Files
scadalink-design/docs/plans/2026-05-12-script-scope-access-design.md
Joseph Doherty 3ed05f0595 docs(scripts): design for template-script scope access
Self / Children / Parent accessors with sync-indexer + async-method
shape. Flattening pipeline emits ScriptScope per resolved script;
ScriptCompilationService seeds the accessors at execution time with
no new actor messages or lookup paths.

Phased: (1) runtime accessors + Scope on ResolvedScript, (2)
flattening + deploy round-trip, (3) editor metadata fetch for child
+ parent shapes, (4) Monaco completion / hover / diagnostics
(SCADA006 unknown attribute, SCADA007 unknown composition).

Out of scope: per-template Roslyn-generated typed accessors,
locking-aware writes (covered by lock-enforcement pass), and
sibling-of-sibling chained navigation.
2026-05-12 05:38:58 -04:00

185 lines
8.4 KiB
Markdown

# Script scope access: self / child / parent
## Goal
Template scripts get an ergonomic read/write API for:
- The current template's attributes (`Attributes["X"]`).
- Child composition attributes (`Children["TempSensor"].Attributes["Temperature"]`).
- Child composition scripts (`Children["TempSensor"].CallScript("Sample")`).
- The parent composition (when this template is composed inside another):
`Parent.Attributes["SpeedRPM"]`, `Parent.CallScript("Trip")`.
Editor (Monaco) provides completion, hover, and diagnostics on all the above.
## What already exists
- Each `Template` has `Attributes`, `Compositions` (named sub-template references),
`Scripts`, `Alarms`.
- Flattening produces `ResolvedAttribute.CanonicalName` as the path-qualified name:
direct attrs are bare, composed attrs are `"InstanceName.MemberName"`.
- `InstanceActor` stores `_attributes[canonicalName]` — flat dict keyed by the
fully composed canonical name.
- `ScriptRuntimeContext.GetAttribute(name)` does a flat lookup. So
`GetAttribute("TempSensor.Temperature")` already works if the canonical name
is in the dict. **What's missing is scope-relative access** — a script on
`TempSensor` cannot say "my Temperature" without knowing it's composed under
some parent path.
- `ScriptRuntimeContext.CallScript(name)` Ask-pattern-routes to a Script Actor.
Cross-composition / parent routing is **not** implemented.
- The actor topology is one Instance Actor per top-level instance — composed
sub-templates are **flattened into the parent's actor state**, not separate
actors. This is good news: parent/child access is path arithmetic, not
ActorRef hopping.
## Runtime API (new)
Three accessors layered on `ScriptGlobals` (in addition to the existing
`Instance.*`, `Parameters`, `Scripts.CallShared`, etc.):
```csharp
Attributes["X"] // read; throws if missing
Attributes["X"] = value // write
Attributes.TryGet<T>("X", out v) // typed read with fallback
Children["TempSensor"].Attributes["Temperature"]
Children["TempSensor"].CallScript("Sample", new { count = 3 })
Parent.Attributes["SpeedRPM"] // null check: Parent is null at the root
Parent.CallScript("Trip")
```
Internally each is a thin wrapper holding a `ScopePath` (string) plus a
reference to `ScriptRuntimeContext`. The indexer / `CallScript` prepend the
scope path to the key and delegate to the existing `Instance.GetAttribute` /
`Instance.SetAttribute` / `Instance.CallScript`. No new actor messages, no
new lookup pathway.
`Children["X"]` returns a new accessor with prefix `SelfPath + "." + X`.
`Parent` returns an accessor with the parent prefix (`null` if no parent).
Chained child/parent navigation works naturally because each accessor is the
same type returning the same type.
## Compile-time scope injection
Every compiled script needs to know its own `ScopePath`. That's captured by
the flattening pipeline and passed into `ScriptGlobals` at execution time:
```csharp
public record ScriptScope(
string SelfPath, // "" for root, "TempSensor" for composed
string? ParentPath, // null if SelfPath == ""
IReadOnlyList<string> ChildInstanceNames);
```
`ResolvedScript` gains a `Scope: ScriptScope` field. The flattening service
already walks the composition tree to compute canonical names — extending it
to emit the scope per script is mechanical.
`ScriptCompilationService.Compile` reads the scope and seeds `ScriptGlobals.
Attributes`, `Children`, `Parent` before the script runs. No code-generation;
the accessors close over the scope path at construction time.
## Editor surface
The editor side carries the same metadata that the runtime gets:
- The current template's attribute set (names + types).
- Each composition: instance name → resolved child template's attribute set
