mirror of
https://github.com/autc04/Retro68.git
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687 lines
17 KiB
Go
687 lines
17 KiB
Go
// Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Package scanner provides a scanner and tokenizer for UTF-8-encoded text.
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// It takes an io.Reader providing the source, which then can be tokenized
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// through repeated calls to the Scan function. For compatibility with
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// existing tools, the NUL character is not allowed. If the first character
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// in the source is a UTF-8 encoded byte order mark (BOM), it is discarded.
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//
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// By default, a Scanner skips white space and Go comments and recognizes all
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// literals as defined by the Go language specification. It may be
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// customized to recognize only a subset of those literals and to recognize
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// different identifier and white space characters.
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package scanner
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import (
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"bytes"
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"fmt"
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"io"
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"os"
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"unicode"
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"unicode/utf8"
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)
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// A source position is represented by a Position value.
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// A position is valid if Line > 0.
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type Position struct {
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Filename string // filename, if any
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Offset int // byte offset, starting at 0
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Line int // line number, starting at 1
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Column int // column number, starting at 1 (character count per line)
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}
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// IsValid reports whether the position is valid.
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func (pos *Position) IsValid() bool { return pos.Line > 0 }
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func (pos Position) String() string {
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s := pos.Filename
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if s == "" {
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s = "<input>"
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}
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if pos.IsValid() {
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s += fmt.Sprintf(":%d:%d", pos.Line, pos.Column)
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}
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return s
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}
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// Predefined mode bits to control recognition of tokens. For instance,
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// to configure a Scanner such that it only recognizes (Go) identifiers,
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// integers, and skips comments, set the Scanner's Mode field to:
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//
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// ScanIdents | ScanInts | SkipComments
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//
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// With the exceptions of comments, which are skipped if SkipComments is
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// set, unrecognized tokens are not ignored. Instead, the scanner simply
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// returns the respective individual characters (or possibly sub-tokens).
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// For instance, if the mode is ScanIdents (not ScanStrings), the string
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// "foo" is scanned as the token sequence '"' Ident '"'.
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//
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const (
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ScanIdents = 1 << -Ident
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ScanInts = 1 << -Int
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ScanFloats = 1 << -Float // includes Ints
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ScanChars = 1 << -Char
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ScanStrings = 1 << -String
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ScanRawStrings = 1 << -RawString
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ScanComments = 1 << -Comment
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SkipComments = 1 << -skipComment // if set with ScanComments, comments become white space
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GoTokens = ScanIdents | ScanFloats | ScanChars | ScanStrings | ScanRawStrings | ScanComments | SkipComments
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)
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// The result of Scan is one of these tokens or a Unicode character.
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const (
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EOF = -(iota + 1)
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Ident
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Int
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Float
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Char
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String
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RawString
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Comment
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skipComment
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)
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var tokenString = map[rune]string{
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EOF: "EOF",
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Ident: "Ident",
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Int: "Int",
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Float: "Float",
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Char: "Char",
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String: "String",
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RawString: "RawString",
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Comment: "Comment",
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}
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// TokenString returns a printable string for a token or Unicode character.
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func TokenString(tok rune) string {
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if s, found := tokenString[tok]; found {
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return s
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}
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return fmt.Sprintf("%q", string(tok))
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}
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// GoWhitespace is the default value for the Scanner's Whitespace field.
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// Its value selects Go's white space characters.
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const GoWhitespace = 1<<'\t' | 1<<'\n' | 1<<'\r' | 1<<' '
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const bufLen = 1024 // at least utf8.UTFMax
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// A Scanner implements reading of Unicode characters and tokens from an io.Reader.
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type Scanner struct {
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// Input
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src io.Reader
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// Source buffer
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srcBuf [bufLen + 1]byte // +1 for sentinel for common case of s.next()
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srcPos int // reading position (srcBuf index)
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srcEnd int // source end (srcBuf index)
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// Source position
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srcBufOffset int // byte offset of srcBuf[0] in source
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line int // line count
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column int // character count
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lastLineLen int // length of last line in characters (for correct column reporting)
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lastCharLen int // length of last character in bytes
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// Token text buffer
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// Typically, token text is stored completely in srcBuf, but in general
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// the token text's head may be buffered in tokBuf while the token text's
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// tail is stored in srcBuf.
