Implement AST unparser and update extract_method_source (BT-977)

[jamesc]

Summary

Implements ADR 0044 Phase 4: a full AST-to-source unparser using the Document/docvec! API, and updates extract_method_source to use it instead of raw byte-range slicing.

Linear issue: https://linear.app/beamtalk/issue/BT-977

Key changes

• New module crates/beamtalk-core/src/unparse/mod.rs (~850 lines of unparse logic + ~450 lines of tests)

  • Covers all 19 Expression variants, ClassDefinition, MethodDefinition, StateDeclaration, ExpressionStatement
  • Emits leading/trailing comments from CommentAttachment
  • Single-expression methods render inline; multi-expression on new lines
  • 26 unit tests including round-trip parse→unparse→parse verification

• Updated extract_method_source in gen_server/methods.rs

  • Replaces byte-range slicing with unparse_method() call
  • Fixes: leading comments no longer silently dropped
  • Fixes: synthesized methods now produce full source instead of just selector name

• 20 codegen snapshots updated — methodSource entries now contain full method text

Test plan

• 26 unparse unit tests (including round-trip tests)
• 1471 Rust tests pass
• 327 snapshot tests pass
• 645 BUnit tests pass (including CompiledMethodTest)
• 2208 Erlang runtime tests pass
• E2E tests pass
• Full just ci passes

🤖 Generated with Claude Code

Summary by CodeRabbit

Release Notes

• New Features

  • Added comprehensive AST unparsing system to convert internal code representations back to readable source code, with support for comments, expressions, blocks, pattern matching, and type annotations.

• Refactor

  • Enhanced method source extraction to use new unparsing system, improving consistency and comment preservation across file-based and synthesized methods.

[coderabbitai]

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📥 Commits

Reviewing files that changed from the base of the PR and between f5ab820 and 38b55d0.

⛔ Files ignored due to path filters (20)

• test-package-compiler/tests/snapshots/compiler_tests__abstract_class_spawn_codegen.snap is excluded by !**/*.snap
• test-package-compiler/tests/snapshots/compiler_tests__class_definition_codegen.snap is excluded by !**/*.snap
• test-package-compiler/tests/snapshots/compiler_tests__class_methods_codegen.snap is excluded by !**/*.snap
• test-package-compiler/tests/snapshots/compiler_tests__empty_method_body_codegen.snap is excluded by !**/*.snap
• test-package-compiler/tests/snapshots/compiler_tests__error_message_codegen.snap is excluded by !**/*.snap
• test-package-compiler/tests/snapshots/compiler_tests__intrinsic_keyword_codegen.snap is excluded by !**/*.snap
• test-package-compiler/tests/snapshots/compiler_tests__method_lookup_codegen.snap is excluded by !**/*.snap
• test-package-compiler/tests/snapshots/compiler_tests__sealed_class_violation_codegen.snap is excluded by !**/*.snap
• test-package-compiler/tests/snapshots/compiler_tests__sealed_method_override_codegen.snap is excluded by !**/*.snap
• test-package-compiler/tests/snapshots/compiler_tests__stdlib_class_dictionary_codegen.snap is excluded by !**/*.snap
• test-package-compiler/tests/snapshots/compiler_tests__stdlib_class_list_codegen.snap is excluded by !**/*.snap
• test-package-compiler/tests/snapshots/compiler_tests__stdlib_class_set_codegen.snap is excluded by !**/*.snap
• test-package-compiler/tests/snapshots/compiler_tests__stdlib_class_tuple_codegen.snap is excluded by !**/*.snap
• test-package-compiler/tests/snapshots/compiler_tests__typed_class_warnings_codegen.snap is excluded by !**/*.snap
• test-package-compiler/tests/snapshots/compiler_tests__typed_methods_codegen.snap is excluded by !**/*.snap
• test-package-compiler/tests/snapshots/compiler_tests__typed_value_type_codegen.snap is excluded by !**/*.snap
• test-package-compiler/tests/snapshots/compiler_tests__value_type_multi_expr_method_codegen.snap is excluded by !**/*.snap
• test-package-compiler/tests/snapshots/compiler_tests__value_type_param_collision_codegen.snap is excluded by !**/*.snap
• test-package-compiler/tests/snapshots/compiler_tests__workspace_binding_cascade_codegen.snap is excluded by !**/*.snap
• test-package-compiler/tests/snapshots/compiler_tests__workspace_binding_send_codegen.snap is excluded by !**/*.snap

📒 Files selected for processing (3)

• crates/beamtalk-core/src/codegen/core_erlang/gen_server/methods.rs
• crates/beamtalk-core/src/lib.rs
• crates/beamtalk-core/src/unparse/mod.rs

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📝 Walkthrough

Walkthrough

This PR introduces a new comprehensive AST unparser module that converts Beamtalk AST nodes back to source text using a Document-based rendering pipeline. It updates the Core Erlang method source extraction to call the unparser instead of slicing source by byte indices, eliminating reliance on source_text and spans. The unparser handles comments, method signatures, class definitions, expressions, literals, and type annotations.

Changes

Cohort / File(s)	Summary
Module Declaration crates/beamtalk-core/src/lib.rs	Adds public module unparse to crate root, exposing the unparser API.
AST Unparser Implementation crates/beamtalk-core/src/unparse/mod.rs	New module implementing comprehensive AST-to-source conversion via Document-based rendering pipeline. Provides public API (unparse_module, unparse_method, unparse_class) and extensive internal builders for all AST node types, including comment handling, method signatures, type annotations, and literal rendering.
Core Erlang Code Generation crates/beamtalk-core/src/codegen/core_erlang/gen_server/methods.rs	Replaces byte-index slicing of source text with call to unparse_method, removing dependency on source spans and source_text while enabling unparsed output including comments for both file-based and synthesized methods.

Estimated code review effort

🎯 4 (Complex) | ⏱️ ~45 minutes

Possibly related PRs

• docs: ADR 0044 - Comments as First-Class AST Nodes #1000: Implements the core AST unparser module and its integration into method source extraction, directly aligning with this PR's changes.
• Parser: attach comments to ClassDefinition, MethodDefinition, StateDeclaration (BT-975) #1011: Attaches comment metadata to AST nodes including MethodDefinition, which the new unparser consumes and emits during source reconstruction.
• Parse type annotations on method parameters and return types (BT-585) #564: Modifies MethodDefinition and ParameterDefinition structures and updates their consumers, including gen_server/methods.rs which this PR also modifies.

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main changes: implementing an AST unparser and updating the extract_method_source function, with the tracking issue reference BT-977.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

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✨ Finishing Touches

• 📝 Generate docstrings (stacked PR)
• 📝 Generate docstrings (commit on current branch)

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch worktree-BT-977

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