internal.go

Documentation: cmd/gofmt

     1  // Copyright 2015 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  // TODO(gri): This file and the file src/go/format/internal.go are
     6  // the same (but for this comment and the package name). Do not modify
     7  // one without the other. Determine if we can factor out functionality
     8  // in a public API. See also #11844 for context.
     9  
    10  package main
    11  
    12  import (
    13  	"bytes"
    14  	"go/ast"
    15  	"go/parser"
    16  	"go/printer"
    17  	"go/token"
    18  	"strings"
    19  )
    20  
    21  // parse parses src, which was read from the named file,
    22  // as a Go source file, declaration, or statement list.
    23  func parse(fset *token.FileSet, filename string, src []byte, fragmentOk bool) (
    24  	file *ast.File,
    25  	sourceAdj func(src []byte, indent int) []byte,
    26  	indentAdj int,
    27  	err error,
    28  ) {
    29  	// Try as whole source file.
    30  	file, err = parser.ParseFile(fset, filename, src, parserMode)
    31  	// If there's no error, return. If the error is that the source file didn't begin with a
    32  	// package line and source fragments are ok, fall through to
    33  	// try as a source fragment. Stop and return on any other error.
    34  	if err == nil || !fragmentOk || !strings.Contains(err.Error(), "expected 'package'") {
    35  		return
    36  	}
    37  
    38  	// If this is a declaration list, make it a source file
    39  	// by inserting a package clause.
    40  	// Insert using a ';', not a newline, so that the line numbers
    41  	// in psrc match the ones in src.
    42  	psrc := append([]byte("package p;"), src...)
    43  	file, err = parser.ParseFile(fset, filename, psrc, parserMode)
    44  	if err == nil {
    45  		sourceAdj = func(src []byte, indent int) []byte {
    46  			// Remove the package clause.
    47  			// Gofmt has turned the ';' into a '\n'.
    48  			src = src[indent+len("package p\n"):]
    49  			return bytes.TrimSpace(src)
    50  		}
    51  		return
    52  	}
    53  	// If the error is that the source file didn't begin with a
    54  	// declaration, fall through to try as a statement list.
    55  	// Stop and return on any other error.
    56  	if !strings.Contains(err.Error(), "expected declaration") {
    57  		return
    58  	}
    59  
    60  	// If this is a statement list, make it a source file
    61  	// by inserting a package clause and turning the list
    62  	// into a function body. This handles expressions too.
    63  	// Insert using a ';', not a newline, so that the line numbers
    64  	// in fsrc match the ones in src. Add an extra '\n' before the '}'
    65  	// to make sure comments are flushed before the '}'.
    66  	fsrc := append(append([]byte("package p; func _() {"), src...), '\n', '\n', '}')
    67  	file, err = parser.ParseFile(fset, filename, fsrc, parserMode)
    68  	if err == nil {
    69  		sourceAdj = func(src []byte, indent int) []byte {
    70  			// Cap adjusted indent to zero.
    71  			if indent < 0 {
    72  				indent = 0
    73  			}
    74  			// Remove the wrapping.
    75  			// Gofmt has turned the "; " into a "\n\n".
    76  			// There will be two non-blank lines with indent, hence 2*indent.
    77  			src = src[2*indent+len("package p\n\nfunc _() {"):]
    78  			// Remove only the "}\n" suffix: remaining whitespaces will be trimmed anyway
    79  			src = src[:len(src)-len("}\n")]
    80  			return bytes.TrimSpace(src)
    81  		}
    82  		// Gofmt has also indented the function body one level.
    83  		// Adjust that with indentAdj.
    84  		indentAdj = -1
    85  	}
    86  
    87  	// Succeeded, or out of options.
    88  	return
    89  }
    90  
    91  // format formats the given package file originally obtained from src
    92  // and adjusts the result based on the original source via sourceAdj
    93  // and indentAdj.
    94  func format(
    95  	fset *token.FileSet,
    96  	file *ast.File,
    97  	sourceAdj func(src []byte, indent int) []byte,
    98  	indentAdj int,
    99  	src []byte,
   100  	cfg printer.Config,
   101  ) ([]byte, error) {
   102  	if sourceAdj == nil {
   103  		// Complete source file.
   104  		var buf bytes.Buffer
   105  		err := cfg.Fprint(&buf, fset, file)
   106  		if err != nil {
   107  			return nil, err
   108  		}
   109  		return buf.Bytes(), nil
   110  	}
   111  
   112  	// Partial source file.
   113  	// Determine and prepend leading space.
   114  	i, j := 0, 0
   115  	for j < len(src) && isSpace(src[j]) {
   116  		if src[j] == '\n' {
   117  			i = j + 1 // byte offset of last line in leading space
   118  		}
   119  		j++
   120  	}
   121  	var res []byte
   122  	res = append(res, src[:i]...)
   123  
   124  	// Determine and prepend indentation of first code line.
   125  	// Spaces are ignored unless there are no tabs,
   126  	// in which case spaces count as one tab.
   127  	indent := 0
   128  	hasSpace := false
   129  	for _, b := range src[i:j] {
   130  		switch b {
   131  		case ' ':
   132  			hasSpace = true
   133  		case '\t':
   134  			indent++
   135  		}
   136  	}
   137  	if indent == 0 && hasSpace {
   138  		indent = 1
   139  	}
   140  	for i := 0; i < indent; i++ {
   141  		res = append(res, '\t')
   142  	}
   143  
   144  	// Format the source.
   145  	// Write it without any leading and trailing space.
   146  	cfg.Indent = indent + indentAdj
   147  	var buf bytes.Buffer
   148  	err := cfg.Fprint(&buf, fset, file)
   149  	if err != nil {
   150  		return nil, err
   151  	}
   152  	out := sourceAdj(buf.Bytes(), cfg.Indent)
   153  
   154  	// If the adjusted output is empty, the source
   155  	// was empty but (possibly) for white space.
   156  	// The result is the incoming source.
   157  	if len(out) == 0 {
   158  		return src, nil
   159  	}
   160  
   161  	// Otherwise, append output to leading space.
   162  	res = append(res, out...)
   163  
   164  	// Determine and append trailing space.
   165  	i = len(src)
   166  	for i > 0 && isSpace(src[i-1]) {
   167  		i--
   168  	}
   169  	return append(res, src[i:]...), nil
   170  }
   171  
   172  // isSpace reports whether the byte is a space character.
   173  // isSpace defines a space as being among the following bytes: ' ', '\t', '\n' and '\r'.
   174  func isSpace(b byte) bool {
   175  	return b == ' ' || b == '\t' || b == '\n' || b == '\r'
   176  }
   177
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