Support the Jacoco filter merge operation in Java branch coverage.

Instructions that are indicated to be merged must have their corresponding
coverage expressions (`CovExp`) combined in a pairwise fashion.

e.g. A pair of branch expressions that should be merged:
`BranchExp(a, b)`, `BranchExp(c, d)`

Becomes:

`BranchExp(a | c, b | d)`

This is distinct from the previous merge operation on BranchExp which
simply joined the branches of the two objects (this has been renamed to
concatenate).

Part of #12696.

Closes #13972.

PiperOrigin-RevId: 396573429

src/java_tools/junitrunner/java/com/google/testing/coverage/BranchExp.java

@@ -15,6 +15,7 @@
 package com.google.testing.coverage;
 
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.List;
 
 /** A branch coverage that must be evaluated as a combination of probes. */
@@ -57,11 +58,33 @@ public void update(int idx, CovExp exp) {
     branches.set(idx, exp);
   }
 
-  /** Make a union of the branches of two BranchExp. */
-  public BranchExp merge(BranchExp other) {
-    List<CovExp> mergedBranches = new ArrayList<>(branches);
-    mergedBranches.addAll(other.branches);
-    return new BranchExp(mergedBranches);
+  /** Make a new BranchExp representing the concatenation of branches in inputs. */
+  public static BranchExp concatenate(BranchExp first, BranchExp second) {
+    List<CovExp> branches = new ArrayList<>(first.branches);
+    branches.addAll(second.branches);
+    return new BranchExp(branches);
+  }
+
+  /** Make a new BranchExp representing the pairwise union of branches in inputs */
+  public static BranchExp zip(BranchExp left, BranchExp right) {
+    List<CovExp> zippedBranches = new ArrayList<>();
+    int leftSize = left.branches.size();
+    int rightSize = right.branches.size();
+    int i;
+    for (i = 0; i < leftSize && i < rightSize; i++) {
+      List<CovExp> branches = Arrays.asList(left.branches.get(i), right.branches.get(i));
+      zippedBranches.add(new BranchExp(branches));
+    }
+    List<CovExp> remainder = leftSize < rightSize ? right.branches : left.branches;
+    for (; i < remainder.size(); i++) {
+      zippedBranches.add(new BranchExp(remainder.get(i)));
+    }
+    return new BranchExp(zippedBranches);
+  }
+
+  /** Wraps a CovExp in a BranchExp if it isn't one already. */
+  public static BranchExp ensureIsBranchExp(CovExp exp) {
+    return exp instanceof BranchExp ? (BranchExp) exp : new BranchExp(exp);
   }
 
   @Override

src/java_tools/junitrunner/java/com/google/testing/coverage/MethodProbesMapper.java

@@ -72,6 +72,7 @@ public class MethodProbesMapper extends MethodProbesVisitor implements IFilterOu
   private IFilter filter;
   private IFilterContext filterContext;
   private HashSet<AbstractInsnNode> ignored = new HashSet<>();
+  private Map<AbstractInsnNode, AbstractInsnNode> unioned = new HashMap<>();
 
   // Result
   private Map<Integer, BranchExp> lineToBranchExp = new TreeMap();
@@ -349,13 +350,6 @@ private boolean updateBranchPredecessor(Instruction predecessor, Instruction ins
   /** Finishing the method */
   @Override
   public void visitEnd() {
-    HashSet<Instruction> ignoredInstructions = new HashSet<>();
-    for (Map.Entry<AbstractInsnNode, Instruction> entry : instructionMap.entrySet()) {
-      if (ignored.contains(entry.getKey())) {
-        ignoredInstructions.add(entry.getValue());
-      }
-    }
-
     for (Jump jump : jumps) {
       Instruction insn = labelToInsn.get(jump.target);
       jump.source.addBranch(insn, jump.branch);
@@ -366,9 +360,6 @@ public void visitEnd() {
     for (Map.Entry<Integer, Instruction> entry : probeToInsn.entrySet()) {
       int probeId = entry.getKey();
       Instruction ins = entry.getValue();
-      if (ignoredInstructions.contains(ins)) {
-        continue;
-      }
 
       Instruction insn = ins;
       CovExp exp = new ProbeExp(probeId);
@@ -411,6 +402,24 @@ public void visitEnd() {
       }
     }
 
+    // Handle merged instructions
+    for (AbstractInsnNode node : unioned.keySet()) {
+      AbstractInsnNode rep = findRepresentative(node);
+      Instruction insn = instructionMap.get(node);
+      Instruction repInsn = instructionMap.get(rep);
+      BranchExp branch = BranchExp.ensureIsBranchExp(insnToCovExp.get(insn));
+      BranchExp repBranch = BranchExp.ensureIsBranchExp(insnToCovExp.get(repInsn));
+      insnToCovExp.put(repInsn, BranchExp.zip(repBranch, branch));
+      ignored.add(node);
+    }
+
+    HashSet<Instruction> ignoredInstructions = new HashSet<>();
+    for (Map.Entry<AbstractInsnNode, Instruction> entry : instructionMap.entrySet()) {
+      if (ignored.contains(entry.getKey())) {
+        ignoredInstructions.add(entry.getValue());
+      }
+    }
+
     // Merge branches in the instructions on the same line
     for (Instruction insn : instructions) {
       if (ignoredInstructions.contains(insn)) {
@@ -424,7 +433,7 @@ public void visitEnd() {
           if (lineExp == null) {
             lineToBranchExp.put(insn.getLine(), exp);
           } else {
-            lineToBranchExp.put(insn.getLine(), lineExp.merge(exp));
+            lineToBranchExp.put(insn.getLine(), BranchExp.concatenate(lineExp, exp));
           }
         } else {
           // If we reach here, the internal data of the mapping is inconsistent, either
@@ -447,14 +456,33 @@ public void ignore(AbstractInsnNode fromInclusive, AbstractInsnNode toInclusive)
 
