feat: add 'for' statement

[mr-cal]

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---

Adds a for statement to craft-grammar. This is the first step towards a new variant of advanced grammar, so some restrictions apply:

• 'for' can't be combined with other statements.
• only one selector may be used in a 'for' statement (for a,b is invalid)

(IMAGECRAFT-38)

[Copilot]

Pull Request Overview

This PR introduces a new 'for' statement to craft-grammar as part of implementing a new variant of advanced grammar. The 'for' statement allows matching against platforms and includes restrictions to prevent mixing with other statement types.

• Adds ForStatement class with platform matching functionality
• Implements variant checking to prevent mixing 'for' with other grammar statements
• Updates base processor to support platforms parameter

Reviewed Changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
craft_grammar/_for.py	New ForStatement implementation with platform matching logic
craft_grammar/_processor.py	Adds variant tracking and 'for' statement parsing
craft_grammar/_base_processor.py	Extends base to accept platforms parameter
craft_grammar/errors.py	Adds ForStatementSyntaxError exception class
tests/unit/test_for.py	Comprehensive test coverage for ForStatement
tests/unit/test_processor.py	Tests for variant mixing prevention
tests/unit/test_to.py	Corrects test function names from 'on' to 'to'
tests/unit/test_errors.py	Tests for new ForStatementSyntaxError
pyproject.toml	Adds "Afor" to codespell ignore list
craft_grammar/init.py	Exports ForStatement class

[upils]

Overall LGTM. I was expecting a bigger change initially, but this is clean and nice!

[lengau]

Suggested change

	- Add a new 'for' statement to select against a platform.
	- Add a new ``for`` statement to select against a platform.

[mr-cal]

Fixed: 493f9fc

[lengau]

Suggested change

	2.1.0 (2025-08-06)
	2.1.0 (2025-08-11)

Even if we merge today let's do that

[mr-cal]

Good call, this should have been undated.

[mr-cal]

Fixed: 493f9fc

[tigarmo]

Since for a,b is invalid, what is the use-case for platforms having more than 1 item? Does this refer to all the possible platforms that a project declares, or just to the single platform that is currently being built?

[mr-cal]

I recall this discussion during the Frankfurt sprint but I don't know if it was written down:

Given

platforms:
  [email protected]:amd64:
  [email protected]:riscv64:
  [email protected]:amd64:
  [email protected]:riscv64:

When craft-application goes to build the [email protected]:riscv64 platform, craft-grammar could be invoked with

GrammarProcessor(
  arch="riscv64",
  target_arch="riscv64",
  platforms=["[email protected]:riscv64", "24.04", "ubuntu", "riscv64"],
)

By default, craft-application would pass a single element list containing the entire platform name. An app can choose to override this and generate a list, like in the example above.

I'm fine to change this parameter to a string or clarify the docstrings.

[tigarmo]

ah I see, I remember some of that conversation now. I think I tripped on "the platforms to build", it made me think of the full set of platforms. Maybe something like "the currently active platform identifiers" would be less confusing? Well, less confusing in this particular aspect I guess

[mr-cal]

Good idea, I cleaned up the whole docstring: 493f9fc