feat(process-tags): signal service name source via svc.user/svc.auto

Emit one of two mutually-exclusive process tags so the Datadog backend
can distinguish user-set vs tracer-resolved service names:

- `svc.user:true` when DD_SERVICE is non-empty (env, INI, OTEL fallback,
  remote config)
- `svc.auto:<default_service_name>` when DD_SERVICE is empty and the
  tracer auto-resolved the name

Runtime mutations of `datadog.service` (via `ini_set` or remote config)
trigger a recompute. The new `ddtrace_process_tags_reload_with_service`
override threads the ZAI `new_str` through because the value is not yet
committed to `get_DD_SERVICE()` at the time the `ini_change` callback
fires.

Implements: RFC "Signal Service Name Source via Process Tags"
https://docs.google.com/document/d/1c47iSTWxIOHMHfZTF2nT9xfyQaIBP9KJvI9sRn5SvpM

Author: Leiyks

ext/ddtrace.c

@@ -416,6 +416,10 @@ bool ddtrace_alter_dd_service(zval *old_value, zval *new_value, zend_string *new
     dd_alter_prop(XtOffsetOf(ddtrace_span_properties, property_service), old_value, new_value, new_str);
     if (DDTRACE_G(request_initialized)) {
         ddtrace_sidecar_submit_root_span_data_direct(&DDTRACE_G(sidecar), NULL, new_str, get_DD_ENV(), get_DD_VERSION());
+        if (ddtrace_process_tags_enabled()) {
+            ddtrace_process_tags_reload_with_service(new_str);
+            ddtrace_sidecar_update_process_tags();
+        }
     }
     return true;
 }

ext/process_tags.c

@@ -11,6 +11,7 @@
 #include <string.h>
 #include "process_tags.h"
 #include "configuration.h"
+#include "serializer.h"
 #include "Zend/zend_smart_str.h"
 #include "components-rs/ddtrace.h"
 #include "SAPI.h"
@@ -24,6 +25,8 @@
 #define TAG_ENTRYPOINT_WORKDIR "entrypoint.workdir"
 #define TAG_ENTRYPOINT_TYPE "entrypoint.type"
 #define TAG_RUNTIME_SAPI "runtime.sapi"
+#define TAG_SVC_USER "svc.user"
+#define TAG_SVC_AUTO "svc.auto"
 
 #define TYPE_SCRIPT "script"
 #define TYPE_EXECUTABLE "executable"
@@ -44,6 +47,7 @@ typedef struct {
 } process_tags_t;
 
 static process_tags_t process_tags = {0};
+static zend_string *pending_service_override = NULL;
 
 static void clear_process_tags(void) {
     for (size_t i = 0; i < process_tags.count; i++) {
@@ -168,6 +172,17 @@ static void collect_process_tags(void) {
 
     add_process_tag(TAG_RUNTIME_SAPI, sapi_module.name);
 
+    zend_string *dd_service = pending_service_override ? pending_service_override : get_DD_SERVICE();
+    if (dd_service && ZSTR_LEN(dd_service) > 0) {
+        add_process_tag(TAG_SVC_USER, "true");
+    } else {
+        zend_string *default_svc = ddtrace_default_service_name();
+        if (default_svc) {
+            add_process_tag(TAG_SVC_AUTO, ZSTR_VAL(default_svc));
+            zend_string_release(default_svc);
+        }
+    }
+
     const char *script = NULL;
     if (SG(request_info).path_translated && *SG(request_info).path_translated) {
         script = SG(request_info).path_translated;
@@ -336,6 +351,13 @@ void ddtrace_process_tags_reload(void) {
     clear_process_tags();
     init_process_tags();
 }
+
+void ddtrace_process_tags_reload_with_service(zend_string *service_override) {
+    pending_service_override = service_override;
+    clear_process_tags();
+    init_process_tags();
+    pending_service_override = NULL;
+}
 void ddtrace_process_tags_mshutdown(void) {
     clear_process_tags();
 }

ext/process_tags.h

@@ -11,6 +11,11 @@
 void ddtrace_process_tags_first_rinit(void);
 // Reload process tags in current request
 void ddtrace_process_tags_reload(void);
+// Reload process tags using the supplied service-name override. Use when the
+// DD_SERVICE INI is being changed but the new value has not yet been committed
+// to the ZAI config runtime (e.g. inside an `ini_change` callback).
+// Pass NULL to fall back to get_DD_SERVICE().
+void ddtrace_process_tags_reload_with_service(zend_string *service_override);
 
 // Called at MSHUTDOWN to free resources
 void ddtrace_process_tags_mshutdown(void);

tests/ext/process_tags.phpt

@@ -47,6 +47,6 @@ if (isset($spans[1]['meta']['_dd.process_tags'])) {
 ?>
 --EXPECTF--
 Process tags present in root span: YES
-Process tags: entrypoint.basedir:ext,entrypoint.name:process_tags,entrypoint.type:script,entrypoint.workdir:%s,runtime.sapi:cli
+Process tags: entrypoint.basedir:ext,entrypoint.name:process_tags,entrypoint.type:script,entrypoint.workdir:%s,runtime.sapi:cli,svc.auto:process_tags.php
 Keys sorted: YES
 Process tags present in child span: NO

