Add readSource, the stored-bytes read, as a base operation

packages/base/operations.ts

@@ -62,7 +62,7 @@ import {
 
 // The behaviors every declaration builds on. Which of them a def carries is
 // implied by the def type rather than written in author code — a `CardDef`
-// has all six, a `FileDef` only `read`, a `FieldDef` none — so
+// has all of them, a `FileDef` only the two reads, a `FieldDef` none — so
 // `getOperations` synthesizes them. A declaration *named* after a base op
 // takes its place: it specializes that behavior when it names the same
 // `base`, and rebinds the verb when it names another — a `delete` declared
@@ -72,6 +72,7 @@ import {
 // and neither is inferred from the other.
 export const BASE_OPERATIONS = [
   'read',
+  'readSource',
   'create',
   'update',
   'delete',
@@ -81,6 +82,25 @@ export const BASE_OPERATIONS = [
 
 export type BaseOperationName = (typeof BASE_OPERATIONS)[number];
 
+// The base operations a declaration may neither build on nor be named after.
+// A stored-bytes read serves what is on disk: there is no payload to reshape,
+// no program stage to run, and no result to project, so a declaration built on
+// it would describe work nothing carries out.
+//
+// Both halves of that refusal matter, because a name and a base are
+// independent. The realm answers one of these by name without reading a
+// definition at all, so a declaration under the name — whatever base it
+// builds on — would be dispatched straight past: the built-in would run and
+// the author's operation would never be reached. Refusing the name here is
+// what keeps a new declaration out of that state, and refusing the base is
+// what stops the behavior being reached under some other name. Lowering
+// refuses the name too, so no stored definition can carry one either.
+const NOT_DECLARABLE: readonly BaseOperationName[] = ['readSource'];
+
+function isNotDeclarable(name: string): boolean {
+  return NOT_DECLARABLE.includes(name as BaseOperationName);
+}
+
 // ============================================================================
 // Typed references
 //
@@ -356,6 +376,19 @@ export type OperationDeclaration =
   | ReadOperationDeclaration
   | QueryOperationDeclaration;
 
+// A base operation a def carries with nothing declared on it. It is not a
+// declaration and the union above deliberately cannot express one: an author
+// writes no clauses for a base operation, and the two `NOT_DECLARABLE` names
+// cannot be written at all, so a declaration type that admitted them would
+// invite exactly what the decorator refuses. `getOperations` returns both
+// shapes, so a consumer reading `base` to dispatch gets every operation a def
+// carries — including the ones no `OperationDeclaration` could name.
+export interface ImpliedOperation {
+  readonly base: BaseOperationName;
+}
+
+export type CarriedOperation = OperationDeclaration | ImpliedOperation;
+
 // The operations declared on a def, read off the class type. Keyed by
 // operation name, so an invocation surface can be typed from the class alone.
 //
@@ -420,6 +453,10 @@ const CLAUSE_KEYS: Record<BaseOperationName, readonly string[]> = {
   update: [],
   delete: [],
   read: [],
+  // A stored-bytes read takes no clauses because it takes no declaration at
+  // all; the entry is here because this table is exhaustive over the base
+  // operations, so a new one has to say what it accepts.
+  readSource: [],
   query: ['query'],
 };
 
@@ -459,6 +496,11 @@ export const operation = function (
     );
   }
   let owner = assertOperationTarget(target, key);
+  if (isNotDeclarable(key)) {
+    throw new Error(
+      `${declarationLabel(owner, key)}: "${key}" is a reserved operation name — a "${key}" serves the bytes stored at the def's URL, which the realm answers without reading a definition, so a declaration under this name would never be reached`,
+    );
+  }
   assertNameAvailable(owner, key);
   if (typeof descriptor?.initializer !== 'function') {
     throw new Error(
@@ -497,14 +539,11 @@ export const operation = function (
 // relied on to carry one, so lower from `getDeclaredOperations`.
 export function getOperations(
   classOrInstance: BaseDef | typeof BaseDef,
-): Record<string, OperationDeclaration> {
+): Record<string, CarriedOperation> {
   let owner = defConstructorFor(classOrInstance, 'getOperations');
-  let operations = emptyOperationRecord();
+  let operations = emptyOperationRecord() as Record<string, CarriedOperation>;
   for (let base of impliedOperations(owner)) {
-    // A base operation with nothing declared on it is the declaration
-    // `{ base }`; the cast is only because a union does not narrow from a
-    // computed discriminant.
-    operations[base] = { base } as OperationDeclaration;
+    operations[base] = { base };
   }
   return Object.assign(operations, declaredOperations(owner));
 }
@@ -547,14 +586,19 @@ function impliedOperations(
   }
   if (isSubclassOf(owner, FileDef)) {
     // A file's metadata is content-derived and read-only: there is no
-    // JSON:API mutation surface for anything else to reach.
+    // JSON:API mutation surface for anything else to reach. Its bytes are the
+    // representation that matters, so it carries the stored-bytes read too.
     return READ_ONLY;
   }
-  // The one operation every addressable def shares.
+  // The operations every addressable def shares.
   return READ_ONLY;
 }
 
