struct.go

Documentation: go/types

     1  // Copyright 2021 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  	"go/ast"
     9  	"go/token"
    10  	"strconv"
    11  )
    12  
    13  // ----------------------------------------------------------------------------
    14  // API
    15  
    16  // A Struct represents a struct type.
    17  type Struct struct {
    18  	fields []*Var   // fields != nil indicates the struct is set up (possibly with len(fields) == 0)
    19  	tags   []string // field tags; nil if there are no tags
    20  }
    21  
    22  // NewStruct returns a new struct with the given fields and corresponding field tags.
    23  // If a field with index i has a tag, tags[i] must be that tag, but len(tags) may be
    24  // only as long as required to hold the tag with the largest index i. Consequently,
    25  // if no field has a tag, tags may be nil.
    26  func NewStruct(fields []*Var, tags []string) *Struct {
    27  	var fset objset
    28  	for _, f := range fields {
    29  		if f.name != "_" && fset.insert(f) != nil {
    30  			panic("multiple fields with the same name")
    31  		}
    32  	}
    33  	if len(tags) > len(fields) {
    34  		panic("more tags than fields")
    35  	}
    36  	s := &Struct{fields: fields, tags: tags}
    37  	s.markComplete()
    38  	return s
    39  }
    40  
    41  // NumFields returns the number of fields in the struct (including blank and embedded fields).
    42  func (s *Struct) NumFields() int { return len(s.fields) }
    43  
    44  // Field returns the i'th field for 0 <= i < NumFields().
    45  func (s *Struct) Field(i int) *Var { return s.fields[i] }
    46  
    47  // Tag returns the i'th field tag for 0 <= i < NumFields().
    48  func (s *Struct) Tag(i int) string {
    49  	if i < len(s.tags) {
    50  		return s.tags[i]
    51  	}
    52  	return ""
    53  }
    54  
    55  func (t *Struct) Underlying() Type { return t }
    56  func (t *Struct) String() string   { return TypeString(t, nil) }
    57  
    58  // ----------------------------------------------------------------------------
    59  // Implementation
    60  
    61  func (s *Struct) markComplete() {
    62  	if s.fields == nil {
    63  		s.fields = make([]*Var, 0)
    64  	}
    65  }
    66  
    67  func (check *Checker) structType(styp *Struct, e *ast.StructType) {
    68  	list := e.Fields
    69  	if list == nil {
    70  		styp.markComplete()
    71  		return
    72  	}
    73  
    74  	// struct fields and tags
    75  	var fields []*Var
    76  	var tags []string
    77  
    78  	// for double-declaration checks
    79  	var fset objset
    80  
    81  	// current field typ and tag
    82  	var typ Type
    83  	var tag string
    84  	add := func(ident *ast.Ident, embedded bool, pos token.Pos) {
    85  		if tag != "" && tags == nil {
    86  			tags = make([]string, len(fields))
    87  		}
    88  		if tags != nil {
    89  			tags = append(tags, tag)
    90  		}
    91  
    92  		name := ident.Name
    93  		fld := NewField(pos, check.pkg, name, typ, embedded)
    94  		// spec: "Within a struct, non-blank field names must be unique."
    95  		if name == "_" || check.declareInSet(&fset, pos, fld) {
    96  			fields = append(fields, fld)
    97  			check.recordDef(ident, fld)
    98  		}
    99  	}
   100  
   101  	// addInvalid adds an embedded field of invalid type to the struct for
   102  	// fields with errors; this keeps the number of struct fields in sync
   103  	// with the source as long as the fields are _ or have different names
   104  	// (issue #25627).
   105  	addInvalid := func(ident *ast.Ident, pos token.Pos) {
   106  		typ = Typ[Invalid]
   107  		tag = ""
   108  		add(ident, true, pos)
   109  	}
   110  
   111  	for _, f := range list.List {
   112  		typ = check.varType(f.Type)
   113  		tag = check.tag(f.Tag)
   114  		if len(f.Names) > 0 {
   115  			// named fields
   116  			for _, name := range f.Names {
   117  				add(name, false, name.Pos())
   118  			}
   119  		} else {
   120  			// embedded field
   121  			// spec: "An embedded type must be specified as a type name T or as a
   122  			// pointer to a non-interface type name *T, and T itself may not be a
   123  			// pointer type."
