Implement file-granularity diff

Author: nikita-tkachenko-datadog

dd-java-agent/agent-ci-visibility/src/main/java/datadog/trace/civisibility/diff/Diff.java

@@ -7,7 +7,8 @@ public interface Diff extends SerializableType {
 
   Diff EMPTY = LineDiff.EMPTY;
 
-  PolymorphicSerializer<Diff> SERIALIZER = new PolymorphicSerializer<>(LineDiff.class);
+  PolymorphicSerializer<Diff> SERIALIZER =
+      new PolymorphicSerializer<>(LineDiff.class, FileDiff.class);
 
   boolean contains(String relativePath, int startLine, int endLine);
 }

dd-java-agent/agent-ci-visibility/src/main/java/datadog/trace/civisibility/diff/FileDiff.java

@@ -0,0 +1,53 @@
+package datadog.trace.civisibility.diff;
+
+import datadog.trace.civisibility.ipc.serialization.Serializer;
+import java.nio.ByteBuffer;
+import java.util.Objects;
+import java.util.Set;
+import javax.annotation.Nonnull;
+
+/** Diff data with per-file granularity. */
+public class FileDiff implements Diff {
+
+  private final @Nonnull Set<String> changedFiles;
+
+  public FileDiff(@Nonnull Set<String> changedFiles) {
+    this.changedFiles = changedFiles;
+  }
+
+  @Override
+  public boolean contains(String relativePath, int startLine, int endLine) {
+    return changedFiles.contains(relativePath);
+  }
+
+  @Override
+  public void serialize(Serializer s) {
+    s.write(changedFiles);
+  }
+
+  public static FileDiff deserialize(ByteBuffer buffer) {
+    return new FileDiff(Serializer.readSet(buffer, Serializer::readString));
+  }
+
+  @Override
+  public boolean equals(Object o) {
+    if (this == o) {
+      return true;
+    }
+    if (o == null || getClass() != o.getClass()) {
+      return false;
+    }
+    FileDiff diff = (FileDiff) o;
+    return Objects.equals(changedFiles, diff.changedFiles);
+  }
+
+  @Override
+  public int hashCode() {
+    return Objects.hashCode(changedFiles);
+  }
+
+  @Override
+  public String toString() {
+    return "FileDiff{changedFiles=" + changedFiles + '}';
+  }
+}

dd-java-agent/agent-ci-visibility/src/test/groovy/datadog/trace/civisibility/diff/DiffTest.groovy

@@ -0,0 +1,32 @@
+package datadog.trace.civisibility.diff
+
+import datadog.trace.civisibility.ipc.serialization.Serializer
+import spock.lang.Specification
+
+import static datadog.trace.civisibility.TestUtils.lines
+
+class DiffTest extends Specification {
+
+  def "test diffs serialization: #diff"() {
+    when:
+    def s = new Serializer()
+    Diff.SERIALIZER.serialize(diff, s)
+    def buffer = s.flush()
+    def diffCopy = Diff.SERIALIZER.deserialize(buffer)
+
+    then:
+    diff == diffCopy
+
+    where:
+    diff << [
+      new FileDiff(Collections.emptySet()),
+      new FileDiff(Collections.singleton("path")),
+      new FileDiff(new HashSet<>(["path-a", "path-b"])),
+      new LineDiff([:]),
+      new LineDiff(["path": lines(10)]),
+      new LineDiff(["path": lines(10, 11, 13)]),
+      new LineDiff(["path": lines(10, 11, 12, 13), "path-b": lines()]),
+      new LineDiff(["path": lines(10, 11, 12, 13), "path-b": lines(8, 18)])
+    ]
+  }
+}

dd-java-agent/agent-ci-visibility/src/test/groovy/datadog/trace/civisibility/diff/FileDiffTest.groovy

@@ -0,0 +1,39 @@
+package datadog.trace.civisibility.diff
+
+import datadog.trace.civisibility.ipc.serialization.Serializer
+import spock.lang.Specification
+
+class FileDiffTest extends Specification {
+
+  def "test diff contains file"() {
+    when:
+    def diff = new FileDiff(new HashSet<>(paths))
+
+    then:
+    diff.contains(path, 0, Integer.MAX_VALUE) == result
+
+    where:
+    paths                | path     | result
+    ["path-a"]           | "path-a" | true
+    ["path-a"]           | "path-b" | false
+    ["path-a", "path-b"] | "path-a" | true
+    ["path-a", "path-b"] | "path-b" | true
+    ["path-a", "path-b"] | "path-c" | false
+  }
+
+  def "test serialization: #paths"() {
+    given:
+    def diff = new FileDiff(new HashSet<>(paths))
+
+    when:
+    def serializer = new Serializer()
+    diff.serialize(serializer)
+    def buf = serializer.flush()
+
+    then:
+    FileDiff.deserialize(buf) == diff
+
+    where:
+    paths << [[], ["path-a"], ["path-a", "path-b"]]
+  }
+}

dd-java-agent/agent-ci-visibility/src/test/groovy/datadog/trace/civisibility/diff/LineDiffTest.groovy

@@ -39,7 +39,6 @@ class LineDiffTest extends Specification {
 
   def "test serialization: #lines"() {
     given:
-
     def diff = new LineDiff(lines)
 
     when: