range.go

     1  // Code generated by "go test -run=Generate -write=all"; DO NOT EDIT.
     2  // Source: ../../cmd/compile/internal/types2/range.go
     3  
     4  // Copyright 2025 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 typechecking of range statements.
     9  
    10  package types
    11  
    12  import (
    13  	"go/ast"
    14  	"go/constant"
    15  	. "internal/types/errors"
    16  )
    17  
    18  // rangeStmt type-checks a range statement of form
    19  //
    20  //	for sKey, sValue = range rangeVar { ... }
    21  //
    22  // where sKey, sValue, sExtra may be nil. isDef indicates whether these
    23  // variables are assigned to only (=) or whether there is a short variable
    24  // declaration (:=). If the latter and there are no variables, an error is
    25  // reported at noNewVarPos.
    26  func (check *Checker) rangeStmt(inner stmtContext, rangeStmt *ast.RangeStmt, noNewVarPos positioner, sKey, sValue, sExtra, rangeVar ast.Expr, isDef bool) {
    27  	// check expression to iterate over
    28  	var x operand
    29  
    30  	// From the spec:
    31  	//   The range expression x is evaluated before beginning the loop,
    32  	//   with one exception: if at most one iteration variable is present
    33  	//   and x or len(x) is constant, the range expression is not evaluated.
    34  	// So we have to be careful not to evaluate the arg in the
    35  	// described situation.
    36  
    37  	check.hasCallOrRecv = false
    38  	check.expr(nil, &x, rangeVar)
    39  
    40  	if isTypes2 && x.mode != invalid && sValue == nil && !check.hasCallOrRecv {
    41  		if t, ok := arrayPtrDeref(under(x.typ)).(*Array); ok {
    42  			for {
    43  				// Put constant info on the thing inside parentheses.
    44  				// That's where (*../noder/writer).expr expects it.
    45  				// See issue 73476.
    46  				p, ok := rangeVar.(*ast.ParenExpr)
    47  				if !ok {
    48  					break
    49  				}
    50  				rangeVar = p.X
    51  			}
    52  			// Override type of rangeVar to be a constant
    53  			// (and thus side-effects will not be computed
    54  			// by the backend).
    55  			check.record(&operand{
    56  				mode: constant_,
    57  				expr: rangeVar,
    58  				typ:  Typ[Int],
    59  				val:  constant.MakeInt64(t.len),
    60  				id:   x.id,
    61  			})
    62  		}
    63  	}
    64  
    65  	// determine key/value types
    66  	var key, val Type
    67  	if x.mode != invalid {
    68  		k, v, cause, ok := rangeKeyVal(check, x.typ, func(v goVersion) bool {
    69  			return check.allowVersion(v)
    70  		})
    71  		switch {
    72  		case !ok && cause != "":
    73  			check.softErrorf(&x, InvalidRangeExpr, "cannot range over %s: %s", &x, cause)
    74  		case !ok:
    75  			check.softErrorf(&x, InvalidRangeExpr, "cannot range over %s", &x)
    76  		case k == nil && sKey != nil:
    77  			check.softErrorf(sKey, InvalidIterVar, "range over %s permits no iteration variables", &x)
    78  		case v == nil && sValue != nil:
    79  			check.softErrorf(sValue, InvalidIterVar, "range over %s permits only one iteration variable", &x)
    80  		case sExtra != nil:
    81  			check.softErrorf(sExtra, InvalidIterVar, "range clause permits at most two iteration variables")
    82  		}
    83  		key, val = k, v
    84  	}
    85  
    86  	// Open the for-statement block scope now, after the range clause.
    87  	// Iteration variables declared with := need to go in this scope (was go.dev/issue/51437).