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tokBuf bytes.Buffer // token text head that is not in srcBuf anymore
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tokPos int // token text tail position (srcBuf index); valid if >= 0
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tokEnd int // token text tail end (srcBuf index)
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// One character look-ahead
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ch rune // character before current srcPos
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// Error is called for each error encountered. If no Error
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// function is set, the error is reported to os.Stderr.
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Error func(s *Scanner, msg string)
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// ErrorCount is incremented by one for each error encountered.
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ErrorCount int
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// The Mode field controls which tokens are recognized. For instance,
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// to recognize Ints, set the ScanInts bit in Mode. The field may be
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// changed at any time.
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Mode uint
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// The Whitespace field controls which characters are recognized
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// as white space. To recognize a character ch <= ' ' as white space,
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// set the ch'th bit in Whitespace (the Scanner's behavior is undefined
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// for values ch > ' '). The field may be changed at any time.
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Whitespace uint64
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// IsIdentRune is a predicate controlling the characters accepted
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// as the ith rune in an identifier. The set of valid characters
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// must not intersect with the set of white space characters.
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// If no IsIdentRune function is set, regular Go identifiers are
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// accepted instead. The field may be changed at any time.
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IsIdentRune func(ch rune, i int) bool
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// Start position of most recently scanned token; set by Scan.
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// Calling Init or Next invalidates the position (Line == 0).
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// The Filename field is always left untouched by the Scanner.
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// If an error is reported (via Error) and Position is invalid,
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// the scanner is not inside a token. Call Pos to obtain an error
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// position in that case, or to obtain the position immediately
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// after the most recently scanned token.
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Position
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}
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// Init initializes a Scanner with a new source and returns s.
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// Error is set to nil, ErrorCount is set to 0, Mode is set to GoTokens,
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// and Whitespace is set to GoWhitespace.
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func (s *Scanner) Init(src io.Reader) *Scanner {
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s.src = src
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// initialize source buffer
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// (the first call to next() will fill it by calling src.Read)
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s.srcBuf[0] = utf8.RuneSelf // sentinel
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s.srcPos = 0
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s.srcEnd = 0
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// initialize source position
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s.srcBufOffset = 0
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s.line = 1
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s.column = 0
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s.lastLineLen = 0
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s.lastCharLen = 0
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// initialize token text buffer
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// (required for first call to next()).
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s.tokPos = -1
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// initialize one character look-ahead
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s.ch = -2 // no char read yet, not EOF
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// initialize public fields
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s.Error = nil
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s.ErrorCount = 0
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s.Mode = GoTokens
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s.Whitespace = GoWhitespace
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s.Line = 0 // invalidate token position
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return s
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}
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// next reads and returns the next Unicode character. It is designed such
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// that only a minimal amount of work needs to be done in the common ASCII
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// case (one test to check for both ASCII and end-of-buffer, and one test
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// to check for newlines).
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func (s *Scanner) next() rune {
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ch, width := rune(s.srcBuf[s.srcPos]), 1
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if ch >= utf8.RuneSelf {
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// uncommon case: not ASCII or not enough bytes
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for s.srcPos+utf8.UTFMax > s.srcEnd && !utf8.FullRune(s.srcBuf[s.srcPos:s.srcEnd]) {
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// not enough bytes: read some more, but first
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// save away token text if any
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if s.tokPos >= 0 {
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s.tokBuf.Write(s.srcBuf[s.tokPos:s.srcPos])
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s.tokPos = 0
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// s.tokEnd is set by Scan()
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}
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// move unread bytes to beginning of buffer
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copy(s.srcBuf[0:], s.srcBuf[s.srcPos:s.srcEnd])
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s.srcBufOffset += s.srcPos
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// read more bytes
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// (an io.Reader must return io.EOF when it reaches
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// the end of what it is reading - simply returning
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// n == 0 will make this loop retry forever; but the
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// error is in the reader implementation in that case)
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i := s.srcEnd - s.srcPos
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n, err := s.src.Read(s.srcBuf[i:bufLen])
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s.srcPos = 0
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s.srcEnd = i + n
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s.srcBuf[s.srcEnd] = utf8.RuneSelf // sentinel
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if err != nil {
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if err != io.EOF {
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s.error(err.Error())
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}
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if s.srcEnd == 0 {
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if s.lastCharLen > 0 {
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// previous character was not EOF
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s.column++
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}
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s.lastCharLen = 0
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return EOF
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}
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// If err == EOF, we won't be getting more
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// bytes; break to avoid infinite loop. If
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// err is something else, we don't know if
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// we can get more bytes; thus also break.
