...
Run Format

Source file src/go/types/call.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  // This file implements typechecking of call and selector expressions.
     6  
     7  package types
     8  
     9  import (
    10  	"go/ast"
    11  	"go/token"
    12  )
    13  
    14  func (check *Checker) call(x *operand, e *ast.CallExpr) exprKind {
    15  	check.exprOrType(x, e.Fun)
    16  
    17  	switch x.mode {
    18  	case invalid:
    19  		check.use(e.Args...)
    20  		x.mode = invalid
    21  		x.expr = e
    22  		return statement
    23  
    24  	case typexpr:
    25  		// conversion
    26  		T := x.typ
    27  		x.mode = invalid
    28  		switch n := len(e.Args); n {
    29  		case 0:
    30  			check.errorf(e.Rparen, "missing argument in conversion to %s", T)
    31  		case 1:
    32  			check.expr(x, e.Args[0])
    33  			if x.mode != invalid {
    34  				check.conversion(x, T)
    35  			}
    36  		default:
    37  			check.errorf(e.Args[n-1].Pos(), "too many arguments in conversion to %s", T)
    38  		}
    39  		x.expr = e
    40  		return conversion
    41  
    42  	case builtin:
    43  		id := x.id
    44  		if !check.builtin(x, e, id) {
    45  			x.mode = invalid
    46  		}
    47  		x.expr = e
    48  		// a non-constant result implies a function call
    49  		if x.mode != invalid && x.mode != constant_ {
    50  			check.hasCallOrRecv = true
    51  		}
    52  		return predeclaredFuncs[id].kind
    53  
    54  	default:
    55  		// function/method call
    56  		sig, _ := x.typ.Underlying().(*Signature)
    57  		if sig == nil {
    58  			check.invalidOp(x.pos(), "cannot call non-function %s", x)
    59  			x.mode = invalid
    60  			x.expr = e
    61  			return statement
    62  		}
    63  
    64  		arg, n, _ := unpack(func(x *operand, i int) { check.multiExpr(x, e.Args[i]) }, len(e.Args), false)
    65  		if arg != nil {
    66  			check.arguments(x, e, sig, arg, n)
    67  		} else {
    68  			x.mode = invalid
    69  		}
    70  
    71  		// determine result
    72  		switch sig.results.Len() {
    73  		case 0:
    74  			x.mode = novalue
    75  		case 1:
    76  			x.mode = value
    77  			x.typ = sig.results.vars[0].typ // unpack tuple
    78  		default:
    79  			x.mode = value
    80  			x.typ = sig.results
    81  		}
    82  
    83  		x.expr = e
    84  		check.hasCallOrRecv = true
    85  
    86  		return statement
    87  	}
    88  }
    89  
    90  // use type-checks each argument.
    91  // Useful to make sure expressions are evaluated
    92  // (and variables are "used") in the presence of other errors.
    93  // The arguments may be nil.
    94  func (check *Checker) use(arg ...ast.Expr) {
    95  	var x operand
    96  	for _, e := range arg {
    97  		// The nil check below is necessary since certain AST fields
    98  		// may legally be nil (e.g., the ast.SliceExpr.High field).
    99  		if e != nil {
   100  			check.rawExpr(&x, e, nil)
   101  		}
   102  	}
   103  }
   104  
   105  // useLHS is like use, but doesn't "use" top-level identifiers.
   106  // It should be called instead of use if the arguments are
   107  // expressions on the lhs of an assignment.
   108  // The arguments must not be nil.
   109  func (check *Checker) useLHS(arg ...ast.Expr) {
   110  	var x operand
   111  	for _, e := range arg {
   112  		// If the lhs is an identifier denoting a variable v, this assignment
   113  		// is not a 'use' of v. Remember current value of v.used and restore
   114  		// after evaluating the lhs via check.rawExpr.
   115  		var v *Var
   116  		var v_used bool
   117  		if ident, _ := unparen(e).(*ast.Ident); ident != nil {
   118  			// never type-check the blank name on the lhs
   119  			if ident.Name == "_" {
   120  				continue
   121  			}
   122  			if _, obj := check.scope.LookupParent(ident.Name, token.NoPos); obj != nil {
   123  				// It's ok to mark non-local variables, but ignore variables
   124  				// from other packages to avoid potential race conditions with
   125  				// dot-imported variables.
