I don't understand why IntelliJ doesn't detect source code for some Kotlin classes. Let me show you an example:
Simple Spring WebFlux project. While debugging I wanted to go to each class, but when I tried to go into Mono.kt class, I saw
// IntelliJ API Decompiler stub source generated from a class file
// Implementation of methods is not available
Ok, maybe I didn't download the source code, but I see all sources
But IntelliJ shows me this:
I am very new to Kotlin development and I came across custom annotation classes in the documentation.
Is there a way for me to use an annotation on a function as a way to pre-populate some variables, or to run a decorator function before running the annotated function?
Something like:
class TestClass {
#Friendly("Hello World")
private fun testFun() {
greet()
//does something else
}
}
with an annotation class like
#Target(AnnotationTarget.FUNCTION)
#Retention(AnnotationRetention.BINARY)
annotation class Friendly(val message: String) {
fun greet() {
println(message)
}
}
I know this isn't valid Kotlin code, but I can't find any examples on how to actually use values from annotations without using reflection (if it's even possible)
Please let me know if I can do something like this, and more usefully, a better resource on annotation classes for Kotlin?
To make use of your custom annotations, you need to either create your own annotation processor (and use kapt Kotlin compiler plugin) to generate some new sources (but not modify existing!) at compile time, or use #Retention(AnnotationRetention.RUNTIME) meta-annotation (which is default in Kotlin), so that they could be accessed via reflection in runtime.
#Retention(AnnotationRetention.BINARY) meta-annotation you're using is equivalent of #Retention(RetentionPolicy.CLASS) in java, which is mostly useless (see https://stackoverflow.com/a/5971247/13968673).
What you're trying to do with annotations (call some additional code before/after method execution) reminds me aspect-oriented programming. Take a look at Spring AOP and AspectJ frameworks, following this paradigm, and their approach for annotations processing. TL;DR: Spring AOP is processing annotations in runtime, generating proxy-classes with respectful code, while AspectJ is using its own compiler (even not an annotation processor, cause it also introduces its own syntactic extension for java language), and can generate respectful bytecode at compile-time. They both are originally java-oriented, but with some configurational pain could be used with Kotlin too.
Can i write in my custom plugin some function like kotlin("jvm")?
plugins {
java
kotlin("jvm") version "1.3.71"
}
I want to write function myplugin("foo") in my custom plugin and then use it like
plugins {
java
kotlin("jvm") version "1.3.71"
custom.plugin
myplugin("foo")
}
How i can do it?
I think that plugins block is some kind of a macro expression. It is parsed and precompiled using a very limited context. Probably, the magic happens somewhere in kotlin-dsl. This is probably the only way to get static accessors and extension functions from plugins to work in Kotlin. I've never seen a mention of this process in Gradle's documentation, but let me explain my thought. Probably, some smart guys from Gradle will correct me.
Let's take a look at some third-party plugin, like Liquibase. It allows you to write something like this in your build.gradle.kts:
liquibase {
activities {
register("name") {
// Configure the activity here
}
}
}
Think about it: in a statically compiled language like Kotlin, in order for this syntaxt to work, there should be an extension named liquibase on a Project type (as it is the type of this object in every build.gradle.kts) available in the classpath of a Gradle's VM that executes the build script.
Indeed, if you click on it, you'll see something like:
fun org.gradle.api.Project.`liquibase`(configure: org.liquibase.gradle.LiquibaseExtension.() -> Unit): Unit =
(this as org.gradle.api.plugins.ExtensionAware).extensions.configure("liquibase", configure)
But take a look at the file where it is defined. In my case it is ~/.gradle/caches/6.3/gradle-kotlin-dsl-accessors/cmljl3ridzazieb8fzn553oa8/cache/src/org/gradle/kotlin/dsl/Accessors39qcxru7gldpadn6lvh8lqs7b.kt. It is definitelly an auto-generated file. A few levels upper in a file tree — at ~/.gradle/caches/6.3/gradle-kotlin-dsl-accessors/ in my case — there are dozens of similar directories. I guess, one by every plugin/version I've ever used with Gradle 6.3. Here is another one for the Detekt plugin:
fun org.gradle.api.Project.`detekt`(configure: io.gitlab.arturbosch.detekt.extensions.DetektExtension.() -> Unit): Unit =
(this as org.gradle.api.plugins.ExtensionAware).extensions.configure("detekt", configure)
So, we have a bunch of .kt files defining all that extensions for different plugins applied to the project. That files are obviously pre-cached and precompiled and their content is available in build.gradle.kts. Indeed, you can find classes directories beside those sources.
