Allow single quote in strings

src/main/java/com/mojang/brigadier/StringReader.java

@@ -7,7 +7,8 @@ import com.mojang.brigadier.exceptions.CommandSyntaxException;
 
 public class StringReader implements ImmutableStringReader {
     private static final char SYNTAX_ESCAPE = '\\';
-    private static final char SYNTAX_QUOTE = '"';
+    private static final char SYNTAX_DOUBLE_QUOTE = '"';
+    private static final char SYNTAX_SINGLE_QUOTE = '\'';
 
     private final String string;
     private int cursor;
@@ -87,6 +88,10 @@ public class StringReader implements ImmutableStringReader {
         return c >= '0' && c <= '9' || c == '.' || c == '-';
     }
 
+    public static boolean isQuotedStringStart(char c) {
+        return c == SYNTAX_DOUBLE_QUOTE || c == SYNTAX_SINGLE_QUOTE;
+    }
+
     public void skipWhitespace() {
         while (canRead() && Character.isWhitespace(peek())) {
             skip();
@@ -180,16 +185,22 @@ public class StringReader implements ImmutableStringReader {
     public String readQuotedString() throws CommandSyntaxException {
         if (!canRead()) {
             return "";
-        } else if (peek() != SYNTAX_QUOTE) {
+        }
+        final char next = peek();
+        if (!isQuotedStringStart(next)) {
             throw CommandSyntaxException.BUILT_IN_EXCEPTIONS.readerExpectedStartOfQuote().createWithContext(this);
         }
         skip();
+        return readStringUntil(next);
+    }
+
+    public String readStringUntil(char terminator) throws CommandSyntaxException {
         final StringBuilder result = new StringBuilder();
         boolean escaped = false;
         while (canRead()) {
             final char c = read();
             if (escaped) {
-                if (c == SYNTAX_QUOTE || c == SYNTAX_ESCAPE) {
+                if (c == terminator || c == SYNTAX_ESCAPE) {
                     result.append(c);
                     escaped = false;
                 } else {
@@ -198,7 +209,7 @@ public class StringReader implements ImmutableStringReader {
                 }
             } else if (c == SYNTAX_ESCAPE) {
                 escaped = true;
-            } else if (c == SYNTAX_QUOTE) {
+            } else if (c == terminator) {
                 return result.toString();
             } else {
                 result.append(c);
@@ -209,11 +220,15 @@ public class StringReader implements ImmutableStringReader {
     }
 
     public String readString() throws CommandSyntaxException {
-        if (canRead() && peek() == SYNTAX_QUOTE) {
-            return readQuotedString();
-        } else {
-            return readUnquotedString();
+        if (!canRead()) {
+            return "";
         }
+        final char next = peek();
+        if (isQuotedStringStart(next)) {
+            skip();
+            return readStringUntil(next);
+        }
+        return readUnquotedString();
     }
 
     public boolean readBoolean() throws CommandSyntaxException {

src/test/java/com/mojang/brigadier/StringReaderTest.java

@@ -156,6 +156,30 @@ public class StringReaderTest {
         assertThat(reader.getRemaining(), equalTo(""));
     }
 
+    @Test
+    public void readSingleQuotedString() throws Exception {
+        final StringReader reader = new StringReader("'hello world'");
+        assertThat(reader.readQuotedString(), equalTo("hello world"));
+        assertThat(reader.getRead(), equalTo("'hello world'"));
+        assertThat(reader.getRemaining(), equalTo(""));
+    }
+
+    @Test
+    public void readMixedQuotedString_doubleInsideSingle() throws Exception {
+        final StringReader reader = new StringReader("'hello \"world\"'");
+        assertThat(reader.readQuotedString(), equalTo("hello \"world\""));
+        assertThat(reader.getRead(), equalTo("'hello \"world\"'"));
+        assertThat(reader.getRemaining(), equalTo(""));
+    }
+
+    @Test
+    public void readMixedQuotedString_singleInsideDouble() throws Exception {
+        final StringReader reader = new StringReader("\"hello 'world'\"");
+        assertThat(reader.readQuotedString(), equalTo("hello 'world'"));
+        assertThat(reader.getRead(), equalTo("\"hello 'world'\""));
+        assertThat(reader.getRemaining(), equalTo(""));
+    }
+
     @Test
     public void readQuotedString_empty() throws Exception {
         final StringReader reader = new StringReader("");
@@ -242,6 +266,40 @@ public class StringReaderTest {
         }
     }
 
+    @Test
+    public void readQuotedString_invalidQuoteEscape() throws Exception {
+        try {
+            new StringReader("'hello\\\"\'world").readQuotedString();
+        } catch (final CommandSyntaxException ex) {
+            assertThat(ex.getType(), is(CommandSyntaxException.BUILT_IN_EXCEPTIONS.readerInvalidEscape()));
+            assertThat(ex.getCursor(), is(7));
+        }
+    }
+
+    @Test
+    public void readString_noQuotes() throws Exception {
+        final StringReader reader = new StringReader("hello world");
+        assertThat(reader.readString(), equalTo("hello"));
+        assertThat(reader.getRead(), equalTo("hello"));
+        assertThat(reader.getRemaining(), equalTo(" world"));
+    }
+
+    @Test
+    public void readString_singleQuotes() throws Exception {
+        final StringReader reader = new StringReader("'hello world'");
+        assertThat(reader.readString(), equalTo("hello world"));
+        assertThat(reader.getRead(), equalTo("'hello world'"));
+        assertThat(reader.getRemaining(), equalTo(""));
+    }
+
+    @Test
+    public void readString_doubleQuotes() throws Exception {
+        final StringReader reader = new StringReader("\"hello world\"");
+        assertThat(reader.readString(), equalTo("hello world"));
+        assertThat(reader.getRead(), equalTo("\"hello world\""));
+        assertThat(reader.getRemaining(), equalTo(""));
+    }
+
     @Test
     public void readInt() throws Exception {
         final StringReader reader = new StringReader("1234567890");