[#1773] Enhancement: Applications can improve startup time by setting…

… system property `picocli.disable.closures` to `true`

Closes #1773

RELEASE-NOTES.md

@@ -7,6 +7,8 @@ This release includes bugfixes and enhancements.
 
 From this release, applications can programmatically set the trace level, and use tracing in custom components.
 
+Applications can improve startup time by setting system property `picocli.disable.closures` to `true` to disable support for [closures in annotations](https://picocli.info/#_closures_in_annotations).
+
 Also, this release has various fixes and enhancements related to the synopsis of the usage help message.
 
 
@@ -89,6 +91,7 @@ Picocli 4.7.0 introduced a `sortSynopsis = false` attribute to let the synopsis
 * [#1571] Enhancement: Variables in values from the default value provider should be interpolated. Thanks to [Bas Passon](https://github.com/bpasson) for raising this.
 * [#1574] API: Add annotation API to control whether synopsis should be sorted alphabetically or by explicit `order`.
 * [#1708][#1712][#1723] API: The `setUsageHelpLongOptionsMaxWidth` method no longer throws an exception when an invalid value is specified; instead, the value is ignored and an INFO-level trace message is logged. Thanks to [Fabio](https://github.com/fabio-franco) for the pull request.
+* [#1773] Enhancement: Applications can improve startup time by setting system property `picocli.disable.closures` to `true` to disable support for [closures in annotations](https://picocli.info/#_closures_in_annotations). Thanks to [patric-r](https://github.com/patric-r) for raising this.
 * [#1408] Enhancement: Synopsis should respect `order` if specified. Thanks to [Simon](https://github.com/sbernard31) for raising this.
 * [#964][#1080] Enhancement: ArgGroup synopsis should respect `order` (if specified). Thanks to [Enderaoe](https://github.com/Lyther) for the pull request with unit tests.
 * [#1706][#1710] Enhancement: Subcommands should get missing messages from parent command resource bundle. Thanks to [Ruud Senden](https://github.com/rsenden) and [Mike Snowden](https://github.com/wtfacoconut) for the pull request.

docs/index.adoc

@@ -13072,6 +13072,7 @@ As you can see in the above example, each closure in the annotation should conta
 <4> Option or Parameters `parameterConsumer`: given a `Stack`, `ArgSpec` and `CommandSpec`, process the remaining arguments. The closure must be cast to `IParameterConsumer`.
 <5> Option or Parameters type `converter` takes an array of closures. Groovy 3.0.7 or greater is required: older versions of Groovy ignore closures in class array annotations. Each closure must have a parameter and be cast to `ITypeConverter`.
 
+NOTE: From picocli version 4.7.0, this feature can be disabled by setting system property `picocli.disable.closures` to `true`. Disabling support for closures in annotations can improve the application startup time.
 
 ==== Older Versions of Groovy
 NOTE: When using a Groovy version older than 2.4.7, use this workaround for the https://issues.apache.org/jira/browse/GROOVY-7613[Grape bug] that causes this error:

picocli-groovy/src/test/groovy/picocli/groovy/ClosureInAnnotationsDisabledTest.groovy

@@ -0,0 +1,47 @@
+package picocli.groovy
+
+import org.junit.AfterClass
+import org.junit.BeforeClass
+import org.junit.Test
+import picocli.CommandLine
+import picocli.CommandLine.InitializationException
+
+class ClosureInAnnotationsDisabledTest {
+    @BeforeClass
+    public static void beforeClass() {
+        System.setProperty("picocli.disable.closures", "true")
+    }
+
+    @AfterClass
+    public static void afterClass() {
+        System.clearProperty("picocli.disable.closures")
+    }
+
+
+    @CommandLine.Command(name = "ClosureDemo",
+        versionProvider = { {-> ["line1" , "line2"] as String[] } as CommandLine.IVersionProvider },
+        defaultValueProvider = {{argSpec -> "some default" } as CommandLine.IDefaultValueProvider}
+    )
+    static class ClosureDemo {
+        @CommandLine.Option(names = '-x', completionCandidates = {["A", "B", "C"]})
+        String x
+
+        @CommandLine.Option(names = '-y',
+            parameterConsumer = {{args, argSpec, commandSpec ->
+                argSpec.setValue(args.toString() + commandSpec.name())
+                args.clear()
+            } as CommandLine.IParameterConsumer })
+        String y
+    }
+
+    @Test
+    void testClosureDemo() {
+        try {
+            new CommandLine(new ClosureDemo())
+        } catch (InitializationException ex) {
+            String name = ClosureDemo.class.getName()
+            assert ex.message.startsWith("Cannot instantiate ${name}\$_closure1: the class has no constructor")
+        }
+    }
+
+}

src/main/java/picocli/CommandLine.java

@@ -5612,6 +5612,10 @@ public interface IFactory {
     private static class DefaultFactory implements IFactory {
         static Class<?> GROOVY_CLOSURE_CLASS = loadClosureClass();
         private static Class<?> loadClosureClass() {
+            if (Boolean.getBoolean("picocli.disable.closures")) {
+                tracer().info("DefaultFactory: groovy Closures in annotations are disabled and will not be loaded");
+                return null;
+            }
             try { return Class.forName("groovy.lang.Closure"); }
             catch (Exception ignored) { return null;}
         }