DRAFT

Micronaut applications can be run in automatic restart mode. In this mode, a change to a project source will trigger

• compilation
• packaging
• application restart

This run mode is not suitable for debugging, as the developer routinely modifies the underlying source, and (seemingly random) restarts would break the debugging context. There still needs to be a "traditional" run mode for work scenarios, where (random) restarts implied by source changes could be harmful, e.g. when the worked-on app maintains some connections to other services, or keeps some context.

The actual implementation should be always delegated to the underlying build/launch system.

• gradle supports continous build mode with -t parameter to the gradle launcher
• maven is extended by micronaut plugin and goal mn:run to do the same

Project Action

A new project action Continuous Run will be defined to handle this special action. Both Maven and Gradle project support action configuration mapping, so implementation in both Gradle and Maven will just provide an action mapping for the new project action. The project action itself should be defined in

• Gradle Projects module: as -t is a Gradle feature, this will enable its use in other Gradle projects, not just Micronaut.
• Micronaut module (for Maven): Maven does not support it itself, but Micronaut's plugin does. Possibly, to reduce dependencies, micronaut.maven bridge module could be created.

This Project Action can be then invoked programmatically, apart from the project UI itself, by a LSP client, too.

 Since the action can be seen as a replacement for traditional Run (depending on project characteristics and user's preferred workflow), it should be configurable as the  default Run action, responding for

• ActionProvider.COMMAND_RUN,
• ActionProvider.COMMAND_RUN_SINGLE.

 Need to define how an (abstract) "Run" action can be remapped to a different action ("run-continuous") defined in nbactions.xml. 

Definition for Maven

    <action>
        <actionName>run.continuous</actionName>
        <packagings>
            <packaging>jar</packaging>
        </packagings>
<!--
		Maybe not necessary to add, if the MavenActionsProvider itself are registered specifically per-plugin

        <activation>
            <plugin>io.micronaut.build:micronaut-maven-plugin</plugin>
        </activation>
-->
        <goals>
            <goal>process-classes</goal>
            <goal>io.micronaut.build:micronaut-maven-plugin:2.0.0:run</goal>
        </goals>
        <properties>
            <mn.jvmArgs>${exec.vmArgs} -classpath %classpath</mn.jvmArgs>
            <mn.appArgs>${exec.appArgs</mn.appArgs>
            <exec.mainClass>${packageClassName}</exec.mainClass>
            <exec.executable>java</exec.executable>
        </properties>
    </action>

Definition for Gradle

Display Action in the IDE

Neither Gradle or Maven support adding technology-specific actions in the project UI. Even if the action is defined in nbactions.xml, it will not appear anywhere in the popup menu, except for custom actions (having CUSTOM- prefix in their action name; maven only). In this case, I would like to display the Continuous Run action alongside the Run and Debug.

• Gradle supports the --continuous flag from version 4.0.x (7 / 2017), so it seems pretty safe to add that action unconditionally to the project menu. There are some limitations documented, the action could warn the user for the 1st time the action is used, if it encounters such an environment.
• The action should not be present for other than micronaut projects (those which contain MN plugin) in Maven. 

 Need to define  a representation of such configuration in the UI. An alternative would be a menu item that

• executes on click,
• can display a submenu which contains
  • Run once
  • Run continuous
• the new state would be remembered

Adding technology-specific actions

Common actions for a project type are placed in Projects/<project-type-id>/Actions. These actions are displayed in the Project's context menu in the filesystem-defined order. I propose to define a layer API that would include also actions from Projects/<project-type-id>/plugin-id/Actions for all plugins participating on the project:

• plugins referenced in the build.gradle,
• plugins configured by active profiles of the maven project 

 Allowing to extend the main project menu may lead to its explosion with many added actions for each technology. A standard grouping action should be created in the OpenAPI and documented, so a technology may eventually add its action into a subgroup. This will not be part of the initial implementation, but could be added later. Note that by default, the Lookups.forPath() collects the whole .../Actions subtree (traversing into subfolders).

Maven implementation

RunJar support

Current "Run" operation relies on RunJar prerequisity checker and late-bound checker to step in, and supply necessary values for ${} variables referenced in the action config. The prerequisity checker checks for specific action IDs when activating. If Micronaut support defines Continuous Run as a different action ID, these checkers will not  be used, and the action may become broken: for example application args, VM args etc as seen in the Project Properties dialog will not be processed, StartupExtenders will not be collected etc. Two (or more ?) options here:

• Micronaut plugin will duplicate the RunJar logic, or
• We export an API from Maven core "Run" support to bind that support to specific executions, so the logic could be reused
  • packaging (already done)
  • project action ID
  • active plugins
• We export an API from either Maven (but see Gradle notes below) or from Project support itself, to categorize actions. Something like boolean isKindOf(abstractActionId, actionId), with an appropriate (declarative ?) SPI that Micronaut can use to declare Continous Run is kind of Run. This way, runJar support may check for categories instead of action Ids.

The logic implemented by Maven (which can be reused by Micronaut) is:

• Selection of the main class: if not defined, UI shows up, eventually recording user's choices in nbactions.xml
• Java platform selection
• StartupExtender VM parameters merge
• ExplicitProcessParameters processing

Micronaut Maven Plugin

While exec:exec goal honours system property exec.executable, that eventually specifies the desired Java executable to be used for application launch, Micronaut maven plugin does not honour any such property and relies on toolchains in maven. NetBeans do not support toolchains much, and our LSP clients also manage JDKs in a different way, not using maven toolchains. Java platform selection will be broken for mn:run goal, unless the whole maven runs on the target JDK.

The Micronaut plugin does not honour the following properties we need to transfer parameters from the IDE, or LSP client:

• mn.jvmArgs - just plugin configuration property is supported, not system property on commandline
• mn.appArg - just plugin configuration property is supported, not system property on commandline
• exec.executable - not supported at all, even as configuration propertyu
• exec.args - whole composed command line

The simplest solution is to enhance the mn:run goal to support some 'exec.executable'-like (i.e. mn.executable) property with a similar semantics.

Gradle implementation

The current parameter-passing implementation could work, mostly, except that it also specifically checks for action IDs. Since Gradle supports Continuous run natively, the JavaExecTokenProvider could also check for the new action ID. But if action categorization (as outlined for Maven) is invented, it would benefit from that - more actions (even user custom ones) could be categorized as "run-like". Other than that, gradle support should work acceptably.