Fix: add package install hint to ImageWriter backend error message

[Talhax55z]

Fixes #7980

Description

When no suitable ImageWriter backend is found, the error message previously
only said "No ImageWriter backend found for {fmt}." which gives the user
no actionable information.

This change adds a clear install hint to the error message, telling the
user which package to install depending on their file format.

Types of changes

• Non-breaking change (fix or new feature that would not break existing functionality).
• Breaking change (fix or new feature that would cause existing functionality to change).
• New tests added to cover the changes.
• Integration tests passed locally by running ./runtests.sh -f -u --net --coverage.
• Quick tests passed locally by running ./runtests.sh --quick --unittests --disttests.
• In-line docstrings updated.
• Documentation updated, tested make html command in the docs/ folder.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

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Reviewing files that changed from the base of the PR and between 1198bd9 and 4029c61.

📒 Files selected for processing (1)

• monai/data/image_writer.py

✅ Files skipped from review due to trivial changes (1)

• monai/data/image_writer.py

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📝 Walkthrough

Walkthrough

The resolve_writer() failure path in monai/data/image_writer.py now raises an OptionalImportError with an expanded message when no suitable ImageWriter backend is found and error_if_not_found=True. The message builds a comma-separated list of supported format keys from SUPPORTED_WRITERS (excluding "*") and suggests likely packages to install (e.g., nibabel, itk, Pillow). No public APIs or function signatures were changed; the modification is limited to the error message content.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	Title clearly and specifically describes the main change: adding package install hints to ImageWriter backend error messages.
Description check	✅ Passed	Description includes all required template sections: issue reference (#7980), clear explanation of the problem and solution, and checkbox selections indicating non-breaking change.
Linked Issues check	✅ Passed	Code changes directly address #7980 by appending install package hints to error messages when no ImageWriter backend is found, providing actionable guidance.
Out of Scope Changes check	✅ Passed	Changes are limited to error message improvement in resolve_writer() function, remaining within scope of #7980 objective with no extraneous modifications.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[coderabbitai]

🧹 Nitpick comments (1)

monai/data/image_writer.py (1)

119-119: Avoid static backend hints that can drift from actual writer registration.

Line 119 hard-codes extension/package guidance and can go stale (for example, registered formats like jpeg, bmp, tiff, and tif are not represented). Prefer deriving the hint from a single shared mapping or from registered writers so messaging stays accurate as init() evolves.

As per coding guidelines, "Suggest any enhancements for code improving efficiency, maintainability, comprehensibility, and correctness."

🤖 Prompt for AI Agents

Verify each finding against the current code and only fix it if needed.

In `@monai/data/image_writer.py` at line 119, The raise in ImageWriter where
OptionalImportError is constructed uses a hard-coded hint string for
packages/extensions; change it to compute the hint dynamically from the shared
writer registry used by init() (e.g., derive supported extensions/packages from
the module-level writer registry or mapping such as the writers registry used by
ImageWriter/init/_writer_registry) and include that generated list in the error
message instead of the static "'nibabel'...'Pillow'" text; update the
OptionalImportError message construction to enumerate current registered formats
(fmt alternatives) and, if you have a mapping of format→package names, build the
suggested package list from that mapping so the message stays accurate as init()
registers new writers.

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Nitpick comments:
In `@monai/data/image_writer.py`:
- Line 119: The raise in ImageWriter where OptionalImportError is constructed
uses a hard-coded hint string for packages/extensions; change it to compute the
hint dynamically from the shared writer registry used by init() (e.g., derive
supported extensions/packages from the module-level writer registry or mapping
such as the writers registry used by ImageWriter/init/_writer_registry) and
include that generated list in the error message instead of the static
"'nibabel'...'Pillow'" text; update the OptionalImportError message construction
to enumerate current registered formats (fmt alternatives) and, if you have a
mapping of format→package names, build the suggested package list from that
mapping so the message stays accurate as init() registers new writers.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

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📥 Commits

Reviewing files that changed from the base of the PR and between b887eae and a517854.

📒 Files selected for processing (1)

• monai/data/image_writer.py

[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Inline comments:
In `@monai/data/image_writer.py`:
- Around line 119-124: The supported-format message currently includes the
wildcard key EXT_WILDCARD ("*") from SUPPORTED_WRITERS, which confuses users;
before building _supported, filter SUPPORTED_WRITERS.keys() to exclude
EXT_WILDCARD (or any literal "*") and then join/sort the remaining keys so the
OptionalImportError message lists only real formats—update the code around the
OptionalImportError raise (where _supported is computed) to perform this
filtering.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

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📥 Commits

Reviewing files that changed from the base of the PR and between a517854 and 1198bd9.

📒 Files selected for processing (1)

• monai/data/image_writer.py