   124  			pos := f.Type.Pos()
   125  			name := embeddedFieldIdent(f.Type)
   126  			if name == nil {
   127  				check.invalidAST(f.Type, "embedded field type %s has no name", f.Type)
   128  				name = ast.NewIdent("_")
   129  				name.NamePos = pos
   130  				addInvalid(name, pos)
   131  				continue
   132  			}
   133  			add(name, true, pos)
   134  
   135  			// Because we have a name, typ must be of the form T or *T, where T is the name
   136  			// of a (named or alias) type, and t (= deref(typ)) must be the type of T.
   137  			// We must delay this check to the end because we don't want to instantiate
   138  			// (via under(t)) a possibly incomplete type.
   139  
   140  			// for use in the closure below
   141  			embeddedTyp := typ
   142  			embeddedPos := f.Type
   143  
   144  			check.later(func() {
   145  				t, isPtr := deref(embeddedTyp)
   146  				switch u := under(t).(type) {
   147  				case *Basic:
   148  					if t == Typ[Invalid] {
   149  						// error was reported before
   150  						return
   151  					}
   152  					// unsafe.Pointer is treated like a regular pointer
   153  					if u.kind == UnsafePointer {
   154  						check.error(embeddedPos, _InvalidPtrEmbed, "embedded field type cannot be unsafe.Pointer")
   155  					}
   156  				case *Pointer:
   157  					check.error(embeddedPos, _InvalidPtrEmbed, "embedded field type cannot be a pointer")
   158  				case *Interface:
   159  					if isTypeParam(t) {
   160  						// The error code here is inconsistent with other error codes for
   161  						// invalid embedding, because this restriction may be relaxed in the
   162  						// future, and so it did not warrant a new error code.
   163  						check.error(embeddedPos, _MisplacedTypeParam, "embedded field type cannot be a (pointer to a) type parameter")
   164  						break
   165  					}
   166  					if isPtr {
   167  						check.error(embeddedPos, _InvalidPtrEmbed, "embedded field type cannot be a pointer to an interface")
   168  					}
   169  				}
   170  			}).describef(embeddedPos, "check embedded type %s", embeddedTyp)
   171  		}
   172  	}
   173  
   174  	styp.fields = fields
   175  	styp.tags = tags
   176  	styp.markComplete()
   177  }
   178  
   179  func embeddedFieldIdent(e ast.Expr) *ast.Ident {
   180  	switch e := e.(type) {
   181  	case *ast.Ident:
   182  		return e
   183  	case *ast.StarExpr:
   184  		// *T is valid, but **T is not
   185  		if _, ok := e.X.(*ast.StarExpr); !ok {
   186  			return embeddedFieldIdent(e.X)
   187  		}
   188  	case *ast.SelectorExpr:
   189  		return e.Sel
   190  	case *ast.IndexExpr:
   191  		return embeddedFieldIdent(e.X)
   192  	case *ast.IndexListExpr:
   193  		return embeddedFieldIdent(e.X)
   194  	}
   195  	return nil // invalid embedded field
   196  }
   197  
   198  func (check *Checker) declareInSet(oset *objset, pos token.Pos, obj Object) bool {
   199  	if alt := oset.insert(obj); alt != nil {
   200  		check.errorf(atPos(pos), _DuplicateDecl, "%s redeclared", obj.Name())
   201  		check.reportAltDecl(alt)
   202  		return false
   203  	}
   204  	return true
   205  }
   206  
   207  func (check *Checker) tag(t *ast.BasicLit) string {
   208  	if t != nil {
   209  		if t.Kind == token.STRING {
   210  			if val, err := strconv.Unquote(t.Value); err == nil {
   211  				return val
   212  			}
   213  		}
   214  		check.invalidAST(t, "incorrect tag syntax: %q", t.Value)
   215  	}
   216  	return ""
   217  }
   218
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