154  // or Typ[Invalid] in case of an error.
   155  // If the initialization check fails, x.mode is set to invalid.
   156  func (check *Checker) initVar(lhs *Var, x *operand, context string) {
   157  	if x.mode == invalid || !isValid(x.typ) || !isValid(lhs.typ) {
   158  		if lhs.typ == nil {
   159  			lhs.typ = Typ[Invalid]
   160  		}
   161  		x.mode = invalid
   162  		return
   163  	}
   164  
   165  	// If lhs doesn't have a type yet, use the type of x.
   166  	if lhs.typ == nil {
   167  		typ := x.typ
   168  		if isUntyped(typ) {
   169  			// convert untyped types to default types
   170  			if typ == Typ[UntypedNil] {
   171  				check.errorf(x, UntypedNilUse, "use of untyped nil in %s", context)
   172  				lhs.typ = Typ[Invalid]
   173  				x.mode = invalid
   174  				return
   175  			}
   176  			typ = Default(typ)
   177  		}
   178  		lhs.typ = typ
   179  	}
   180  
   181  	check.assignment(x, lhs.typ, context)
   182  }
   183  
   184  // lhsVar checks a lhs variable in an assignment and returns its type.
   185  // lhsVar takes care of not counting a lhs identifier as a "use" of
   186  // that identifier. The result is nil if it is the blank identifier,
   187  // and Typ[Invalid] if it is an invalid lhs expression.
   188  func (check *Checker) lhsVar(lhs ast.Expr) Type {
   189  	// Determine if the lhs is a (possibly parenthesized) identifier.
   190  	ident, _ := ast.Unparen(lhs).(*ast.Ident)
   191  
   192  	// Don't evaluate lhs if it is the blank identifier.
   193  	if ident != nil && ident.Name == "_" {
   194  		check.recordDef(ident, nil)
   195  		return nil
   196  	}
   197  
   198  	// If the lhs is an identifier denoting a variable v, this reference
   199  	// is not a 'use' of v. Remember current value of v.used and restore
   200  	// after evaluating the lhs via check.expr.
   201  	var v *Var
   202  	var v_used bool
   203  	if ident != nil {
   204  		if obj := check.lookup(ident.Name); obj != nil {
   205  			// It's ok to mark non-local variables, but ignore variables
   206  			// from other packages to avoid potential race conditions with
   207  			// dot-imported variables.
   208  			if w, _ := obj.(*Var); w != nil && w.pkg == check.pkg {
   209  				v = w
   210  				v_used = v.used
   211  			}
   212  		}
   213  	}
   214  
   215  	var x operand
   216  	check.expr(nil, &x, lhs)
   217  
   218  	if v != nil {
   219  		v.used = v_used // restore v.used
   220  	}
   221  
   222  	if x.mode == invalid || !isValid(x.typ) {
   223  		return Typ[Invalid]
   224  	}
   225  
   226  	// spec: "Each left-hand side operand must be addressable, a map index
   227  	// expression, or the blank identifier. Operands may be parenthesized."
   228  	switch x.mode {
   229  	case invalid:
   230  		return Typ[Invalid]
   231  	case variable, mapindex:
   232  		// ok
   233  	default:
   234  		if sel, ok := x.expr.(*ast.SelectorExpr); ok {
   235  			var op operand
   236  			check.expr(nil, &op, sel.X)
   237  			if op.mode == mapindex {
   238  				check.errorf(&x, UnaddressableFieldAssign, "cannot assign to struct field %s in map", ExprString(x.expr))
   239  				return Typ[Invalid]
   240  			}
   241  		}
   242  		check.errorf(&x, UnassignableOperand, "cannot assign to %s (neither addressable nor a map index expression)", x.expr)
   243  		return Typ[Invalid]
   244  	}
   245  
   246  	return x.typ
   247  }
   248  
   249  // assignVar checks the assignment lhs = rhs (if x == nil), or lhs = x (if x != nil).
   250  // If x != nil, it must be the evaluation of rhs (and rhs will be ignored).
   251  // If the assignment check fails and x != nil, x.mode is set to invalid.
