Refined String-escaping behaviour (#22)

## What is the goal of this PR?

During the recent refactor of Graql grammar, we accidentally the lexer for `STRING_` to be too strict: we disallowed `/` character. The reason for this was that the unescape-and-escape behaviour over `/` was not symmetrical. `unescape('/') -> '/'` and `escape('/') -> '\/'`, which means the user reads back characters that they did not write, and that's not acceptable. 

However, we need to bring back `/` characters in strings (issue #21) because it is widely used.

During the investigation, we discovered that there is no need for Graql to be escaping/unescaping strings that are provided by the user in the first place. Given that the String that is parsed by ANTLR is already a valid String, we can store it "as is" (with the exception for Regular Expression, that still requires a special escape operation). I.e. what the user writes, is what the user reads, for any Unicode character accepted by ANTLR.

Fixing the above also resulted in fixing our tests to expect the correct behaviour from Graql.

## What are the changes implemented in this PR?

1) Relaxed Graql grammar to accept `/` (fixes #21)
2) Remove `escapeString()` and `unescapeString()` from `StringUtil`, and all it's usage.
3) Introduced `escapeRegex()` and `escapeRegex()` in `StringUtil`, and used them in parsing and printing regex.
4) Fixed tests to comply with the newly refined behaviour of Graql string and regex parsing/printing.
5) Additionally, we reimplement `StringUtils.repeat()` with a simple `spaces(int len)` in `SyntaxError`, so we can remove the dependency to `org.apache.commons.lang`

