Source file src/cmd/compile/internal/types/sym.go

Documentation: cmd/compile/internal/types

     1  // Copyright 2017 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  	"cmd/internal/obj"
     9  	"cmd/internal/src"
    10  	"unicode"
    11  	"unicode/utf8"
    12  )
    13  
    14  // Sym represents an object name in a segmented (pkg, name) namespace.
    15  // Most commonly, this is a Go identifier naming an object declared within a package,
    16  // but Syms are also used to name internal synthesized objects.
    17  //
    18  // As an exception, field and method names that are exported use the Sym
    19  // associated with localpkg instead of the package that declared them. This
    20  // allows using Sym pointer equality to test for Go identifier uniqueness when
    21  // handling selector expressions.
    22  //
    23  // Ideally, Sym should be used for representing Go language constructs,
    24  // while cmd/internal/obj.LSym is used for representing emitted artifacts.
    25  //
    26  // NOTE: In practice, things can be messier than the description above
    27  // for various reasons (historical, convenience).
    28  type Sym struct {
    29  	Importdef *Pkg   // where imported definition was found
    30  	Linkname  string // link name
    31  
    32  	Pkg  *Pkg
    33  	Name string // object name
    34  
    35  	// saved and restored by dcopy
    36  	Def        *Node    // definition: ONAME OTYPE OPACK or OLITERAL
    37  	Block      int32    // blocknumber to catch redeclaration
    38  	Lastlineno src.XPos // last declaration for diagnostic
    39  
    40  	flags   bitset8
    41  	Label   *Node // corresponding label (ephemeral)
    42  	Origpkg *Pkg  // original package for . import
    43  }
    44  
    45  const (
    46  	symOnExportList = 1 << iota // added to exportlist (no need to add again)
    47  	symUniq
    48  	symSiggen // type symbol has been generated
    49  	symAsm    // on asmlist, for writing to -asmhdr
    50  	symAlgGen // algorithm table has been generated
    51  	symFunc   // function symbol; uses internal ABI
    52  )
    53  
    54  func (sym *Sym) OnExportList() bool { return sym.flags&symOnExportList != 0 }
    55  func (sym *Sym) Uniq() bool         { return sym.flags&symUniq != 0 }
    56  func (sym *Sym) Siggen() bool       { return sym.flags&symSiggen != 0 }
    57  func (sym *Sym) Asm() bool          { return sym.flags&symAsm != 0 }
    58  func (sym *Sym) AlgGen() bool       { return sym.flags&symAlgGen != 0 }
    59  func (sym *Sym) Func() bool         { return sym.flags&symFunc != 0 }
    60  
    61  func (sym *Sym) SetOnExportList(b bool) { sym.flags.set(symOnExportList, b) }
    62  func (sym *Sym) SetUniq(b bool)         { sym.flags.set(symUniq, b) }
    63  func (sym *Sym) SetSiggen(b bool)       { sym.flags.set(symSiggen, b) }
    64  func (sym *Sym) SetAsm(b bool)          { sym.flags.set(symAsm, b) }
    65  func (sym *Sym) SetAlgGen(b bool)       { sym.flags.set(symAlgGen, b) }
    66  func (sym *Sym) SetFunc(b bool)         { sym.flags.set(symFunc, b) }
    67  
    68  func (sym *Sym) IsBlank() bool {
    69  	return sym != nil && sym.Name == "_"
    70  }
    71  
    72  func (sym *Sym) LinksymName() string {
    73  	if sym.IsBlank() {
    74  		return "_"
    75  	}
    76  	if sym.Linkname != "" {
    77  		return sym.Linkname
    78  	}
    79  	return sym.Pkg.Prefix + "." + sym.Name
    80  }
    81  
    82  func (sym *Sym) Linksym() *obj.LSym {
    83  	if sym == nil {
    84  		return nil
    85  	}
    86  	if sym.Func() {
    87  		// This is a function symbol. Mark it as "internal ABI".
    88  		return Ctxt.LookupABI(sym.LinksymName(), obj.ABIInternal)
    89  	}
    90  	return Ctxt.Lookup(sym.LinksymName())
    91  }
    92  
    93  // Less reports whether symbol a is ordered before symbol b.
    94  //
    95  // Symbols are ordered exported before non-exported, then by name, and
    96  // finally (for non-exported symbols) by package height and path.
    97  //
    98  // Ordering by package height is necessary to establish a consistent
    99  // ordering for non-exported names with the same spelling but from
   100  // different packages. We don't necessarily know the path for the
   101  // package being compiled, but by definition it will have a height
   102  // greater than any other packages seen within the compilation unit.
   103  // For more background, see issue #24693.
   104  func (a *Sym) Less(b *Sym) bool {
   105  	if a == b {
   106  		return false
   107  	}
   108  
   109  	// Exported symbols before non-exported.
   110  	ea := IsExported(a.Name)
   111  	eb := IsExported(b.Name)
   112  	if ea != eb {
   113  		return ea
   114  	}
   115  
   116  	// Order by name and then (for non-exported names) by package
   117  	// height and path.
   118  	if a.Name != b.Name {
   119  		return a.Name < b.Name
   120  	}
   121  	if !ea {
   122  		if a.Pkg.Height != b.Pkg.Height {
   123  			return a.Pkg.Height < b.Pkg.Height
   124  		}
   125  		return a.Pkg.Path < b.Pkg.Path
   126  	}
   127  	return false
   128  }
   129  
   130  // IsExported reports whether name is an exported Go symbol (that is,
   131  // whether it begins with an upper-case letter).
   132  func IsExported(name string) bool {
   133  	if r := name[0]; r < utf8.RuneSelf {
   134  		return 'A' <= r && r <= 'Z'
   135  	}
   136  	r, _ := utf8.DecodeRuneInString(name)
   137  	return unicode.IsUpper(r)
   138  }
   139  

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