/*

The MIT License (MIT)

Copyright (c) 2021 Robert Einhorn

Permission is hereby granted, free of charge, to any person obtaining a copy

of this software and associated documentation files (the "Software"), to deal

in the Software without restriction, including without limitation the rights

to use, copy, modify, merge, publish, distribute, sublicense, and/or sell

copies of the Software, and to permit persons to whom the Software is

furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in

all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR

IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,

FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE

AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER

LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,

OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN

THE SOFTWARE.

*/

/*

*

* Project : A helper class for an ANTLR4 Python lexer grammar that assists in tokenizing indentation

*

* Developed by : Robert Einhorn, [email protected]

*

*/

'use strict';

import { Token, Lexer } from "antlr4";

import PythonLexer from "./PythonLexer.js";

export default class PythonLexerBase extends Lexer {

// A stack that keeps track of the indentation lengths

#indentLengthStack;

// A list where tokens are waiting to be loaded into the token stream

#pendingTokens;

// Last pending token types

#previousPendingTokenType;

#lastPendingTokenTypeFromDefaultChannel;

// Count of open parentheses, square brackets, and curly braces

#opened;

#wasSpaceIndentation;

#wasTabIndentation;

#wasIndentationMixedWithSpacesAndTabs;

#curToken; // current (under processing) token

#ffgToken; // following (look ahead) token

get #INVALID_LENGTH() { return -1; }

get #ERR_TXT() { return " ERROR: "; }

constructor(input) {

super(input);

this.#init();

}

nextToken() { // reading the input stream until a return EOF

this.#checkNextToken();

return this.#pendingTokens.shift() /* .pollFirst() */; // Add the queued token to the token stream

}

reset() {

this.#init();

super.reset();

}

#init() {

this.#indentLengthStack = [];

this.#pendingTokens = [];

this.#previousPendingTokenType = 0;

this.#lastPendingTokenTypeFromDefaultChannel = 0;

this.#opened = 0;

this.#wasSpaceIndentation = false;

this.#wasTabIndentation = false;

this.#wasIndentationMixedWithSpacesAndTabs = false;

this.#curToken = null;

this.#ffgToken = null;

}

#checkNextToken() {

if (this.#previousPendingTokenType === Token.EOF) return;

this.#setCurrentAndFollowingTokens();

if (this.#indentLengthStack.length === 0) { // We're at the first token

this.#handleStartOfInput();

}

switch (this.#curToken.type) {

case PythonLexer.LPAR:

case PythonLexer.LSQB:

case PythonLexer.LBRACE:

this.#opened++;

this.#addPendingToken(this.#curToken);

break;

case PythonLexer.RPAR:

case PythonLexer.RSQB:

case PythonLexer.RBRACE:

this.#opened--;

this.#addPendingToken(this.#curToken);

break;

case PythonLexer.NEWLINE:

this.#handleNEWLINEtoken();

break;

case PythonLexer.ERRORTOKEN:

this.#reportLexerError(`token recognition error at: '${this.#curToken.text}'`);

this.#addPendingToken(this.#curToken);

break;

case Token.EOF:

this.#handleEOFtoken();

break;

default:

this.#addPendingToken(this.#curToken);

}

}

#setCurrentAndFollowingTokens() {

this.#curToken = this.#ffgToken == undefined ?

super.nextToken() :

this.#ffgToken;

this.#ffgToken = this.#curToken.type === Token.EOF ?

this.#curToken :

super.nextToken();

}

// initialize the _indentLengthStack

// hide the leading NEWLINE token(s)

// if exists, find the first statement (not NEWLINE, not EOF token) that comes from the default channel

// insert a leading INDENT token if necessary

#handleStartOfInput() {

// initialize the stack with a default 0 indentation length

this.#indentLengthStack.push(0); // this will never be popped off

while (this.#curToken.type !== Token.EOF) {

if (this.#curToken.channel === Token.DEFAULT_CHANNEL) {

if (this.#curToken.type === PythonLexer.NEWLINE) {

// all the NEWLINE tokens must be ignored before the first statement

this.#hideAndAddPendingToken(this.#curToken);

} else { // We're at the first statement

this.#insertLeadingIndentToken();

return; // continue the processing of the current token with #checkNextToken()

}

} else {

this.#addPendingToken(this.#curToken); // it can be WS, EXPLICIT_LINE_JOINING or COMMENT token

}

this.#setCurrentAndFollowingTokens();

} // continue the processing of the EOF token with #checkNextToken()

}

#insertLeadingIndentToken() {

if (this.#previousPendingTokenType === PythonLexer.WS) {

let prevToken = this.#pendingTokens.at(- 1) /* stack peek */; // WS token

if (this.#getIndentationLength(prevToken.text) !== 0) { // there is an "indentation" before the first statement

const errMsg = "first statement indented";

this.#reportLexerError(errMsg);

// insert an INDENT token before the first statement to trigger an 'unexpected indent' error later in the parser

this.#createAndAddPendingToken(PythonLexer.INDENT, Token.DEFAULT_CHANNEL, this.#ERR_TXT + errMsg, this.#curToken);

}

}

}

#handleNEWLINEtoken() {

if (this.#opened > 0) { // We're in an implicit line joining, ignore the current NEWLINE token

this.#hideAndAddPendingToken(this.#curToken);

return;

