feat(emitter):add structured data output with JSON and table formatting by dharapandya85 · Pull Request #380 · canonical/craft-cli

dharapandya85 · 2025-08-25T04:24:27Z

Fixes : #348

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This PR extends the Emitter class to support structured data output in multiple formats(JSON,table), with a registry for adding formats.
Implementation Details

A method on the emitter to write structured data to stdout
Output methods: TableFormatter for human-readable tables,JSONFormatterfor machine-readable JSON
Implemented usage in examples.py
Unit tests covering all formatters and edge cases
Added Emitter.data() method which accepts structured data(list[dict]) and uses registered formatter based on the --format flag.
Implemented JSONFormatter to fetch JSON outputs with json.dumps
Implemented TableFormatter for printing rows and columns
Emitter.register_formate(name,formatter) allows registering new formats
Default registry includes JSON and table
Updated CLI (dispatcher.py) to add -- format{json,table}
Added example_36 in examples.py to demo usage.
Added unit tests in test_messages_emitter.py
TableFomattter, handles list of dicts, empty list and dict input
JSONFormatter serializes list of data

Example Run

python examples.py 36 table
>>> Running example_33 with args: ('table',)
TABLE output:
name  | status   | version
--------------------------
App A | active   | 1.0.1
App B | inactive | 2.3.0

python examples.py 36 json
>>> Running example_33 with args: ('json',)
JSON output:
[
  {
    "name": "App A",
    "version": "1.0.1",
    "status": "active"
  },
  {
    "name": "App B",
    "version": "2.3.0",
    "status": "inactive"
  }
]

craft_cli/messages.py

lengau

Hi, please fix the broken tests and lint errors here.

docs/how-to-guides/change-logfile.rst

beliaev-maksim · 2025-11-27T11:33:01Z

craft_cli/pytest_plugin.py

+    # messages.emit._initiated = False
+    # messages.emit._stopped = True


should it be here?

beliaev-maksim · 2025-11-27T11:33:29Z

examples.py

+    # emit.message("Table output:")
+    # emit.data(sample_data,format="table")
+
+    # emit.structured(sample_data,fmt=fmt)


Problem solved, and no doc changes that require my review.

beliaev-maksim · 2025-12-04T11:56:16Z

pyproject.toml

-    "FBT002", # Boolean default value in function definition (preserving for backwards-comp)
-    "S101",   # Use of `assert` detected
-]
+


something looks wrong with this file. Lot's of unnecessary changes

Copilot

Pull request overview

This PR adds structured data output capabilities to the Emitter class, supporting JSON and table formatting for machine and human-readable output. The implementation includes a formatter registry pattern, CLI integration, and comprehensive test coverage.

Key changes:

Added BaseFormatter, JSONFormatter, and TableFormatter classes for flexible output formatting
Implemented Emitter.data(), Emitter.table(), and Emitter.json() methods for structured data output
Added --format CLI argument with json/table choices (filtered from help output)

Reviewed changes

Copilot reviewed 13 out of 14 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
craft_cli/messages.py	Core formatter classes and Emitter methods for structured data output
craft_cli/dispatcher.py	Added `--format` CLI argument and filtered it from command help
craft_cli/helptexts.py	Fixed help text generation when options list is empty
craft_cli/printer.py	Added `raw_output` parameter support to `show()` method
examples.py	Added example_36 demonstrating structured output formats
tests/unit/test_messages_emitter.py	Added unit tests for formatters and updated double init test
tests/unit/test_help.py	Updated tests to reflect filtered global options from help
tests/integration/test_messages_integration.py	Adjusted timing thresholds for test stability
craft_cli/init.py	Exposed `Emitter` and `complete` in public API
craft_cli/pytest_plugin.py	Added type ignore comments for pytest imports
craft_cli/completion/completion.py	Added explicit type annotation for template render
docs/conf.py	Added type ignore comment for sphinx import
pyproject.toml	File deleted (full file removal)

Comments suppressed due to low confidence (1)

pyproject.toml:1

The entire pyproject.toml file has been deleted. This removes critical project metadata, dependencies, and build configuration. This change should be reverted unless there's a deliberate migration to a different build system.

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craft_cli/messages.py

examples.py

Copilot · 2025-12-05T20:47:18Z

craft_cli/messages.py

+
+    Example:
+    -------
+    >>> formatter = JsonFormatter()


Class name in docstring example should be JSONFormatter (matching the actual class name) instead of JsonFormatter.

Suggested change

>>> formatter = JsonFormatter()

>>> formatter = JSONFormatter()

Copilot · 2025-12-05T20:47:19Z

craft_cli/messages.py

+    Example:
+    -------
+    >>> formatter = JsonFormatter()
+    >>> formatter.format([{"name":"Alice","age":30})


The example code is missing a closing bracket ] and has unbalanced parentheses. Should be formatter.format([{\"name\":\"Alice\",\"age\":30}]).

