Refactor MAL codegen into focused classes, fix CI issues (#13763)

**1. Refactor MALClassGenerator (1484 → 5 focused classes)**

Split by responsibility with clear comments showing which MAL expressions each class handles:

| Class | Lines | Responsibility |
|---|---|---|
| MALClassGenerator | ~350 | Public API + orchestration |
| MALExprCodegen | ~310 | Expression → Java source (variable-per-expression model) |
| MALMethodChainCodegen | ~340 | Method chain + extension + argument codegen |
| MALMetadataExtractor | ~370 | Static AST → metadata extraction |
| MALBytecodeHelper | ~290 | Javassist class naming, debug, bytecode attrs |

**2. Variable-per-expression codegen (replaces shared `sf` variable)**

Each metric expression gets its own named variable (e.g. `_metric1`, `_metric2`). Chain calls reassign to the same variable. Binary operations combine variables directly. No save/restore dance. Extension `::` calls work everywhere including sub-expressions.

Before:
```java
SampleFamily sf;
sf = ((SF) samples.getOrDefault("metric1", EMPTY));
sf = sf.sum(...);
SampleFamily _t0 = sf;       // save
sf = ((SF) samples.getOrDefault("metric2", EMPTY));
sf = sf.avg(...);
sf = _t0.plus(sf);            // restore + combine
return sf;
```

After:
```java
SampleFamily _metric1 = ((SF) samples.getOrDefault("metric1", EMPTY));
_metric1 = _metric1.sum(...);
SampleFamily _metric2 = ((SF) samples.getOrDefault("metric2", EMPTY));
_metric2 = _metric2.avg(...);
_metric1 = _metric1.plus(_metric2);
return _metric1;
```

**3. Unified codegen path**

Removed the inline expression codegen path. Complex expression arguments are pre-computed to temp variables via the statement-based path. Single codegen strategy eliminates duplication.

**4. Developer extension docs**

New docs under Contributing Guides > Project Extensions:
- `docs/en/guides/mal-extension.md` — MAL `namespace::method()` SPI for developers
- `docs/en/guides/lal-extension.md` — LAL custom input/output types for developers
- Renamed `source-extension.md` title to "OAL Extension"
- Clear boundary: user docs (`concepts-and-designs/`) for script syntax, developer docs (`guides/`) for SPI implementation

**5. Other improvements**

- Extract `generateFilterTestBody()` shared by `compileFilter()` and `generateFilterSource()`
- Fail fast on unknown inline expression types
- Fix upload-artifact v4 conflict (`overwrite: true`)
- Fix Node.js 20 deprecation (`FORCE_JAVASCRIPT_ACTIONS_TO_NODE24=true`, checkout v4→v6)