    88  	check.openScope(rangeStmt, "range")
    89  	defer check.closeScope()
    90  
    91  	// check assignment to/declaration of iteration variables
    92  	// (irregular assignment, cannot easily map to existing assignment checks)
    93  
    94  	// lhs expressions and initialization value (rhs) types
    95  	lhs := [2]ast.Expr{sKey, sValue} // sKey, sValue may be nil
    96  	rhs := [2]Type{key, val}         // key, val may be nil
    97  
    98  	rangeOverInt := isInteger(x.typ)
    99  
   100  	if isDef {
   101  		// short variable declaration
   102  		var vars []*Var
   103  		for i, lhs := range lhs {
   104  			if lhs == nil {
   105  				continue
   106  			}
   107  
   108  			// determine lhs variable
   109  			var obj *Var
   110  			if ident, _ := lhs.(*ast.Ident); ident != nil {
   111  				// declare new variable
   112  				name := ident.Name
   113  				obj = newVar(LocalVar, ident.Pos(), check.pkg, name, nil)
   114  				check.recordDef(ident, obj)
   115  				// _ variables don't count as new variables
   116  				if name != "_" {
   117  					vars = append(vars, obj)
   118  				}
   119  			} else {
   120  				check.errorf(lhs, InvalidSyntaxTree, "cannot declare %s", lhs)
   121  				obj = newVar(LocalVar, lhs.Pos(), check.pkg, "_", nil) // dummy variable
   122  			}
   123  			assert(obj.typ == nil)
   124  
   125  			// initialize lhs iteration variable, if any
   126  			typ := rhs[i]
   127  			if typ == nil || typ == Typ[Invalid] {
   128  				// typ == Typ[Invalid] can happen if allowVersion fails.
   129  				obj.typ = Typ[Invalid]
   130  				check.usedVars[obj] = true // don't complain about unused variable
   131  				continue
   132  			}
   133  
   134  			if rangeOverInt {
   135  				assert(i == 0) // at most one iteration variable (rhs[1] == nil or Typ[Invalid] for rangeOverInt)
   136  				check.initVar(obj, &x, "range clause")
   137  			} else {
   138  				var y operand
   139  				y.mode = value
   140  				y.expr = lhs // we don't have a better rhs expression to use here
   141  				y.typ = typ
   142  				check.initVar(obj, &y, "assignment") // error is on variable, use "assignment" not "range clause"
   143  			}
   144  			assert(obj.typ != nil)
   145  		}
   146  
   147  		// declare variables
   148  		if len(vars) > 0 {
   149  			scopePos := rangeStmt.Body.Pos()
   150  			for _, obj := range vars {
   151  				check.declare(check.scope, nil /* recordDef already called */, obj, scopePos)
   152  			}
   153  		} else {
   154  			check.error(noNewVarPos, NoNewVar, "no new variables on left side of :=")
   155  		}
   156  	} else if sKey != nil /* lhs[0] != nil */ {
   157  		// ordinary assignment
   158  		for i, lhs := range lhs {
   159  			if lhs == nil {
   160  				continue
   161  			}
   162  
   163  			// assign to lhs iteration variable, if any
   164  			typ := rhs[i]
   165  			if typ == nil || typ == Typ[Invalid] {
   166  				continue
   167  			}
   168  
   169  			if rangeOverInt {
   170  				assert(i == 0) // at most one iteration variable (rhs[1] == nil or Typ[Invalid] for rangeOverInt)
   171  				check.assignVar(lhs, nil, &x, "range clause")
   172  				// If the assignment succeeded, if x was untyped before, it now
   173  				// has a type inferred via the assignment. It must be an integer.
   174  				// (go.dev/issues/67027)
   175  				if x.mode != invalid && !isInteger(x.typ) {
   176  					check.softErrorf(lhs, InvalidRangeExpr, "cannot use iteration variable of type %s", x.typ)
   177  				}
   178  			} else {
   179  				var y operand
   180  				y.mode = value
   181  				y.expr = lhs // we don't have a better rhs expression to use here
   182  				y.typ = typ
   183  				check.assignVar(lhs, nil, &y, "assignment") // error is on variable, use "assignment" not "range clause"
   184  			}
   185  		}
   186  	} else if rangeOverInt {
   187  		// If we don't have any iteration variables, we still need to
   188  		// check that a (possibly untyped) integer range expression x
   189  		// is valid.
   190  		// We do this by checking the assignment _ = x. This ensures
   191  		// that an untyped x can be converted to a value of its default
   192  		// type (rune or int).