-const READ_ONLY = ['read'] as const;
+// The two reads, neither of which writes. A `read` serves the def's indexed
+// document; a `readSource` serves the bytes stored at the instance's URL, a
+// representation every addressable def has whether or not its document is the
+// interesting one — for a file it is the bytes that are the point.
+const READ_ONLY = ['read', 'readSource'] as const;
 
 function declaredOperations(
   owner: typeof BaseDef,
@@ -694,6 +738,11 @@ function assertValidDeclaration(
       `${label}: \`base\` must name the built-in behavior this operation builds on — one of ${quoteList(BASE_OPERATIONS)}`,
     );
   }
+  if (isNotDeclarable(base)) {
+    throw new Error(
+      `${label}: a "${base}" operation serves the bytes stored at the def's URL, so there is nothing for a declaration to specialize or rebind`,
+    );
+  }
   // An author may only specialize a base operation the def type actually
   // carries. Read from the same list `getOperations` synthesizes: only a card
   // has a mutation surface, and a file's metadata is content-derived and

packages/host/tests/integration/operations-test.ts

@@ -29,6 +29,17 @@ let card: (typeof OperationsModule)['card'];
 let bxl: (typeof OperationsModule)['bxl'];
 let linkTo: (typeof OperationsModule)['linkTo'];
 
+// The entry `getOperations` synthesizes for a base operation a def carries.
+// The cast is load-bearing rather than convenience: `OperationDeclaration`
+// deliberately cannot express `base: 'readSource'`, because nothing may
+// declare one and the authoring types are the first place that is refused —
+// while `getOperations` still reports the entry every card and file def
+// carries. That asymmetry lives here rather than being spelled out at each
+// expectation.
+function implied(base: string): OperationsModule.OperationDeclaration {
+  return { base } as OperationsModule.OperationDeclaration;
+}
+
 // Compile-time assertions. The call does nothing at run time; it fails to
 // type-check unless the two types are identical, so the call is the assertion.
 type Identical<Left, Right> =
@@ -126,6 +137,7 @@ module('Integration | operations', function (hooks) {
         'listMine',
         'query',
         'read',
+        'readSource',
         'transform',
         'update',
       ],
@@ -172,14 +184,15 @@ module('Integration | operations', function (hooks) {
     assert.deepEqual(
       getOperations(CardDef),
       {
-        read: { base: 'read' },
-        create: { base: 'create' },
-        update: { base: 'update' },
-        delete: { base: 'delete' },
-        query: { base: 'query' },
-        transform: { base: 'transform' },
+        read: implied('read'),
+        readSource: implied('readSource'),
+        create: implied('create'),
+        update: implied('update'),
+        delete: implied('delete'),
+        query: implied('query'),
+        transform: implied('transform'),
       },
-      'a card def carries all six, implied by the def type',
+      'a card def carries every base operation, implied by the def type',
     );
     assert.deepEqual(
       Object.keys(getDeclaredOperations(CardDef)),
@@ -188,8 +201,8 @@ module('Integration | operations', function (hooks) {
     );
     assert.deepEqual(
       getOperations(FileDef),
-      { read: { base: 'read' } },
-      "a file's metadata is read-only, so a file def carries only read",
+      { read: implied('read'), readSource: implied('readSource') },
+      "a file's metadata is read-only, so a file def carries only its two reads",
     );
     assert.deepEqual(
       getOperations(FieldDef),
@@ -211,7 +224,15 @@ module('Integration | operations', function (hooks) {
     );
     assert.deepEqual(
       Object.keys(getOperations(Report)).sort(),
-      ['create', 'delete', 'query', 'read', 'transform', 'update'],
+      [
+        'create',
+        'delete',
+        'query',
+        'read',
+        'readSource',
+        'transform',
+        'update',
+      ],
       'and adds no name, because it is that base operation',
     );
 
