ANTLR is a powerful parser generator for multiple programming languages including Java.

ANTLR contains 2 major modules:

• Runtime - For building and executing parsers/lexers generated in Java.
• Tool (The Parser Generator) - For generating parsers/lexers Java class.

ANTLR Tool Source Code files are provided in the distribution packge (antlr4-4.10.1.zip). You can download them at ANTLR Website.

You can also browse the source code below:

⏎ org/antlr/v4/codegen/Target.java

/*
 * Copyright (c) 2012-2017 The ANTLR Project. All rights reserved.
 * Use of this file is governed by the BSD 3-clause license that
 * can be found in the LICENSE.txt file in the project root.
 */

package org.antlr.v4.codegen;

import org.antlr.v4.Tool;
import org.antlr.v4.codegen.model.RuleFunction;
import org.antlr.v4.codegen.model.SerializedATN;
import org.antlr.v4.misc.CharSupport;
import org.antlr.v4.misc.Utils;
import org.antlr.v4.parse.ANTLRParser;
import org.antlr.v4.runtime.RuntimeMetaData;
import org.antlr.v4.runtime.Token;
import org.antlr.v4.tool.ErrorType;
import org.antlr.v4.tool.Grammar;
import org.antlr.v4.tool.Rule;
import org.antlr.v4.tool.ast.GrammarAST;
import org.stringtemplate.v4.NumberRenderer;
import org.stringtemplate.v4.ST;
import org.stringtemplate.v4.STErrorListener;
import org.stringtemplate.v4.STGroup;
import org.stringtemplate.v4.STGroupFile;
import org.stringtemplate.v4.StringRenderer;
import org.stringtemplate.v4.misc.STMessage;

import java.util.HashMap;
import java.util.Map;
import java.util.Set;

/** */
public abstract class Target {
	protected final CodeGenerator gen;
	private STGroup templates;

	protected static final Map<Character, String> defaultCharValueEscape;
	static {
		// https://docs.oracle.com/javase/tutorial/java/data/characters.html
		HashMap<Character, String> map = new HashMap<>();
		addEscapedChar(map, '\t', 't');
		addEscapedChar(map, '\b', 'b');
		addEscapedChar(map, '\n', 'n');
		addEscapedChar(map, '\r', 'r');
		addEscapedChar(map, '\f', 'f');
		addEscapedChar(map, '\'');
		addEscapedChar(map, '\"');
		addEscapedChar(map, '\\');
		defaultCharValueEscape = map;
	}

	protected Target(CodeGenerator gen) {
		this.gen = gen;
	}

	/** For pure strings of Unicode char, how can we display
	 *  it in the target language as a literal. Useful for dumping
	 *  predicates and such that may refer to chars that need to be escaped
	 *  when represented as strings.  Also, templates need to be escaped so
	 *  that the target language can hold them as a string.
	 *  Each target can have a different set in memory at same time.
	 */
	public Map<Character, String> getTargetCharValueEscape() {
		return defaultCharValueEscape;
	}

	protected static void addEscapedChar(HashMap<Character, String> map, char key) {
		addEscapedChar(map, key, key);
	}

	protected static void addEscapedChar(HashMap<Character, String> map, char key, char representation) {
		map.put(key, "\\" + representation);
	}

	public String getLanguage() { return gen.language; }

	public CodeGenerator getCodeGenerator() {
		return gen;
	}

	/** ANTLR tool should check output templates / target are compatible with tool code generation.
	 *  For now, a simple string match used on x.y of x.y.z scheme. We use a method to avoid mismatches
	 *  between a template called VERSION. This value is checked against Tool.VERSION during load of templates.
	 *
	 *  This additional method forces all targets 4.3 and beyond to add this method.
	 *
	 * @since 4.3
	 */
	public String getVersion() {
		return Tool.VERSION;
	}