   126  				if w, _ := obj.(*Var); w != nil && w.pkg == check.pkg {
   127  					v = w
   128  					v_used = v.used
   129  				}
   130  			}
   131  		}
   132  		check.rawExpr(&x, e, nil)
   133  		if v != nil {
   134  			v.used = v_used // restore v.used
   135  		}
   136  	}
   137  }
   138  
   139  // useGetter is like use, but takes a getter instead of a list of expressions.
   140  // It should be called instead of use if a getter is present to avoid repeated
   141  // evaluation of the first argument (since the getter was likely obtained via
   142  // unpack, which may have evaluated the first argument already).
   143  func (check *Checker) useGetter(get getter, n int) {
   144  	var x operand
   145  	for i := 0; i < n; i++ {
   146  		get(&x, i)
   147  	}
   148  }
   149  
   150  // A getter sets x as the i'th operand, where 0 <= i < n and n is the total
   151  // number of operands (context-specific, and maintained elsewhere). A getter
   152  // type-checks the i'th operand; the details of the actual check are getter-
   153  // specific.
   154  type getter func(x *operand, i int)
   155  
   156  // unpack takes a getter get and a number of operands n. If n == 1, unpack
   157  // calls the incoming getter for the first operand. If that operand is
   158  // invalid, unpack returns (nil, 0, false). Otherwise, if that operand is a
   159  // function call, or a comma-ok expression and allowCommaOk is set, the result
   160  // is a new getter and operand count providing access to the function results,
   161  // or comma-ok values, respectively. The third result value reports if it
   162  // is indeed the comma-ok case. In all other cases, the incoming getter and
   163  // operand count are returned unchanged, and the third result value is false.
   164  //
   165  // In other words, if there's exactly one operand that - after type-checking
   166  // by calling get - stands for multiple operands, the resulting getter provides
   167  // access to those operands instead.
   168  //
   169  // If the returned getter is called at most once for a given operand index i
   170  // (including i == 0), that operand is guaranteed to cause only one call of
   171  // the incoming getter with that i.
   172  //
   173  func unpack(get getter, n int, allowCommaOk bool) (getter, int, bool) {
   174  	if n != 1 {
   175  		// zero or multiple values
   176  		return get, n, false
   177  	}
   178  	// possibly result of an n-valued function call or comma,ok value
   179  	var x0 operand
   180  	get(&x0, 0)
   181  	if x0.mode == invalid {
   182  		return nil, 0, false
   183  	}
   184  
   185  	if t, ok := x0.typ.(*Tuple); ok {
   186  		// result of an n-valued function call
   187  		return func(x *operand, i int) {
   188  			x.mode = value
   189  			x.expr = x0.expr
   190  			x.typ = t.At(i).typ
   191  		}, t.Len(), false
   192  	}
   193  
   194  	if x0.mode == mapindex || x0.mode == commaok {
   195  		// comma-ok value
   196  		if allowCommaOk {
   197  			a := [2]Type{x0.typ, Typ[UntypedBool]}
   198  			return func(x *operand, i int) {
   199  				x.mode = value
   200  				x.expr = x0.expr
   201  				x.typ = a[i]
   202  			}, 2, true
   203  		}
   204  		x0.mode = value
   205  	}
   206  
   207  	// single value
   208  	return func(x *operand, i int) {
   209  		if i != 0 {
   210  			unreachable()
   211  		}
   212  		*x = x0
   213  	}, 1, false
   214  }
   215  
   216  // arguments checks argument passing for the call with the given signature.
   217  // The arg function provides the operand for the i'th argument.
   218  func (check *Checker) arguments(x *operand, call *ast.CallExpr, sig *Signature, arg getter, n int) {
   219  	if call.Ellipsis.IsValid() {
   220  		// last argument is of the form x...
   221  		if !sig.variadic {
   222  			check.errorf(call.Ellipsis, "cannot use ... in call to non-variadic %s", call.Fun)
   223  			check.useGetter(arg, n)
   224  			return
   225  		}
   226  		if len(call.Args) == 1 && n > 1 {
   227  			// f()... is not permitted if f() is multi-valued
   228  			check.errorf(call.Ellipsis, "cannot use ... with %d-valued %s", n, call.Args[0])
   229  			check.useGetter(arg, n)
   230  			return
   231  		}
   232  	}
   233  
   234  	// evaluate arguments
   235  	for i := 0; i < n; i++ {
   236  		arg(x, i)
   237  		if x.mode != invalid {
   238  			var ellipsis token.Pos
   239  			if i == n-1 && call.Ellipsis.IsValid() {
   240  				ellipsis = call.Ellipsis
   241  			}
   242  			check.argument(call.Fun, sig, i, x, ellipsis)
   243  		}
   244  	}
   245  
   246  	// check argument count
   247  	if sig.variadic {
   248  		// a variadic function accepts an "empty"
   249  		// last argument: count one extra
   250  		n++
   251  	}
   252  	if n < sig.params.Len() {
   253  		check.errorf(call.Rparen, "too few arguments in call to %s", call.Fun)
   254  		// ok to continue
   255  	}
   256  }
   257  
   258  // argument checks passing of argument x to the i'th parameter of the given signature.