@@ -230,7 +251,15 @@ module('Integration | operations', function (hooks) {
     );
     assert.deepEqual(
       Object.keys(getOperations(Archivable)).sort(),
-      ['create', 'delete', 'query', 'read', 'transform', 'update'],
+      [
+        'create',
+        'delete',
+        'query',
+        'read',
+        'readSource',
+        'transform',
+        'update',
+      ],
       'which stands in for the removal rather than beside it',
     );
   });
@@ -390,7 +419,7 @@ module('Integration | operations', function (hooks) {
     );
   });
 
-  test('a file definition can only declare read operations', function (assert) {
+  test('a file definition can only declare document reads', function (assert) {
     class Attachment extends FileDef {
       @operation static readRedacted = { base: 'read', output: { name: true } };
     }
@@ -409,11 +438,64 @@ module('Integration | operations', function (hooks) {
         }
         return Mutable;
       },
-      /carries only "read"/,
+      /carries only "read", "readSource"/,
       'file metadata is content-derived, so it has no mutation surface',
     );
   });
 
+  test('a stored-bytes read takes no declaration at all', function (assert) {
+    // The other half of the realm's definition-free dispatch: it answers a
+    // `readSource` without consulting a definition, which is only safe while
+    // no declaration can take that name. Refusing here is what makes it so.
+    for (let Def of [CardDef, FileDef]) {
+      assert.throws(
+        () => {
+          class Exported extends (Def as typeof CardDef) {
+            @operation static exportBytes = { base: 'readSource' };
+          }
+          return Exported;
+        },
+        /serves the bytes stored at the def's URL/,
+        `a ${Def.name} cannot build an operation on a stored-bytes read`,
+      );
+    }
+    assert.throws(
+      () => {
+        class Redacted extends CardDef {
+          // Not even under its own name: specializing it is the same ask as
+          // rebinding a verb onto it, since there is no stage to specialize.
+          @operation static readSource = {
+            base: 'readSource',
+            output: { redacted: true },
+          };
+        }
+        return Redacted;
+      },
+      /reserved operation name/,
+      'and it cannot be specialized under its own name either',
+    );
+
+    // The name is reserved independently of the base, because the two are
+    // independent everywhere else: a declaration is invoked under its name and
+    // carried out by its base. The realm answers this name without reading a
+    // definition, so a declaration under it — whatever base it builds on —
+    // would be dispatched straight past, and the built-in would run in place
+    // of what the author wrote.
+    assert.throws(
+      () => {
+        class Sneaky extends CardDef {
+          @operation static readSource = {
+            base: 'read',
+            output: { redacted: true },
+          };
+        }
+        return Sneaky;
+      },
+      /reserved operation name/,
+      'a declaration cannot take the name by building on another base',
+    );
+  });
+
   test('the decorator rejects an operation name that is already a static', function (assert) {
     assert.throws(
       () => {
@@ -1378,12 +1460,12 @@ module('Integration | operations', function (hooks) {
     }
   });
 
-  test('a def with no mutation surface carries only read', function (assert) {
+  test('a def with no mutation surface carries only its reads', function (assert) {
     class Bare extends cardAPI.BaseDef {}
     assert.deepEqual(
       getOperations(Bare),
-      { read: { base: 'read' } },
-      'read is the one operation every addressable def shares',
+      { read: implied('read'), readSource: implied('readSource') },
+      'the two reads are what every addressable def shares',
     );
     assert.throws(
       () => {
@@ -1395,7 +1477,7 @@ module('Integration | operations', function (hooks) {
         }
         return Mutable;
       },
-      /carries only "read"/,
+      /carries only "read", "readSource"/,
       'and a def that carries no mutation base cannot declare one',
     );
   });