fix(islands): propagate notebook filename through MarimoIslandGenerator.from_file

[ljchang]

Summary

Closes #9391

MarimoIslandGenerator.from_file(path) previously discarded the source path. build() then constructed AppFileManager with filename=None, the kernel inherited app_metadata.filename = None, and create_main_module(file=None) fell through to sys.modules['__main__'].__file__ — i.e. the host process's launcher script. Cells inside notebooks rendered through islands therefore saw __file__ (and mo.notebook_dir()) resolve to the calling script (or to the installed CLI's .venv/bin/<entry> shim) rather than to the notebook source. marimo edit and marimo export were unaffected; only the islands code path was broken.

The fix threads the source path through:

• MarimoIslandGenerator.__init__ gains a _source_filename field (defaults to None, so manual MarimoIslandGenerator() + add_code() flows are unchanged).
• from_file() records the path on the instance.
• build() passes it to AppFileManager.from_app(self._app, filename=…).
• AppFileManager.from_app accepts a new optional filename kwarg and assigns _filename directly. All existing single-arg callers (29 in tests + 1 here) continue to work.

run_app_until_completion already populates AppMetadata(filename=file_manager.path, …), so once the file manager knows the path the existing kernel / patch_main_module plumbing delivers the correct __file__ — no further changes in _runtime/.

Before / after (issue's exact repro)

/tmp/repro/notebooks/nb.py prints __file__ and mo.notebook_dir() from a cell. /tmp/repro/scripts/render.py calls MarimoIslandGenerator.from_file(...).

Before:

__file__ = '/tmp/repro/scripts/render.py'
notebook_dir() = PosixPath('/tmp/repro/scripts')

After:

__file__ = '/tmp/repro/notebooks/nb.py'
notebook_dir() = PosixPath('/tmp/repro/notebooks')

Note on backward compatibility

This restores the documented / expected semantics, but it is a behavior change for any island user who relied on __file__ resolving to the host process. @mscolnick noted in #9391 that this may warrant a breaking-change classification — happy to take labeling / release-note guidance.

Pre-Review Checklist

• For large changes, or changes that affect the public API: this change was discussed or approved through an issue — see @mscolnick's comment on MarimoIslandGenerator: __file__ and notebook_dir() resolve to the host's __main__ instead of the notebook source #9391: "this does look like a real issue. we'd gladly accept the contribution to fix this."
• Any AI generated code has been reviewed line-by-line by the human PR author, who stands by it.
• Video or media evidence is provided for any visual changes (optional). — N/A, no visual change.

Merge Checklist

• I have read the contributor guidelines.
• Documentation has been updated where applicable, including docstrings for API changes. — AppFileManager.from_app docstring updated to document the new filename parameter.
• Tests have been added for the changes made. — tests/_islands/test_island_generator.py::test_from_file_propagates_filename_to_cells.

Verification

• pytest tests/_islands/ — 11 passed (10 existing + 1 new regression test)
• pytest tests/_server/test_file_manager.py tests/_server/test_sessions.py tests/_server/export/test_exporter.py — 81 passed (the 15 deselected test_export_html* failures are pre-existing on main due to no make fe artifact and unrelated to this change)
• ruff check / ruff format --check — clean on changed files
• mypy marimo --exclude=marimo/_tutorials/ — same 14 pre-existing errors as main; zero new errors introduced

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Project	Deployment	Actions	Updated (UTC)
marimo-docs	Ready	Preview, Comment	May 5, 2026 4:32pm

[github-actions]

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[ljchang]

I have read the CLA Document and I hereby sign the CLA

[cubic-dev-ai]

1 issue found across 3 files

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="marimo/_islands/_island_generator.py">

<violation number="1" location="marimo/_islands/_island_generator.py:281">
P2: Use the resolved file path instead of the raw input filename; otherwise relative paths can make `__file__`/`mo.notebook_dir()` depend on the current CWD at build time.</violation>
</file>

