Jean-Pierre

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RFD 086: Line-oriented stdin input for CLI arguments ​

Summary ​

This RFD establishes a project-wide CLI convention with two clauses:

  1. For a multi-value argument that accepts stdin input, the value - means "read this argument's values from standard input."
  2. That stdin input is line-oriented: one value per line.

The rule is a convention, not a command feature: any multi-value argument that chooses to read stdin does so via -, line-oriented — there is no second spelling, and the rule does not require every argument to read stdin. Its first and only opt-in so far is conversation targeting — jp c archive -, jp c rm -, and the other multi-ID commands — which lets the ID-list output of one command pipe straight into the next.

Single-value arguments are out of scope: - is rejected on them for now (see Non-Goals).

Motivation ​

JP's management commands (archive, rm, print, path) take one or more conversation IDs. Today the only ways to supply them are literal IDs on the command line, keywords (+pinned, +session), or the interactive picker. There is no way to feed a computed set of IDs — "every conversation whose title matches \Apr-triage:\d{3}\z" — without hand-copying IDs out of one command and into another.

The motivating workflow is archiving a batch of conversations selected by a pattern:

sh
jp c grep --output ids --regex '\Apr-triage:\d{3}\z' | jp c archive -

RFD 050 defines the production half of this story for conversation new and conversation fork: they print one conversation ID per line (JSON array under -F json). jp c grep --output ids emits the same line-oriented ID format. This RFD defines the consumption half — the matching input convention — so the line-oriented ID output of one JP command is valid input to another with no jq/xargs glue.

Doing nothing leaves two costs. Users assemble per-command shell glue (... | jq -r '.[].id' | xargs ...) that leaks JP's opaque ID format into scripts, and every command that might one day read stdin reinvents the handling ad hoc, with no shared rule for what - means.

Design ​

The convention ​

For a multi-value argument that accepts stdin input, the value - means "read this argument's values from stdin," one value per line. It applies whether the argument is positional (jp c archive -) or a multi-value flag. Phase 1 opts in only conversation targeting; other multi-value arguments (--scope, --mount, …) keep their current behavior until they explicitly opt in. It is the rule users already know from cat -, git, and most Unix tools (Principle of Least Astonishment).

The format - consumes is the line-oriented ID list: one opaque conversation ID per nonblank line. This is the same format conversation new, conversation fork, and grep --output ids emit in text mode — a deliberate, stable machine format, distinct from the human-facing rendered output that JP changes freely. - does not consume JSON: -F json emits an array, which a tool transforms (jq -r '.[].id') before piping into -.

What the user sees ​

sh
# positional, multi-ID
jp c grep --output ids --regex '\Apr-triage:\d{3}\z' | jp c archive -

# explicit producer, same shape
jp c ls -F json | jq -r '.[].id' | jp c rm -

The IDs arrive resolved before the command runs, exactly as if typed on the command line. Commands stay ignorant of stdin — archive and rm never read it themselves.

Where the read happens ​

Reading stdin is I/O and belongs in the imperative shell, not in argument parsing. So - parses to a sentinel, and the read happens once, later, when the shell resolves the argument:

  • Parsing records "stdin requested" — no I/O, parsing stays pure.
  • The shell reads stdin a single time, splits on newlines, normalizes, and expands the sentinel into concrete values.

For conversation targeting this slots into the existing seam with no new machinery. ConversationTarget::parse maps - to a new Stdin variant, and ConversationTarget::resolve (in cmd/target.rs) reads stdin and resolves it, the same way AllSession resolves one token into many IDs.

Affected commands ​

resolve — not resolve_request — is the seam. Every path that turns a target into IDs funnels through it, including the commands that resolve targets internally, so - reaches every conversation-target command, not only the four in the motivation:

Command(s)Resolution pathNotes
archive, rmresolve_requestdestructive; confirmation applies
print, path, ls, showresolve_requestread-only
edit, fork, compactresolve_requestmutate state
grepresolve_requestproducer and consumer both
unarchiveinternal resolve_idsbypasses resolve_request, but
still calls resolve

This breadth is intended: - is a generic targeting source, so a reader has no reason to expect print - to work but show - not to.

