fluffos/docs/apply/master/inherit_program.md
Yucong Sun 55956a24b7
Add inherit_program / include_file master applies; auto hot-reload demo (#1230)
* Add inherit_program / include_file master applies; auto hot-reload demo

New compile-time master applies, consulted for every inherit statement
and #include directive:

* mixed inherit_program(string from, string path, int priv)
  Called while compiling `from` for `inherit "path";` (priv nonzero for
  private inherits). A string return is an alternate path for the
  inherited file; an array-of-strings return is the inherited program's
  source itself (compiled via load_object_from_source under the inherit
  statement's name, through the existing load_object retry loop); any
  other return prevents the inheritance.

* mixed include_file(string compiled, string from, string path)
  Called when `from` is about to include `path` while compiling
  `compiled`. A string return is the translated path (resolved absolute
  from the mudlib root or relative to the includer; returning `path`
  unchanged keeps the "..."-vs-<...> search semantics); an
  array-of-strings return is the included text itself (pushed as an
  in-memory include buffer with the usual file-identity bookkeeping);
  any other return prevents the inclusion.

Both follow the valid_override/get_include_path precedent for calling
master LPC mid-compile (skipped without a VM context or master object),
and a missing apply keeps stock behavior.

The applies expose the full compile-time dependency graph, which the
testsuite uses to demonstrate mudlib auto hot-reload on file changes:
/single/hot_reload.lpc registers as the master's compile hooks, records
which source files each program's bytecode was built from (own source,
includes, inherited programs, transitively), and its call_out poller
destructs+reloads watched blueprints whose dependency closure changed
on disk - including reloading a stale parent when only the parent's
include changed.

Testsuite: single/tests/compiler/{inherit_program,include_file}.lpc pin
the apply semantics (redirect, inline source, deny, priv flag, argument
shapes on nested includes) via the scriptable /clone/compile_hook;
single/tests/applies/hot_reload.lpc demonstrates end-to-end hot reload
over a runtime-written inherit+include fixture chain. Docs added for
both applies.

Validated: full LPC suite (532 files) x2 on RelWithDebInfo, x2 on
Debug+ASan/UBSan, plus the 297 GTest unit tests.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018DGhzJfPhDGJA94EPh1gEK

* docs: add hot reload guide for the new compile-time master applies

New concepts page (concepts/general/hot_reload.md) explaining why
"file changed -> reload" needs the compile-time dependency graph, how
the inherit_program / include_file master applies expose it, and a
step-by-step mudlib implementation with examples: master delegation,
dependency recording, closure computation, change detection with
size+mtime snapshots, parent-first reload ordering, and the call_out
poller. Documents blueprint-reload semantics and caveats (clones keep
the old program, no compiles inside the applies, records only complete
for compiles observed by the daemon), pointing at the testsuite
reference implementation. Cross-linked from both apply reference pages
and the concepts indices.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018DGhzJfPhDGJA94EPh1gEK

* docs/testsuite: say "master copy", not "blueprint"

Align the hot-reload guide, apply reference, daemon, and test comments
with the project's terminology for the object loaded from a file (see
clonep(3): "the master copy").

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018DGhzJfPhDGJA94EPh1gEK

* testsuite: edge cases for the compile-time applies; docs review fixes

compile_hooks_edge.lpc pins that unusual inherit_program/include_file
return values produce clean LPC errors or the documented behavior,
never a driver crash: empty array, non-string elements, redirect to
self, empty-string redirect, inline source vs already-loaded object,
multiline inline content, the apply itself throwing mid-compile
(safe_apply falls back to default resolution), extension-spelled
redirects, and denying the auto-included global include file.
Fixtures in /clone/adv_*; /clone/adv_hook wraps the scriptable hook
with a throwing include_file.

Docs fixes from review: the apply-page examples now look the daemon up
with find_object() instead of a path call_other (which would load the
target and trigger a compile mid-compile -- the exact pattern the same
pages forbid), and the hot-reload guide's ancestors() snippet carries
the seen-mapping argument to match the reference daemon.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018DGhzJfPhDGJA94EPh1gEK

* hot_reload: fix multi-watch and failed-reload handling; harden tests

Three defects from the LPC review round, each now pinned by the
demonstration test:

* check_now() collected and reloaded in one pass, so the first reload's
  snapshot refresh erased the change evidence for every other watched
  program sharing the dependency (a common header, or a watched parent
  iterating before its watched child - which then stayed bound to the
  destructed old parent forever). The stale set is now collected before
  any reload runs.

