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

craft_cli/pytest_plugin.py

examples.py

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

pyproject.toml

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

craft_cli/messages.py

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 is correct here.

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.

Agreed, this unit test is unrelated to the PR, so these changes should be reverted.

craft_cli/dispatcher.py

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.

craft_cli/dispatcher.py

tests/unit/test_messages_emitter.py

mr-cal · 2026-03-11T23:03:40Z

craft_cli/completion/completion.py

+    result: str = template.render(
        shell_cmd=shell_cmd,
        commands=command_map,
        global_opts=global_opts,
    )
+    return result


This can be reverted, the type checkers are able to deduce the type.

mr-cal · 2026-03-11T23:09:09Z

craft_cli/messages.py

 from typing import TYPE_CHECKING, Any, Literal, TextIO, TypeVar, cast

-import platformdirs
+import platformdirs  # type: ignore [import-not-found]


Please revert this, the import should be found.

mr-cal · 2026-03-11T23:09:22Z

craft_cli/messages.py

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


Copilot is correct here.

mr-cal · 2026-03-11T23:09:54Z

craft_cli/messages.py

+        """Output structured data to the terminal in a specific format.
+
+        :param data: The structured data to output( list of dicts or a single dict).
+        :param format: The format( defaults to 'table')


Suggested change

:param format: The format( defaults to 'table')

:param format: The format (defaults to 'table')

mr-cal · 2026-03-11T23:11:55Z

craft_cli/messages.py

+    """
+
+    def format(self, data: TabularData, headers: dict[str, str] | None = None) -> str:
+        _ = headers


I don't see this getting used.

mr-cal · 2026-03-11T23:38:10Z

tests/unit/test_messages_emitter.py

+    assert out.strip() == expected.strip()
+
+
+def test_table_formatter_empty_list():


Can you test?

empty list

empty dict

Both as json and a table?

mr-cal · 2026-03-11T23:38:38Z

tests/unit/test_messages_emitter.py

+
+
+def test_table_formatter_simple_dict_list():
+    data = [{"a": 1, "b": 2}, {"a": 3, "b": 4}]


Can you exercise printing the following data types as json and as a table?

str

int

float

bool

None

mr-cal · 2026-03-11T23:39:37Z

tests/unit/test_messages_emitter.py

Can you test a single column table?

mr-cal · 2026-03-11T23:40:07Z

tests/integration/test_messages_integration.py

Please revert the changes here.

mr-cal · 2026-03-11T23:42:28Z

craft_cli/messages.py

+            rows = [[str(row.get(h, "")) for h in table_headers] for row in data]
+        else:
+            table_headers = ["Key", "Value"]
+            rows = [[str(k), str(v)] for k, v in data.items()]


This is one reason I want to change the TabularData type in https://github.com/canonical/craft-cli/pull/380/changes#r2921516309.

…sertions

fix JSON formatter

… changes

dharapandya85 · 2026-03-25T18:42:00Z

Thank you @mr-cal for detailed review. Please check now for further improvements. Some tests and linting checks are failing for now.

In messages.py, I used Mapping, to avoid strict dict types, if string, and other value types, are passed.

ValueType = str | int | float | bool | None
Row = Mapping[str, ValueType]
TabularData = Sequence[Row] | Row

and here, it is failing

if isinstance(data, Mapping):
            rows_data: Sequence[Row] = [data]
                     -------------   ^^^^^^ Incompatible value of type `list[(Sequence[Mapping[str, str | int | float | None]] & Top[Mapping[Unknown, object]]) | Mapping[str, str | int | float | None]]`

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

lengau reviewed Sep 9, 2025

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

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

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dharapandya85 added 6 commits March 25, 2026 18:10

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

207451e

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

1525b17

…sertions

feat: resolve linting, formatting, and testing issues

521a38a

fix: docstring placement in table formatter

076c03e

fix JSON formatter

fix: improve formatter test and fix structured output handling

8314657

fix: improve JSON and table formatter tests and revert back unrelated…

06fb779

… changes

dharapandya85 force-pushed the feat/emitter-data-output branch from ec07206 to 06fb779 Compare March 25, 2026 18:29

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

	:param format: The format( defaults to 'table')
	:param format: The format (defaults to 'table')

		assert out.strip() == expected.strip()


		def test_table_formatter_empty_list():



		def test_table_formatter_simple_dict_list():
		data = [{"a": 1, "b": 2}, {"a": 3, "b": 4}]

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Pull request overview

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dharapandya85 commented Mar 25, 2026

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dharapandya85 commented Aug 25, 2025 •

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