Merge branch '317989-support-line-number-zero' into 'master'

Add support for line numbers equal to 0.

Closes #317989

See merge request asm/asm!367

4 files changed, 12 insertions, 8 deletions

diff --git a/asm-test/src/main/resources/jdk3/ArtificialStructures.class b/asm-test/src/main/resources/jdk3/ArtificialStructures.class
index 0ba4240b..68477215 100644
--- a/asm-test/src/main/resources/jdk3/ArtificialStructures.class
+++ b/asm-test/src/main/resources/jdk3/ArtificialStructures.class
diff --git a/asm-test/src/resources/java/jdk3/DumpArtificialStructures.java b/asm-test/src/resources/java/jdk3/DumpArtificialStructures.java
index 3701472d..b316d1c0 100644
--- a/asm-test/src/resources/java/jdk3/DumpArtificialStructures.java
+++ b/asm-test/src/resources/java/jdk3/DumpArtificialStructures.java
@@ -47,7 +47,7 @@ import org.objectweb.asm.Opcodes;
  *   <li>non standard class, field, method and code attributes,
  *   <li>the nop and swap instructions,
  *   <li>some variants of the dup_x2 and dup2_x2 instructions,
- *   <li>several line numbers per bytecode offset.
+ *   <li>several line numbers per bytecode offset, and line numbers equal to 0.
  * </ul>
  *
  * Ideally we should not use ASM to generate this class (which is later used to test ASM), but this
@@ -103,7 +103,7 @@ public class DumpArtificialStructures implements Opcodes {
     Label endIfLabel = new Label();
     methodVisitor.visitJumpInsn(GOTO, endIfLabel);
     methodVisitor.visitLabel(elseLabel);
-    methodVisitor.visitLineNumber(1, elseLabel);
+    methodVisitor.visitLineNumber(0, elseLabel);
     methodVisitor.visitLineNumber(3, elseLabel);
     methodVisitor.visitLdcInsn("0");
     methodVisitor.visitLabel(endIfLabel);
diff --git a/asm-util/src/test/resources/jdk3.ArtificialStructures.txt b/asm-util/src/test/resources/jdk3.ArtificialStructures.txt
index ae5c1aa9..2f31e255 100644
--- a/asm-util/src/test/resources/jdk3.ArtificialStructures.txt
+++ b/asm-util/src/test/resources/jdk3.ArtificialStructures.txt
@@ -31,7 +31,7 @@ public class jdk3/ArtificialStructures {
     LDC "1"
     GOTO L1
    L0
-    LINENUMBER 1 L0
+    LINENUMBER 0 L0
     LINENUMBER 3 L0
    FRAME FULL [U I] [U]
     LDC "0"
diff --git a/asm/src/main/java/org/objectweb/asm/Label.java b/asm/src/main/java/org/objectweb/asm/Label.java
index 926f719e..4bcf7c56 100644
--- a/asm/src/main/java/org/objectweb/asm/Label.java
+++ b/asm/src/main/java/org/objectweb/asm/Label.java
@@ -81,6 +81,9 @@ public class Label {
   /** A flag indicating that the basic block corresponding to a label is the end of a subroutine. */
   static final int FLAG_SUBROUTINE_END = 64;
 
+  /** A flag indicating that this label has at least one associated line number. */
+  static final int FLAG_LINE_NUMBER = 128;
+
   /**
    * The number of elements to add to the {@link #otherLineNumbers} array when it needs to be
    * resized to store a new source line number.
@@ -145,9 +148,9 @@ public class Label {
   short flags;
 
   /**
-   * The source line number corresponding to this label, or 0. If there are several source line
-   * numbers corresponding to this label, the first one is stored in this field, and the remaining
-   * ones are stored in {@link #otherLineNumbers}.
+   * The source line number corresponding to this label, if {@link #FLAG_LINE_NUMBER} is set. If
+   * there are several source line numbers corresponding to this label, the first one is stored in
+   * this field, and the remaining ones are stored in {@link #otherLineNumbers}.
    */
   private short lineNumber;
 
@@ -332,7 +335,8 @@ public class Label {
    * @param lineNumber a source line number (which should be strictly positive).
    */
   final void addLineNumber(final int lineNumber) {
-    if (this.lineNumber == 0) {
+    if ((flags & FLAG_LINE_NUMBER) == 0) {
+      flags |= FLAG_LINE_NUMBER;
       this.lineNumber = (short) lineNumber;
     } else {
       if (otherLineNumbers == null) {
@@ -356,7 +360,7 @@ public class Label {
    */
   final void accept(final MethodVisitor methodVisitor, final boolean visitLineNumbers) {
     methodVisitor.visitLabel(this);
-    if (visitLineNumbers && lineNumber != 0) {
+    if (visitLineNumbers && (flags & FLAG_LINE_NUMBER) != 0) {
       methodVisitor.visitLineNumber(lineNumber & 0xFFFF, this);
       if (otherLineNumbers != null) {
         for (int i = 1; i <= otherLineNumbers[0]; ++i) {