The sources are generated based on the content of the applied plugins. It is probably a tricky task that includes some magic, reflection and introspection. Sometimes this magic doesn't work (due too chatic Groovy nature) and then you need to use some crappy DSL from this package.
How are they generated? I see no other way, but to
Parse the build.script.kts with an embedded Kotlin compiler / lexer
Extract all the plugins sections
Compile them, probably against some mocks (remember that Project is not yet available: we're not executing the build.gradle.kts itself yet!)
Resolve the declared plugins from Gradle Plugin repository (with some nuances coming from settngs.gradle.kts)
Introspect plugin's artifacts
Generate the sources
Compile the sources
Add the resulting classes to the script's classpath
And here is the gotcha: there is a very limited context (classpath, classes, methods — call it whatever) available when compiling the plugins block. Actually, no plugins are yet applied! Because, you know, you're parsing the block that applies plugins. Chickens, eggs, and their problems, huh…
So, and we're getting closer to the answer on your question, to provide custom DSL in plugins block, you need to modify that classpath. It's not a classpath of your build.gradle.kts, it's the classpath of the VM that parses build.gradle.kts. Basically, it's Gradle's own classpath — all the classes bundled in a Gradle distribution.
So, probably the only way to provide really custom DSLs in plugins block is to create a custom Gradle distribution.
EDIT:
Indeed, totally forgot to test the buildSrc. I've created a file PluginExtensions.kt in it, with a content
inline val org.gradle.plugin.use.PluginDependenciesSpec.`jawa`: org.gradle.plugin.use.PluginDependencySpec
get() = id("org.gradle.war") // Randomly picked
inline fun org.gradle.plugin.use.PluginDependenciesSpec.`jawa`(): org.gradle.plugin.use.PluginDependencySpec {
return id("org.gradle.cunit") // Randomly picked
}
And it seems to be working:
plugins {
jawa
jawa()
}
However, this is only working when PluginExtensions.kt is in the default package. Whenever I put it into a sub-package, the extensions are not recognized, even with an import:
Magic!
The kotlin function is just a simple extension function wrapping the traditional id method, not hard to define:
fun PluginDependenciesSpec.kotlin(module: String): PluginDependencySpec =
id("org.jetbrains.kotlin.$module")
However, this extension function is part of the standard gradle kotlin DSL API, which means it's available without any plugin. If you want to make a custom function like this available, you would need a plugin. A plugin to load your plugin. Not very practical.
I also tried using the buildSrc module to make an extension function like the above. But it turns out that buildSrc definitions aren't even available from the plugins DSL block, which has a very constrained syntax. That wouldn't have been very practical anyway, you would have needed to make a buildSrc folder for every project in which you have wanted to use the extension.
I'm not sure if this is possible at all. Try asking on https://discuss.gradle.org/.
I've always used IntelliJ's "replace constructor with builder" to autogenerate builder from constructor for Java classes. I don't see a way to do this for Kotlin. Is there such a feature that I'm just not seeing?
I'd like to write a plugin for Intellij IDEA that should modify a Java and Kotlin code.
I use the method
PsiClass.getMethods()
in order to get all methods of Java and Kotlin classes. So far so good, so then I use methods like
PsiClass.add(), PsiClass.addAfter(), PsiClass.addBefore()
that all work fine once they are called on Java files, but start to throw an exception
IncorrectOperationException
once I called them on a Kotlin class.
I'd appreciate any hint on how I can modify Kotlin and Java classes (preferably using the same approach).
When you search for a Kotlin class via the JavaPsiFacade, it returns the light class which is a shallow representation that is just based on the information in the class file. In order to add PSI elements, you have to call navigationElement on it. Then, IJ will parse the source and build a full PSI tree that can be modified.
However, if the class is a Kotlin class, navigationElement will return a KtClass which is not derived from PsiClass. You will have to use the facilities in the Kotlin hierarchy to modify it. Method instances in Kotlin are also not instances of PsiMethod, but instances of KtMethod.
For analyzing Java and Kotlin sources in a common fashion there is a different syntax tree called "UAST", but for modifications you need a language-specific approach.