dependencies/maven/dependencies.bzl

@@ -72,7 +72,6 @@ def list_dependencies():
     {"artifact": "com.google.errorprone:error_prone_annotations:2.0.18", "lang": "java", "sha1": "5f65affce1684999e2f4024983835efc3504012e", "sha256": "cb4cfad870bf563a07199f3ebea5763f0dec440fcda0b318640b1feaa788656b", "repository": "https://repo.maven.apache.org/maven2/", "url": "https://repo.maven.apache.org/maven2/com/google/errorprone/error_prone_annotations/2.0.18/error_prone_annotations-2.0.18.jar", "source": {"sha1": "220c1232fa6d13b427c10ccc1243a87f5f501d31", "sha256": "dbe7b49dd0584704d5c306b4ac7273556353ea3c0c6c3e50adeeca8df47047be", "repository": "https://repo.maven.apache.org/maven2/", "url": "https://repo.maven.apache.org/maven2/com/google/errorprone/error_prone_annotations/2.0.18/error_prone_annotations-2.0.18-sources.jar"} , "name": "com-google-errorprone-error_prone_annotations", "actual": "@com-google-errorprone-error_prone_annotations//jar", "bind": "jar/com/google/errorprone/error-prone-annotations"},
     {"artifact": "com.google.guava:guava:23.0", "lang": "java", "sha1": "c947004bb13d18182be60077ade044099e4f26f1", "sha256": "7baa80df284117e5b945b19b98d367a85ea7b7801bd358ff657946c3bd1b6596", "repository": "https://repo.maven.apache.org/maven2/", "url": "https://repo.maven.apache.org/maven2/com/google/guava/guava/23.0/guava-23.0.jar", "source": {"sha1": "ed233607c5c11e1a13a3fd760033ed5d9fe525c2", "sha256": "37fe8ba804fb3898c3c8f0cbac319cc9daa58400e5f0226a380ac94fb2c3ca14", "repository": "https://repo.maven.apache.org/maven2/", "url": "https://repo.maven.apache.org/maven2/com/google/guava/guava/23.0/guava-23.0-sources.jar"} , "name": "com-google-guava-guava", "actual": "@com-google-guava-guava//jar", "bind": "jar/com/google/guava/guava"},
     {"artifact": "com.google.j2objc:j2objc-annotations:1.1", "lang": "java", "sha1": "ed28ded51a8b1c6b112568def5f4b455e6809019", "sha256": "2994a7eb78f2710bd3d3bfb639b2c94e219cedac0d4d084d516e78c16dddecf6", "repository": "https://repo.maven.apache.org/maven2/", "url": "https://repo.maven.apache.org/maven2/com/google/j2objc/j2objc-annotations/1.1/j2objc-annotations-1.1.jar", "source": {"sha1": "1efdf5b737b02f9b72ebdec4f72c37ec411302ff", "sha256": "2cd9022a77151d0b574887635cdfcdf3b78155b602abc89d7f8e62aba55cfb4f", "repository": "https://repo.maven.apache.org/maven2/", "url": "https://repo.maven.apache.org/maven2/com/google/j2objc/j2objc-annotations/1.1/j2objc-annotations-1.1-sources.jar"} , "name": "com-google-j2objc-j2objc-annotations", "actual": "@com-google-j2objc-j2objc-annotations//jar", "bind": "jar/com/google/j2objc/j2objc-annotations"},
-    {"artifact": "commons-lang:commons-lang:2.6", "lang": "java", "sha1": "0ce1edb914c94ebc388f086c6827e8bdeec71ac2", "sha256": "50f11b09f877c294d56f24463f47d28f929cf5044f648661c0f0cfbae9a2f49c", "repository": "https://repo.maven.apache.org/maven2/", "url": "https://repo.maven.apache.org/maven2/commons-lang/commons-lang/2.6/commons-lang-2.6.jar", "source": {"sha1": "67313d715fbf0ea4fd0bdb69217fb77f807a8ce5", "sha256": "66c2760945cec226f26286ddf3f6ffe38544c4a69aade89700a9a689c9b92380", "repository": "https://repo.maven.apache.org/maven2/", "url": "https://repo.maven.apache.org/maven2/commons-lang/commons-lang/2.6/commons-lang-2.6-sources.jar"} , "name": "commons-lang-commons-lang", "actual": "@commons-lang-commons-lang//jar", "bind": "jar/commons-lang/commons-lang"},
     {"artifact": "org.antlr:antlr4-runtime:4.7.1", "lang": "java", "sha1": "946f8aa9daa917dd81a8b818111bec7e288f821a", "sha256": "43516d19beae35909e04d06af6c0c58c17bc94e0070c85e8dc9929ca640dc91d", "repository": "https://repo.maven.apache.org/maven2/", "url": "https://repo.maven.apache.org/maven2/org/antlr/antlr4-runtime/4.7.1/antlr4-runtime-4.7.1.jar", "source": {"sha1": "1e68e18aa14f3229b95820d354a594846134af38", "sha256": "a33d52d0d64e68c60d5e3ae2c1098fe7200d57cff59032c19930fd9d487fc7d4", "repository": "https://repo.maven.apache.org/maven2/", "url": "https://repo.maven.apache.org/maven2/org/antlr/antlr4-runtime/4.7.1/antlr4-runtime-4.7.1-sources.jar"} , "name": "org-antlr-antlr4-runtime", "actual": "@org-antlr-antlr4-runtime//jar", "bind": "jar/org/antlr/antlr4-runtime"},
     {"artifact": "org.codehaus.mojo:animal-sniffer-annotations:1.14", "lang": "java", "sha1": "775b7e22fb10026eed3f86e8dc556dfafe35f2d5", "sha256": "2068320bd6bad744c3673ab048f67e30bef8f518996fa380033556600669905d", "repository": "https://repo.maven.apache.org/maven2/", "url": "https://repo.maven.apache.org/maven2/org/codehaus/mojo/animal-sniffer-annotations/1.14/animal-sniffer-annotations-1.14.jar", "source": {"sha1": "886474da3f761d39fcbb723d97ecc5089e731f42", "sha256": "d821ae1f706db2c1b9c88d4b7b0746b01039dac63762745ef3fe5579967dd16b", "repository": "https://repo.maven.apache.org/maven2/", "url": "https://repo.maven.apache.org/maven2/org/codehaus/mojo/animal-sniffer-annotations/1.14/animal-sniffer-annotations-1.14-sources.jar"} , "name": "org-codehaus-mojo-animal-sniffer-annotations", "actual": "@org-codehaus-mojo-animal-sniffer-annotations//jar", "bind": "jar/org/codehaus/mojo/animal-sniffer-annotations"},
     {"artifact": "org.hamcrest:hamcrest-core:1.3", "lang": "java", "sha1": "42a25dc3219429f0e5d060061f71acb49bf010a0", "sha256": "66fdef91e9739348df7a096aa384a5685f4e875584cce89386a7a47251c4d8e9", "repository": "https://repo.maven.apache.org/maven2/", "url": "https://repo.maven.apache.org/maven2/org/hamcrest/hamcrest-core/1.3/hamcrest-core-1.3.jar", "source": {"sha1": "1dc37250fbc78e23a65a67fbbaf71d2e9cbc3c0b", "sha256": "e223d2d8fbafd66057a8848cc94222d63c3cedd652cc48eddc0ab5c39c0f84df", "repository": "https://repo.maven.apache.org/maven2/", "url": "https://repo.maven.apache.org/maven2/org/hamcrest/hamcrest-core/1.3/hamcrest-core-1.3-sources.jar"} , "name": "org-hamcrest-hamcrest-core", "actual": "@org-hamcrest-hamcrest-core//jar", "bind": "jar/org/hamcrest/hamcrest-core"},

