gnodet commented on code in PR #12694:
URL: https://github.com/apache/maven/pull/12694#discussion_r4357257256


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api/maven-api-core/src/main/java/org/apache/maven/api/build/report/LogEvent.java:
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@@ -0,0 +1,189 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.maven.api.build.report;
+
+import java.time.Instant;
+
+import org.apache.maven.api.annotations.Experimental;
+import org.apache.maven.api.annotations.Immutable;
+import org.apache.maven.api.annotations.Nonnull;
+import org.apache.maven.api.annotations.Nullable;
+
+/**
+ * A structured log event captured during the build.
+ * <p>
+ * Each event carries the log level, timestamp, message, and optionally
+ * the logger name and a stack trace. This replaces raw log line strings
+ * in the build report, enabling programmatic filtering by level and
+ * correlation by timestamp.
+ * <p>
+ * Events originating from the Maven Log API or from JUL
+ * ({@code java.util.logging}) carry additional source metadata: the
+ * source class name, source method name, and thread identifier.
+ * For Log API events the source class name is the mojo implementation
+ * FQCN; for JUL events it comes from {@code LogRecord}.  Events from
+ * direct SLF4J logging have these fields set to {@code null}.
+ *
+ * @since 4.1.0
+ */
+@Experimental
+@Immutable
+public interface LogEvent {
+
+    /**
+     * When this log event was produced (wall-clock time).
+     *
+     * @return the event instant, never {@code null}
+     */
+    @Nonnull
+    Instant timestamp();
+
+    /**
+     * The severity level of this log event.
+     *
+     * @return the log level, never {@code null}
+     */
+    @Nonnull
+    LogLevel level();
+
+    /**
+     * The log message, without level prefix or timestamp formatting.
+     *
+     * @return the log message, never {@code null}
+     */
+    @Nonnull
+    String message();
+
+    /**
+     * The name of the logger that produced this event
+     * (e.g. {@code "org.apache.maven.plugins.compiler.CompilerMojo"}).
+     *
+     * @return the logger name, or {@code null} if unavailable
+     */
+    @Nullable
+    String loggerName();
+
+    /**
+     * The stack trace associated with this event, if an exception was logged.
+     * <p>
+     * The trace is formatted as a multi-line string and may be truncated
+     * for very deep stack traces.
+     *
+     * @return the stack trace string, or {@code null} if no exception was 
logged
+     */
+    @Nullable
+    String stackTrace();

Review Comment:
   Agreed that keeping the raw `Throwable` is richer for consumers. The reason 
I went with a pre-formatted `String` was:
   
   1. `LogEvent` is `@Immutable` and is designed to be serialisable / 
archivable in build reports. Keeping a live `Throwable` reference would prevent 
that.
   2. In practice the event is captured at log time and may outlive the 
exception (e.g. stored in the report, exported to JSON). A pre-formatted string 
is always safe.
   3. Different SLF4J backends may not route `Throwable` reliably — JUL's 
`LogRecord` does carry it via `getThrown()`, but the SLF4J normalization path 
in `MavenBaseLogger` doesn't always have it.
   
   That said, I see your point: if a consumer wants to do something smarter 
with the exception (e.g. filter by exception type, extract the message without 
the stack, or format it in a structured error report), a `String` is opaque.
   
   Possible compromise: keep `stackTrace()` as `String` (always available, 
serialisation-safe) and add a default-null `Throwable throwable()` for the 
cases where the original exception is available. Consumers that just need the 
formatted trace use `stackTrace()`; consumers that need the live object use 
`throwable()`. WDYT?



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