Author: wu-sheng

.github/workflows/skywalking.yaml

@@ -26,6 +26,7 @@ concurrency:
   cancel-in-progress: true
 
 env:
+  FORCE_JAVASCRIPT_ACTIONS_TO_NODE24: true
   SW_AGENT_JDK_VERSION: 8
   MAVEN_OPTS: -Dhttp.keepAlive=false -Dmaven.wagon.http.pool=false -Dmaven.wagon.httpconnectionManager.ttlSeconds=120
   SEGMENT_DOWNLOAD_TIMEOUT_MINS: 5 # Cache restore timeout
@@ -37,7 +38,7 @@ jobs:
     runs-on: ubuntu-latest
     timeout-minutes: 10
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
         with:
           submodules: true
           persist-credentials: false
@@ -50,7 +51,7 @@ jobs:
     runs-on: ubuntu-latest
     timeout-minutes: 10
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
         with:
           submodules: true
           persist-credentials: false
@@ -66,7 +67,7 @@ jobs:
     runs-on: ubuntu-latest
     timeout-minutes: 30
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
         with:
           submodules: true
           persist-credentials: false
@@ -115,7 +116,7 @@ jobs:
       pom: ${{ steps.filter.outputs.pom }}
       ui: ${{ steps.filter.outputs.ui }}
     steps:
-      - uses: actions/checkout@v4 # required for push event
+      - uses: actions/checkout@v6 # required for push event
         with:
           fetch-depth: 0
           submodules: true
@@ -166,7 +167,7 @@ jobs:
     runs-on: ubuntu-latest
     timeout-minutes: 30
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
         with:
           submodules: true
           persist-credentials: false
@@ -201,7 +202,7 @@ jobs:
       matrix:
         java-version: [11, 17, 25]
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
         with:
           submodules: true
           persist-credentials: false
@@ -248,7 +249,7 @@ jobs:
           - os: ubuntu-latest
             java-version: 25
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
         with:
           submodules: true
           persist-credentials: false
@@ -277,7 +278,7 @@ jobs:
       matrix:
         java-version: [11, 17, 21, 25]
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
         with:
           submodules: true
           persist-credentials: false
@@ -312,7 +313,7 @@ jobs:
           - name: ElasticSearch / OpenSearch
             class: org.apache.skywalking.library.elasticsearch.ElasticSearchIT
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
         with:
           submodules: true
           persist-credentials: false
@@ -713,7 +714,7 @@ jobs:
           - name: Pprof MySQL
             config: test/e2e-v2/cases/profiling/pprof/mysql/e2e.yaml
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
         with:
           submodules: true
           persist-credentials: false
@@ -771,6 +772,7 @@ jobs:
         with:
           name: test-logs-${{ matrix.test.name }}
           path: "${{ env.SW_INFRA_E2E_LOG_DIR }}"
+          overwrite: true
 
   e2e-test-istio:
     if: |
@@ -805,7 +807,7 @@ jobs:
             kubernetes: 28
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
         with:
           submodules: true
           persist-credentials: false
@@ -847,6 +849,7 @@ jobs:
         with:
           name: test-logs-${{ matrix.test.name }}
           path: "${{ env.SW_INFRA_E2E_LOG_DIR }}"
+          overwrite: true
 
   e2e-test-istio-ambient:
     if: |
@@ -876,7 +879,7 @@ jobs:
           - istio: 1.29.0
             kubernetes: 28
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
         with:
           submodules: true
           persist-credentials: false
@@ -918,6 +921,7 @@ jobs:
         with:
           name: test-istio-ambient-logs-${{ matrix.versions.istio }}-${{ matrix.versions.kubernetes }}-${{ matrix.analyzer }}
           path: "${{ env.SW_INFRA_E2E_LOG_DIR }}"
+          overwrite: true
 
   e2e-test-java-versions:
     if: |
@@ -932,7 +936,7 @@ jobs:
       matrix:
         java-version: [11, 17, 25]
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
         with:
           submodules: true
           persist-credentials: false
@@ -986,7 +990,7 @@ jobs:
           - name: BanyanDB Stages
             config: test/e2e-v2/cases/storage/banyandb/stages/e2e.yaml
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
         with:
           submodules: true
           persist-credentials: false
@@ -1073,6 +1077,7 @@ jobs:
         with:
           name: test-logs-${{ matrix.test.name }}
           path: "${{ env.SW_INFRA_E2E_LOG_DIR }}"
+          overwrite: true
 
   required:
     if: always()

docs/en/concepts-and-designs/lal.md

@@ -611,8 +611,15 @@ See bundled LAL scripts for complete examples:
 
 ### Extending: custom output types
 
-You can create custom output types to transform logs into any entity type for your own use cases. There are two approaches:
+For developers who need to create custom output types (implementing `LALOutputBuilder`, extending
+`AbstractLog`, registering `LALSourceTypeProvider` SPI, or defining custom input types), see the
+[LAL Extension Developer Guide](../guides/lal-extension.md).
 