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break
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}
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}
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// at least one byte
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ch = rune(s.srcBuf[s.srcPos])
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if ch >= utf8.RuneSelf {
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// uncommon case: not ASCII
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ch, width = utf8.DecodeRune(s.srcBuf[s.srcPos:s.srcEnd])
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if ch == utf8.RuneError && width == 1 {
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// advance for correct error position
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s.srcPos += width
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s.lastCharLen = width
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s.column++
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s.error("illegal UTF-8 encoding")
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return ch
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}
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}
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}
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// advance
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s.srcPos += width
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s.lastCharLen = width
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s.column++
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// special situations
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switch ch {
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case 0:
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// for compatibility with other tools
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s.error("illegal character NUL")
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case '\n':
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s.line++
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s.lastLineLen = s.column
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s.column = 0
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}
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return ch
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}
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// Next reads and returns the next Unicode character.
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// It returns EOF at the end of the source. It reports
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// a read error by calling s.Error, if not nil; otherwise
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// it prints an error message to os.Stderr. Next does not
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// update the Scanner's Position field; use Pos() to
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// get the current position.
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func (s *Scanner) Next() rune {
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s.tokPos = -1 // don't collect token text
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s.Line = 0 // invalidate token position
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ch := s.Peek()
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if ch != EOF {
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s.ch = s.next()
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}
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return ch
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}
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// Peek returns the next Unicode character in the source without advancing
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// the scanner. It returns EOF if the scanner's position is at the last
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// character of the source.
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func (s *Scanner) Peek() rune {
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if s.ch == -2 {
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// this code is only run for the very first character
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s.ch = s.next()
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if s.ch == '\uFEFF' {
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s.ch = s.next() // ignore BOM
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}
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}
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return s.ch
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}
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func (s *Scanner) error(msg string) {
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s.ErrorCount++
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if s.Error != nil {
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s.Error(s, msg)
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return
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}
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pos := s.Position
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if !pos.IsValid() {
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pos = s.Pos()
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}
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fmt.Fprintf(os.Stderr, "%s: %s\n", pos, msg)
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}
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func (s *Scanner) isIdentRune(ch rune, i int) bool {
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if s.IsIdentRune != nil {
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return s.IsIdentRune(ch, i)
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}
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return ch == '_' || unicode.IsLetter(ch) || unicode.IsDigit(ch) && i > 0
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}
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func (s *Scanner) scanIdentifier() rune {
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// we know the zero'th rune is OK; start scanning at the next one
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ch := s.next()
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for i := 1; s.isIdentRune(ch, i); i++ {
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ch = s.next()
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}
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return ch
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}
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func digitVal(ch rune) int {
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switch {
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case '0' <= ch && ch <= '9':
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return int(ch - '0')
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case 'a' <= ch && ch <= 'f':
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return int(ch - 'a' + 10)
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case 'A' <= ch && ch <= 'F':
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return int(ch - 'A' + 10)
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}
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return 16 // larger than any legal digit val
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}
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func isDecimal(ch rune) bool { return '0' <= ch && ch <= '9' }
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func (s *Scanner) scanMantissa(ch rune) rune {
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for isDecimal(ch) {
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ch = s.next()
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}
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return ch
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}
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func (s *Scanner) scanFraction(ch rune) rune {
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if ch == '.' {
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ch = s.scanMantissa(s.next())
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}
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return ch
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}
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func (s *Scanner) scanExponent(ch rune) rune {
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if ch == 'e' || ch == 'E' {
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ch = s.next()
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if ch == '-' || ch == '+' {
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ch = s.next()
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}
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ch = s.scanMantissa(ch)
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}
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return ch
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}
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func (s *Scanner) scanNumber(ch rune) (rune, rune) {
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// isDecimal(ch)
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if ch == '0' {
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// int or float
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ch = s.next()
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if ch == 'x' || ch == 'X' {
