Fix lru_cache(...) resetting when cell is rerun

[leoadberg]

📝 Summary

Previously @mo.lru_cache(maxsize=128) (or similar) would reset after the cell is rerun because the extra wrapping call caused the frame offset to point one frame too high, causing the _cache_call._set_context to think the function isn't global.

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Project	Deployment	Actions	Updated (UTC)
marimo-docs	Ready	Preview, Comment	May 19, 2026 5:55pm

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[leoadberg]

recheck

[cubic-dev-ai]

No issues found across 2 files

Architecture diagram

sequenceDiagram
    participant User
    participant Kernel as Marimo Kernel
    participant ExecReq as ExecReqProvider
    participant Cell as Cell Executor
    participant LRUCache as @mo.lru_cache Decorator
    participant CacheLogic as _cache_call._set_context
    participant Globals as Kernel Globals

    Note over User,Globals: LRU Cache Persistence Across Cell Reruns

    User->>Kernel: Run cell with @lru_cache(maxsize=128)
    Kernel->>ExecReq: Build execution request
    ExecReq-->>Kernel: Execution request with cell code
    Kernel->>Cell: Execute cell code

    Cell->>LRUCache: Apply @lru_cache(maxsize=128)
    alt Decorator called with parentheses (callable=True)
        LRUCache->>LRUCache: _frame_offset=1
    else Decorator called as @lru_cache (callable=False)
        LRUCache->>LRUCache: _frame_offset=2
    end
    LRUCache->>CacheLogic: _set_context() to determine scope

    alt Frame offset correct (global scope detected)
        CacheLogic-->>LRUCache: Context set as global
        LRUCache->>Globals: Register cached function
        Cell->>LRUCache: Execute foo()
        LRUCache->>Globals: Check cache miss
        Globals-->>LRUCache: No cache entry
        LRUCache->>Cell: Execute foo() body (print "ran")
        Cell-->>LRUCache: Return result
        LRUCache->>Globals: Store result in cache
        Cell->>LRUCache: Execute foo() again
        LRUCache->>Globals: Check cache hit
        Globals-->>LRUCache: Cached result
        LRUCache-->>Cell: Return cached result (no print)
    else Frame offset wrong (local scope detected)
        CacheLogic-->>LRUCache: Context set as local
        Note over LRUCache,Globals: This path caused cache reset on rerun
    end

    Cell-->>Kernel: Cell execution complete
    Kernel-->>User: Cell output (printed "ran" once)

    Note over User,Kernel: Cell rerun (same cell)

    User->>Kernel: Rerun the same cell
    Kernel->>Cell: Execute cell code again
    Cell->>LRUCache: Re-apply decorator
    LRUCache->>CacheLogic: _set_context() with corrected frame offset

    alt Correct frame offset (PR fix)
        CacheLogic-->>LRUCache: Context set as global
        LRUCache->>Globals: Reuse existing cached function
        Cell->>LRUCache: Execute foo()
        LRUCache->>Globals: Check cache hit
        Globals-->>LRUCache: Previous cache entry exists
        LRUCache-->>Cell: Return cached result (no re-execution)
        Note over Cell,Globals: foo() body not re-run, "ran" not printed again
        Cell->>LRUCache: Execute foo() again
        LRUCache->>Globals: Another cache hit
        Globals-->>LRUCache: Cached result
        LRUCache-->>Cell: Return cached result
    end

    Cell-->>Kernel: Cell execution complete
    Kernel-->>User: No additional output (cache persisted across rerun)

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[leoadberg]

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