* A reload whose recompile throws (a syntax error mid-edit - the most
  common event in a hot-reload workflow) unwound poll() before the
  re-arm, killing the poller forever and leaving the watched master
  copy destructed. poll() re-arms first, check_now() catches per
  program, reload_count only counts successes, and closure_changed()
  treats a watched-but-not-loaded program as stale so the retry
  self-heals once the file compiles again.

* The three apply tests registered master compile hooks (and the
  hot-reload test armed the poller and wrote /data/hot) with cleanup on
  the success path only; a thrown check would leave the hook routing
  every remaining compile of the randomized run. Each test now runs its
  checks under catch and unhooks/tears down unconditionally, re-raising
  the error afterward.

The demo test now also covers the shared-dependency pass (watch parent
and child, change the common include, both reload in one pass) and the
broken-edit recovery cycle. The hot-reload guide's snippets are updated
to match the daemon.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018DGhzJfPhDGJA94EPh1gEK

* simulate: let inline inherit source resolve its own unloaded inherits

From the C++ review round: master::inherit_program returning inline
source whose text itself inherits a not-yet-loaded program failed the
whole load with "#inherit is not supported when compiling from
in-memory source" -- reachable in the feature's primary use case, since
synthesized programs routinely inherit ordinary on-disk library files.

load_object_from_source() now runs the same iterative dance as
load_object(): when the compile aborts on an unloaded parent, load that
parent (from disk, or from further master-supplied inline source, so
synthesized-inheriting-synthesized chains work), then recompile the
same source string -- which is in hand, unlike the historical
no-filename rationale for rejecting #inherit here. Mirrors
load_object()'s guards: illegal-to-inherit-self, the duplicate-name
check after the parent's arbitrary LPC ran, and an inherit-chain bound
on the retry loop as a backstop against a master that redirects to a
fresh unloaded name on every recompile.

The inherit_program test now covers both new shapes (inline inheriting
unloaded on-disk, and two levels of inline source); the apply doc drops
the already-loaded-only caveat.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018DGhzJfPhDGJA94EPh1gEK

---------

Co-authored-by: Claude <noreply@anthropic.com>
2026-07-10 10:27:27 -04:00

2.7 KiB

title
master / inherit_program

inherit_program

NAME

inherit_program - control, redirect, or synthesize inheritance at
compile time

SYNOPSIS

mixed inherit_program( string from, string path, int priv );

DESCRIPTION

The driver calls this apply on the master object each time the
compiler processes an `inherit "path";` statement while compiling
the program `from`. The flag `priv` is nonzero when the inheritance
is private (`private inherit "path";`).

**Arguments:**
- `from`: the file being compiled (with its source extension, e.g.
  `"/obj/sword.lpc"`)
- `path`: the inherit statement's path, exactly as written
- `priv`: 1 for `private inherit`, 0 otherwise

**Return Value:**
- a *string*: an alternate path for the inherited file; the
  inheritance proceeds as if that path had been written. Returning
  `path` unchanged keeps the default behavior.
- an *array of strings*: the source code of the inherited file
  itself, one element per line. The program is compiled from that
  text and its master copy materializes under `path`'s name, with no
  backing file. Note that if an object named `path` is already
  loaded, it is inherited directly and the supplied source is not
  consulted. Inherit statements inside the supplied source resolve
  as usual: an unloaded parent is loaded from disk, or from further
  inline source if this apply supplies one for it too.
- *any other value* prevents inheritance of the file `path`: the
  compile fails with an error.

If the master object does not define this apply (or no master is
loaded yet), inheritance behaves as usual.

The apply runs in the middle of a compile. Like valid_override(4)
and get_include_path(4) it must not trigger another compile (do not
load or clone unloaded objects from it).

EXAMPLE

```c
mixed inherit_program(string from, string path, int priv) {
    // record the dependency graph for a hot-reload daemon
    // (find_object never loads -- a path call_other could trigger
    // a compile, which is forbidden here)
    object d = find_object(HOT_RELOAD_D);
    if (d) d->note_inherit(from, path, priv);

    // map a versioned library namespace
    if (sscanf(path, "/lib/v1/%*s"))
        return "/lib/v2" + path[7..];

    // forbid privately inheriting the security library
    if (priv && path == "/secure/acl")
        return 0;

    return path;   // default behavior
}
```

SEE ALSO

include_file(4), compile_object(4), valid_override(4),
get_include_path(4)

The hot reload guide shows how to build mudlib auto-reloading on top of this apply.