Architecture diagram

sequenceDiagram
    participant Client as Host Script
    participant Gen as MarimoIslandGenerator
    participant FM as AppFileManager
    participant Runtime as run_app_until_completion
    participant Kernel as Cell Execution Context

    Note over Client,Kernel: Initialization via Notebook File
    
    Client->>Gen: from_file(path)
    Gen->>Gen: NEW: Store path in _source_filename
    Gen-->>Client: generator instance

    Note over Client,Kernel: Build / Execution Flow
    
    Client->>Gen: build()
    
    Gen->>FM: CHANGED: from_app(app, filename=path)
    Note right of FM: assigns _filename directly
    FM-->>Gen: file_manager instance
    
    Gen->>Runtime: run_app_until_completion(file_manager)
    
    Runtime->>Runtime: Create AppMetadata(filename=file_manager.path)
    
    Runtime->>Kernel: Start Kernel with AppMetadata
    
    Kernel->>Kernel: Patch __main__ module (sys.modules)
    Note over Kernel: Kernel uses AppMetadata.filename<br/>to set __file__ and notebook_dir()

    Kernel->>Kernel: Execute Notebook Cells
    
    alt Happy Path: Path is provided
        Kernel-->>Gen: Cells see notebook path in __file__
    else Fallback: No path (manual generator flow)
        Kernel-->>Gen: Cells see host script path (sys.argv[0])
    end

    Runtime-->>Gen: session (execution results)
    Gen-->>Client: Ready to render HTML islands

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_{Reply with feedback, questions, or to request a fix. Tag @cubic-dev-ai to re-run a review, or fix all with cubic.}

[Copilot]

Pull request overview

This PR fixes the islands rendering path so notebook cells see the correct __file__ / mo.notebook_dir() when the app is built via MarimoIslandGenerator.from_file(...), by propagating the notebook source filename through to AppFileManager and the kernel metadata.

Changes:

• Track a source filename on MarimoIslandGenerator created via from_file() and pass it into build().
• Extend AppFileManager.from_app(...) with an optional filename parameter used to populate AppMetadata.filename.
• Add regression tests covering __file__/notebook_dir() correctness and relative-path snapshot semantics.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
marimo/_islands/_island_generator.py	Captures absolute source path in from_file() and forwards it into AppFileManager.from_app(...) during build().
marimo/_session/notebook/file_manager.py	Adds filename kwarg to from_app(...) and stores it on the manager so AppMetadata.filename is set.
tests/_islands/test_island_generator.py	Adds regression tests ensuring cells see the notebook’s path (including relative-path capture-time behavior).

[Copilot]

from_app(..., filename=...) stores filename as a raw Path via _maybe_path, and path later computes os.path.abspath(str(self._filename)). If callers ever pass a relative filename, file_manager.path (and therefore AppMetadata.filename / __file__) can change based on a subsequent chdir. Consider normalizing filename to an absolute path at assignment time (and prefer using the filename property setter instead of writing _filename directly) so the value is snapshotted when from_app is called.

[mscolnick]

@ljchang this seems like a good suggestion.

also, main was in a bad state. mind rebasing off origin/main to fix CI

[ljchang]

@mscolnick thanks for the review! Pushed two changes:

1. Addressed Copilot's file_manager.py suggestion in 63f327355: AppFileManager.from_app(..., filename=...) now os.path.abspaths at assignment time and routes through the filename property setter instead of writing _filename directly. Added a unit test (test_from_app_snapshots_relative_filename_to_absolute) to lock in the snapshot semantics at this layer too — the previous regression test only covered the MarimoIslandGenerator.from_file entry point.
2. Rebased onto origin/main (was 21 commits behind, including the CellManager/NotebookDocument consolidate refactor). Clean replay, no conflicts. CI should be green now.

Local run: 84 tests pass across tests/_server/test_file_manager* + tests/_islands/test_island_generator.py.

Happy to add a label if you let me know which fits best (bug? enhancement?) — enforce-label was the only non-flaky CI failure, and it needs a maintainer-set label.