AND script list. The form already loads compositions in `TemplateEdit`.
- The parent template's attribute and script lists, ONLY when the open
template is composed inside another. We surface this as `null` otherwise.
New completion contexts:
| In code | Suggests |
|---|---|
| `Attributes["X"]` | declared attribute names of current template |
| `Children["X"]` | composition instance names |
| `Children["X"].Attributes["Y"]` | attribute names of the resolved child template |
| `Children["X"].CallScript("Y"` | script names of the resolved child template |
| `Parent.Attributes["X"]` | parent template's attribute names |
| `Parent.CallScript("X"` | parent template's script names |
New diagnostics:
- **SCADA006**: unknown attribute name on the appropriate scope.
- **SCADA007**: unknown child composition name in `Children["X"]`.
Existing `Instance.GetAttribute("X")` / `Instance.CallScript("X")` keep working
unchanged. Editor support for those can fall out of the same metadata if we
want it.
## Hover + signature help
- Hover `Attributes["X"]``attribute X: <Type> on <TemplateName>`.
- Hover `Children["X"]``composition X: <ChildTemplateName>`.
- Signature help for `Children["X"].CallScript(...)` reuses the existing
shape pipeline once the child template's scripts are reachable as
`ScriptShape[]`.
## What needs to be passed from the form
`TemplateEdit` already loads the open template's attributes and scripts.
Two new pieces:
1. **Resolved child compositions**: for each `Composition` row, fetch the
composed template's `Attributes` and `Scripts`. The repository already
has `GetTemplateByIdAsync` — call it for each composition.
2. **Parent template (if any)**: query the repository for templates that
compose this one. If exactly one, pass its shape. If multiple or none,
pass `null` and emit `Parent.X` accesses as diagnostics-by-the-user (since
the parent context is ambiguous in design time — the runtime knows because
it's running inside one specific deployment, but the editor doesn't).
Edge case: a template composed into multiple parents has no single parent at
edit time. Acceptable behaviour: `Parent` autocompletion is suppressed; using
it still compiles but emits a warning at deploy time. Document this clearly.
## Phased rollout
1. **Runtime first**. Add `Attributes` / `Children` / `Parent` accessors.
Wire scope into `ResolvedScript` and the flattening pipeline. Test with
existing flat templates (Scope.SelfPath = ""). Verify a composed script's
`Attributes["Temperature"]` reads through correctly. Site-runtime tests.
2. **Flattening + deployment**. Verify the deployed artifact carries the new
`Scope` field through `ResolvedScript``FlattenedScript` → site-side.
Run a round-trip deploy + execute.
3. **Editor metadata**. `TemplateEdit` fetches child template shapes for each
composition and optionally the parent. New Monaco context fields.
4. **Editor completion + diagnostics**. New string-literal completion
contexts. SCADA006 / SCADA007 diagnostics on the Diagnose path. Hover.
Each phase is a separate commit and independently shippable.
## Out of scope
- Composing the same template multiple times under different names on the
same parent (already supported by the data model; the editor just lists
each composition).
- Sibling-of-sibling access (`Children["A"].Parent.Children["B"]`). The
accessor API supports it naturally but we don't actively suggest it.
- Locking-aware writes (`Attributes["X"] = v` when X is locked). The
attribute lock is enforced at deployment validation, not at script-write
time; runtime writes that hit a locked attribute should reject. Out of
scope for this design — covered by the existing lock-enforcement pass.
- A formal type for `Children` / `Parent` in the editor's Roslyn analysis
(the strict Roslyn route would auto-generate per-template accessor types).
We use a dictionary-style indexer for both runtime and editor, with editor
awareness coming from the metadata pipeline, not from per-template C#
types.
## Open questions
- Should `Attributes["X"]` throw or return `null` on unknown key? The
existing `GetAttribute` logs a warning and returns `null`. Same here for
consistency.
- ~~Async vs sync indexer?~~ **Decided: both.** Sync `Attributes["X"]` /
`Attributes["X"] = v` indexer for ergonomics, plus
`Attributes.GetAsync("X")` / `Attributes.SetAsync("X", v)` for callers
that want to be explicit about the actor Ask. The sync path internally
blocks on `.GetAwaiter().GetResult()` — acceptable because all script
bodies already run on a dedicated blocking-I/O dispatcher per the project
conventions in CLAUDE.md.