dependencies/maven/dependencies.yaml

@@ -43,11 +43,6 @@ dependencies:
       version: "23.0"
       lang: java
 
-  commons-lang:
-    commons-lang:
-      version: "2.6"
-      lang: java
-
   org.antlr:
     antlr4-runtime:
       version: "4.7.1" # sync version with @antlr4_runtime//jar

grammar/Graql.g4

@@ -302,8 +302,8 @@ DATE            : 'date'        ;
 BOOLEAN_        : TRUE | FALSE  ; // order of lexer declaration matters
 TRUE            : 'true'        ;
 FALSE           : 'false'       ;
-STRING_         : '"'  (~["\\/] | ESCAPE_SEQ_ )* '"'
-                | '\'' (~['\\/] | ESCAPE_SEQ_ )* '\''   ;
+STRING_         : '"'  (~["\\] | ESCAPE_SEQ_ )* '"'
+                | '\'' (~['\\] | ESCAPE_SEQ_ )* '\''   ;
 INTEGER_        : ('+' | '-')? [0-9]+                   ;
 REAL_           : ('+' | '-')? [0-9]+ '.' [0-9]+        ;
 DATE_           : DATE_FRAGMENT_                        ;

java/BUILD

@@ -26,7 +26,6 @@ java_library(
     srcs = ["//grammar:graql-java"] + glob(["**/*.java"], exclude = ["**/test/**"]),
     deps = [
         # External dependencies
-        "//dependencies/maven/artifacts/commons-lang:commons-lang",
         "//dependencies/maven/artifacts/com/google/guava:guava",
         "//dependencies/maven/artifacts/com/google/code/findbugs:jsr305",
         "//dependencies/maven/artifacts/org/antlr:antlr4-runtime", # sync version with @antlr4_runtime//jar

java/parser/Parser.java

@@ -67,6 +67,7 @@
 import static graql.lang.Graql.not;
 import static graql.lang.Graql.type;
 import static graql.lang.util.Collections.triple;
+import static graql.lang.util.StringUtil.unescapeRegex;
 import static java.util.stream.Collectors.toList;
 
 /**
@@ -973,9 +974,7 @@ public ValueProperty.Operation<?> visitComparison(GraqlParser.ComparisonContext
 
     @Override
     public String visitRegex(GraqlParser.RegexContext ctx) {
-        // Remove surrounding /.../
-        String unquoted = unquoteString(ctx.STRING_());
-        return unquoted.replaceAll("\\\\/", "/");
+        return unescapeRegex(unquoteString(ctx.STRING_()));
     }
 
     @Override
@@ -1022,8 +1021,7 @@ public Object visitLiteral(GraqlParser.LiteralContext ctx) {
 
     private String getString(TerminalNode string) {
         // Remove surrounding quotes
-        String unquoted = unquoteString(string);
-        return StringUtil.unescapeString(unquoted);
+        return unquoteString(string);
     }
 
     private String unquoteString(TerminalNode string) {

java/parser/SyntaxError.java

@@ -19,7 +19,6 @@
 package graql.lang.parser;
 
 import graql.lang.exception.ErrorMessage;
-import org.apache.commons.lang.StringUtils;
 
 public class SyntaxError {
 
@@ -38,6 +37,15 @@ public SyntaxError(String queryLine, int line, int charPositionInLine, String ms
         this.msg = msg;
     }
 
+    private String spaces(int len) {
+        char ch = ' ';
+        char[] output = new char[len];
+        for (int i = len - 1; i >= 0; i--) {
+            output[i] = ch;
+        }
+        return new String(output);
+    }
+
     @Override
     public String toString() {
         if (queryLine == null) {
@@ -49,7 +57,7 @@ public String toString() {
             // match $
             //       ^
             // blah blah antlr blah
-            String pointer = StringUtils.repeat(" ", charPositionInLine) + "^";
+            String pointer = spaces(charPositionInLine) + "^";
             return ErrorMessage.SYNTAX_ERROR.getMessage(line, queryLine, pointer, msg);
         }
     }

java/parser/test/ParserTest.java

@@ -99,6 +99,15 @@ public void testSimpleQuery() {
         assertQueryEquals(expected, parsed, query);
     }
 