   252  func (check *Checker) assignVar(lhs, rhs ast.Expr, x *operand, context string) {
   253  	T := check.lhsVar(lhs) // nil if lhs is _
   254  	if !isValid(T) {
   255  		if x != nil {
   256  			x.mode = invalid
   257  		} else {
   258  			check.use(rhs)
   259  		}
   260  		return
   261  	}
   262  
   263  	if x == nil {
   264  		var target *target
   265  		// avoid calling ExprString if not needed
   266  		if T != nil {
   267  			if _, ok := under(T).(*Signature); ok {
   268  				target = newTarget(T, ExprString(lhs))
   269  			}
   270  		}
   271  		x = new(operand)
   272  		check.expr(target, x, rhs)
   273  	}
   274  
   275  	if T == nil && context == "assignment" {
   276  		context = "assignment to _ identifier"
   277  	}
   278  	check.assignment(x, T, context)
   279  }
   280  
   281  // operandTypes returns the list of types for the given operands.
   282  func operandTypes(list []*operand) (res []Type) {
   283  	for _, x := range list {
   284  		res = append(res, x.typ)
   285  	}
   286  	return res
   287  }
   288  
   289  // varTypes returns the list of types for the given variables.
   290  func varTypes(list []*Var) (res []Type) {
   291  	for _, x := range list {
   292  		res = append(res, x.typ)
   293  	}
   294  	return res
   295  }
   296  
   297  // typesSummary returns a string of the form "(t1, t2, ...)" where the
   298  // ti's are user-friendly string representations for the given types.
   299  // If variadic is set and the last type is a slice, its string is of
   300  // the form "...E" where E is the slice's element type.
   301  // If hasDots is set, the last argument string is of the form "T..."
   302  // where T is the last type.
   303  // Only one of variadic and hasDots may be set.
   304  func (check *Checker) typesSummary(list []Type, variadic, hasDots bool) string {
   305  	assert(!(variadic && hasDots))
   306  	var res []string
   307  	for i, t := range list {
   308  		var s string
   309  		switch {
   310  		case t == nil:
   311  			fallthrough // should not happen but be cautious
   312  		case !isValid(t):
   313  			s = "unknown type"
   314  		case isUntyped(t): // => *Basic
   315  			if isNumeric(t) {
   316  				// Do not imply a specific type requirement:
   317  				// "have number, want float64" is better than
   318  				// "have untyped int, want float64" or
   319  				// "have int, want float64".
   320  				s = "number"
   321  			} else {
   322  				// If we don't have a number, omit the "untyped" qualifier
   323  				// for compactness.
   324  				s = strings.Replace(t.(*Basic).name, "untyped ", "", -1)
   325  			}
   326  		default:
   327  			s = check.sprintf("%s", t)
   328  		}
   329  		// handle ... parameters/arguments
   330  		if i == len(list)-1 {
   331  			switch {
   332  			case variadic:
   333  				// In correct code, the parameter type is a slice, but be careful.
   334  				if t, _ := t.(*Slice); t != nil {
   335  					s = check.sprintf("%s", t.elem)
   336  				}
   337  				s = "..." + s
   338  			case hasDots:
   339  				s += "..."
   340  			}
   341  		}
   342  		res = append(res, s)
   343  	}
   344  	return "(" + strings.Join(res, ", ") + ")"
   345  }
   346  
   347  func measure(x int, unit string) string {
   348  	if x != 1 {
   349  		unit += "s"
   350  	}
   351  	return fmt.Sprintf("%d %s", x, unit)
   352  }
   353  
   354  func (check *Checker) assignError(rhs []ast.Expr, l, r int) {
   355  	vars := measure(l, "variable")
   356  	vals := measure(r, "value")
   357  	rhs0 := rhs[0]
   358  
   359  	if len(rhs) == 1 {
   360  		if call, _ := ast.Unparen(rhs0).(*ast.CallExpr); call != nil {
   361  			check.errorf(rhs0, WrongAssignCount, "assignment mismatch: %s but %s returns %s", vars, call.Fun, vals)
   362  			return
   363  		}
   364  	}
   365  	check.errorf(rhs0, WrongAssignCount, "assignment mismatch: %s but %s", vars, vals)
   366  }
   367  
   368  func (check *Checker) returnError(at positioner, lhs []*Var, rhs []*operand) {
   369  	l, r := len(lhs), len(rhs)
   370  	qualifier := "not enough"
   371  	if r > l {
   372  		at = rhs[l] // report at first extra value
   373  		qualifier = "too many"
   374  	} else if r > 0 {
   375  		at = rhs[r-1] // report at last value
   376  	}
   377  	err := check.newError(WrongResultCount)
   378  	err.addf(at, "%s return values", qualifier)
   379  	err.addf(noposn, "have %s", check.typesSummary(operandTypes(rhs), false, false))
   380  	err.addf(noposn, "want %s", check.typesSummary(varTypes(lhs), false, false))
   381  	err.report()
   382  }
   383  
   384  // initVars type-checks assignments of initialization expressions orig_rhs
   385  // to variables lhs.
