fix: capture STACK_LOG output via a Logback appender instead of System.err

grails-core/src/test/groovy/grails/util/GrailsUtilStackFiltererSpec.groovy

@@ -105,8 +105,8 @@ class GrailsUtilStackFiltererSpec extends Specification {
     }
 
     def 'installed DefaultStackTraceFilterer honours logFullStackTraceOnFilter=false'() {
-        given: 'a configured log appender to capture the StackTrace log entry'
-        def logCapture = new LogCapture('StackTrace')
+        given: 'a capture of the dedicated STACK_LOG logger'
+        def logCapture = new LogCapture(DefaultStackTraceFilterer.STACK_LOG_NAME)
 
         and: 'a filterer with the side-effect emission disabled'
         def quietFilterer = new DefaultStackTraceFilterer()
@@ -117,15 +117,15 @@ class GrailsUtilStackFiltererSpec extends Specification {
         GrailsUtil.deepSanitize(exceptionWithApplicationFrame())
 
         then: "no 'Full Stack Trace:' entry is emitted"
-        logCapture.events.count { it.formattedMessage.contains(StackTraceFilterer.FULL_STACK_TRACE_MESSAGE) } == 0
+        logCapture.events.every { !it.formattedMessage.contains(StackTraceFilterer.FULL_STACK_TRACE_MESSAGE) }
 
         cleanup:
         logCapture.close()
     }
 
     def 'installed DefaultStackTraceFilterer emits Full Stack Trace by default'() {
-        given: 'a configured log appender to capture the StackTrace log entry'
-        def logCapture = new LogCapture('StackTrace')
+        given: 'a capture of the dedicated STACK_LOG logger'
+        def logCapture = new LogCapture(DefaultStackTraceFilterer.STACK_LOG_NAME)
 
         and: 'a filterer with the default (enabled) side-effect emission'
         def loudFilterer = new DefaultStackTraceFilterer()

grails-core/src/test/groovy/org/apache/grails/core/GrailsBootstrapRegistryInitializerSpec.groovy

@@ -226,14 +226,14 @@ class GrailsBootstrapRegistryInitializerSpec extends Specification {
         def context = contextWithProperties([
                 (Settings.SETTING_LOG_FULL_STACKTRACE_ON_FILTER): 'false'
         ])
-        def logCapture = new LogCapture('StackTrace')
+        def logCapture = new LogCapture(DefaultStackTraceFilterer.STACK_LOG_NAME)
 
         when:
         closeBootstrapContext(context)
         GrailsUtil.deepSanitize(exceptionWithApplicationFrame())
 
         then: "no 'Full Stack Trace:' entry is emitted"
-        logCapture.events.count { it.formattedMessage.contains(StackTraceFilterer.FULL_STACK_TRACE_MESSAGE) } == 0
+        logCapture.events.every { !it.formattedMessage.contains(StackTraceFilterer.FULL_STACK_TRACE_MESSAGE) }
 
         cleanup:
         logCapture.close()
@@ -242,7 +242,7 @@ class GrailsBootstrapRegistryInitializerSpec extends Specification {
     def 'defaults logFullStackTraceOnFilter to true on the promoted DefaultStackTraceFilterer'() {
         given:
         def context = contextWithProperties([:])
-        def logCapture = new LogCapture('StackTrace')
+        def logCapture = new LogCapture(DefaultStackTraceFilterer.STACK_LOG_NAME)
 
         when:
         closeBootstrapContext(context)

grails-web-mvc/build.gradle

@@ -62,7 +62,7 @@ dependencies {
     api 'org.slf4j:jcl-over-slf4j'
 
     // Testing
-    testImplementation 'org.slf4j:slf4j-simple'
+    testImplementation(testFixtures(project(':grails-core')))
     testImplementation 'org.spockframework:spock-core'
 }
 

grails-web-mvc/src/test/groovy/org/grails/web/errors/GrailsExceptionResolverSpec.groovy

@@ -22,6 +22,7 @@ import grails.config.Config
 import grails.core.GrailsApplication
 import grails.web.mapping.UrlMappingsHolder
 import grails.web.mapping.exceptions.UrlMappingException
+import org.apache.grails.core.testing.support.LogCapture
 import org.grails.exceptions.reporting.DefaultStackTraceFilterer
 import org.apache.grails.core.GrailsBootstrapRegistryInitializer
 import org.grails.exceptions.reporting.StackTraceFilterer
@@ -53,10 +54,9 @@ class GrailsExceptionResolverSpec extends Specification {
     }
 
     void "logStackTrace emits only the resolver log"() {
-        given: "Captured System.err"
-        def originalErr = System.err
-        def baos = new ByteArrayOutputStream()
-        System.setErr(new PrintStream(baos, true))
+        given: "captures of both the resolver logger and the StackTrace logger"
+        def resolverLog = new LogCapture(GrailsExceptionResolver)
+        def stackLog = new LogCapture(DefaultStackTraceFilterer.STACK_LOG_NAME)
 