   259  // If ellipsis is valid, the argument is followed by ... at that position in the call.
   260  func (check *Checker) argument(fun ast.Expr, sig *Signature, i int, x *operand, ellipsis token.Pos) {
   261  	check.singleValue(x)
   262  	if x.mode == invalid {
   263  		return
   264  	}
   265  
   266  	n := sig.params.Len()
   267  
   268  	// determine parameter type
   269  	var typ Type
   270  	switch {
   271  	case i < n:
   272  		typ = sig.params.vars[i].typ
   273  	case sig.variadic:
   274  		typ = sig.params.vars[n-1].typ
   275  		if debug {
   276  			if _, ok := typ.(*Slice); !ok {
   277  				check.dump("%s: expected unnamed slice type, got %s", sig.params.vars[n-1].Pos(), typ)
   278  			}
   279  		}
   280  	default:
   281  		check.errorf(x.pos(), "too many arguments")
   282  		return
   283  	}
   284  
   285  	if ellipsis.IsValid() {
   286  		// argument is of the form x... and x is single-valued
   287  		if i != n-1 {
   288  			check.errorf(ellipsis, "can only use ... with matching parameter")
   289  			return
   290  		}
   291  		if _, ok := x.typ.Underlying().(*Slice); !ok && x.typ != Typ[UntypedNil] { // see issue #18268
   292  			check.errorf(x.pos(), "cannot use %s as parameter of type %s", x, typ)
   293  			return
   294  		}
   295  	} else if sig.variadic && i >= n-1 {
   296  		// use the variadic parameter slice's element type
   297  		typ = typ.(*Slice).elem
   298  	}
   299  
   300  	check.assignment(x, typ, check.sprintf("argument to %s", fun))
   301  }
   302  
   303  func (check *Checker) selector(x *operand, e *ast.SelectorExpr) {
   304  	// these must be declared before the "goto Error" statements
   305  	var (
   306  		obj      Object
   307  		index    []int
   308  		indirect bool
   309  	)
   310  
   311  	sel := e.Sel.Name
   312  	// If the identifier refers to a package, handle everything here
   313  	// so we don't need a "package" mode for operands: package names
   314  	// can only appear in qualified identifiers which are mapped to
   315  	// selector expressions.
   316  	if ident, ok := e.X.(*ast.Ident); ok {
   317  		_, obj := check.scope.LookupParent(ident.Name, check.pos)
   318  		if pname, _ := obj.(*PkgName); pname != nil {
   319  			assert(pname.pkg == check.pkg)
   320  			check.recordUse(ident, pname)
   321  			pname.used = true
   322  			pkg := pname.imported
   323  			exp := pkg.scope.Lookup(sel)
   324  			if exp == nil {
   325  				if !pkg.fake {
   326  					check.errorf(e.Pos(), "%s not declared by package %s", sel, pkg.name)
   327  				}
   328  				goto Error
   329  			}
   330  			if !exp.Exported() {
   331  				check.errorf(e.Pos(), "%s not exported by package %s", sel, pkg.name)
   332  				// ok to continue
   333  			}
   334  			check.recordUse(e.Sel, exp)
   335  
   336  			// Simplified version of the code for *ast.Idents:
   337  			// - imported objects are always fully initialized
   338  			switch exp := exp.(type) {
   339  			case *Const:
   340  				assert(exp.Val() != nil)
   341  				x.mode = constant_
   342  				x.typ = exp.typ
   343  				x.val = exp.val
   344  			case *TypeName:
   345  				x.mode = typexpr
   346  				x.typ = exp.typ
   347  			case *Var:
   348  				x.mode = variable
   349  				x.typ = exp.typ
   350  			case *Func:
   351  				x.mode = value
   352  				x.typ = exp.typ
   353  			case *Builtin:
   354  				x.mode = builtin
   355  				x.typ = exp.typ
   356  				x.id = exp.id
   357  			default:
   358  				check.dump("unexpected object %v", exp)
   359  				unreachable()
   360  			}
   361  			x.expr = e
   362  			return
   363  		}
   364  	}
   365  
   366  	check.exprOrType(x, e.X)
   367  	if x.mode == invalid {
   368  		goto Error
   369  	}
   370  
   371  	obj, index, indirect = LookupFieldOrMethod(x.typ, x.mode == variable, check.pkg, sel)
