range.go

     1  // Copyright 2025 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  // This file implements typechecking of range statements.
     6  
     7  package types2
     8  
     9  import (
    10  	"cmd/compile/internal/syntax"
    11  	"go/constant"
    12  	"internal/buildcfg"
    13  	. "internal/types/errors"
    14  )
    15  
    16  // rangeStmt type-checks a range statement of form
    17  //
    18  //	for sKey, sValue = range rangeVar { ... }
    19  //
    20  // where sKey, sValue, sExtra may be nil. isDef indicates whether these
    21  // variables are assigned to only (=) or whether there is a short variable
    22  // declaration (:=). If the latter and there are no variables, an error is
    23  // reported at noNewVarPos.
    24  func (check *Checker) rangeStmt(inner stmtContext, rangeStmt *syntax.ForStmt, noNewVarPos poser, sKey, sValue, sExtra, rangeVar syntax.Expr, isDef bool) {
    25  	// check expression to iterate over
    26  	var x operand
    27  
    28  	// From the spec:
    29  	//   The range expression x is evaluated before beginning the loop,
    30  	//   with one exception: if at most one iteration variable is present
    31  	//   and x or len(x) is constant, the range expression is not evaluated.
    32  	// So we have to be careful not to evaluate the arg in the
    33  	// described situation.
    34  
    35  	check.hasCallOrRecv = false
    36  	check.expr(nil, &x, rangeVar)
    37  
    38  	if isTypes2 && x.mode != invalid && sValue == nil && !check.hasCallOrRecv {
    39  		if t, ok := arrayPtrDeref(under(x.typ)).(*Array); ok {
    40  			for {
    41  				// Put constant info on the thing inside parentheses.
    42  				// That's where (*../noder/writer).expr expects it.
    43  				// See issue 73476.
    44  				p, ok := rangeVar.(*syntax.ParenExpr)
    45  				if !ok {
    46  					break
    47  				}
    48  				rangeVar = p.X
    49  			}
    50  			// Override type of rangeVar to be a constant
    51  			// (and thus side-effects will not be computed
    52  			// by the backend).
    53  			check.record(&operand{
    54  				mode: constant_,
    55  				expr: rangeVar,
    56  				typ:  Typ[Int],
    57  				val:  constant.MakeInt64(t.len),
    58  				id:   x.id,
    59  			})
    60  		}
    61  	}
    62  
    63  	// determine key/value types
    64  	var key, val Type
    65  	if x.mode != invalid {
    66  		k, v, cause, ok := rangeKeyVal(check, x.typ, func(v goVersion) bool {
    67  			return check.allowVersion(v)
    68  		})
    69  		switch {
    70  		case !ok && cause != "":
    71  			check.softErrorf(&x, InvalidRangeExpr, "cannot range over %s: %s", &x, cause)
    72  		case !ok:
    73  			check.softErrorf(&x, InvalidRangeExpr, "cannot range over %s", &x)
    74  		case k == nil && sKey != nil:
    75  			check.softErrorf(sKey, InvalidIterVar, "range over %s permits no iteration variables", &x)
    76  		case v == nil && sValue != nil:
    77  			check.softErrorf(sValue, InvalidIterVar, "range over %s permits only one iteration variable", &x)
    78  		case sExtra != nil:
    79  			check.softErrorf(sExtra, InvalidIterVar, "range clause permits at most two iteration variables")
    80  		}
    81  		key, val = k, v
    82  	}
    83  
    84  	// Open the for-statement block scope now, after the range clause.
    85  	// Iteration variables declared with := need to go in this scope (was go.dev/issue/51437).