+    @Test
+    public void testParseStringWithSlash() {
+        String query = "match $x isa person, has name 'alice/bob'; get;";
+        GraqlGet parsed = Graql.parse(query).asGet();
+        GraqlGet expected = match(var("x").isa("person").has("name", "alice/bob")).get();
+
+        assertQueryEquals(expected, parsed, query.replace("'", "\""));
+    }
+
     @Test
     public void testRelationQuery() {
         String query = "match\n" +
@@ -664,12 +673,13 @@ public void testDefineDataTypeQuery() {
 
     @Test
     public void testEscapeString() {
-        String unescaped = "This has \"double quotes\" and a single-quoted backslash: '\\'";
-        String escaped = "This has \\\"double quotes\\\" and a single-quoted backslash: \\'\\\\\\'";
+        // ANTLR will see this as a string that looks like:
+        // "This has \"double quotes\" and a single-quoted backslash: '\\'"
+        String input = "This has \\\"double quotes\\\" and a single-quoted backslash: \\'\\\\\\'";
 
-        String query = "insert $_ isa movie, has title \"" + escaped + "\";";
+        String query = "insert $_ isa movie, has title \"" + input + "\";";
         GraqlInsert parsed = Graql.parse(query).asInsert();
-        GraqlInsert expected = insert(var().isa("movie").has("title", unescaped));
+        GraqlInsert expected = insert(var().isa("movie").has("title", input));
 
         assertQueryEquals(expected, parsed, query);
     }
@@ -1096,29 +1106,52 @@ public void whenParsingAggregateWithWrongName_Throw() {
         parse("match $x isa name; get; hello $x;");
     }
 
+    @Test
+    public void regexAttributeProperty() {
+        String query = "define digit sub attribute, regex '\\d';";
+        GraqlDefine parsed = parse(query);
+        GraqlDefine expected = define(type("digit").sub("attribute").regex("\\d"));
+        assertQueryEquals(expected, parsed, query.replace("'", "\""));
+    }
+
     @Test
     public void regexPredicateParsesCharacterClassesCorrectly() {
-        assertEquals(match(var("x").like("\\d")).get(), parse("match $x like '\\d'; get;"));
+        String query = "match $x like '\\d'; get;";
+        GraqlGet parsed = parse(query);
+        GraqlGet expected = match(var("x").like("\\d")).get();
+        assertQueryEquals(expected, parsed, query.replace("'", "\""));
     }
 
     @Test
     public void regexPredicateParsesQuotesCorrectly() {
-        assertEquals(match(var("x").like("\"")).get(), parse("match $x like '\"'; get;"));
+        String query = "match $x like '\\\"'; get;";
+        GraqlGet parsed = parse(query);
+        GraqlGet expected = match(var("x").like("\\\"")).get();
+        assertQueryEquals(expected, parsed, query.replace("'", "\""));
     }
 
     @Test
     public void regexPredicateParsesBackslashesCorrectly() {
-        assertEquals(match(var("x").like("\\\\")).get(), parse("match $x like '\\\\'; get;"));
+        String query = "match $x like '\\\\'; get;";
+        GraqlGet parsed = parse(query);
+        GraqlGet expected = match(var("x").like("\\\\")).get();
+        assertQueryEquals(expected, parsed, query.replace("'", "\""));
     }
 
     @Test
     public void regexPredicateParsesNewlineCorrectly() {
-        assertEquals(match(var("x").like("\\n")).get(), parse("match $x like '\\n'; get;"));
+        String query = "match $x like '\\n'; get;";
+        GraqlGet parsed = parse(query);
+        GraqlGet expected = match(var("x").like("\\n")).get();
+        assertQueryEquals(expected, parsed, query.replace("'", "\""));
     }
 
     @Test
     public void regexPredicateParsesForwardSlashesCorrectly() {
-        assertEquals(match(var("x").like("/")).get(), parse("match $x like '\\/'; get;"));
+        String query = "match $x like '\\/'; get;";
+        GraqlGet parsed = parse(query);
+        GraqlGet expected = match(var("x").like("/")).get();
+        assertQueryEquals(expected, parsed, query.replace("'", "\""));
     }
 
     @Test

java/pattern/Disjunction.java

@@ -18,11 +18,11 @@
 
 package graql.lang.pattern;
 
-import com.google.common.collect.ImmutableSet;
 import com.google.common.collect.Sets;
 import graql.lang.Graql;
 import graql.lang.statement.Statement;
 import graql.lang.statement.Variable;
+import graql.lang.util.Collections;
 
 import javax.annotation.CheckReturnValue;
 import java.util.Iterator;
@@ -78,7 +78,7 @@ public Disjunction<Conjunction<Pattern>> getNegationDNF() {
 