+<!--
+Developer-facing content below is kept for reference but the canonical guide is lal-extension.md.
+-->
+
+<!--
 #### Approach 1: Implement `LALOutputBuilder`
 
 Use this when you need full control over validation and dispatching, or when the output is not a simple `AbstractLog` subclass.
@@ -716,3 +723,4 @@ public class MyLayerSourceTypeProvider implements LALSourceTypeProvider {
 ```
 
 Register it in `META-INF/services/org.apache.skywalking.oap.log.analyzer.v2.spi.LALSourceTypeProvider`.
+-->

docs/en/concepts-and-designs/mal.md

@@ -248,12 +248,13 @@ Extension functions are called with a `::` separator between the namespace and m
 
 ```
 metric.sum(['svc']).myext::transform(2.0)
-metric.genai::estimateCost()
 ```
 
 The `::` separator distinguishes extension calls from built-in `SampleFamily` methods (like `.sum()`,
 `.tag()`, `.filter()`). Method names only need to be unique within their namespace.
 
+Available extension namespaces depend on which extension modules are deployed with the OAP server.
+
 ### Supported Parameter Types
 
 Extension methods accept the following argument types from MAL expressions:
@@ -275,6 +276,11 @@ The MAL compiler validates extension calls at compile time:
 - Mismatched argument count results in a compilation error.
 - Type mismatches between MAL arguments and Java parameter types result in a compilation error.
 
+### Building Extensions
+
+For developers who want to create custom MAL extension functions, see the
+[MAL Extension Developer Guide](../guides/mal-extension.md).
+
 ## Down Sampling Operation
 MAL should instruct meter-system on how to downsample for metrics. It doesn't only refer to aggregate raw samples to
 `minute` level, but also expresses data from `minute` in higher levels, such as `hour` and `day`.

docs/en/guides/lal-extension.md

@@ -0,0 +1,55 @@
+# LAL Extension: Custom Input/Output Types for Developers
+
+LAL (Log Analysis Language) supports custom input and output types for extending log processing
+beyond the built-in `Log` type. This enables receiver plugins and custom modules to define
+domain-specific log entities (e.g., slow SQL records, sampled traces, network profiling logs).
+
+## Overview
+
+LAL provides two extension mechanisms:
+
+1. **`outputType` per rule** — set in YAML config to transform logs into custom entities
+2. **`LALSourceTypeProvider` SPI** — register default input/output types for a receiver plugin
+
+Both are documented in detail in the [LAL user guide](../concepts-and-designs/lal.md#output-type),
+including:
+- Built-in output types (`SlowSQL`, `SampledTrace`)
+- Creating custom output types (Source subclass or `LALOutputBuilder` interface)
+- Custom input types for non-standard log formats
+- SPI registration for receiver-level defaults
+
+## Quick Reference
+
+### Per-rule output type (YAML config)
+
+```yaml
+rules:
+  - name: slow_sql
+    outputType: SlowSQL
+    dsl: |
+      filter { ... }
+      extractor {
+        statement log.body
+      }
+      sink { }
+```
+
+### LALSourceTypeProvider SPI (receiver plugin default)
+
+```java
+public class MyLayerSourceTypeProvider implements LALSourceTypeProvider {
+    @Override
+    public String layer() { return "MY_LAYER"; }
+
+    @Override
+    public Class<?> inputType() { return MyProtoMessage.class; }
+
+    @Override
+    public Class<? extends Source> outputType() { return MyCustomBuilder.class; }
+}
+```
+
+Register in `META-INF/services/org.apache.skywalking.oap.log.analyzer.v2.spi.LALSourceTypeProvider`.
+
+For complete examples and implementation details, see the
+[Output Type section in the LAL documentation](../concepts-and-designs/lal.md#output-type).

docs/en/guides/mal-extension.md

@@ -0,0 +1,100 @@
+# MAL Extension Functions for Developers
+
+MAL (Meter Analysis Language) supports custom extension functions callable from scripts using the
+`namespace::method()` syntax. Extensions are discovered at startup via Java `ServiceLoader`, requiring
+no changes to the MAL compiler or grammar.
+
+## Creating an Extension
+
+### 1. Implement `MalFunctionExtension`
+