         and: "A resolver with no grailsApplication wired"
         def resolver = new GrailsExceptionResolver()
@@ -67,21 +67,17 @@ class GrailsExceptionResolverSpec extends Specification {
         resolver.logStackTrace(exception, request)
 
         then: "Only the GrailsExceptionResolver logger emits; StackTrace logger is silent"
-        System.err.flush()
-        def captured = baos.toString()
-        captured.contains('o.g.web.errors.GrailsExceptionResolver') ||
-                captured.contains('org.grails.web.errors.GrailsExceptionResolver')
-        !captured.contains('ERROR StackTrace ')
+        resolverLog.events.any { it.loggerName == GrailsExceptionResolver.name }
+        stackLog.events.isEmpty()
 
         cleanup:
-        System.setErr(originalErr)
+        resolverLog.close()
+        stackLog.close()
     }
 
     void "logFullStackTraceIfEnabled is a no-op when the opt-in property is unset"() {
-        given: "Captured System.err"
-        def originalErr = System.err
-        def baos = new ByteArrayOutputStream()
-        System.setErr(new PrintStream(baos, true))
+        given: "a capture of the StackTrace logger"
+        def stackLog = new LogCapture(DefaultStackTraceFilterer.STACK_LOG_NAME)
 
         and: "A resolver with no grailsApplication wired"
         def resolver = new GrailsExceptionResolver()
@@ -91,11 +87,10 @@ class GrailsExceptionResolverSpec extends Specification {
         resolver.logFullStackTraceIfEnabled(exception)
 
         then: "No StackTrace log entry is emitted"
-        System.err.flush()
-        !baos.toString().contains('ERROR StackTrace ')
+        stackLog.events.isEmpty()
 
         cleanup:
-        System.setErr(originalErr)
+        stackLog.close()
     }
 
     void "getRequestLogMessage appends auditor when logAuditor is enabled and the lookup returns a value"() {
@@ -264,10 +259,9 @@ class GrailsExceptionResolverSpec extends Specification {
     }
 
     void "logFullStackTraceIfEnabled emits the unfiltered trace when opt-in is enabled, and filterStackTrace then removes internal frames so the resolver log only sees the filtered trace"() {
-        given: "Captured System.err"
-        def originalErr = System.err
-        def baos = new ByteArrayOutputStream()
-        System.setErr(new PrintStream(baos, true))
+        given: "captures of both the resolver logger and the StackTrace logger"
+        def resolverLog = new LogCapture(GrailsExceptionResolver)
+        def stackLog = new LogCapture(DefaultStackTraceFilterer.STACK_LOG_NAME)
 
         and: "A resolver whose config opts in to full stack trace logging"
         def config = Mock(Config)
@@ -297,22 +291,30 @@ class GrailsExceptionResolverSpec extends Specification {
         resolver.filterStackTrace(exception)
         resolver.logStackTrace(exception, request)
 
-        then: "Both loggers emit"
-        System.err.flush()
-        def captured = baos.toString()
-        captured.contains('ERROR StackTrace ')
-        captured.contains('Full Stack Trace:')
-        captured.contains('o.g.web.errors.GrailsExceptionResolver') ||
-                captured.contains('org.grails.web.errors.GrailsExceptionResolver')
+        then: "Both loggers emit exactly once"
+        stackLog.events.size() == 1
+        resolverLog.events.size() == 1
+        stackLog.events[0].formattedMessage.contains(StackTraceFilterer.FULL_STACK_TRACE_MESSAGE)
+        resolverLog.events[0].loggerName == GrailsExceptionResolver.name
 
-        and: "The application frame appears in both log entries"
-        captured.count('com.example.MyController.show(MyController.groovy:10)') == 2
+        and: "The application frame appears in both the unfiltered and filtered log entries"
+        [stackLog.events[0], resolverLog.events[0]].every { event ->
+            event.throwableProxy.stackTraceElementProxyArray.any {
+                it.stackTraceElement.className == 'com.example.MyController'
+            }
+        }
 
-        and: "The internal frame appears only once — in the unfiltered StackTrace entry, not in the filtered resolver entry"
-        captured.count('java.lang.reflect.Method.invoke(Method.java:580)') == 1
+        and: "The internal frame appears only in the unfiltered StackTrace entry, not in the filtered resolver entry"
+        stackLog.events[0].throwableProxy.stackTraceElementProxyArray.any {
+            it.stackTraceElement.className == 'java.lang.reflect.Method'
+        }
+        resolverLog.events[0].throwableProxy.stackTraceElementProxyArray.every {
+            it.stackTraceElement.className != 'java.lang.reflect.Method'
+        }
 
         cleanup:
-        System.setErr(originalErr)
+        resolverLog.close()
+        stackLog.close()
     }
 
     void "getRequestLogMessage masks excluded request parameters case-insensitively"() {