eu.numberfour.n4js.antlr.UnicodeKeywordHelper.java Source code

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Here is the source code for eu.numberfour.n4js.antlr.UnicodeKeywordHelper.java

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/**
 * Copyright (c) 2016 NumberFour AG.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *   NumberFour AG - Initial API and implementation
 */
package eu.numberfour.n4js.antlr;

import static com.ibm.icu.lang.UCharacterEnums.ECharacterCategory.LETTER_NUMBER;
import static com.ibm.icu.lang.UCharacterEnums.ECharacterCategory.LOWERCASE_LETTER;
import static com.ibm.icu.lang.UCharacterEnums.ECharacterCategory.MODIFIER_LETTER;
import static com.ibm.icu.lang.UCharacterEnums.ECharacterCategory.OTHER_LETTER;
import static com.ibm.icu.lang.UCharacterEnums.ECharacterCategory.TITLECASE_LETTER;
import static com.ibm.icu.lang.UCharacterEnums.ECharacterCategory.UPPERCASE_LETTER;

import org.eclipse.xtext.generator.parser.antlr.AntlrGrammarGenUtil;

import com.google.common.base.Strings;
import com.ibm.icu.lang.UCharacter;

/**
 * A keyword helper that produces lexer rules with support for unicode escapes. Used by Xtend 1 extension
 * UnicodeKeywordHelper.ext.
 */
public class UnicodeKeywordHelper {

    /**
     * Creates lexer rule for given keyword in order to handle JavaScript's unicode masks. E.g.:
     *
     * <pre>
     * If :
     *    ( 'i' | '\\' 'u' '0''0''6''9' )
     *    ( 'f' | '\\' 'u' '0''0''6''6' );
     * </pre>
     *
     * @param keyword
     *            the keyword as string, e.g. 'if'
     * @return the lexer body, e.g.
     *
     *         <pre>
     * ( 'i' | '\\' 'u' '0''0''6''9' ) ( 'f' | '\\' 'u' '0''0''6''6' )
     *         </pre>
     */
    public static String toUnicodeKeyword(String keyword) {
        if (keyword.equals("async ")) {
            keyword = "async";
        }
        if (isIdentifier(keyword)) {
            StringBuilder result = new StringBuilder(keyword.length() * 30);
            for (char c : keyword.toCharArray()) {
                result.append("\n\t( '");
                result.append(c);
                result.append("' | '\\\\' 'u' ");
                String unicodeEscape = Strings.padStart(Integer.toHexString(c), 4, '0');
                for (char u : unicodeEscape.toCharArray()) {
                    if ('0' <= u && u <= '9') {
                        result.append("'");
                        result.append(u);
                        result.append("'");
                    } else {
                        result.append("( '");
                        result.append(u);
                        result.append("' | '");
                        result.append(Character.toUpperCase(u));
                        result.append("' )");
                    }
                }
                result.append(" )");
            }
            return result.toString();
        }
        return "'" + AntlrGrammarGenUtil.toAntlrString(keyword) + "'";
    }

    private static boolean isIdentifier(String keyword) {
        boolean wasTrue = false;
        for (char c : keyword.toCharArray()) {
            if (isLetter(c)) {
                wasTrue = true;
            } else {
                if (wasTrue) {
                    throw new IllegalArgumentException(
                            keyword + " starts with letter but is not alphanumeric. Surprise!");
                }
            }
        }
        return wasTrue;
    }

    private static boolean isLetter(int c) {
        int type = UCharacter.getType(c);
        boolean result = type == UPPERCASE_LETTER || type == LOWERCASE_LETTER || type == TITLECASE_LETTER
                || type == MODIFIER_LETTER || type == OTHER_LETTER || type == LETTER_NUMBER;
        return result;
    }
}