8270265: LineBreakMeasurer calculates incorrect line breaks with zero-width characters

Reviewed-by: achung, prr

Author: Daniel Gredler

src/java.desktop/share/classes/sun/font/ExtendedTextSourceLabel.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1998, 2017, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1998, 2025, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -493,10 +493,9 @@ public int getLineBreakIndex(int start, float width) {
     --start;
     while (width >= -epsilon && ++start < length) {
       int cidx = l2v(start) * numvals + advx;
-      if (cidx >= charinfo.length) {
-          break; // layout bailed for some reason
-      }
-      float adv = charinfo[cidx];
+      float adv = cidx < charinfo.length ?
+                  charinfo[cidx] : // layout provided info for this glyph
+                  0; // glyph info omitted, assume no advance
       if (adv != 0) {
           width -= adv + advTracking;
       }

src/java.desktop/share/native/libfontmanager/HBShaper.c

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2015, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2015, 2025, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -272,6 +272,7 @@ JNIEXPORT jboolean JNICALL Java_sun_font_SunLayoutEngine_shape
 
      buffer = hb_buffer_create();
      hb_buffer_set_script(buffer, getHBScriptCode(script));
+     hb_buffer_set_invisible_glyph(buffer, INVISIBLE_GLYPH_ID);
      hb_buffer_set_language(buffer,
                             hb_ot_tag_to_language(HB_OT_TAG_DEFAULT_LANGUAGE));
      if ((flags & TYPO_RTL) != 0) {

src/java.desktop/share/native/libfontmanager/HBShaper_Panama.c

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2023, 2024, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2023, 2025, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -107,6 +107,7 @@ JDKEXPORT void jdk_hb_shape(
 
      buffer = hb_buffer_create();
      hb_buffer_set_script(buffer, getHBScriptCode(script));
+     hb_buffer_set_invisible_glyph(buffer, INVISIBLE_GLYPH_ID);
      hb_buffer_set_language(buffer,
                             hb_ot_tag_to_language(HB_OT_TAG_DEFAULT_LANGUAGE));
      if ((flags & TYPO_RTL) != 0) {

src/java.desktop/share/native/libfontmanager/hb-jdk-p.h

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2023, 2024, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2023, 2025, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -48,6 +48,8 @@
 extern "C" {
 #endif
 
+// Matches sun.font.CharToGlyphMapper.INVISIBLE_GLYPH_ID
+#define INVISIBLE_GLYPH_ID 0xffff
 
 hb_font_t* jdk_font_create_hbp(
                hb_face_t* face,

src/java.desktop/share/native/libfontmanager/hb-jdk.h

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2015, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2015, 2025, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -50,6 +50,9 @@ typedef struct JDKFontInfo_Struct {
 #define HBFloatToFixedScale ((float)(1 << 16))
 #define HBFloatToFixed(f) ((unsigned int)((f) * HBFloatToFixedScale))
 
+// Matches sun.font.CharToGlyphMapper.INVISIBLE_GLYPH_ID
+#define INVISIBLE_GLYPH_ID 0xffff
+
 /*
  * Note:
  *

test/jdk/java/awt/font/TextLayout/FormatCharAdvanceTest.java

@@ -23,7 +23,7 @@
 
 /**
  * @test
- * @bug 8208377 6562489
+ * @bug 8208377 6562489 8270265
  * @summary Confirm that format-category glyphs are not rendered or measured.
  */
 
@@ -275,6 +275,12 @@ private static void testChar(char c, BufferedImage image, Graphics2D g2d, Font f
         g2d.drawString(as2.getIterator(), w / 2, h / 2);
         ab2 = findTextBoundingBox(image).width;
         assertEqual(ab1, ab2, "drawString (using AttributedCharacterIterator)", c, font);
+
+        int max = metrics.stringWidth("AB") + 2; // add a little wiggle room to the max width
+        LineBreakMeasurer measurer1 = new LineBreakMeasurer(as1.getIterator(), frc);
+        LineBreakMeasurer measurer2 = new LineBreakMeasurer(as2.getIterator(), frc);
+        assertEqual(2, measurer1.nextOffset(max), "nextOffset 1", c, font);
+        assertEqual(7, measurer2.nextOffset(max), "nextOffset 2", c, font);
     }
 
     private static void assertEqual(int i1, int i2, String scenario, char c, Font font) {