Fix logic for checking if text blocks are already deindented

Check the last line instead of the first line of the text block contents. Empty lines in the text block have no leading whitespace but do not indicate the contents are deindented, only non-empty lines should be considered. The last line will never be empty, it contains at least the close delimiter.

PiperOrigin-RevId: 697437392

core/src/main/java/com/google/googlejavaformat/java/StringWrapper.java

@@ -207,7 +207,8 @@ private void indentTextBlocks(
         String stripped = stripIndent(initialLines.stream().skip(1).collect(joining(separator)));
         ImmutableList<String> lines = stripped.lines().collect(toImmutableList());
         int deindent =
-            initialLines.get(1).stripTrailing().length() - lines.get(0).stripTrailing().length();
+            getLast(initialLines).stripTrailing().length()
+                - getLast(lines).stripTrailing().length();
 
         String prefix =
             (deindent == 0

core/src/test/java/com/google/googlejavaformat/java/StringWrapperTest.java

@@ -174,6 +174,33 @@ public void textBlockSpaceTabMix() throws Exception {
     assertThat(actual).isEqualTo(expected);
   }
 
+  @Test
+  public void leadingBlankLine() throws Exception {
+    assumeTrue(Runtime.version().feature() >= 15);
+    String input =
+        lines(
+            "public class T {",
+            "  String s =",
+            "      \"\"\"",
+            "",
+            "      lorem",
+            "      ipsum",
+            "      \"\"\";",
+            "}");
+    String expected =
+        lines(
+            "public class T {",
+            "  String s =",
+            "      \"\"\"",
+            "",
+            "      lorem",
+            "      ipsum",
+            "      \"\"\";",
+            "}");
+    String actual = StringWrapper.wrap(100, input, new Formatter());
+    assertThat(actual).isEqualTo(expected);
+  }
+
   private static String lines(String... line) {
     return Joiner.on('\n').join(line) + '\n';
   }