tests/ext/svc_auto_tag_cli.phpt

@@ -0,0 +1,23 @@
+--TEST--
+Process tags include svc.auto:<default> when DD_SERVICE is unset (CLI)
+--ENV--
+DD_EXPERIMENTAL_PROPAGATE_PROCESS_TAGS_ENABLED=1
+DD_TRACE_GENERATE_ROOT_SPAN=0
+DD_TRACE_AUTO_FLUSH_ENABLED=0
+--FILE--
+<?php
+$span = \DDTrace\start_span();
+$span->name = 'op';
+\DDTrace\close_span();
+
+$spans = dd_trace_serialize_closed_spans();
+$processTags = $spans[0]['meta']['_dd.tags.process'];
+
+echo "has svc.user: " . (strpos($processTags, 'svc.user') !== false ? 'YES' : 'NO') . "\n";
+echo "has svc.auto: " . (strpos($processTags, 'svc.auto:') !== false ? 'YES' : 'NO') . "\n";
+echo "auto value matches script: " . (strpos($processTags, 'svc.auto:svc_auto_tag_cli.php') !== false ? 'YES' : 'NO') . "\n";
+?>
+--EXPECT--
+has svc.user: NO
+has svc.auto: YES
+auto value matches script: YES

tests/ext/svc_auto_tag_otel.phpt

@@ -0,0 +1,24 @@
+--TEST--
+OTEL_SERVICE_NAME counts as user-defined (emits svc.user:true)
+--ENV--
+DD_EXPERIMENTAL_PROPAGATE_PROCESS_TAGS_ENABLED=1
+OTEL_SERVICE_NAME=otel-app
+DD_TRACE_GENERATE_ROOT_SPAN=0
+DD_TRACE_AUTO_FLUSH_ENABLED=0
+--FILE--
+<?php
+$span = \DDTrace\start_span();
+$span->name = 'op';
+\DDTrace\close_span();
+
+$spans = dd_trace_serialize_closed_spans();
+$processTags = $spans[0]['meta']['_dd.tags.process'];
+
+echo "DD_SERVICE resolved to: " . ini_get('datadog.service') . "\n";
+echo "has svc.user:true: " . (strpos($processTags, 'svc.user:true') !== false ? 'YES' : 'NO') . "\n";
+echo "has svc.auto:    : " . (strpos($processTags, 'svc.auto:') !== false ? 'YES' : 'NO') . "\n";
+?>
+--EXPECT--
+DD_SERVICE resolved to: otel-app
+has svc.user:true: YES
+has svc.auto:    : NO

tests/ext/svc_runtime_change.phpt

@@ -0,0 +1,33 @@
+--TEST--
+Changing datadog.service at runtime recomputes svc.user/svc.auto process tags
+--ENV--
+DD_EXPERIMENTAL_PROPAGATE_PROCESS_TAGS_ENABLED=1
+DD_TRACE_GENERATE_ROOT_SPAN=0
+DD_TRACE_AUTO_FLUSH_ENABLED=0
+--FILE--
+<?php
+$span1 = \DDTrace\start_span();
+$span1->name = 'before';
+\DDTrace\close_span();
+
+$spans = dd_trace_serialize_closed_spans();
+$tagsBefore = $spans[0]['meta']['_dd.tags.process'];
+echo "BEFORE has svc.auto: " . (strpos($tagsBefore, 'svc.auto:') !== false ? 'YES' : 'NO') . "\n";
+echo "BEFORE has svc.user: " . (strpos($tagsBefore, 'svc.user') !== false ? 'YES' : 'NO') . "\n";
+
+ini_set('datadog.service', 'changed-svc');
+
+$span2 = \DDTrace\start_span();
+$span2->name = 'after';
+\DDTrace\close_span();
+
+$spans = dd_trace_serialize_closed_spans();
+$tagsAfter = $spans[0]['meta']['_dd.tags.process'];
+echo "AFTER has svc.user:true: " . (strpos($tagsAfter, 'svc.user:true') !== false ? 'YES' : 'NO') . "\n";
+echo "AFTER has svc.auto:    : " . (strpos($tagsAfter, 'svc.auto:') !== false ? 'YES' : 'NO') . "\n";
+?>
+--EXPECT--
+BEFORE has svc.auto: YES
+BEFORE has svc.user: NO
+AFTER has svc.user:true: YES
+AFTER has svc.auto:    : NO

tests/ext/svc_user_tag.phpt

@@ -0,0 +1,22 @@
+--TEST--
+Process tags include svc.user:true when DD_SERVICE is set
+--ENV--
+DD_EXPERIMENTAL_PROPAGATE_PROCESS_TAGS_ENABLED=1
+DD_SERVICE=my-app
+DD_TRACE_GENERATE_ROOT_SPAN=0
+DD_TRACE_AUTO_FLUSH_ENABLED=0
+--FILE--
+<?php
+$span = \DDTrace\start_span();
+$span->name = 'op';
+\DDTrace\close_span();
+
+$spans = dd_trace_serialize_closed_spans();
+$processTags = $spans[0]['meta']['_dd.tags.process'];
+
+echo "has svc.user:true: " . (strpos($processTags, 'svc.user:true') !== false ? 'YES' : 'NO') . "\n";
+echo "has svc.auto:    : " . (strpos($processTags, 'svc.auto:') !== false ? 'YES' : 'NO') . "\n";
+?>
+--EXPECT--
+has svc.user:true: YES
+has svc.auto:    : NO

tests/ext/telemetry/telemetry_process_tags.phpt

@@ -46,7 +46,7 @@ if ($i == 300) {
 ?>
 --EXPECTF--
 Included
-string(%d) "entrypoint.basedir:telemetry,entrypoint.name:telemetry_process_tags,entrypoint.type:script,entrypoint.workdir:%s,runtime.sapi:cli"
+string(%d) "entrypoint.basedir:telemetry,entrypoint.name:telemetry_process_tags,entrypoint.type:script,entrypoint.workdir:%s,runtime.sapi:cli,svc.auto:telemetry_process_tags.php"
 --CLEAN--
 <?php