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// hexadecimal int
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ch = s.next()
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hasMantissa := false
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for digitVal(ch) < 16 {
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ch = s.next()
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hasMantissa = true
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}
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if !hasMantissa {
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s.error("illegal hexadecimal number")
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}
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} else {
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// octal int or float
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has8or9 := false
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for isDecimal(ch) {
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if ch > '7' {
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has8or9 = true
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}
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ch = s.next()
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}
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if s.Mode&ScanFloats != 0 && (ch == '.' || ch == 'e' || ch == 'E') {
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// float
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ch = s.scanFraction(ch)
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ch = s.scanExponent(ch)
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return Float, ch
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}
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// octal int
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if has8or9 {
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s.error("illegal octal number")
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}
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}
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return Int, ch
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}
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// decimal int or float
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ch = s.scanMantissa(ch)
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if s.Mode&ScanFloats != 0 && (ch == '.' || ch == 'e' || ch == 'E') {
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// float
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ch = s.scanFraction(ch)
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ch = s.scanExponent(ch)
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return Float, ch
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}
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return Int, ch
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}
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func (s *Scanner) scanDigits(ch rune, base, n int) rune {
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for n > 0 && digitVal(ch) < base {
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ch = s.next()
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n--
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}
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if n > 0 {
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s.error("illegal char escape")
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}
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return ch
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}
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func (s *Scanner) scanEscape(quote rune) rune {
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ch := s.next() // read character after '/'
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switch ch {
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case 'a', 'b', 'f', 'n', 'r', 't', 'v', '\\', quote:
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// nothing to do
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ch = s.next()
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case '0', '1', '2', '3', '4', '5', '6', '7':
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ch = s.scanDigits(ch, 8, 3)
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case 'x':
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ch = s.scanDigits(s.next(), 16, 2)
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case 'u':
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ch = s.scanDigits(s.next(), 16, 4)
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case 'U':
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ch = s.scanDigits(s.next(), 16, 8)
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default:
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s.error("illegal char escape")
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}
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return ch
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}
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func (s *Scanner) scanString(quote rune) (n int) {
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ch := s.next() // read character after quote
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for ch != quote {
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if ch == '\n' || ch < 0 {
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s.error("literal not terminated")
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return
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}
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if ch == '\\' {
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ch = s.scanEscape(quote)
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} else {
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ch = s.next()
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}
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n++
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}
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return
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}
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func (s *Scanner) scanRawString() {
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ch := s.next() // read character after '`'
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for ch != '`' {
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if ch < 0 {
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s.error("literal not terminated")
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return
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}
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ch = s.next()
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}
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}
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func (s *Scanner) scanChar() {
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if s.scanString('\'') != 1 {
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s.error("illegal char literal")
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}
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}
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func (s *Scanner) scanComment(ch rune) rune {
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// ch == '/' || ch == '*'
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if ch == '/' {
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// line comment
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ch = s.next() // read character after "//"
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for ch != '\n' && ch >= 0 {
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ch = s.next()
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}
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return ch
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}
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// general comment
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ch = s.next() // read character after "/*"
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for {
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if ch < 0 {
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s.error("comment not terminated")
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break
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}
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ch0 := ch
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ch = s.next()
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if ch0 == '*' && ch == '/' {
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ch = s.next()
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break
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}
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}
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return ch
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}
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|
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// Scan reads the next token or Unicode character from source and returns it.
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|
// It only recognizes tokens t for which the respective Mode bit (1<<-t) is set.
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// It returns EOF at the end of the source. It reports scanner errors (read and
|
|
// token errors) by calling s.Error, if not nil; otherwise it prints an error
|
|
// message to os.Stderr.
