Merge pull request #1319 from HubSpot/rw-correctly-parse-empty-string

fix: Handle empty strings in StrictWhitespaceControlParser

Author: rewaddell

src/main/java/com/hubspot/jinjava/tree/parse/StrictWhitespaceControlParser.java

@@ -4,21 +4,23 @@ public class StrictWhitespaceControlParser implements WhitespaceControlParser {
 
   @Override
   public boolean hasLeftTrim(String unwrapped) {
-    return unwrapped.charAt(0) == '-';
+    return !unwrapped.isEmpty() && unwrapped.charAt(0) == '-';
   }
 
   @Override
   public String stripLeft(String unwrapped) {
-    return unwrapped.substring(1);
+    return unwrapped.isEmpty() ? unwrapped : unwrapped.substring(1);
   }
 
   @Override
   public boolean hasRightTrim(String unwrapped) {
-    return unwrapped.charAt(unwrapped.length() - 1) == '-';
+    return !unwrapped.isEmpty() && unwrapped.charAt(unwrapped.length() - 1) == '-';
   }
 
   @Override
   public String stripRight(String unwrapped) {
-    return unwrapped.substring(0, unwrapped.length() - 1);
+    return unwrapped.isEmpty()
+      ? unwrapped
+      : unwrapped.substring(0, unwrapped.length() - 1);
   }
 }

src/test/java/com/hubspot/jinjava/interpret/LegacyWhitespaceControlParsingTest.java

@@ -82,4 +82,11 @@ public void itErrorsOnSpacedDashesOnBothSides() {
       .isThrownBy(() -> modern.render(template, new HashMap<>()))
       .withMessageContaining("syntax error at position 9");
   }
+
+  @Test
+  public void itHandlesEmptyExpressionToken() {
+    String template = "{{}}";
+
+    assertThat(modern.render(template, new HashMap<>())).isEqualTo("");
+  }
 }

src/test/java/com/hubspot/jinjava/tree/parse/StrictWhitespaceControlParserTest

@@ -0,0 +1,48 @@
+package com.hubspot.jinjava.tree.parse;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.junit.Before;
+import org.junit.Test;
+
+public class StrictWhitespaceControlParserTest {
+
+  StrictWhitespaceControlParser parser;
+
+  @Before
+  public void setUp() {
+    parser = new StrictWhitespaceControlParser();
+  }
+
+  @Test
+  public void itDoesNotTrimEmptyTokenOnLeft() {
+    assertThat(parser.hasLeftTrim("")).isFalse();
+  }
+
+  @Test
+  public void itDoesNotTrimEmptyTokenOnRight() {
+    assertThat(parser.hasRightTrim("")).isFalse();
+  }
+
+  @Test
+  public void itStripsLeftOfEmptyTokenWithoutThrowing() {
+    assertThat(parser.stripLeft("")).isEqualTo("");
+  }
+
+  @Test
+  public void itStripsRightOfEmptyTokenWithoutThrowing() {
+    assertThat(parser.stripRight("")).isEqualTo("");
+  }
+
+  @Test
+  public void itDetectsLeftTrim() {
+    assertThat(parser.hasLeftTrim("-foo")).isTrue();
+    assertThat(parser.stripLeft("-foo")).isEqualTo("foo");
+  }
+
+  @Test
+  public void itDetectsRightTrim() {
+    assertThat(parser.hasRightTrim("foo-")).isTrue();
+    assertThat(parser.stripRight("foo-")).isEqualTo("foo");
+  }
+}