   372  	if obj == nil {
   373  		switch {
   374  		case index != nil:
   375  			// TODO(gri) should provide actual type where the conflict happens
   376  			check.invalidOp(e.Pos(), "ambiguous selector %s", sel)
   377  		case indirect:
   378  			check.invalidOp(e.Pos(), "%s is not in method set of %s", sel, x.typ)
   379  		default:
   380  			check.invalidOp(e.Pos(), "%s has no field or method %s", x, sel)
   381  		}
   382  		goto Error
   383  	}
   384  
   385  	if x.mode == typexpr {
   386  		// method expression
   387  		m, _ := obj.(*Func)
   388  		if m == nil {
   389  			check.invalidOp(e.Pos(), "%s has no method %s", x, sel)
   390  			goto Error
   391  		}
   392  
   393  		check.recordSelection(e, MethodExpr, x.typ, m, index, indirect)
   394  
   395  		// the receiver type becomes the type of the first function
   396  		// argument of the method expression's function type
   397  		var params []*Var
   398  		sig := m.typ.(*Signature)
   399  		if sig.params != nil {
   400  			params = sig.params.vars
   401  		}
   402  		x.mode = value
   403  		x.typ = &Signature{
   404  			params:   NewTuple(append([]*Var{NewVar(token.NoPos, check.pkg, "", x.typ)}, params...)...),
   405  			results:  sig.results,
   406  			variadic: sig.variadic,
   407  		}
   408  
   409  		check.addDeclDep(m)
   410  
   411  	} else {
   412  		// regular selector
   413  		switch obj := obj.(type) {
   414  		case *Var:
   415  			check.recordSelection(e, FieldVal, x.typ, obj, index, indirect)
   416  			if x.mode == variable || indirect {
   417  				x.mode = variable
   418  			} else {
   419  				x.mode = value
   420  			}
   421  			x.typ = obj.typ
   422  
   423  		case *Func:
   424  			// TODO(gri) If we needed to take into account the receiver's
   425  			// addressability, should we report the type &(x.typ) instead?
   426  			check.recordSelection(e, MethodVal, x.typ, obj, index, indirect)
   427  
   428  			if debug {
   429  				// Verify that LookupFieldOrMethod and MethodSet.Lookup agree.
   430  				typ := x.typ
   431  				if x.mode == variable {
   432  					// If typ is not an (unnamed) pointer or an interface,
   433  					// use *typ instead, because the method set of *typ
   434  					// includes the methods of typ.
   435  					// Variables are addressable, so we can always take their
   436  					// address.
   437  					if _, ok := typ.(*Pointer); !ok && !IsInterface(typ) {
   438  						typ = &Pointer{base: typ}
   439  					}
   440  				}
   441  				// If we created a synthetic pointer type above, we will throw
   442  				// away the method set computed here after use.
   443  				// TODO(gri) Method set computation should probably always compute
   444  				// both, the value and the pointer receiver method set and represent
   445  				// them in a single structure.
   446  				// TODO(gri) Consider also using a method set cache for the lifetime
   447  				// of checker once we rely on MethodSet lookup instead of individual
   448  				// lookup.
   449  				mset := NewMethodSet(typ)
   450  				if m := mset.Lookup(check.pkg, sel); m == nil || m.obj != obj {
   451  					check.dump("%s: (%s).%v -> %s", e.Pos(), typ, obj.name, m)
   452  					check.dump("%s\n", mset)
   453  					panic("method sets and lookup don't agree")
   454  				}
   455  			}
   456  
   457  			x.mode = value
   458  
   459  			// remove receiver
   460  			sig := *obj.typ.(*Signature)
   461  			sig.recv = nil
   462  			x.typ = &sig
   463  
   464  			check.addDeclDep(obj)
   465  
   466  		default:
   467  			unreachable()
   468  		}
   469  	}
   470  
   471  	// everything went well
   472  	x.expr = e
   473  	return
   474  
   475  Error:
   476  	x.mode = invalid
   477  	x.expr = e
   478  }
   479  

View as plain text