feat(Cel-Based Sampler): Minor changes from PR review

- Added @trask, @jack-berg and @breedx-splk as additional code owners
- Added the project to the topmost README.md list of Provided Libraries
- Made the list of expressions passed to the sampler immutable
- Calculate the string representation of an expression on demand and not
  set it as a class private property

.github/component_owners.yml

@@ -27,6 +27,9 @@ components:
     - zeitlinger
   cel-sampler:
     - dol
+    - trask
+    - jack-berg
+    - breedx-splk
   cloudfoundry-resources:
     - KarstenSchnitter
   compressors:

README.md

@@ -21,6 +21,7 @@ feature or via instrumentation, this project is hopefully for you.
 | alpha   | [AWS X-Ray Propagator](./aws-xray-propagator/README.md)           |
 | alpha   | [Baggage Processors](./baggage-processor/README.md)               |
 | alpha   | [zstd Compressor](./compressors/compressor-zstd/README.md)        |
+| alpha   | [CEL-Based Sampler](./cel-sampler/README.md)                     |
 | alpha   | [Consistent Sampling](./consistent-sampling/README.md)            |
 | alpha   | [Disk Buffering](./disk-buffering/README.md)                      |
 | alpha   | [GCP Authentication Extension](./gcp-auth-extension/README.md)    |

cel-sampler/README.md

@@ -75,6 +75,8 @@ tracer_provider:
 ## Component owners
 
 * [Dominic Lüchinger](https://github.com/dol), SIX Group
-* TBD
+* [Jack Berg](https://github.com/jack-berg), New Relic
+* [Jason Plumb](https://github.com/breedx-splk), Splunk
+* [Trask Stalnaker](https://github.com/trask), Microsoft
 
 Learn more about component owners in [component_owners.yml](../.github/component_owners.yml).

cel-sampler/src/main/java/io/opentelemetry/contrib/sampler/cel/CelBasedSampler.java

@@ -21,6 +21,8 @@ import io.opentelemetry.context.Context;
 import io.opentelemetry.sdk.trace.data.LinkData;
 import io.opentelemetry.sdk.trace.samplers.Sampler;
 import io.opentelemetry.sdk.trace.samplers.SamplingResult;
+import java.util.ArrayList;
+import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
@@ -67,7 +69,9 @@ public final class CelBasedSampler implements Sampler {
    * @param fallback The fallback sampler to use when no expressions match
    */
   public CelBasedSampler(List<CelBasedSamplingExpression> expressions, Sampler fallback) {
-    this.expressions = requireNonNull(expressions, "expressions must not be null");
+    this.expressions =
+        Collections.unmodifiableList(
+            new ArrayList<>(requireNonNull(expressions, "expressions must not be null")));
     this.expressions.forEach(
         expr -> {
           if (!expr.getAbstractSyntaxTree().isChecked()) {
@@ -111,7 +115,7 @@ public final class CelBasedSampler implements Sampler {
         CelRuntime.Program program = celRuntime.createProgram(expression.getAbstractSyntaxTree());
         Object result = program.eval(evaluationContext);
         // Happy path: Perform sampling based on the boolean result
-        if (result instanceof Boolean && ((Boolean) result)) {
+        if (Boolean.TRUE.equals(result)) {
           return expression
               .getDelegate()
               .shouldSample(parentContext, traceId, name, spanKind, attributes, parentLinks);

cel-sampler/src/main/java/io/opentelemetry/contrib/sampler/cel/CelBasedSamplingExpression.java

@@ -21,7 +21,6 @@ import javax.annotation.Nullable;
  */
 public final class CelBasedSamplingExpression {
   private final CelAbstractSyntaxTree abstractSyntaxTree;
-  private final String expression;
   private final Sampler delegate;
 
   /**
@@ -33,7 +32,6 @@ public final class CelBasedSamplingExpression {
   CelBasedSamplingExpression(CelAbstractSyntaxTree abstractSyntaxTree, Sampler delegate) {
     this.abstractSyntaxTree =
         requireNonNull(abstractSyntaxTree, "abstractSyntaxTree must not be null");
-    this.expression = abstractSyntaxTree.getSource().getContent().toString();
     this.delegate = requireNonNull(delegate, "delegate must not be null");
   }
 
@@ -52,7 +50,7 @@ public final class CelBasedSamplingExpression {
    * @return The expression string
    */
   String getExpression() {
-    return expression;
+    return abstractSyntaxTree.getSource().getContent().toString();
   }
 
   /**
@@ -68,7 +66,7 @@ public final class CelBasedSamplingExpression {
   public String toString() {
     return "CelBasedSamplingExpression{"
         + "expression='"
-        + expression
+        + getExpression()
         + "', delegate="
         + delegate
         + "}";
@@ -84,12 +82,12 @@ public final class CelBasedSamplingExpression {
     }
     CelBasedSamplingExpression that = (CelBasedSamplingExpression) o;
     return Objects.equals(abstractSyntaxTree, that.abstractSyntaxTree)
-        && Objects.equals(expression, that.expression)
+        && Objects.equals(getExpression(), that.getExpression())
         && Objects.equals(delegate, that.delegate);
   }
 
   @Override
   public int hashCode() {
-    return Objects.hash(abstractSyntaxTree, expression, delegate);
+    return Objects.hash(abstractSyntaxTree, getExpression(), delegate);
   }
 }