Gradle groovy build-logic can't use any import statements

LexManos This is a known limitation, tracked as IDEA-260351. A *.gradle precompiled script plugin is resolved against the build script classpath, not against the compile classpath of the module that holds it. Your convention module declares commons-lang3 and the gradleutils plugin marker, so both classes are on that module's compile classpath, and the editor does not see that classpath. The import goes red, getByType falls back to Object, and every property access after that degrades. Gradle compiles the same file correctly, which matches what you see.

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There is no IDE-side setting that fixes it, but moving the logic out of the script does. Write the convention as a Groovy class that implements Plugin<Project> under build-logic/convention/src/main/groovy, then register that class in a gradlePlugin { plugins { ... } } block instead of relying on the *.gradle file name. A .groovy file is an ordinary module source, so the editor resolves it against the module's own dependencies.

 One build-logic/convention module, both variants importing the same two classes, one of them from the module's own source root: the *.gradle script reports Cannot resolve symbol as an error on both import lines, and the Plugin<Project> class reports nothing. Gradle configures and runs both.

It stays in Groovy, so it doesn’t push your Eclipse users to the Kotlin DSL, and the result is a plain plugin jar. I ran it on a minimal project rather than on yours.