	public STGroup getTemplates() {
		if (templates == null) {
			String version = getVersion();
			if ( version==null ||
				 !RuntimeMetaData.getMajorMinorVersion(version).equals(RuntimeMetaData.getMajorMinorVersion(Tool.VERSION)))
			{
				gen.tool.errMgr.toolError(ErrorType.INCOMPATIBLE_TOOL_AND_TEMPLATES, version, Tool.VERSION, getLanguage());
			}
			templates = loadTemplates();
		}

		return templates;
	}

	protected abstract Set<String> getReservedWords();

	public String escapeIfNeeded(String identifier) {
		return getReservedWords().contains(identifier) ? escapeWord(identifier) : identifier;
	}

	protected String escapeWord(String word) {
		return word + "_";
	}

	protected void genFile(Grammar g, ST outputFileST, String fileName)
	{
		getCodeGenerator().write(outputFileST, fileName);
	}

	/** Get a meaningful name for a token type useful during code generation.
	 *  Literals without associated names are converted to the string equivalent
	 *  of their integer values. Used to generate x==ID and x==34 type comparisons
	 *  etc...  Essentially we are looking for the most obvious way to refer
	 *  to a token type in the generated code.
	 */
	public String getTokenTypeAsTargetLabel(Grammar g, int ttype) {
		String name = g.getTokenName(ttype);
		// If name is not valid, return the token type instead
		if ( Grammar.INVALID_TOKEN_NAME.equals(name) ) {
			return String.valueOf(ttype);
		}

		return name;
	}

	public String[] getTokenTypesAsTargetLabels(Grammar g, int[] ttypes) {
		String[] labels = new String[ttypes.length];
		for (int i=0; i<ttypes.length; i++) {
			labels[i] = getTokenTypeAsTargetLabel(g, ttypes[i]);
		}
		return labels;
	}

	/** Given a random string of Java unicode chars, return a new string with
	 *  optionally appropriate quote characters for target language and possibly
	 *  with some escaped characters.  For example, if the incoming string has
	 *  actual newline characters, the output of this method would convert them
	 *  to the two char sequence \n for Java, C, C++, ...  The new string has
	 *  double-quotes around it as well.  Example String in memory:
	 *
	 *     a"[newlinechar]b'c[carriagereturnchar]d[tab]e\f
	 *
	 *  would be converted to the valid Java s:
	 *
	 *     "a\"\nb'c\rd\te\\f"
	 *
	 *  or
	 *
	 *     a\"\nb'c\rd\te\\f
	 *
	 *  depending on the quoted arg.
	 */
	public String getTargetStringLiteralFromString(String s, boolean quoted) {
		if ( s==null ) {
			return null;
		}

		StringBuilder buf = new StringBuilder();
		if ( quoted ) {
			buf.append('"');
		}
		for (int i=0; i < s.length(); ) {
			int c = s.codePointAt(i);
			String escaped = c <= Character.MAX_VALUE ? getTargetCharValueEscape().get((char)c) : null;
			if (c != '\'' && escaped != null) { // don't escape single quotes in strings for java
				buf.append(escaped);
			}
			else if (shouldUseUnicodeEscapeForCodePointInDoubleQuotedString(c)) {
				appendUnicodeEscapedCodePoint(i, buf);
			}
			else
			{
				buf.appendCodePoint(c);
			}
			i += Character.charCount(c);
		}
		if ( quoted ) {
			buf.append('"');
		}
		return buf.toString();
	}

	private void appendUnicodeEscapedCodePoint(int codePoint, StringBuilder sb, boolean escape) {
		if (escape) {
			sb.append("\\");
		}
		appendUnicodeEscapedCodePoint(codePoint, sb);
	}

