Source file src/go/parser/interface.go

     1  // Copyright 2009 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 contains the exported entry points for invoking the parser.
     6  
     7  package parser
     8  
     9  import (
    10  	"bytes"
    11  	"errors"
    12  	"go/ast"
    13  	"go/token"
    14  	"io"
    15  	"io/fs"
    16  	"os"
    17  	"path/filepath"
    18  	"strings"
    19  )
    20  
    21  // If src != nil, readSource converts src to a []byte if possible;
    22  // otherwise it returns an error. If src == nil, readSource returns
    23  // the result of reading the file specified by filename.
    24  func readSource(filename string, src any) ([]byte, error) {
    25  	if src != nil {
    26  		switch s := src.(type) {
    27  		case string:
    28  			return []byte(s), nil
    29  		case []byte:
    30  			return s, nil
    31  		case *bytes.Buffer:
    32  			// is io.Reader, but src is already available in []byte form
    33  			if s != nil {
    34  				return s.Bytes(), nil
    35  			}
    36  		case io.Reader:
    37  			return io.ReadAll(s)
    38  		}
    39  		return nil, errors.New("invalid source")
    40  	}
    41  	return os.ReadFile(filename)
    42  }
    43  
    44  // A Mode value is a set of flags (or 0).
    45  // They control the amount of source code parsed and other optional
    46  // parser functionality.
    47  type Mode uint
    48  
    49  const (
    50  	PackageClauseOnly    Mode             = 1 << iota // stop parsing after package clause
    51  	ImportsOnly                                       // stop parsing after import declarations
    52  	ParseComments                                     // parse comments and add them to AST
    53  	Trace                                             // print a trace of parsed productions
    54  	DeclarationErrors                                 // report declaration errors
    55  	SpuriousErrors                                    // same as AllErrors, for backward-compatibility
    56  	SkipObjectResolution                              // skip deprecated identifier resolution; see ParseFile
    57  	AllErrors            = SpuriousErrors             // report all errors (not just the first 10 on different lines)
    58  )
    59  
    60  // ParseFile parses the source code of a single Go source file and returns
    61  // the corresponding [ast.File] node. The source code may be provided via
    62  // the filename of the source file, or via the src parameter.
    63  //
    64  // If src != nil, ParseFile parses the source from src and the filename is
    65  // only used when recording position information. The type of the argument
    66  // for the src parameter must be string, []byte, or [io.Reader].
    67  // If src == nil, ParseFile parses the file specified by filename.
    68  //
    69  // The mode parameter controls the amount of source text parsed and
    70  // other optional parser functionality. If the [SkipObjectResolution]
    71  // mode bit is set (recommended), the object resolution phase of
    72  // parsing will be skipped, causing File.Scope, File.Unresolved, and
    73  // all Ident.Obj fields to be nil. Those fields are deprecated; see
    74  // [ast.Object] for details.
    75  //
    76  // Position information is recorded in the file set fset, which must not be
    77  // nil.
    78  //
    79  // If the source couldn't be read, the returned AST is nil and the error
    80  // indicates the specific failure. If the source was read but syntax
    81  // errors were found, the result is a partial AST (with [ast.Bad]* nodes
    82  // representing the fragments of erroneous source code). Multiple errors
    83  // are returned via a scanner.ErrorList which is sorted by source position.
    84  func ParseFile(fset *token.FileSet, filename string, src any, mode Mode) (f *ast.File, err error) {
    85  	if fset == nil {
    86  		panic("parser.ParseFile: no token.FileSet provided (fset == nil)")
    87  	}
    88  
    89  	// get source
    90  	text, err := readSource(filename, src)
    91  	if err != nil {
    92  		return nil, err
    93  	}
    94  
    95  	var p parser
    96  	defer func() {
    97  		if e := recover(); e != nil {
    98  			// resume same panic if it's not a bailout
    99  			bail, ok := e.(bailout)
   100  			if !ok {
   101  				panic(e)
   102  			} else if bail.msg != "" {
   103  				p.errors.Add(p.file.Position(bail.pos), bail.msg)
   104  			}
   105  		}
   106  
   107  		// set result values
   108  		if f == nil {
   109  			// source is not a valid Go source file - satisfy
   110  			// ParseFile API and return a valid (but) empty
   111  			// *ast.File
   112  			f = &ast.File{
   113  				Name:  new(ast.Ident),
   114  				Scope: ast.NewScope(nil),
   115  			}
   116  		}
   117  
   118  		p.errors.Sort()
   119  		err = p.errors.Err()
   120  	}()
   121  
   122  	// parse source
   123  	p.init(fset, filename, text, mode)
   124  	f = p.parseFile()
   125  
   126  	return
   127  }
   128  
   129  // ParseDir calls [ParseFile] for all files with names ending in ".go" in the
   130  // directory specified by path and returns a map of package name -> package
   131  // AST with all the packages found.
