Revise Grammar-Kit configuration

.gitignore

@@ -23,4 +23,3 @@ hs_err_pid*
 *.iml
 **/.gradle
 build
-src/gen

build.gradle.kts

@@ -65,11 +65,12 @@ grammarKit {
     grammarKitRelease = "2021.1.2"
 }
 
+val lexerSource = layout.buildDirectory.dir("generated/sources/lexer/java/main")
 sourceSets {
     main {
         java {
-            srcDir("src/gen/java")
-            srcDir("src/main/java")
+            srcDir(lexerSource)
+            srcDir(tasks.generateParser)
         }
     }
 }
@@ -104,23 +105,24 @@ tasks {
     }
 
     generateLexer {
-        sourceFile = file("src/main/lang/Nix.flex")
-        targetOutputDir = file("src/gen/java/org/nixos/idea/lang")
+        sourceFile = layout.projectDirectory.file("src/main/lang/Nix.flex")
+        targetOutputDir = lexerSource.map { it.dir("org/nixos/idea/lang") }
         purgeOldFiles = true
     }
 
     generateParser {
-        sourceFile = file("src/main/lang/Nix.bnf")
-        targetRootOutputDir = file("src/gen/java")
-        pathToParser = "/org/nixos/idea/lang/NixParser"
-        pathToPsiRoot = "/org/nixos/idea/psi"
+        sourceFile = layout.projectDirectory.file("src/main/lang/Nix.bnf")
+        targetRootOutputDir = layout.buildDirectory.dir("generated/sources/parser/java/main")
+        // Maybe we can remove the following properties in the future
+        // https://github.com/JetBrains/gradle-grammar-kit-plugin/issues/178
+        pathToParser = "org/nixos/idea/lang/NixParser.java"
+        pathToPsiRoot = "org/nixos/idea/psi"
         purgeOldFiles = true
-        // Task :generateLexer deletes files generated by this task when executed afterward.
-        mustRunAfter(generateLexer)
     }
 
     compileJava {
-        dependsOn(generateLexer, generateParser)
+        dependsOn(generateLexer)
+        // dependency to generateParser is implicitly detected by Gradle
     }
 
     test {

src/main/lang/Nix.flex

@@ -38,6 +38,7 @@ import static org.nixos.idea.psi.NixTypes.*;
   }
 %}
 
+%abstract
 %class _NixLexer
 %implements FlexLexer
 %function advance