|
|
func (s *Scanner) Scan() rune {
|
|
ch := s.Peek()
|
|
|
|
// reset token text position
|
|
s.tokPos = -1
|
|
s.Line = 0
|
|
|
|
redo:
|
|
// skip white space
|
|
for s.Whitespace&(1<<uint(ch)) != 0 {
|
|
ch = s.next()
|
|
}
|
|
|
|
// start collecting token text
|
|
s.tokBuf.Reset()
|
|
s.tokPos = s.srcPos - s.lastCharLen
|
|
|
|
// set token position
|
|
// (this is a slightly optimized version of the code in Pos())
|
|
s.Offset = s.srcBufOffset + s.tokPos
|
|
if s.column > 0 {
|
|
// common case: last character was not a '\n'
|
|
s.Line = s.line
|
|
s.Column = s.column
|
|
} else {
|
|
// last character was a '\n'
|
|
// (we cannot be at the beginning of the source
|
|
// since we have called next() at least once)
|
|
s.Line = s.line - 1
|
|
s.Column = s.lastLineLen
|
|
}
|
|
|
|
// determine token value
|
|
tok := ch
|
|
switch {
|
|
case s.isIdentRune(ch, 0):
|
|
if s.Mode&ScanIdents != 0 {
|
|
tok = Ident
|
|
ch = s.scanIdentifier()
|
|
} else {
|
|
ch = s.next()
|
|
}
|
|
case isDecimal(ch):
|
|
if s.Mode&(ScanInts|ScanFloats) != 0 {
|
|
tok, ch = s.scanNumber(ch)
|
|
} else {
|
|
ch = s.next()
|
|
}
|
|
default:
|
|
switch ch {
|
|
case EOF:
|
|
break
|
|
case '"':
|
|
if s.Mode&ScanStrings != 0 {
|
|
s.scanString('"')
|
|
tok = String
|
|
}
|
|
ch = s.next()
|
|
case '\'':
|
|
if s.Mode&ScanChars != 0 {
|
|
s.scanChar()
|
|
tok = Char
|
|
}
|
|
ch = s.next()
|
|
case '.':
|
|
ch = s.next()
|
|
if isDecimal(ch) && s.Mode&ScanFloats != 0 {
|
|
tok = Float
|
|
ch = s.scanMantissa(ch)
|
|
ch = s.scanExponent(ch)
|
|
}
|
|
case '/':
|
|
ch = s.next()
|
|
if (ch == '/' || ch == '*') && s.Mode&ScanComments != 0 {
|
|
if s.Mode&SkipComments != 0 {
|
|
s.tokPos = -1 // don't collect token text
|
|
ch = s.scanComment(ch)
|
|
goto redo
|
|
}
|
|
ch = s.scanComment(ch)
|
|
tok = Comment
|
|
}
|
|
case '`':
|
|
if s.Mode&ScanRawStrings != 0 {
|
|
s.scanRawString()
|
|
tok = String
|
|
}
|
|
ch = s.next()
|
|
default:
|
|
ch = s.next()
|
|
}
|
|
}
|
|
|
|
// end of token text
|
|
s.tokEnd = s.srcPos - s.lastCharLen
|
|
|
|
s.ch = ch
|
|
return tok
|
|
}
|
|
|
|
// Pos returns the position of the character immediately after
|
|
// the character or token returned by the last call to Next or Scan.
|
|
// Use the Scanner's Position field for the start position of the most
|
|
// recently scanned token.
|
|
func (s *Scanner) Pos() (pos Position) {
|
|
pos.Filename = s.Filename
|
|
pos.Offset = s.srcBufOffset + s.srcPos - s.lastCharLen
|
|
switch {
|
|
case s.column > 0:
|
|
// common case: last character was not a '\n'
|
|
pos.Line = s.line
|
|
pos.Column = s.column
|
|
case s.lastLineLen > 0:
|
|
// last character was a '\n'
|
|
pos.Line = s.line - 1
|
|
pos.Column = s.lastLineLen
|
|
default:
|
|
// at the beginning of the source
|
|
pos.Line = 1
|
|
pos.Column = 1
|
|
}
|
|
return
|
|
}
|
|
|
|
// TokenText returns the string corresponding to the most recently scanned token.
|
|
// Valid after calling Scan().
|
|
func (s *Scanner) TokenText() string {
|
|
if s.tokPos < 0 {
|
|
// no token text
|
|
return ""
|
|
}
|
|
|
|
if s.tokEnd < 0 {
|
|
// if EOF was reached, s.tokEnd is set to -1 (s.srcPos == 0)
|
|
s.tokEnd = s.tokPos
|
|
}
|
|
|
|
if s.tokBuf.Len() == 0 {
|
|
// common case: the entire token text is still in srcBuf
|
|
return string(s.srcBuf[s.tokPos:s.tokEnd])
|
|
}
|
|
|
|
// part of the token text was saved in tokBuf: save the rest in
|
|
// tokBuf as well and return its content
|
|
s.tokBuf.Write(s.srcBuf[s.tokPos:s.tokEnd])
|
|
s.tokPos = s.tokEnd // ensure idempotency of TokenText() call
|
|
return s.tokBuf.String()
|
|
}
|