   @Override
   public void merge(AbstractInsnNode i1, AbstractInsnNode i2) {
-    // TODO(cmita): Implement as part of https://github.com/bazelbuild/bazel/issues/12696
+    // Track nodes to be merged using a union-find algorithm.
+    i1 = findRepresentative(i1);
+    i2 = findRepresentative(i2);
+    if (i1 != i2) {
+      unioned.put(i1, i2);
+    }
   }
 
   @Override
   public void replaceBranches(AbstractInsnNode source, Set<AbstractInsnNode> newTargets) {
     // TODO(cmita): Implement as part of https://github.com/bazelbuild/bazel/issues/12696
   }
 
+  private AbstractInsnNode findRepresentative(AbstractInsnNode node) {
+    // The "find" part of union-find. Walk the chain of nodes to find the representative node
+    // (at the root), flattening the tree a little as we go.
+    AbstractInsnNode parent;
+    AbstractInsnNode grandParent;
+    while ((parent = unioned.get(node)) != null) {
+      if ((grandParent = unioned.get(parent)) != null) {
+        unioned.put(node, grandParent);
+      }
+      node = parent;
+    }
+    return node;
+  }
+
   /** Jumps between instructions and labels */
   class Jump {
     public final Instruction source;

src/test/shell/bazel/bazel_coverage_java_test.sh

@@ -889,12 +889,8 @@ BRDA:9,0,3,0
 BRDA:12,0,0,-
 BRDA:12,0,1,-
 BRDA:18,0,0,0
-BRDA:18,0,1,0
-BRDA:18,0,2,0
-BRDA:18,0,3,0
-BRDA:18,0,4,0
-BRDA:18,0,5,1
-BRF:12
+BRDA:18,0,1,1
+BRF:8
 BRH:3"
   assert_coverage_result "$expected_result" "$coverage_file_path"
 
@@ -911,13 +907,9 @@ BRDA:9,0,2,0
 BRDA:9,0,3,1
 BRDA:12,0,0,1
 BRDA:12,0,1,0
-BRDA:18,0,0,0
-BRDA:18,0,1,0
-BRDA:18,0,2,1
-BRDA:18,0,3,1
-BRDA:18,0,4,0
-BRDA:18,0,5,0
-BRF:12
+BRDA:18,0,0,1
+BRDA:18,0,1,1
+BRF:8
 BRH:5"
   assert_coverage_result "$expected_result" "$coverage_file_path"
 
@@ -935,12 +927,8 @@ BRDA:9,0,3,1
 BRDA:12,0,0,1
 BRDA:12,0,1,1
 BRDA:18,0,0,1
-BRDA:18,0,1,0
-BRDA:18,0,2,0
-BRDA:18,0,3,1
-BRDA:18,0,4,0
-BRDA:18,0,5,0
-BRF:12
+BRDA:18,0,1,1
+BRF:8
 BRH:6"
   assert_coverage_result "$expected_result" "$coverage_file_path"
 
@@ -957,13 +945,9 @@ BRDA:9,0,2,0
 BRDA:9,0,3,1
 BRDA:12,0,0,0
 BRDA:12,0,1,1
-BRDA:18,0,0,0
+BRDA:18,0,0,1
 BRDA:18,0,1,1
-BRDA:18,0,2,0
-BRDA:18,0,3,0
-BRDA:18,0,4,1
-BRDA:18,0,5,0
-BRF:12
+BRF:8
 BRH:6"
   assert_coverage_result "$expected_result" "$coverage_file_path"
 
@@ -982,12 +966,27 @@ BRDA:12,0,0,1
 BRDA:12,0,1,1
 BRDA:18,0,0,0
 BRDA:18,0,1,1
-BRDA:18,0,2,0
-BRDA:18,0,3,1
-BRDA:18,0,4,0
-BRDA:18,0,5,0
-BRF:12
-BRH:6"
+BRF:8
+BRH:5"
+  assert_coverage_result "$expected_result" "$coverage_file_path"
+
+  bazel coverage --test_output=all //:test \
+    --coverage_report_generator=@bazel_tools//tools/test:coverage_report_generator \
+    --combined_report=lcov &>$TEST_log \
+    --test_filter=".*(testOdd|testException)" \
+   || echo "Coverage for //:test failed"
+
+  local coverage_file_path="$( get_coverage_file_path_from_test_log )"
+  local expected_result="BRDA:9,0,0,1
+BRDA:9,0,1,1
+BRDA:9,0,2,0
+BRDA:9,0,3,1
+BRDA:12,0,0,1
+BRDA:12,0,1,0
+BRDA:18,0,0,1
+BRDA:18,0,1,0
+BRF:8
+BRH:5"
   assert_coverage_result "$expected_result" "$coverage_file_path"
 }