Fix StackOverflowError when mocking methods returning ArrayList #1464
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- Refactored MethodDescriptor.parseParamTypes() to avoid using Kotlin collection operations (dropLastWhile, filter) that call isEmpty() on collections, which could trigger the mock dispatcher and cause infinite recursion when mocking classes that extend ArrayList or other collections. - Used a two-pass approach: first count parameters, then parse into a pre-allocated array, avoiding mutable list operations entirely. - Added ArrayListReturnTypeTest for Android instrumented testing. Co-authored-by: oleksiyp <[email protected]>
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oleksiyp due to an error
December 1, 2025 12:36
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- Ensure first and second pass use identical logic via shared hasNonWhitespaceContent() helper function - Add custom trimSubstring() to avoid String.trim() which may trigger collection operations - Improve code consistency and reduce risk of array bounds issues Co-authored-by: oleksiyp <[email protected]>
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Done. I've addressed the code review feedback and completed the remaining checks. The changes in commit
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[WIP] Fix stack overflow error in mockk usage
Fix StackOverflowError when mocking methods returning ArrayList
Dec 2, 2025
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@Raibaz this looks safe change |
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Fixes StackOverflowError when using
every/verifywith methods returningArrayListor other concrete collection types on Android.Root Cause
The
MethodDescriptorconstructor was using Kotlin collection operations (dropLastWhile,filter) that internally callisEmpty()on collections. When the collection class (likeArrayList) is being mocked, this triggers the mock dispatcher, which callsAdvice.getOrigin(), which creates a newMethodDescriptor, causing infinite recursion.Solution
Rewrote
MethodDescriptor.parseParamTypes()to use a two-pass approach that avoids collection operations entirely:This approach avoids:
dropLastWhile { it.isEmpty() }- callsisEmpty()on collectionsfilter { it != "" }- also calls collection methodsString.trim()- replaced with customtrimSubstring()to avoid any potential collection operationsHelper functions
hasNonWhitespaceContent()andtrimSubstring()ensure consistent logic between both passes and avoid triggering mocked methods.Testing
ArrayListReturnTypeTest.ktfor Android instrumented testingFixes #1450
Original prompt
This section details on the original issue you should resolve
<issue_title>java.lang.StackOverflowError when use every/verify{/a method return ArrayList/} on a mock class after 1.13.8</issue_title>
<issue_description>I update the mockk from 1.12 to 1.13.x/1.14.x to support Android 14, but it will throw StackOverflowError when run some cases, after my testing, find the way to reproduce it.
Test code:
It always throw this StackOverflowError
Workaround:
Test code:
But actually, we need mock the class from SDK, we cannot change the return type.
Would anyone have any idea to fix it?</issue_description>
Comments on the Issue (you are @copilot in this section)
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