	/**
	 * Escape the Unicode code point appropriately for this language
	 * and append the escaped value to {@code sb}.
	 * It exists for flexibility and backward compatibility with external targets
	 * The static method {@link UnicodeEscapes#appendEscapedCodePoint(StringBuilder, int, String)} can be used as well
	 * if default escaping method (Java) is used or language is officially supported
	 */
	protected void appendUnicodeEscapedCodePoint(int codePoint, StringBuilder sb) {
		UnicodeEscapes.appendEscapedCodePoint(sb, codePoint, getLanguage());
	}

	public String getTargetStringLiteralFromString(String s) {
		return getTargetStringLiteralFromString(s, true);
	}

	public String getTargetStringLiteralFromANTLRStringLiteral(CodeGenerator generator, String literal, boolean addQuotes) {
		return getTargetStringLiteralFromANTLRStringLiteral(generator, literal, addQuotes, false);
	}

	/**
	 * <p>Convert from an ANTLR string literal found in a grammar file to an
	 * equivalent string literal in the target language.
	 *</p>
	 * <p>
	 * For Java, this is the translation {@code 'a\n"'} &rarr; {@code "a\n\""}.
	 * Expect single quotes around the incoming literal. Just flip the quotes
	 * and replace double quotes with {@code \"}.
	 * </p>
	 * <p>
	 * Note that we have decided to allow people to use '\"' without penalty, so
	 * we must build the target string in a loop as {@link String#replace}
	 * cannot handle both {@code \"} and {@code "} without a lot of messing
	 * around.
	 * </p>
	 */
	public String getTargetStringLiteralFromANTLRStringLiteral(
		CodeGenerator generator,
		String literal,
		boolean addQuotes,
		boolean escapeSpecial)
	{
		StringBuilder sb = new StringBuilder();

		if ( addQuotes ) sb.append('"');

		for (int i = 1; i < literal.length() -1; ) {
			int codePoint = literal.codePointAt(i);
			int toAdvance = Character.charCount(codePoint);
			if  (codePoint == '\\') {
				// Anything escaped is what it is! We assume that
				// people know how to escape characters correctly. However
				// we catch anything that does not need an escape in Java (which
				// is what the default implementation is dealing with and remove
				// the escape. The C target does this for instance.
				//
				int escapedCodePoint = literal.codePointAt(i+toAdvance);
				toAdvance++;
				switch (escapedCodePoint) {
					// Pass through any escapes that Java also needs
					//
					case    'n':
					case    'r':
					case    't':
					case    'b':
					case    'f':
					case    '\\':
						// Pass the escape through
						if (escapeSpecial && escapedCodePoint != '\\') {
							sb.append('\\');
						}
						sb.append('\\');
						sb.appendCodePoint(escapedCodePoint);
						break;

					case    'u':    // Either unnnn or u{nnnnnn}
						if (literal.charAt(i+toAdvance) == '{') {
							while (literal.charAt(i+toAdvance) != '}') {
								toAdvance++;
							}
							toAdvance++;
						}
						else {
							toAdvance += 4;
						}
						if ( i+toAdvance <= literal.length() ) { // we might have an invalid \\uAB or something
							String fullEscape = literal.substring(i, i+toAdvance);
							appendUnicodeEscapedCodePoint(
								CharSupport.getCharValueFromCharInGrammarLiteral(fullEscape),
								sb,
								escapeSpecial);
						}
						break;
					default:
						if (shouldUseUnicodeEscapeForCodePointInDoubleQuotedString(escapedCodePoint)) {
							appendUnicodeEscapedCodePoint(escapedCodePoint, sb, escapeSpecial);
						}
						else {
							sb.appendCodePoint(escapedCodePoint);
						}
						break;
				}
			}
			else {
				if (codePoint == 0x22) {
					// ANTLR doesn't escape " in literal strings,
					// but every other language needs to do so.
					sb.append("\\\"");
				}
				else if (shouldUseUnicodeEscapeForCodePointInDoubleQuotedString(codePoint)) {
					appendUnicodeEscapedCodePoint(codePoint, sb, escapeSpecial);
				}
				else {
					sb.appendCodePoint(codePoint);
				}
			}
			i += toAdvance;
		}

		if ( addQuotes ) sb.append('"');