+Create a class that implements the SPI interface and add static methods annotated with `@MALContextFunction`:
+
+```java
+package com.example;
+
+import org.apache.skywalking.oap.meter.analyzer.v2.dsl.SampleFamily;
+import org.apache.skywalking.oap.meter.analyzer.v2.spi.MALContextFunction;
+import org.apache.skywalking.oap.meter.analyzer.v2.spi.MalFunctionExtension;
+
+public class MyExtension implements MalFunctionExtension {
+    @Override
+    public String name() {
+        return "myext";  // namespace used in MAL scripts
+    }
+
+    @MALContextFunction
+    public static SampleFamily scale(SampleFamily sf, double factor) {
+        return sf.multiply(Double.valueOf(factor));
+    }
+
+    @MALContextFunction
+    public static SampleFamily filterByTag(SampleFamily sf, String key, String value) {
+        return sf.tagEqual(key, value);
+    }
+}
+```
+
+### 2. Register via SPI
+
+Create the file `META-INF/services/org.apache.skywalking.oap.meter.analyzer.v2.spi.MalFunctionExtension`:
+```
+com.example.MyExtension
+```
+
+### 3. Use in MAL scripts
+
+```yaml
+metricsRules:
+  - name: scaled_metric
+    exp: metric.sum(['svc']).myext::scale(2.0)
+  - name: filtered_metric
+    exp: metric.myext::filterByTag("env", "prod").sum(['svc'])
+```
+
+## Method Requirements
+
+- Methods **must** be `static`
+- First parameter **must** be `SampleFamily` (auto-bound to the current chain value in the expression)
+- Return type **must** be `SampleFamily`
+- Non-static or invalid methods throw `IllegalArgumentException` at startup
+- Duplicate namespace names throw `IllegalArgumentException` at startup
+- Duplicate method names within the same namespace throw `IllegalArgumentException` at startup
+
+## Supported Parameter Types
+
+| Java Type | MAL Argument | Example |
+|-----------|-------------|---------|
+| `String` | String literal | `"value"` |
+| `double` | Number literal | `2.0` |
+| `float` | Number literal | `3.0` |
+| `long` | Number literal | `100` |
+| `int` | Number literal | `10` |
+| `List<String>` | String list | `["tag1", "tag2"]` |
+
+Only `List<String>` is supported for list parameters. Other generic list types (e.g., `List<Integer>`)
+are rejected at startup.
+
+## How It Works
+
+The MAL compiler generates **direct static method calls** at compile time — no reflection at runtime.
+Each metric gets a named variable (e.g., `_metric`), and extension calls are emitted as static calls
+on the variable:
+
+For `metric.sum(['svc']).myext::scale(2.0)`:
+```java
+SampleFamily _metric = ((SampleFamily) samples.getOrDefault("metric", SampleFamily.EMPTY));
+_metric = _metric.sum(java.util.Arrays.asList(new String[]{"svc"}));
+_metric = com.example.MyExtension.scale(_metric, 2.0);
+return _metric;
+```
+
+## Compile-Time Validation
+
+The compiler validates at expression compilation time:
+- Namespace exists in the SPI registry
+- Method exists in that namespace
+- Argument count matches (excluding the implicit `SampleFamily` first parameter)
+- Argument types are compatible with the method signature
+
+Any validation failure results in a compilation error with a clear message.

docs/en/guides/source-extension.md

@@ -1,4 +1,4 @@
-# Source and scope extension for new metrics
+# OAL Extension: Source and Scope for New Metrics
 From the [OAL scope introduction](../concepts-and-designs/oal.md#from), you should already have understood what a scope is.
 If you would like to create more extensions, you need to have a deeper understanding of what a **source** is. 
 

docs/menu.yml

@@ -430,8 +430,12 @@ catalog:
             catalog:
               - name: "Component Library Settings"
                 path: "/en/guides/component-library-settings"
-              - name: "Extend An OAL Source"
+              - name: "OAL Source and Scope Extension"
                 path: "/en/guides/source-extension"
+              - name: "MAL Extension Functions"
+                path: "/en/guides/mal-extension"
+              - name: "LAL Custom Input/Output Types"
+                path: "/en/guides/lal-extension"
           - name: "Dependencies"
             catalog:
               - name: "Project Dependencies Check"