Kotlin: Avoid infinite recursion when extracting recursive interfaces

[igfoo]

It's not perfect, but I think a proper fix will need to wait until we think about this properly in the planned rewrite.

[Copilot]

Pull Request Overview

This PR addresses an infinite recursion issue that occurs when extracting recursive interfaces in Kotlin code. The fix adds a ClassInstanceStack to track classes being extracted and detects potential cycles, falling back to raw types when recursion is detected.

Key Changes:

• Introduced a ClassInstanceStack utility class to track class extraction recursion
• Modified the extraction logic to detect and avoid infinite recursion by using raw types
• Added test cases for both nested generic types and recursive interface hierarchies

Reviewed Changes

Copilot reviewed 16 out of 16 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
java/kotlin-extractor/src/main/kotlin/utils/ClassInstanceStack.kt	New utility class that tracks class extraction state and detects cyclic type arguments
java/kotlin-extractor/src/main/kotlin/KotlinUsesExtractor.kt	Added avoidInfiniteRecursion method that uses the stack to detect cycles and fall back to raw types
java/kotlin-extractor/src/main/kotlin/KotlinFileExtractor.kt	Wraps supertype extraction in try-finally to manage the class instance stack
java/kotlin-extractor/src/main/kotlin/KotlinExtractorExtension.kt	Instantiates and threads the ClassInstanceStack through the extraction pipeline
java/kotlin-extractor/src/main/kotlin/ExternalDeclExtractor.kt	Accepts and passes through the ClassInstanceStack parameter
java/ql/test-kotlin2/library-tests/nested_types/test.kt	Test case for nested generic types
java/ql/test-kotlin2/library-tests/nested_types/types.ql	Query to verify nested type extraction
java/ql/test-kotlin2/library-tests/nested_types/types.expected	Expected results for nested types test
java/ql/integration-tests/kotlin/all-platforms/recursive_interfaces/*.java	Test cases with recursive interface hierarchies
java/ql/integration-tests/kotlin/all-platforms/recursive_interfaces/test.kt	Kotlin test file using the recursive interfaces
java/ql/integration-tests/kotlin/all-platforms/recursive_interfaces/types.ql	Query to verify recursive interface extraction
java/ql/integration-tests/kotlin/all-platforms/recursive_interfaces/types.expected	Expected results for recursive interfaces test
java/ql/integration-tests/kotlin/all-platforms/recursive_interfaces/test.py	Test configuration for the integration test

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[Copilot]

Line 5's condition checking for %MyType% is redundant since line 6 already filters for specific type patterns that would include MyType. This creates a logical AND that makes line 5 unnecessary - any type matching the patterns in line 6 will contain MyType. Consider removing line 5 to simplify the query logic.

Suggested change

t.getName().matches("%MyType%") and

[Copilot]

[nitpick] The pop() method returns the popped value but none of the call sites use the return value. Consider changing the return type to Unit to make the API clearer about its intent, or add a comment explaining why the return value is exposed if future use is anticipated.

Suggested change

	fun pop() = stack.pop()
	fun pop() { stack.pop() }

[Copilot]

[nitpick] The else clause is unnecessary here since the if block returns. Remove the else keyword and unindent line 552 to reduce nesting and improve readability.

Suggested change

	} else {
	return pair
	}
	}
	return pair

[smowton]

Looks plausible