		return sb.toString();
	}

	protected boolean shouldUseUnicodeEscapeForCodePointInDoubleQuotedString(int codePoint) {
		// We don't want anyone passing 0x0A (newline) or 0x22
		// (double-quote) here because Java treats \\u000A as
		// a literal newline and \\u0022 as a literal
		// double-quote, so Unicode escaping doesn't help.
		assert codePoint != 0x0A && codePoint != 0x22;

		return
			codePoint < 0x20  || // control characters up to but not including space
			codePoint == 0x5C || // backslash
			codePoint >= 0x7F;   // DEL and beyond (keeps source code 7-bit US-ASCII)
	}

	/** Assume 16-bit char */
	public String encodeInt16AsCharEscape(int v) {
		if (v < Character.MIN_VALUE || v > Character.MAX_VALUE) {
			throw new IllegalArgumentException(String.format("Cannot encode the specified value: %d", v));
		}

		if ( isATNSerializedAsInts() ) {
			return Integer.toString(v);
		}

		char c = (char)v;
		String escaped = getTargetCharValueEscape().get(c);
		if (escaped != null) {
			return escaped;
		}

		switch (Character.getType(c)) {
			case Character.CONTROL:
			case Character.LINE_SEPARATOR:
			case Character.PARAGRAPH_SEPARATOR:
				return escapeChar(v);
			default:
				if ( v<=127 ) {
					return String.valueOf(c);  // ascii chars can be as-is, no encoding
				}
				// else we use hex encoding to ensure pure ascii chars generated
				return escapeChar(v);
		}
	}

	protected String escapeChar(int v) {
		return String.format("\\u%04x", v);
	}

	public String getLoopLabel(GrammarAST ast) {
		return "loop"+ ast.token.getTokenIndex();
	}

	public String getLoopCounter(GrammarAST ast) {
		return "cnt"+ ast.token.getTokenIndex();
	}

	public String getListLabel(String label) {
		ST st = getTemplates().getInstanceOf("ListLabelName");
		st.add("label", label);
		return st.render();
	}

	public String getRuleFunctionContextStructName(Rule r) {
		if ( r.g.isLexer() ) {
			return getTemplates().getInstanceOf("LexerRuleContext").render();
		}
		return Utils.capitalize(r.name)+getTemplates().getInstanceOf("RuleContextNameSuffix").render();
	}

	public String getAltLabelContextStructName(String label) {
		return Utils.capitalize(label)+getTemplates().getInstanceOf("RuleContextNameSuffix").render();
	}

	/** If we know which actual function, we can provide the actual ctx type.
	 *  This will contain implicit labels etc...  From outside, though, we
	 *  see only ParserRuleContext unless there are externally visible stuff
	 *  like args, locals, explicit labels, etc...
	 */
	public String getRuleFunctionContextStructName(RuleFunction function) {
		Rule r = function.rule;
		if ( r.g.isLexer() ) {
			return getTemplates().getInstanceOf("LexerRuleContext").render();
		}
		return Utils.capitalize(r.name)+getTemplates().getInstanceOf("RuleContextNameSuffix").render();
	}

	// should be same for all refs to same token like ctx.ID within single rule function
	// for literals like 'while', we gen _s<ttype>
	public String getImplicitTokenLabel(String tokenName) {
		ST st = getTemplates().getInstanceOf("ImplicitTokenLabel");
		int ttype = getCodeGenerator().g.getTokenType(tokenName);
		if ( tokenName.startsWith("'") ) {
			return "s"+ttype;
		}
		String text = getTokenTypeAsTargetLabel(getCodeGenerator().g, ttype);
		st.add("tokenName", text);
		return st.render();
	}

