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Trace by default in REPL-driven development

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A repl or nREPL session now turns tail-frame tracing on, so an uncaught error in
evaluated/reloaded code shows a tail-frame backtrace with no JOLT_TRACE set. The
REPL and nREPL catch errors themselves rather than going through the uncaught
reporter, so they now print the history backtrace via a new jolt.host/backtrace-
string (history-only — the live continuation in a REPL is just REPL machinery).

Because the recording is baked in at compile time, only code compiled while a
session is live is traced; reload a namespace to trace already-loaded code.
JOLT_TRACE=1 still forces it on for a whole run (a plain -M:run traces its own
load); JOLT_TRACE=0 forces it off even in a session.

No seed change — jolt.main/jolt.nrepl are runtime-loaded and compile-eval.ss /
source-registry.ss are host files.
This commit is contained in:
Yogthos 2026-07-04 15:23:17 -04:00
parent a3e2365217
commit 7167af4830
6 changed files with 89 additions and 23 deletions
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docs/tools-deps.md
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@ -190,11 +190,21 @@ binary the frames map to `ns/name (file:line)`; on the runtime eval path they ar
the surviving fn names. Tail-call optimization erases tail-called frames, so the
default trace shows only the non-tail spine.
Set `JOLT_TRACE=1` to opt into a fuller **tail-frame history**. Each compiled fn
then records itself on entry into a bounded ring-of-rings buffer, so the trace
recovers TCO-elided frames (including the immediate error site) while a tight tail
loop stays bounded and its non-tail caller context is preserved. It costs a small
per-call overhead, so it is off by default and never emitted into a built binary.
A fuller **tail-frame history** recovers the frames TCO erases: each compiled fn
records itself on entry into a bounded ring-of-rings buffer, so the trace shows
TCO-elided frames (including the immediate error site) while a tight tail loop
stays bounded and its non-tail caller context is preserved.
It is **on by default in REPL-driven development** — a `repl` or nREPL session
turns it on, so an error in code you evaluate or reload shows a tail-frame trace
with no setup. Because the recording is baked in at compile time, only code
compiled while a session is live is traced; reload a namespace to trace code that
was already loaded (e.g. an app's initial `-M:run` load before its nREPL started).
Elsewhere it is off (a small per-call cost, and never emitted into a `jolt build`
binary). Override with the environment: `JOLT_TRACE=1` forces it on for a whole
run — including a plain `-M:run`, so the app's own load is traced — and
`JOLT_TRACE=0` forces it off, even in a REPL/nREPL session.
## Conformance