     @Override
     public Set<Variable> variables() {
-        return getPatterns().stream().map(Pattern::variables).reduce(Sets::intersection).orElse(ImmutableSet.of());
+        return getPatterns().stream().map(Pattern::variables).reduce(Sets::intersection).orElse(Collections.set());
     }
 
     @Override

java/pattern/Pattern.java

@@ -79,4 +79,7 @@ default Set<Statement> statements() {
      */
     @CheckReturnValue
     default Negation<?> asNegation(){ throw new UnsupportedOperationException(); }
+
+    @Override
+    String toString();
 }

java/property/RegexProperty.java

@@ -20,7 +20,9 @@
 
 import graql.lang.Graql;
 import graql.lang.statement.StatementType;
-import graql.lang.util.StringUtil;
+
+import static graql.lang.util.StringUtil.escapeRegex;
+import static graql.lang.util.StringUtil.quoteString;
 
 /**
  * Represents the {@code regex} property on a AttributeType. This property can be queried and inserted.
@@ -49,7 +51,7 @@ public String keyword() {
 
     @Override
     public String property() {
-        return "\"" + StringUtil.escapeString(regex()) + "\"";
+        return quoteString(escapeRegex(regex()));
     }
 
     @Override

java/property/ValueProperty.java

@@ -27,6 +27,9 @@
 import java.time.LocalDateTime;
 import java.util.stream.Stream;
 
+import static graql.lang.util.StringUtil.escapeRegex;
+import static graql.lang.util.StringUtil.quoteString;
+
 /**
  * Represents the {@code value} property on an attribute.
  * This property can be queried or inserted.
@@ -243,9 +246,9 @@ public java.lang.String toString() {
 
                     operation.append(comparator()).append(Graql.Token.Char.SPACE);
                     if (comparator().equals(Graql.Token.Comparator.LIKE)) {
-                        operation.append("\"").append(value().replaceAll("/", "\\\\/")).append("\"");
+                        operation.append(quoteString(escapeRegex(value())));
                     } else {
-                        operation.append(StringUtil.quoteString(value()));
+                        operation.append(quoteString(value()));
                     }
 
                     return operation.toString();

java/query/test/GraqlQueryTest.java

@@ -116,15 +116,14 @@ public void testInsertQueryToString() {
 
     @Test
     public void testEscapeStrings() {
-        assertEquals("insert $x \"hello\\nworld\";", Graql.insert(var("x").val("hello\nworld")).toString());
+        assertEquals("insert $x \"hello\nworld\";", Graql.insert(var("x").val("hello\nworld")).toString());
+        assertEquals("insert $x \"hello\\nworld\";", Graql.insert(var("x").val("hello\\nworld")).toString());
     }
 
     @Test
     public void testQuoteIds() {
-        assertEquals(
-                "match $a (\"hello\\tworld\");",
-                match(var("a").rel(type("hello\tworld"))).toString()
-        );
+        assertEquals("match $a (\"hello\tworld\");", match(var("a").rel(type("hello\tworld"))).toString());
+        assertEquals("match $a (\"hello\\tworld\");", match(var("a").rel(type("hello\\tworld"))).toString());
     }
 
     @Test

java/util/StringUtil.java

@@ -20,7 +20,6 @@
 
 import graql.grammar.GraqlLexer;
 import graql.lang.Graql;
-import org.apache.commons.lang.StringEscapeUtils;
 
 import java.text.DecimalFormat;
 import java.text.DecimalFormatSymbols;
@@ -39,28 +38,20 @@ public class StringUtil {
             Arrays.asList("min", "max", "median", "mean", "std", "sum", "count", "path", "cluster", "degrees", "members", "persist")
     );
 
-    /**
-     * @param string the string to unescape
-     * @return the unescaped string, replacing any backslash escapes with the real characters
-     */
-    public static String unescapeString(String string) {
-        return StringEscapeUtils.unescapeJavaScript(string);
+    public static String unescapeRegex(String regex) {
+        return regex.replaceAll("\\\\/", "/");
     }
 
-    /**
-     * @param string the string to escape
-     * @return the escaped string, replacing any escapable characters with backslashes
-     */
-    public static String escapeString(String string) {
-        return StringEscapeUtils.escapeJavaScript(string);
+    public static String escapeRegex(String regex) {
+        return regex.replaceAll("/", "\\\\/");
     }
 
     /**
      * @param string a string to quote and escape
      * @return a string, surrounded with double quotes and escaped
      */
     public static String quoteString(String string) {
-        return "\"" + escapeString(string) + "\"";
+        return "\"" + string + "\"";
     }
 
     public static String escapeLabelOrId(String value) {