	// x=(A|B)
	public String getImplicitSetLabel(String id) {
		ST st = getTemplates().getInstanceOf("ImplicitSetLabel");
		st.add("id", id);
		return st.render();
	}

	public String getImplicitRuleLabel(String ruleName) {
		ST st = getTemplates().getInstanceOf("ImplicitRuleLabel");
		st.add("ruleName", ruleName);
		return st.render();
	}

	public String getElementListName(String name) {
		ST st = getTemplates().getInstanceOf("ElementListName");
		st.add("elemName", getElementName(name));
		return st.render();
	}

	public String getElementName(String name) {
		if (".".equals(name)) {
			return "_wild";
		}

		if ( getCodeGenerator().g.getRule(name)!=null ) return name;
		int ttype = getCodeGenerator().g.getTokenType(name);
		if ( ttype==Token.INVALID_TYPE ) return name;
		return getTokenTypeAsTargetLabel(getCodeGenerator().g, ttype);
	}

	/** Generate TParser.java and TLexer.java from T.g4 if combined, else
	 *  just use T.java as output regardless of type.
	 */
	public String getRecognizerFileName(boolean header) {
		ST extST = getTemplates().getInstanceOf("codeFileExtension");
		String recognizerName = gen.g.getRecognizerName();
		return recognizerName+extST.render();
	}

	/** A given grammar T, return the listener name such as
	 *  TListener.java, if we're using the Java target.
 	 */
	public String getListenerFileName(boolean header) {
		assert gen.g.name != null;
		ST extST = getTemplates().getInstanceOf("codeFileExtension");
		String listenerName = gen.g.name + "Listener";
		return listenerName+extST.render();
	}

	/** A given grammar T, return the visitor name such as
	 *  TVisitor.java, if we're using the Java target.
 	 */
	public String getVisitorFileName(boolean header) {
		assert gen.g.name != null;
		ST extST = getTemplates().getInstanceOf("codeFileExtension");
		String listenerName = gen.g.name + "Visitor";
		return listenerName+extST.render();
	}

	/** A given grammar T, return a blank listener implementation
	 *  such as TBaseListener.java, if we're using the Java target.
 	 */
	public String getBaseListenerFileName(boolean header) {
		assert gen.g.name != null;
		ST extST = getTemplates().getInstanceOf("codeFileExtension");
		String listenerName = gen.g.name + "BaseListener";
		return listenerName+extST.render();
	}

	/** A given grammar T, return a blank listener implementation
	 *  such as TBaseListener.java, if we're using the Java target.
 	 */
	public String getBaseVisitorFileName(boolean header) {
		assert gen.g.name != null;
		ST extST = getTemplates().getInstanceOf("codeFileExtension");
		String listenerName = gen.g.name + "BaseVisitor";
		return listenerName+extST.render();
	}

	/**
	 * Gets the maximum number of 16-bit unsigned integers that can be encoded
	 * in a single segment (a declaration in target language) of the serialized ATN.
	 * E.g., in C++, a small segment length results in multiple decls like:
	 *
	 *   static const int32_t serializedATNSegment1[] = {
	 *     0x7, 0x12, 0x2, 0x13, 0x7, 0x13, 0x2, 0x14, 0x7, 0x14, 0x2, 0x15, 0x7,
	 *        0x15, 0x2, 0x16, 0x7, 0x16, 0x2, 0x17, 0x7, 0x17, 0x2, 0x18, 0x7,
	 *        0x18, 0x2, 0x19, 0x7, 0x19, 0x2, 0x1a, 0x7, 0x1a, 0x2, 0x1b, 0x7,
	 *        0x1b, 0x2, 0x1c, 0x7, 0x1c, 0x2, 0x1d, 0x7, 0x1d, 0x2, 0x1e, 0x7,
	 *        0x1e, 0x2, 0x1f, 0x7, 0x1f, 0x2, 0x20, 0x7, 0x20, 0x2, 0x21, 0x7,
	 *        0x21, 0x2, 0x22, 0x7, 0x22, 0x2, 0x23, 0x7, 0x23, 0x2, 0x24, 0x7,
	 *        0x24, 0x2, 0x25, 0x7, 0x25, 0x2, 0x26,
	 *   };
	 *
	 * instead of one big one.  Targets are free to ignore this like JavaScript does.
	 *
	 * This is primarily needed by Java target to limit size of any single ATN string
	 * to 65k length.
	 *
	 * @see SerializedATN#getSegments
	 *
	 * @return the serialized ATN segment limit
	 */
	public int getSerializedATNSegmentLimit() {
		return Integer.MAX_VALUE;
	}