The invariant the implementation must hold: every command that turns targets into IDs forwards non-Id targets to ConversationTarget::resolve rather than pattern-matching Id and dropping the rest. A command that silently ignores a Stdin target would accept - and do nothing. unarchive already satisfies this; new commands must too.

Normalization ​

Two layers, kept separate so the global convention does not constrain future argument types:

Global convention — true for any argument that opts into stdin input:

  • - reads values from stdin.
  • Input is line-oriented: one value per line, unless the argument defines another format.

Conversation-ID behavior — specific to the conversation-target consumer:

  • Trim each line; drop blank lines. Dropping blanks is required, not cosmetic: a well-formed pipe ends in a trailing newline (printf 'id1\nid2\n'), so without it the stream would yield a spurious empty final value.
  • Parse each nonblank line as a ConversationId, with the same error an unparseable ID produces on the command line.
  • Preserve order and duplicates. The resolved list is exactly the lines, so printf 'jp-c1\njp-c1\n' | jp c fork - forks twice — identical to jp c fork jp-c1 jp-c1. Commands that want set semantics deduplicate themselves, as they already must for repeated command-line IDs.

Trimming and blank-line dropping are conversation-ID conveniences, not global guarantees: an argument with whitespace- or order-significant values would define its own stdin parsing instead.

Edge cases ​

  • Empty input. Because blank lines are dropped, an empty or whitespace-only stdin resolves to zero values. This is an explicit error ("no conversation IDs provided on stdin"), not a silent no-op — a mistyped upstream filter fails loudly instead of quietly doing nothing.
  • Terminal stdin. If - is requested but stdin is a terminal (nothing piped), the command errors rather than blocking on keyboard EOF. This mirrors the existing picker guards in target resolution (resolve_picker, resolve_multi_picker), which already refuse picker fallback when stdin is not a terminal.
  • No mixing. - must be the sole target. Combining it with literal IDs (jp c archive id1 -) or with keywords and pickers (+pinned, ?) is rejected. A request either takes its IDs from the command line or from stdin, never both — which keeps resolution unambiguous and sidesteps ordering questions.

Single-consumer invariant ​

Stdin can be drained once, so at most one consumer may read it per invocation. jp query already reads piped stdin implicitly and prepends it to the prompt (cmd/query.rs); that is a pre-existing, command-specific consumer. query takes no multi-ID argument, so there is no live collision — but the invariant is what guarantees that stays true as commands evolve. A command that grows both a - argument and content-from-stdin must fail that combination rather than race over a single stream.

Relationship to RFD 048 ​

RFD 048 defines JP's channel model: stdin is the data channel, never the prompt channel. Prompts and interactive input always come from /dev/tty (or the detached policy in RFD 049), so echo "y" | jp query "..." is query content, not a prompt answer.

This RFD does not touch that rule. It refines what the data channel carries: stdin supplies either implicit query content (jp query, unchanged) or the explicit - argument values defined here, and at most one of them per invocation. The prompt-channel guarantee from RFD 048 is preserved intact — which is why this RFD extends RFD 048 rather than contradicting it.

Convention now, generic mechanism later ​

This RFD fixes the convention for the whole CLI. The mechanism starts minimal: the only consumer is conversation targeting, so the sentinel lives in ConversationTarget. A shared, command-agnostic stdin-argument facility is worth extracting only when a second, non-conversation consumer appears (YAGNI, and the midlayer mistake). Until then, the documented rule is what keeps future arguments consistent.