    86  	check.openScope(rangeStmt, "range")
    87  	defer check.closeScope()
    88  
    89  	// check assignment to/declaration of iteration variables
    90  	// (irregular assignment, cannot easily map to existing assignment checks)
    91  
    92  	// lhs expressions and initialization value (rhs) types
    93  	lhs := [2]syntax.Expr{sKey, sValue} // sKey, sValue may be nil
    94  	rhs := [2]Type{key, val}            // key, val may be nil
    95  
    96  	rangeOverInt := isInteger(x.typ)
    97  
    98  	if isDef {
    99  		// short variable declaration
   100  		var vars []*Var
   101  		for i, lhs := range lhs {
   102  			if lhs == nil {
   103  				continue
   104  			}
   105  
   106  			// determine lhs variable
   107  			var obj *Var
   108  			if ident, _ := lhs.(*syntax.Name); ident != nil {
   109  				// declare new variable
   110  				name := ident.Value
   111  				obj = newVar(LocalVar, ident.Pos(), check.pkg, name, nil)
   112  				check.recordDef(ident, obj)
   113  				// _ variables don't count as new variables
   114  				if name != "_" {
   115  					vars = append(vars, obj)
   116  				}
   117  			} else {
   118  				check.errorf(lhs, InvalidSyntaxTree, "cannot declare %s", lhs)
   119  				obj = newVar(LocalVar, lhs.Pos(), check.pkg, "_", nil) // dummy variable
   120  			}
   121  			assert(obj.typ == nil)
   122  
   123  			// initialize lhs iteration variable, if any
   124  			typ := rhs[i]
   125  			if typ == nil || typ == Typ[Invalid] {
   126  				// typ == Typ[Invalid] can happen if allowVersion fails.
   127  				obj.typ = Typ[Invalid]
   128  				check.usedVars[obj] = true // don't complain about unused variable
   129  				continue
   130  			}
   131  
   132  			if rangeOverInt {
   133  				assert(i == 0) // at most one iteration variable (rhs[1] == nil or Typ[Invalid] for rangeOverInt)
   134  				check.initVar(obj, &x, "range clause")
   135  			} else {
   136  				var y operand
   137  				y.mode = value
   138  				y.expr = lhs // we don't have a better rhs expression to use here
   139  				y.typ = typ
   140  				check.initVar(obj, &y, "assignment") // error is on variable, use "assignment" not "range clause"
   141  			}
   142  			assert(obj.typ != nil)
   143  		}
   144  
   145  		// declare variables
   146  		if len(vars) > 0 {
   147  			scopePos := rangeStmt.Body.Pos()
   148  			for _, obj := range vars {
   149  				check.declare(check.scope, nil /* recordDef already called */, obj, scopePos)
   150  			}
   151  		} else {
   152  			check.error(noNewVarPos, NoNewVar, "no new variables on left side of :=")
   153  		}
   154  	} else if sKey != nil /* lhs[0] != nil */ {
   155  		// ordinary assignment
   156  		for i, lhs := range lhs {
   157  			if lhs == nil {
   158  				continue
   159  			}
   160  
   161  			// assign to lhs iteration variable, if any
   162  			typ := rhs[i]
   163  			if typ == nil || typ == Typ[Invalid] {
   164  				continue
   165  			}
   166  
   167  			if rangeOverInt {
   168  				assert(i == 0) // at most one iteration variable (rhs[1] == nil or Typ[Invalid] for rangeOverInt)
   169  				check.assignVar(lhs, nil, &x, "range clause")
   170  				// If the assignment succeeded, if x was untyped before, it now
   171  				// has a type inferred via the assignment. It must be an integer.
   172  				// (go.dev/issues/67027)
   173  				if x.mode != invalid && !isInteger(x.typ) {
   174  					check.softErrorf(lhs, InvalidRangeExpr, "cannot use iteration variable of type %s", x.typ)
   175  				}
   176  			} else {
   177  				var y operand
   178  				y.mode = value
   179  				y.expr = lhs // we don't have a better rhs expression to use here
   180  				y.typ = typ
   181  				check.assignVar(lhs, nil, &y, "assignment") // error is on variable, use "assignment" not "range clause"
   182  			}
   183  		}
   184  	} else if rangeOverInt {
   185  		// If we don't have any iteration variables, we still need to
   186  		// check that a (possibly untyped) integer range expression x
   187  		// is valid.
   188  		// We do this by checking the assignment _ = x. This ensures
   189  		// that an untyped x can be converted to a value of its default
   190  		// type (rune or int).