   386  // If returnStmt is non-nil, initVars type-checks the implicit assignment
   387  // of result expressions orig_rhs to function result parameters lhs.
   388  func (check *Checker) initVars(lhs []*Var, orig_rhs []ast.Expr, returnStmt ast.Stmt) {
   389  	context := "assignment"
   390  	if returnStmt != nil {
   391  		context = "return statement"
   392  	}
   393  
   394  	l, r := len(lhs), len(orig_rhs)
   395  
   396  	// If l == 1 and the rhs is a single call, for a better
   397  	// error message don't handle it as n:n mapping below.
   398  	isCall := false
   399  	if r == 1 {
   400  		_, isCall = ast.Unparen(orig_rhs[0]).(*ast.CallExpr)
   401  	}
   402  
   403  	// If we have a n:n mapping from lhs variable to rhs expression,
   404  	// each value can be assigned to its corresponding variable.
   405  	if l == r && !isCall {
   406  		var x operand
   407  		for i, lhs := range lhs {
   408  			desc := lhs.name
   409  			if returnStmt != nil && desc == "" {
   410  				desc = "result variable"
   411  			}
   412  			check.expr(newTarget(lhs.typ, desc), &x, orig_rhs[i])
   413  			check.initVar(lhs, &x, context)
   414  		}
   415  		return
   416  	}
   417  
   418  	// If we don't have an n:n mapping, the rhs must be a single expression
   419  	// resulting in 2 or more values; otherwise we have an assignment mismatch.
   420  	if r != 1 {
   421  		// Only report a mismatch error if there are no other errors on the rhs.
   422  		if check.use(orig_rhs...) {
   423  			if returnStmt != nil {
   424  				rhs := check.exprList(orig_rhs)
   425  				check.returnError(returnStmt, lhs, rhs)
   426  			} else {
   427  				check.assignError(orig_rhs, l, r)
   428  			}
   429  		}
   430  		// ensure that LHS variables have a type
   431  		for _, v := range lhs {
   432  			if v.typ == nil {
   433  				v.typ = Typ[Invalid]
   434  			}
   435  		}
   436  		return
   437  	}
   438  
   439  	rhs, commaOk := check.multiExpr(orig_rhs[0], l == 2 && returnStmt == nil)
   440  	r = len(rhs)
   441  	if l == r {
   442  		for i, lhs := range lhs {
   443  			check.initVar(lhs, rhs[i], context)
   444  		}
   445  		// Only record comma-ok expression if both initializations succeeded
   446  		// (go.dev/issue/59371).
   447  		if commaOk && rhs[0].mode != invalid && rhs[1].mode != invalid {
   448  			check.recordCommaOkTypes(orig_rhs[0], rhs)
   449  		}
   450  		return
   451  	}
   452  
   453  	// In all other cases we have an assignment mismatch.
   454  	// Only report a mismatch error if there are no other errors on the rhs.
   455  	if rhs[0].mode != invalid {
   456  		if returnStmt != nil {
   457  			check.returnError(returnStmt, lhs, rhs)
   458  		} else {
   459  			check.assignError(orig_rhs, l, r)
   460  		}
   461  	}
   462  	// ensure that LHS variables have a type
   463  	for _, v := range lhs {
   464  		if v.typ == nil {
   465  			v.typ = Typ[Invalid]
   466  		}
   467  	}
   468  	// orig_rhs[0] was already evaluated
   469  }
   470  
   471  // assignVars type-checks assignments of expressions orig_rhs to variables lhs.
   472  func (check *Checker) assignVars(lhs, orig_rhs []ast.Expr) {
   473  	l, r := len(lhs), len(orig_rhs)
   474  
   475  	// If l == 1 and the rhs is a single call, for a better
   476  	// error message don't handle it as n:n mapping below.
   477  	isCall := false
   478  	if r == 1 {
   479  		_, isCall = ast.Unparen(orig_rhs[0]).(*ast.CallExpr)
   480  	}
   481  
   482  	// If we have a n:n mapping from lhs variable to rhs expression,
   483  	// each value can be assigned to its corresponding variable.
   484  	if l == r && !isCall {
   485  		for i, lhs := range lhs {
   486  			check.assignVar(lhs, orig_rhs[i], nil, "assignment")
   487  		}
   488  		return
   489  	}
   490  
   491  	// If we don't have an n:n mapping, the rhs must be a single expression
   492  	// resulting in 2 or more values; otherwise we have an assignment mismatch.
   493  	if r != 1 {
   494  		// Only report a mismatch error if there are no other errors on the lhs or rhs.
