adding LocalRootSpan (open-telemetry#1310)

* adding LocalRootSpan class
this is based on Java's implementation, https://github.com/open-telemetry/opentelemetry-java-instrumentation/blob/v2.3.0/instrumentation-api/src/main/java/io/opentelemetry/instrumentation/api/instrumenter/LocalRootSpan.java
and adds the ability to identify and locate the "local root span" in a trace. The local root span is the top-level active span which has either
an invalid or remote parent.
It's tracked automatically as part of making a span active, either via `Span::activate()` or `Span::storeInContext()`, and can be retrieved in
a couple of ways, but most easily via `LocalRootSpan::current()`.

* remove redundant local root span check

* move context key to api

* internal

* adding example

* mark LocalRootSpan as experimental

* adding an example of local root span usage

* style, fix broken build

examples/traces/features/local_root_span.php

@@ -0,0 +1,42 @@
+<?php
+
+declare(strict_types=1);
+
+use OpenTelemetry\API\Trace\LocalRootSpan;
+use OpenTelemetry\API\Trace\Span;
+use OpenTelemetry\API\Trace\SpanKind;
+use OpenTelemetry\SDK\Common\Util\ShutdownHandler;
+use OpenTelemetry\SDK\Propagation\PropagatorFactory;
+use OpenTelemetry\SDK\Trace\TracerProviderFactory;
+
+putenv('OTEL_TRACES_EXPORTER=console');
+putenv('OTEL_PHP_DETECTORS=none');
+
+require_once __DIR__ . '/../../../vendor/autoload.php';
+
+$provider = (new TracerProviderFactory())->create();
+$propagator = (new PropagatorFactory())->create();
+ShutdownHandler::register([$provider, 'shutdown']);
+$tracer = $provider->getTracer('example');
+
+//start and activate a root span
+$root = $tracer
+    ->spanBuilder('root')
+    ->setSpanKind(SpanKind::KIND_SERVER)
+    ->startSpan();
+$rootScope = $root->activate();
+
+//start and activate a child span
+$child = $tracer
+    ->spanBuilder('child')
+    ->startSpan();
+$childScope = $child->activate();
+
+//update the name of the root span
+LocalRootSpan::current()->updateName('updated')->setAttribute('my-attr', true);
+
+//end spans and detach contexts
+$child->end();
+$childScope->detach();
+$root->end();
+$rootScope->detach();

examples/traces/features/local_root_span_with_remote_parent.php

@@ -0,0 +1,58 @@
+<?php
+
+declare(strict_types=1);
+/**
+ * @see https://opentelemetry.io/docs/specs/semconv/messaging/messaging-spans/#consumer-spans
+ */
+
+use OpenTelemetry\API\Trace\LocalRootSpan;
+use OpenTelemetry\API\Trace\Span;
+use OpenTelemetry\API\Trace\SpanContext;
+use OpenTelemetry\API\Trace\SpanKind;
+use OpenTelemetry\Context\Context;
+use OpenTelemetry\SDK\Common\Util\ShutdownHandler;
+use OpenTelemetry\SDK\Propagation\PropagatorFactory;
+use OpenTelemetry\SDK\Trace\TracerProviderFactory;
+
+putenv('OTEL_TRACES_EXPORTER=console');
+putenv('OTEL_PHP_DETECTORS=none');
+
+require_once __DIR__ . '/../../../vendor/autoload.php';
+
+$provider = (new TracerProviderFactory())->create();
+$propagator = (new PropagatorFactory())->create();
+ShutdownHandler::register([$provider, 'shutdown']);
+$tracer = $provider->getTracer('example');
+
+// “Receive” spans SHOULD be created for operations of passing messages to the application when those operations are initiated by the application code (pull-based scenarios).
+$root = $tracer
+    ->spanBuilder('receive')
+    ->setSpanKind(SpanKind::KIND_CONSUMER)
+    ->startSpan();
+
+$rootScope = $root
+    ->storeInContext(Context::getCurrent())
+    ->activate();
+assert(LocalRootSpan::fromContext(Context::getCurrent()) === $root);
+
+$root->addLink(SpanContext::createFromRemoteParent('fabebb164f22d4afc51df50d9a3ff629', '87c6836d8610ac6d', 768));
+
+// “Process” spans MAY be created in addition to “Receive” spans for pull-based scenarios for operations of processing messages.
+$child = $tracer
+    ->spanBuilder('process')
+    ->startSpan();
+$childScope = $child
+    //->storeInContext($remoteContext) // preserve remote baggage etc.
+    ->storeInContext(Context::getCurrent())
+    ->activate();
+$child->setAttribute('local_root', LocalRootSpan::current() === Span::getCurrent());
+
+try {
+    assert(LocalRootSpan::current() === $root);
+    assert(LocalRootSpan::current() !== Span::getCurrent());
+} finally {
+    $root->end();
+    $child->end();
+    $childScope->detach();
+    $rootScope->detach();
+}

src/API/Logs/LateBindingLogger.php

@@ -20,4 +20,9 @@ public function emit(LogRecord $logRecord): void
     {
         ($this->logger ??= ($this->factory)())->emit($logRecord);
     }
+
+    public function enabled(): bool
+    {
+        return true;
+    }
 }

src/API/Trace/LateBindingTracer.php

@@ -20,4 +20,9 @@ public function spanBuilder(string $spanName): SpanBuilderInterface
     {
         return ($this->tracer ??= ($this->factory)())->spanBuilder($spanName);
     }
+
+    public function enabled(): bool
+    {
+        return true;
+    }
 }