   132  //
   133  // If filter != nil, only the files with [fs.FileInfo] entries passing through
   134  // the filter (and ending in ".go") are considered. The mode bits are passed
   135  // to [ParseFile] unchanged. Position information is recorded in fset, which
   136  // must not be nil.
   137  //
   138  // If the directory couldn't be read, a nil map and the respective error are
   139  // returned. If a parse error occurred, a non-nil but incomplete map and the
   140  // first error encountered are returned.
   141  func ParseDir(fset *token.FileSet, path string, filter func(fs.FileInfo) bool, mode Mode) (pkgs map[string]*ast.Package, first error) {
   142  	list, err := os.ReadDir(path)
   143  	if err != nil {
   144  		return nil, err
   145  	}
   146  
   147  	pkgs = make(map[string]*ast.Package)
   148  	for _, d := range list {
   149  		if d.IsDir() || !strings.HasSuffix(d.Name(), ".go") {
   150  			continue
   151  		}
   152  		if filter != nil {
   153  			info, err := d.Info()
   154  			if err != nil {
   155  				return nil, err
   156  			}
   157  			if !filter(info) {
   158  				continue
   159  			}
   160  		}
   161  		filename := filepath.Join(path, d.Name())
   162  		if src, err := ParseFile(fset, filename, nil, mode); err == nil {
   163  			name := src.Name.Name
   164  			pkg, found := pkgs[name]
   165  			if !found {
   166  				pkg = &ast.Package{
   167  					Name:  name,
   168  					Files: make(map[string]*ast.File),
   169  				}
   170  				pkgs[name] = pkg
   171  			}
   172  			pkg.Files[filename] = src
   173  		} else if first == nil {
   174  			first = err
   175  		}
   176  	}
   177  
   178  	return
   179  }
   180  
   181  // ParseExprFrom is a convenience function for parsing an expression.
   182  // The arguments have the same meaning as for [ParseFile], but the source must
   183  // be a valid Go (type or value) expression. Specifically, fset must not
   184  // be nil.
   185  //
   186  // If the source couldn't be read, the returned AST is nil and the error
   187  // indicates the specific failure. If the source was read but syntax
   188  // errors were found, the result is a partial AST (with [ast.Bad]* nodes
   189  // representing the fragments of erroneous source code). Multiple errors
   190  // are returned via a scanner.ErrorList which is sorted by source position.
   191  func ParseExprFrom(fset *token.FileSet, filename string, src any, mode Mode) (expr ast.Expr, err error) {
   192  	if fset == nil {
   193  		panic("parser.ParseExprFrom: no token.FileSet provided (fset == nil)")
   194  	}
   195  
   196  	// get source
   197  	text, err := readSource(filename, src)
   198  	if err != nil {
   199  		return nil, err
   200  	}
   201  
   202  	var p parser
   203  	defer func() {
   204  		if e := recover(); e != nil {
   205  			// resume same panic if it's not a bailout
   206  			bail, ok := e.(bailout)
   207  			if !ok {
   208  				panic(e)
   209  			} else if bail.msg != "" {
   210  				p.errors.Add(p.file.Position(bail.pos), bail.msg)
   211  			}
   212  		}
   213  		p.errors.Sort()
   214  		err = p.errors.Err()
   215  	}()
   216  
   217  	// parse expr
   218  	p.init(fset, filename, text, mode)
   219  	expr = p.parseRhs()
   220  
   221  	// If a semicolon was inserted, consume it;
   222  	// report an error if there's more tokens.
   223  	if p.tok == token.SEMICOLON && p.lit == "\n" {
   224  		p.next()
   225  	}
   226  	p.expect(token.EOF)
   227  
   228  	return
   229  }
   230  
   231  // ParseExpr is a convenience function for obtaining the AST of an expression x.
   232  // The position information recorded in the AST is undefined. The filename used
   233  // in error messages is the empty string.
   234  //
   235  // If syntax errors were found, the result is a partial AST (with [ast.Bad]* nodes
   236  // representing the fragments of erroneous source code). Multiple errors are
   237  // returned via a scanner.ErrorList which is sorted by source position.
   238  func ParseExpr(x string) (ast.Expr, error) {
   239  	return ParseExprFrom(token.NewFileSet(), "", []byte(x), 0)
   240  }
   241  

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