   495  		okLHS := check.useLHS(lhs...)
   496  		okRHS := check.use(orig_rhs...)
   497  		if okLHS && okRHS {
   498  			check.assignError(orig_rhs, l, r)
   499  		}
   500  		return
   501  	}
   502  
   503  	rhs, commaOk := check.multiExpr(orig_rhs[0], l == 2)
   504  	r = len(rhs)
   505  	if l == r {
   506  		for i, lhs := range lhs {
   507  			check.assignVar(lhs, nil, rhs[i], "assignment")
   508  		}
   509  		// Only record comma-ok expression if both assignments succeeded
   510  		// (go.dev/issue/59371).
   511  		if commaOk && rhs[0].mode != invalid && rhs[1].mode != invalid {
   512  			check.recordCommaOkTypes(orig_rhs[0], rhs)
   513  		}
   514  		return
   515  	}
   516  
   517  	// In all other cases we have an assignment mismatch.
   518  	// Only report a mismatch error if there are no other errors on the rhs.
   519  	if rhs[0].mode != invalid {
   520  		check.assignError(orig_rhs, l, r)
   521  	}
   522  	check.useLHS(lhs...)
   523  	// orig_rhs[0] was already evaluated
   524  }
   525  
   526  func (check *Checker) shortVarDecl(pos positioner, lhs, rhs []ast.Expr) {
   527  	top := len(check.delayed)
   528  	scope := check.scope
   529  
   530  	// collect lhs variables
   531  	seen := make(map[string]bool, len(lhs))
   532  	lhsVars := make([]*Var, len(lhs))
   533  	newVars := make([]*Var, 0, len(lhs))
   534  	hasErr := false
   535  	for i, lhs := range lhs {
   536  		ident, _ := lhs.(*ast.Ident)
   537  		if ident == nil {
   538  			check.useLHS(lhs)
   539  			// TODO(gri) This is redundant with a go/parser error. Consider omitting in go/types?
   540  			check.errorf(lhs, BadDecl, "non-name %s on left side of :=", lhs)
   541  			hasErr = true
   542  			continue
   543  		}
   544  
   545  		name := ident.Name
   546  		if name != "_" {
   547  			if seen[name] {
   548  				check.errorf(lhs, RepeatedDecl, "%s repeated on left side of :=", lhs)
   549  				hasErr = true
   550  				continue
   551  			}
   552  			seen[name] = true
   553  		}
   554  
   555  		// Use the correct obj if the ident is redeclared. The
   556  		// variable's scope starts after the declaration; so we
   557  		// must use Scope.Lookup here and call Scope.Insert
   558  		// (via check.declare) later.
   559  		if alt := scope.Lookup(name); alt != nil {
   560  			check.recordUse(ident, alt)
   561  			// redeclared object must be a variable
   562  			if obj, _ := alt.(*Var); obj != nil {
   563  				lhsVars[i] = obj
   564  			} else {
   565  				check.errorf(lhs, UnassignableOperand, "cannot assign to %s", lhs)
   566  				hasErr = true
   567  			}
   568  			continue
   569  		}
   570  
   571  		// declare new variable
   572  		obj := NewVar(ident.Pos(), check.pkg, name, nil)
   573  		lhsVars[i] = obj
   574  		if name != "_" {
   575  			newVars = append(newVars, obj)
   576  		}
   577  		check.recordDef(ident, obj)
   578  	}
   579  
   580  	// create dummy variables where the lhs is invalid
   581  	for i, obj := range lhsVars {
   582  		if obj == nil {
   583  			lhsVars[i] = NewVar(lhs[i].Pos(), check.pkg, "_", nil)
   584  		}
   585  	}
   586  
   587  	check.initVars(lhsVars, rhs, nil)
   588  
   589  	// process function literals in rhs expressions before scope changes
   590  	check.processDelayed(top)
   591  
   592  	if len(newVars) == 0 && !hasErr {
   593  		check.softErrorf(pos, NoNewVar, "no new variables on left side of :=")
   594  		return
   595  	}
   596  
   597  	// declare new variables
   598  	// spec: "The scope of a constant or variable identifier declared inside
   599  	// a function begins at the end of the ConstSpec or VarSpec (ShortVarDecl
   600  	// for short variable declarations) and ends at the end of the innermost
   601  	// containing block."
   602  	scopePos := endPos(rhs[len(rhs)-1])
   603  	for _, obj := range newVars {
   604  		check.declare(scope, nil, obj, scopePos) // id = nil: recordDef already called
   605  	}
   606  }
   607
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