src/API/Trace/LocalRootSpan.php

@@ -0,0 +1,63 @@
+<?php
+
+declare(strict_types=1);
+
+namespace OpenTelemetry\API\Trace;
+
+use OpenTelemetry\Context\Context;
+use OpenTelemetry\Context\ContextInterface;
+use OpenTelemetry\Context\ContextKeyInterface;
+
+/**
+ * @experimental
+ */
+class LocalRootSpan
+{
+    /**
+     * Retrieve the local root span. This is the root-most active span which has
+     * a remote or invalid parent.
+     * If there is no active local root span, then an invalid span is returned.
+     * @experimental
+     */
+    public static function current(): SpanInterface
+    {
+        return self::fromContext(Context::getCurrent());
+    }
+
+    /**
+     * Retrieve the local root span from a Context.
+     * @experimental
+     */
+    public static function fromContext(ContextInterface $context): SpanInterface
+    {
+        return $context->get(self::key()) ?? Span::getInvalid();
+    }
+
+    /**
+     * @internal
+     */
+    public static function store(ContextInterface $context, SpanInterface $span): ContextInterface
+    {
+        return $context->with(self::key(), $span);
+    }
+
+    /**
+     * @internal
+     */
+    public static function key(): ContextKeyInterface
+    {
+        static $key;
+
+        return $key ??= Context::createKey(self::class);
+    }
+
+    /**
+     * @internal
+     */
+    public static function isLocalRoot(ContextInterface $parentContext): bool
+    {
+        $spanContext = Span::fromContext($parentContext)->getContext();
+
+        return !$spanContext->isValid() || $spanContext->isRemote();
+    }
+}

src/API/Trace/Span.php

@@ -54,6 +54,10 @@ final public function activate(): ScopeInterface
     /** @inheritDoc */
     final public function storeInContext(ContextInterface $context): ContextInterface
     {
+        if (LocalRootSpan::isLocalRoot($context)) {
+            $context = LocalRootSpan::store($context, $this);
+        }
+
         return $context->with(ContextKeys::span(), $this);
     }
 }

tests/Integration/SDK/LocalRootSpanTest.php

@@ -0,0 +1,49 @@
+<?php
+
+declare(strict_types=1);
+
+namespace OpenTelemetry\Tests\Integration\SDK;
+
+use OpenTelemetry\API\Trace\LocalRootSpan;
+use OpenTelemetry\API\Trace\Span;
+use OpenTelemetry\API\Trace\SpanInterface;
+use OpenTelemetry\Context\Context;
+use OpenTelemetry\SDK\Trace\TracerProvider;
+use PHPUnit\Framework\Attributes\CoversNothing;
+use PHPUnit\Framework\TestCase;
+
+#[CoversNothing]
+class LocalRootSpanTest extends TestCase
+{
+    private SpanInterface $span;
+
+    public function setUp(): void
+    {
+        $tracerProvider = new TracerProvider();
+        $this->span = $tracerProvider->getTracer('test')->spanBuilder('my-local-root-span')->startSpan();
+    }
+
+    public function test_active_root_span_is_local_root(): void
+    {
+        $scope = $this->span->activate();
+
+        try {
+            $this->assertSame($this->span, LocalRootSpan::current());
+        } finally {
+            $scope->detach();
+        }
+        $this->assertSame(Span::getInvalid(), LocalRootSpan::current(), 'root span ended, a local root span does not exist');
+    }
+
+    public function test_root_span_stored_in_context_is_local_root(): void
+    {
+        $root = Context::getRoot();
+        Context::storage()->attach($this->span->storeInContext($root));
+        $this->assertSame($this->span, LocalRootSpan::current());
+        $scope = Context::storage()->scope();
+        $this->assertNotNull($scope);
+        $this->assertSame($this->span, Span::fromContext($scope->context()));
+        $scope->detach();
+        $this->assertSame(Span::getInvalid(), LocalRootSpan::current(), 'root span ended, a local root span does not exist');
+    }
+}

tests/Unit/API/Trace/LocalRootSpanTest.php

@@ -0,0 +1,58 @@
+<?php
+
+declare(strict_types=1);
+
+namespace OpenTelemetry\Tests\Unit\API\Trace;
+
+use OpenTelemetry\API\Trace\LocalRootSpan;
+use OpenTelemetry\API\Trace\Span;
+use OpenTelemetry\API\Trace\SpanContext;
+use OpenTelemetry\Context\Context;
+use PHPUnit\Framework\Attributes\CoversClass;
+use PHPUnit\Framework\TestCase;
+
+#[CoversClass(LocalRootSpan::class)]
+class LocalRootSpanTest extends TestCase
+{
+    public function test_span_with_remote_parent_is_local_root(): void
+    {
+        $context = Context::getRoot()->with(
+            LocalRootSpan::key(),
+            Span::wrap(
+                SpanContext::createFromRemoteParent(
+                    '00000000000000000000000000000001',
+                    '0000000000000002',
+                )
+            )
+        );
+        $this->assertTrue(LocalRootSpan::isLocalRoot($context));
+    }
+
+    public function test_get_local_root_span(): void
+    {
+        $span = Span::getInvalid();
+        $context = LocalRootSpan::store(Context::getCurrent(), $span);
+        $scope = $context->activate();
+
+        try {
+            $this->assertSame($span, LocalRootSpan::fromContext($context));
+            $this->assertSame($span, LocalRootSpan::current());
+        } finally {
+            $scope->detach();
+        }
+    }
+
+    public function test_get_local_root_span_when_not_set(): void
+    {
+        $context = Context::getRoot();
+        $scope = $context->activate();
+
+        try {
+            $this->assertFalse(LocalRootSpan::fromContext($context)->getContext()->isValid());
+            $this->assertFalse(LocalRootSpan::current()->getContext()->isValid());
+            $this->assertSame(Span::getInvalid(), LocalRootSpan::current());
+        } finally {
+            $scope->detach();
+        }
+    }
+}