	/** How many bits should be used to do inline token type tests? Java assumes
	 *  a 64-bit word for bitsets.  Must be a valid wordsize for your target like
	 *  8, 16, 32, 64, etc...
	 *
	 *  @since 4.5
	 */
	public int getInlineTestSetWordSize() { return 64; }

	public boolean grammarSymbolCausesIssueInGeneratedCode(GrammarAST idNode) {
		switch (idNode.getParent().getType()) {
			case ANTLRParser.ASSIGN:
				switch (idNode.getParent().getParent().getType()) {
					case ANTLRParser.ELEMENT_OPTIONS:
					case ANTLRParser.OPTIONS:
						return false;

					default:
						break;
				}

				break;

			case ANTLRParser.AT:
			case ANTLRParser.ELEMENT_OPTIONS:
				return false;

			case ANTLRParser.LEXER_ACTION_CALL:
				if (idNode.getChildIndex() == 0) {
					// first child is the command name which is part of the ANTLR language
					return false;
				}

				// arguments to the command should be checked
				break;

			default:
				break;
		}

		return getReservedWords().contains(idNode.getText());
	}

	@Deprecated
	protected boolean visibleGrammarSymbolCausesIssueInGeneratedCode(GrammarAST idNode) {
		return getReservedWords().contains(idNode.getText());
	}

	public boolean templatesExist() {
		return loadTemplatesHelper(false) != null;
	}

	protected STGroup loadTemplates() {
		STGroup result = loadTemplatesHelper(true);
		if (result == null) {
			return null;
		}
		result.registerRenderer(Integer.class, new NumberRenderer());
		result.registerRenderer(String.class, new StringRenderer());
		result.setListener(new STErrorListener() {
			@Override
			public void compileTimeError(STMessage msg) {
				reportError(msg);
			}

			@Override
			public void runTimeError(STMessage msg) {
				reportError(msg);
			}

			@Override
			public void IOError(STMessage msg) {
				reportError(msg);
			}

			@Override
			public void internalError(STMessage msg) {
				reportError(msg);
			}

			private void reportError(STMessage msg) {
				getCodeGenerator().tool.errMgr.toolError(ErrorType.STRING_TEMPLATE_WARNING, msg.cause, msg.toString());
			}
		});

		return result;
	}

	private STGroup loadTemplatesHelper(boolean reportErrorIfFail) {
		String language = getLanguage();
		String groupFileName = CodeGenerator.TEMPLATE_ROOT + "/" + language + "/" + language + STGroup.GROUP_FILE_EXTENSION;
		try {
			return new STGroupFile(groupFileName);
		}
		catch (IllegalArgumentException iae) {
			if (reportErrorIfFail) {
				gen.tool.errMgr.toolError(ErrorType.MISSING_CODE_GEN_TEMPLATES, iae, getLanguage());
			}
			return null;
		}
	}

	/**
	 * @since 4.3
	 */
	public boolean wantsBaseListener() {
		return true;
	}

	/**
	 * @since 4.3
	 */
	public boolean wantsBaseVisitor() {
		return true;
	}

	/**
	 * @since 4.3
	 */
	public boolean supportsOverloadedMethods() {
		return true;
	}

	public boolean isATNSerializedAsInts() {
		return true;
	}

	/** @since 4.6 */
	public boolean needsHeader() { return false; } // Override in targets that need header files.
}

⏎ org/antlr/v4/codegen/Target.java

Or download all of them as a single archive file:

File name: antlr-tool-4.10.1-sources.jar
File size: 347718 bytes
Release date: 2022-04-15
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