   191  		check.assignment(&x, nil, "range clause")
   192  	}
   193  
   194  	check.stmt(inner, rangeStmt.Body)
   195  }
   196  
   197  // rangeKeyVal returns the key and value type produced by a range clause
   198  // over an expression of type orig.
   199  // If allowVersion != nil, it is used to check the required language version.
   200  // If the range clause is not permitted, rangeKeyVal returns ok = false.
   201  // When ok = false, rangeKeyVal may also return a reason in cause.
   202  // The check parameter is only used in case of an error; it may be nil.
   203  func rangeKeyVal(check *Checker, orig Type, allowVersion func(goVersion) bool) (key, val Type, cause string, ok bool) {
   204  	bad := func(cause string) (Type, Type, string, bool) {
   205  		return Typ[Invalid], Typ[Invalid], cause, false
   206  	}
   207  
   208  	rtyp, err := commonUnder(orig, func(t, u Type) *typeError {
   209  		// A channel must permit receive operations.
   210  		if ch, _ := u.(*Chan); ch != nil && ch.dir == SendOnly {
   211  			return typeErrorf("receive from send-only channel %s", t)
   212  		}
   213  		return nil
   214  	})
   215  	if rtyp == nil {
   216  		return bad(err.format(check))
   217  	}
   218  
   219  	switch typ := arrayPtrDeref(rtyp).(type) {
   220  	case *Basic:
   221  		if isString(typ) {
   222  			return Typ[Int], universeRune, "", true // use 'rune' name
   223  		}
   224  		if isInteger(typ) {
   225  			if allowVersion != nil && !allowVersion(go1_22) {
   226  				return bad("requires go1.22 or later")
   227  			}
   228  			return orig, nil, "", true
   229  		}
   230  	case *Array:
   231  		return Typ[Int], typ.elem, "", true
   232  	case *Slice:
   233  		return Typ[Int], typ.elem, "", true
   234  	case *Map:
   235  		return typ.key, typ.elem, "", true
   236  	case *Chan:
   237  		assert(typ.dir != SendOnly)
   238  		return typ.elem, nil, "", true
   239  	case *Signature:
   240  		if !buildcfg.Experiment.RangeFunc && allowVersion != nil && !allowVersion(go1_23) {
   241  			return bad("requires go1.23 or later")
   242  		}
   243  		// check iterator arity
   244  		switch {
   245  		case typ.Params().Len() != 1:
   246  			return bad("func must be func(yield func(...) bool): wrong argument count")
   247  		case typ.Results().Len() != 0:
   248  			return bad("func must be func(yield func(...) bool): unexpected results")
   249  		}
   250  		assert(typ.Recv() == nil)
   251  		// check iterator argument type
   252  		u, err := commonUnder(typ.Params().At(0).Type(), nil)
   253  		cb, _ := u.(*Signature)
   254  		switch {
   255  		case cb == nil:
   256  			if err != nil {
   257  				return bad(check.sprintf("func must be func(yield func(...) bool): in yield type, %s", err.format(check)))
   258  			} else {
   259  				return bad("func must be func(yield func(...) bool): argument is not func")
   260  			}
   261  		case cb.Params().Len() > 2:
   262  			return bad("func must be func(yield func(...) bool): yield func has too many parameters")
   263  		case cb.Results().Len() != 1 || !Identical(cb.Results().At(0).Type(), universeBool):
   264  			// see go.dev/issues/71131, go.dev/issues/71164
   265  			if cb.Results().Len() == 1 && isBoolean(cb.Results().At(0).Type()) {
   266  				return bad("func must be func(yield func(...) bool): yield func returns user-defined boolean, not bool")
   267  			} else {
   268  				return bad("func must be func(yield func(...) bool): yield func does not return bool")
   269  			}
   270  		}
   271  		assert(cb.Recv() == nil)
   272  		// determine key and value types, if any
   273  		if cb.Params().Len() >= 1 {
   274  			key = cb.Params().At(0).Type()
   275  		}
   276  		if cb.Params().Len() >= 2 {
   277  			val = cb.Params().At(1).Type()
   278  		}
   279  		return key, val, "", true
   280  	}
   281  	return
   282  }
   283
View as plain text