From 4e6e7edf0ddb06523391c3e644a5c6cfb507518d Mon Sep 17 00:00:00 2001
From: parrt <parrt@cs.usfca.edu>
Date: Mon, 21 Nov 2016 13:45:05 -0800
Subject: [PATCH] Fixes #1317

---
 .../antlr/v4/test/tool/TestCompositeGrammars.java  | 14 +++++++++++++-
 tool/src/org/antlr/v4/tool/Grammar.java            |  5 +++++
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/tool-testsuite/test/org/antlr/v4/test/tool/TestCompositeGrammars.java b/tool-testsuite/test/org/antlr/v4/test/tool/TestCompositeGrammars.java
index 709be7a8a..b096ebad3 100644
--- a/tool-testsuite/test/org/antlr/v4/test/tool/TestCompositeGrammars.java
+++ b/tool-testsuite/test/org/antlr/v4/test/tool/TestCompositeGrammars.java
@@ -69,7 +69,19 @@ public class TestCompositeGrammars extends BaseJavaTest {
 			"WS : (' '|'\\n') -> skip ;\n" ;
 		writeFile(tmpdir, "M.g4", master);
 		ErrorQueue equeue = antlr("M.g4", false, "-lib", subdir);
-		assertEquals(equeue.size(), 0);
+		assertEquals(0, equeue.size());
+	}
+
+	// Test for https://github.com/antlr/antlr4/issues/1317
+	@Test public void testImportSelfLoop() throws Exception {
+		mkdir(tmpdir);
+		String master =
+			"grammar M;\n" +
+			"import M;\n" +
+			"s : 'a' ;\n";
+		writeFile(tmpdir, "M.g4", master);
+		ErrorQueue equeue = antlr("M.g4", false, "-lib", tmpdir);
+		assertEquals(0, equeue.size());
 	}
 
 	@Test public void testDelegatesSeeSameTokenType() throws Exception {
diff --git a/tool/src/org/antlr/v4/tool/Grammar.java b/tool/src/org/antlr/v4/tool/Grammar.java
index 4aec8ad05..65e736152 100644
--- a/tool/src/org/antlr/v4/tool/Grammar.java
+++ b/tool/src/org/antlr/v4/tool/Grammar.java
@@ -392,6 +392,8 @@ public class Grammar implements AttributeResolver {
 		if ( ast==null ) return;
         GrammarAST i = (GrammarAST)ast.getFirstChildWithType(ANTLRParser.IMPORT);
         if ( i==null ) return;
+	    Set<String> visited = new HashSet<>();
+	    visited.add(this.name);
         importedGrammars = new ArrayList<Grammar>();
         for (Object c : i.getChildren()) {
             GrammarAST t = (GrammarAST)c;
@@ -403,6 +405,9 @@ public class Grammar implements AttributeResolver {
             else if ( t.getType()==ANTLRParser.ID ) {
                 importedGrammarName = t.getText();
 			}
+			if ( visited.contains(importedGrammarName) ) { // ignore circular refs
+				continue;
+			}
 			Grammar g;
 			try {
 				g = tool.loadImportedGrammar(this, t);