   193  		check.assignment(&x, nil, "range clause")
   194  	}
   195  
   196  	check.stmt(inner, rangeStmt.Body)
   197  }
   198  
   199  // rangeKeyVal returns the key and value type produced by a range clause
   200  // over an expression of type orig.
   201  // If allowVersion != nil, it is used to check the required language version.
   202  // If the range clause is not permitted, rangeKeyVal returns ok = false.
   203  // When ok = false, rangeKeyVal may also return a reason in cause.
   204  // The check parameter is only used in case of an error; it may be nil.
   205  func rangeKeyVal(check *Checker, orig Type, allowVersion func(goVersion) bool) (key, val Type, cause string, ok bool) {
   206  	bad := func(cause string) (Type, Type, string, bool) {
   207  		return Typ[Invalid], Typ[Invalid], cause, false
   208  	}
   209  
   210  	rtyp, err := commonUnder(orig, func(t, u Type) *typeError {
   211  		// A channel must permit receive operations.
   212  		if ch, _ := u.(*Chan); ch != nil && ch.dir == SendOnly {
   213  			return typeErrorf("receive from send-only channel %s", t)
   214  		}
   215  		return nil
   216  	})
   217  	if rtyp == nil {
   218  		return bad(err.format(check))
   219  	}
   220  
   221  	switch typ := arrayPtrDeref(rtyp).(type) {
   222  	case *Basic:
   223  		if isString(typ) {
   224  			return Typ[Int], universeRune, "", true // use 'rune' name
   225  		}
   226  		if isInteger(typ) {
   227  			if allowVersion != nil && !allowVersion(go1_22) {
   228  				return bad("requires go1.22 or later")
   229  			}
   230  			return orig, nil, "", true
   231  		}
   232  	case *Array:
   233  		return Typ[Int], typ.elem, "", true
   234  	case *Slice:
   235  		return Typ[Int], typ.elem, "", true
   236  	case *Map:
   237  		return typ.key, typ.elem, "", true
   238  	case *Chan:
   239  		assert(typ.dir != SendOnly)
   240  		return typ.elem, nil, "", true
   241  	case *Signature:
   242  		if allowVersion != nil && !allowVersion(go1_23) {
   243  			return bad("requires go1.23 or later")
   244  		}
   245  		// check iterator arity
   246  		switch {
   247  		case typ.Params().Len() != 1:
   248  			return bad("func must be func(yield func(...) bool): wrong argument count")
   249  		case typ.Results().Len() != 0:
   250  			return bad("func must be func(yield func(...) bool): unexpected results")
   251  		}
   252  		assert(typ.Recv() == nil)
   253  		// check iterator argument type
   254  		u, err := commonUnder(typ.Params().At(0).Type(), nil)
   255  		cb, _ := u.(*Signature)
   256  		switch {
   257  		case cb == nil:
   258  			if err != nil {
   259  				return bad(check.sprintf("func must be func(yield func(...) bool): in yield type, %s", err.format(check)))
   260  			} else {
   261  				return bad("func must be func(yield func(...) bool): argument is not func")
   262  			}
   263  		case cb.Params().Len() > 2:
   264  			return bad("func must be func(yield func(...) bool): yield func has too many parameters")
   265  		case cb.Results().Len() != 1 || !Identical(cb.Results().At(0).Type(), universeBool):
   266  			// see go.dev/issues/71131, go.dev/issues/71164
   267  			if cb.Results().Len() == 1 && isBoolean(cb.Results().At(0).Type()) {
   268  				return bad("func must be func(yield func(...) bool): yield func returns user-defined boolean, not bool")
   269  			} else {
   270  				return bad("func must be func(yield func(...) bool): yield func does not return bool")
   271  			}
   272  		}
   273  		assert(cb.Recv() == nil)
   274  		// determine key and value types, if any
   275  		if cb.Params().Len() >= 1 {
   276  			key = cb.Params().At(0).Type()
   277  		}
   278  		if cb.Params().Len() >= 2 {
   279  			val = cb.Params().At(1).Type()
   280  		}
   281  		return key, val, "", true
   282  	}
   283  	return
   284  }
   285
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