Drawbacks ​

  • Two stdin models coexist. jp query consumes stdin implicitly (no -); everything else is explicit (- opts in). That is a deliberate inconsistency — query's behavior predates this convention and is relied on for interactive use, so it is grandfathered rather than changed. New stdin consumers follow the explicit rule.
  • A convention is only as good as adherence. Nothing in the type system forces a future multi-value argument to honor -. The rule lives in docs and review until a shared mechanism exists, so there is drift risk.
  • - becomes reserved for stdin-capable arguments. A multi-value argument that opts into stdin input cannot also use bare - as a literal value. Single-value flags with their own established - meaning are unaffected — --log-file=- (write tracing to stderr, RFD 048) keeps working. A future stdin-capable argument that genuinely needs literal - would have to define an escape or alternate spelling.

Alternatives ​

Per-command stdin handling ​

Each command reads stdin itself. Rejected: it duplicates parsing across archive/rm/print/path and punches an I/O hole through the clean "commands receive resolved handles" boundary. One shortcut compounds into N.

A conversation-only Stdin target, without stating the general rule ​

The mechanism would be identical, but framing it as a conversation feature leaves the next argument that wants stdin input to reinvent what - means. Stating the rule once is the difference; the implementation is the same first step either way.

Implicit stdin for all commands (the query model, generalized) ​

Every command auto-reads piped stdin. Rejected: it is ambiguous (a command can't tell "piped IDs" from "piped content"), it can't coexist with the interactive picker, and it makes stdin consumption invisible at the call site. Explicit - is the safer default.

xargs / jq at the shell level ​

Works today without any JP change, but it is per-command glue that leaks the opaque ID format into user scripts and gives up JP-side validation and confirmation (e.g. titles in the archive prompt). The convention makes the common case glue-free.

Non-Goals ​

  • Single-value arguments. - is accepted only for multi-value arguments; single-value targets reject it for now. The motivating workflows use multi-value commands (archive, rm), where a one-line stdin is simply a one-element list — so single-value stdin buys little beyond jp query --id -, which is also the one command that already owns stdin for prompt content. Designing that arbitration (inline query vs. editor vs. stdin) belongs in a dedicated query-input RFD, not here.
  • Changing jp query's prompt-from-stdin behavior. It keeps reading piped stdin as prompt content. This RFD governs argument values, not that pre-existing consumer.
  • Building a generic cross-command stdin-argument framework now. The convention is stated; the shared mechanism is extracted when a second consumer needs it.
  • The producer side. jp c grep's regex matching and --output ids output, which feed the pipeline above, emit the line-oriented ID format but are implemented as separate work, not specified by this convention.

Implementation Plan ​

Phase 1: - for conversation targeting ​

  • Add ConversationTarget::Stdin; ConversationTarget::parse maps - to it.
  • In ConversationTarget::resolve (cmd/target.rs), read stdin once for a Stdin target: split on newlines, trim, drop blanks, parse each as a ConversationId (order and duplicates preserved), with the terminal-stdin guard and the empty-input error.
  • Extend validate_multi (cmd/conversation_id.rs) so - is rejected when combined with any other target, and rejected on single-value targets.
  • Available to every conversation-target command at once, because they all funnel non-Id targets through resolve — including unarchive, which resolves internally.
  • Audit every prompt reachable after stdin resolution — the archive and rm confirmations and the target pickers. Input is already safe: inquire reads the terminal (/dev/tty), not stdin, so draining stdin for IDs does not starve the prompt. Output needs care: prompts render via Printer::prompt_writer, which renders to /dev/tty when one is open but falls back to stdout when none is — and for these stdin-targeted commands stdout is the data channel a downstream pipe consumes. So when no prompt channel is available, the command must follow the RFD 049 detached policy (e.g. require --yes) rather than writing the prompt to stdout and proceeding. Changing prompt_writer's fallback globally is out of scope — other callers (the init wizard, lock prompts) may want it; the guard belongs on the destructive commands when they adopt RFD 049's non-interactive handling.
  • Independently mergeable.

Phase 2 (deferred): shared stdin-argument facility ​

Extract a command-agnostic helper only when a non-conversation multi-value argument needs -. Not built now.

References ​