}

let nlToken = this.#curToken.clone(); // save the current NEWLINE token

const isLookingAhead = this.#ffgToken.type === PythonLexer.WS;

if (isLookingAhead) {

this.#setCurrentAndFollowingTokens(); // set the next two tokens

}

switch (this.#ffgToken.type) {

case PythonLexer.NEWLINE: // We're before a blank line

case PythonLexer.COMMENT: // We're before a comment

this.#hideAndAddPendingToken(nlToken);

if (isLookingAhead) {

this.#addPendingToken(this.#curToken); // WS token

}

break;

default:

this.#addPendingToken(nlToken);

if (isLookingAhead) { // We're on whitespace(s) followed by a statement

const indentationLength = this.#ffgToken.type === Token.EOF ?

0 :

this.#getIndentationLength(this.#curToken.text);

if (indentationLength !== this.#INVALID_LENGTH) {

this.#addPendingToken(this.#curToken); // WS token

this.#insertIndentOrDedentToken(indentationLength); // may insert INDENT token or DEDENT token(s)

} else {

this.#reportError("inconsistent use of tabs and spaces in indentation");

}

} else { // We're at a newline followed by a statement (there is no whitespace before the statement)

this.#insertIndentOrDedentToken(0); // may insert DEDENT token(s)

}

}

}

#insertIndentOrDedentToken(curIndentLength) {

let prevIndentLength = this.#indentLengthStack.at(-1) /* stack peek */;

if (curIndentLength > prevIndentLength) {

this.#createAndAddPendingToken(PythonLexer.INDENT, Token.DEFAULT_CHANNEL, null, this.#ffgToken);

this.#indentLengthStack.push(curIndentLength);

} else {

while (curIndentLength < prevIndentLength) { // more than 1 DEDENT token may be inserted to the token stream

this.#indentLengthStack.pop();

prevIndentLength = this.#indentLengthStack.at(-1) /* stack peek */;

if (curIndentLength <= prevIndentLength) {

this.#createAndAddPendingToken(PythonLexer.DEDENT, Token.DEFAULT_CHANNEL, null, this.#ffgToken);

} else {

this.#reportError("inconsistent dedent");

}

}

}

}

#insertTrailingTokens() {

switch (this.#lastPendingTokenTypeFromDefaultChannel) {

case PythonLexer.NEWLINE:

case PythonLexer.DEDENT:

break; // no trailing NEWLINE token is needed

default:

// insert an extra trailing NEWLINE token that serves as the end of the last statement

this.#createAndAddPendingToken(PythonLexer.NEWLINE, Token.DEFAULT_CHANNEL, null, this.#ffgToken); // _ffgToken is EOF

}

this.#insertIndentOrDedentToken(0); // Now insert as much trailing DEDENT tokens as needed

}

#handleEOFtoken() {

if (this.#lastPendingTokenTypeFromDefaultChannel > 0) {

// there was a statement in the input (leading NEWLINE tokens are hidden)

this.#insertTrailingTokens();

}

this.#addPendingToken(this.#curToken);

}

#hideAndAddPendingToken(originalToken) {

originalToken.channel = Token.HIDDEN_CHANNEL;

this.#addPendingToken(originalToken);

}

#createAndAddPendingToken(type, channel, text, originalToken) {

const token = originalToken.clone();

token.type = type;

token.channel = channel;

token.stop = originalToken.start - 1;

token.text = text == null ?

`<${this.getSymbolicNames()[type]}>` :

text;

this.#addPendingToken(token);

}

#addPendingToken(token) {

// save the last pending token type because the _pendingTokens linked list can be empty by the nextToken()

this.#previousPendingTokenType = token.type;

if (token.channel === Token.DEFAULT_CHANNEL) {

this.#lastPendingTokenTypeFromDefaultChannel = this.#previousPendingTokenType;

}

this.#pendingTokens.push(token) /* .addLast(token) */;

}

#getIndentationLength(indentText) { // the indentText may contain spaces, tabs or form feeds

const TAB_LENGTH = 8; // the standard number of spaces to replace a tab to spaces

let length = 0;

for (let ch of indentText) {

switch (ch) {

case " ":

this.#wasSpaceIndentation = true;

length += 1;

break;

case "\t":

this.#wasTabIndentation = true;

length += TAB_LENGTH - (length % TAB_LENGTH);

break;

case "\f": // form feed

length = 0;

break;

}

}

if (this.#wasTabIndentation && this.#wasSpaceIndentation) {

if (!this.#wasIndentationMixedWithSpacesAndTabs) {

this.#wasIndentationMixedWithSpacesAndTabs = true;

length = this.#INVALID_LENGTH; // only for the first inconsistent indent

}

}

return length;

}

#reportLexerError(errMsg) {

this.getErrorListener().syntaxError(this, this.#curToken.type, this.#curToken.line, this.#curToken.column, " LEXER" + this.#ERR_TXT + errMsg, null);

}

#reportError(errMsg) {

this.#reportLexerError(errMsg);

this.#createAndAddPendingToken(PythonLexer.ERRORTOKEN, Token.DEFAULT_CHANNEL, this.#ERR_TXT + errMsg, this.#ffgToken);

// the ERRORTOKEN also triggers a parser error

}

}