feat(ast): extract Bash function and file documentation #1677

Objective

Provide a named shdoc source profile and explicit optional inference for Bash documentation.

Umbrella: #1654 · Planning ID: D20
Completion prerequisites: D25: #1662, D26: #1663

LANG coverage: Bash.

Development can start after D05/D06 interfaces exist. Completion is blocked by D25/D26 infrastructure and requires this adapter's own conformance cases, scaling probes for new work and fuzz seeds.

Shared architecture and constraints

Follow the umbrella's shared contracts. AST recognition serves two consumers: exact legacy convention/coverage streaming for root LOC, and richer source documentation for owner lookup and local text. Source attachment, profile eligibility and physical metric ownership are separate. Preserve the legacy candidate view before run selection, original emission timing, and metrics-only early exits.

Documentation fragments, logical documents and convention-qualified owner edges have separate identities. Source offsets refer to the actual parsed buffer and included ranges. The index is caller-owned, immutable and source-bound; lookup validates tree/index identity. Complete text means local decoded/cleaned content with forward source mapping, not inherited or generator-expanded documentation.

Implementation touchpoints

• big-code-analysis-ast/src/roles/bash.rs: current shared role recognition; read the contributor reference in roles/mod.rs.

• big-code-analysis-ast/src/roles/doc_tests/: existing per-language recognition fixtures; add independent owner/text expectations.

• big-code-analysis-ast/src/checker/bash.rs

• big-code-analysis-ast/src/lang_helpers/bash.rs

• big-code-analysis-ast/src/documentation Bash adapter

Implementation steps

• Integrate the named shdoc profile with role-derived candidates and a bounded source-segment treatment of lexical continuation gaps.

• Recognize shdoc file/function blocks and structural owner markers using AST comments and declarations.

• Support common function spellings and exact same-scope adjacency boundaries. Generic leading-comment inference is opt-in and marked with provenance.

• Separate file headers, shebang/tool directives and function docs; do not classify string/heredoc contents as comments.

• Return cleaned comment text and forward mappings; extraction alone does not widen legacy DLOC.

Tests and edge cases

• Bare continuation before code/comment/EOF, trailing backslash in an ordinary Bash comment, heredoc-looking annotations, and shdoc blocks around both function forms with current LOC tuples.

• function f { ... } and f() { ... }, adjacent differently documented functions and file @file/@description blocks.

• Blank lines, intervening commands and nested functions under the stated profile.

• Shebang and shellcheck directives, quoted # text and heredocs with documentation-looking lines.

• Explicit versus inferred profile results and exact source mappings; no generic inference enabled by accident.

Use independently specified expected owners, fragment counts/order, byte ranges, text and availability. Pair them with separate legacy metric assertions where relevant. Do not sort/trim observed results, rely only on facade/delegate equality, or accept generated snapshots without an expected-value anchor. Use verbatim source for EOF/CRLF cases. Perturb the decision-bearing expression and confirm the intended assertion fails; use the maintained utils/perturb.py only on tracked, clean targets, recording or stashing real work first. Multi-target cargo runs require --no-fail-fast; include the mutated crate and dependent crates before claiming a unique guard. Keep irreproducible fixtures/manifests in tests, maintained utils or an issue attachment, following .claude/rules/temp-files.md.

Acceptance criteria

• A concrete Bash function has nonempty local documentation text.
• Named-profile and inference outputs are distinguishable and negative cases discriminate.
• Legacy metrics, run-width probes and Bash seeds pass.

Verification and completion evidence

• Follow current role-census/role-coverage/role-bypass requirements and applicable role-parity-corpus checks. Preserve independent semantic fixtures; refresh .role-coverage-observed.txt when any sampled corpus gitlink changes.

• Put revisions, exact commands, tool versions and durable input links beside parity/coverage claims; host-local evidence paths are not citations.

• Recheck current source and the prerequisite contracts/baseline applicable to this issue; record intentional changes to the premises.

• Run focused production-path tests and affected language siblings. Use package-isolated -p big-code-analysis-ast / -p big-code-analysis feature builds; workspace feature unification is not isolation.

• Run the repository's required checks for the touched surfaces. For implementation changes: make worktree-setup, make pre-commit read from its BCA_GATE: verdict, and relevant test-language membership comparison. Add scaling and chain-audit checks for traversal changes; run make fuzz-check and seed replay for fuzz changes.

• Record exact test/perturbation/probe evidence in a completion comment and update this body. Review unexpected metric drift before snapshot acceptance; follow baseline and integration-submodule discipline if behavior deliberately changes.

• Land public API documentation, re-export/stability review and changelog entries with the originating API change. Keep unrelated CLI/web/Python surfaces outside this issue unless explicitly listed.

Revalidation against main (2026-11-04)

Source baseline inspected: 07822c69211fe851c452ac6c0ebbd99cf92589a5. Relevant landed work: PR #1717, PR #1769, PR #1804. These are implementation updates to the existing acceptance criteria; this review does not mark extraction work complete.

• Use Bash Comment/FuncOpener/Container/StringLit role recognition without treating absent legacy doc rows as absence of a supported source convention.

• PR fix: batch 2026-11-03-2 (8 issues) #1804 now accounts for bare backslash rows in gaps; Bash comments do not continue with a trailing backslash, unlike Tcl/iRules. Preserve this distinction when segmenting shdoc blocks.

• Physical gap-row accounting lives in root LOC and must not become an AST-to-metrics dependency. Reuse or factor only structural source facts if extraction needs them.