Suggested change

>>> formatter.format([{"name":"Alice","age":30})

>>> formatter.format([{"name":"Alice","age":30}])

Copilot · 2025-12-05T20:47:19Z

tests/unit/test_messages_emitter.py

-        messages, "_get_log_filepath", lambda appname: tmp_path / FAKE_LOG_NAME
-    )
-
+    monkeypatch.setattr(messages, "_get_log_filepath", None)


Setting _get_log_filepath to None will cause an error when it's called as a function. This should be a lambda or mock function that returns a path.

Copilot · 2025-12-05T20:47:19Z

craft_cli/dispatcher.py


 class _CustomArgumentParser(argparse.ArgumentParser):
    """ArgumentParser with custom error manager."""



[nitpick] This class attribute appears to be added without context. If this is documenting an existing attribute for type checking, consider adding a comment explaining its purpose.

Suggested change

# Type annotation for instance attribute set in __init__; aids type checking.

mr-cal · 2026-01-21T18:06:14Z

Hi @dharapandya85,

Are you still actively working on this? I haven't seen any activity or responses to the open comments since 2025-Dec-05.

dharapandya85 · 2026-01-22T10:56:34Z

Hi @dharapandya85,

Are you still actively working on this? I haven't seen any activity or responses to the open comments since 2025-Dec-05.

@mr-cal, working on this project.

…sertions

fix JSON formatter

lengau · 2026-01-26T18:41:21Z

craft_cli/dispatcher.py

 class _CustomArgumentParser(argparse.ArgumentParser):
    """ArgumentParser with custom error manager."""

+    _help_builder: HelpBuilder


I don't understand why this is here?

lengau · 2026-01-26T18:41:59Z

craft_cli/dispatcher.py

+        parser.add_argument(
+            "--format",
+            choices=["json", "table"],
+            default="table",
+            help="Format for structured output",
+        )


This should not be included by default on commands, as in many cases there is no structured output.

lengau · 2026-01-26T18:42:29Z

craft_cli/dispatcher.py


        # produce the complete help message for the command
-        command_options = self._get_global_options()
+        command_options: list[tuple[str, str]] = []


Doesn't this cause the global options to disappear?

lengau · 2026-01-26T18:43:35Z

tests/unit/test_messages_emitter.py

+    out = fmt.format({"foo": "bar"})
+    assert "foo" in out
+    assert "bar" in out


Please test the full tabular output, not just that there are parts in it.

dharapandya85 requested a review from tigarmo as a code owner August 25, 2025 04:24

lengau reviewed Sep 9, 2025

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craft_cli/messages.py Show resolved Hide resolved

lengau requested changes Sep 30, 2025

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dharapandya85 requested review from a team and medubelko as code owners October 1, 2025 11:49

medubelko previously requested changes Oct 1, 2025

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docs/how-to-guides/change-logfile.rst Show resolved Hide resolved

dharapandya85 force-pushed the feat/emitter-data-output branch from f33ec01 to 7a4f4b5 Compare October 23, 2025 13:45

dharapandya85 force-pushed the feat/emitter-data-output branch from ae4958a to 00bd742 Compare November 27, 2025 09:05

beliaev-maksim reviewed Nov 27, 2025

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beliaev-maksim reviewed Dec 4, 2025

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dharapandya85 force-pushed the feat/emitter-data-output branch 3 times, most recently from e64a8dc to 2afdf38 Compare December 4, 2025 18:40

lengau requested a review from Copilot December 5, 2025 20:46

Copilot AI reviewed Dec 5, 2025

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dharapandya85 force-pushed the feat/emitter-data-output branch 2 times, most recently from 000a63a to 1887069 Compare January 22, 2026 13:29

dharapandya85 added 3 commits January 22, 2026 13:40

feat(emitter):add structured data output with JSON and table formatting

6b24777

feat: Ensure Emitter is initiated before use and fix help argument as…

6521a50

…sertions

feat: resolve linting, formatting, and testing issues

6667b89

dharapandya85 force-pushed the feat/emitter-data-output branch from 1887069 to 1bcd53d Compare January 22, 2026 13:42

fix: docstring placement in table formatter

19bdba0

fix JSON formatter

dharapandya85 force-pushed the feat/emitter-data-output branch from 1bcd53d to 19bdba0 Compare January 23, 2026 17:59

mr-cal requested a review from lengau January 23, 2026 18:14

lengau reviewed Jan 26, 2026

View reviewed changes

fix: improve formatter test and fix structured output handling

ced4c2c

		# messages.emit._initiated = False
		# messages.emit._stopped = True

	>>> formatter = JsonFormatter()
	>>> formatter = JSONFormatter()

	>>> formatter.format([{"name":"Alice","age":30})
	>>> formatter.format([{"name":"Alice","age":30}])


		class _CustomArgumentParser(argparse.ArgumentParser):
		"""ArgumentParser with custom error manager."""



	# Type annotation for instance attribute set in __init__; aids type checking.

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dharapandya85 commented Aug 25, 2025 •

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