Implement short-circuiting

Author: NullVoxPopuli

packages/@glimmer-workspace/integration-tests/test/keywords/and-test.ts

@@ -6,6 +6,40 @@ import { template } from '@ember/template-compiler';
 class KeywordAnd extends RenderTest {
   static suiteName = 'keyword helper: and';
 
+  @test
+  'references are lazy'(assert: Assert) {
+    const obj = {
+      get a() {
+        assert.step('a');
+        return 1;
+      },
+      get b() {
+        assert.step('b');
+        return 89;
+      },
+      get c() {
+        assert.step('c');
+        return false;
+      },
+      get d() {
+        assert.step('d');
+        return 'unexpected!!!';
+      },
+    };
+
+    const compiled = template('{{and obj.a obj.b obj.c obj.d}}', {
+      strictMode: true,
+      scope: () => ({ obj }),
+    });
+
+    this.renderComponent(compiled);
+    this.assertHTML('false');
+    assert.verifySteps(
+      ['a', 'b', 'c'],
+      'd not evaluated because obj.c was the last to be evaluated and short-circuited'
+    );
+  }
+
   @test
   'explicit scope'() {
     let a = 'yes';

packages/@glimmer-workspace/integration-tests/test/keywords/or-test.ts

@@ -6,6 +6,40 @@ import { template } from '@ember/template-compiler';
 class KeywordOr extends RenderTest {
   static suiteName = 'keyword helper: or';
 
+  @test
+  'references are lazy'(assert: Assert) {
+    const obj = {
+      get a() {
+        assert.step('a');
+        return false;
+      },
+      get b() {
+        assert.step('b');
+        return null;
+      },
+      get c() {
+        assert.step('c');
+        return 2;
+      },
+      get d() {
+        assert.step('d');
+        return 'unexpected!!!';
+      },
+    };
+
+    const compiled = template('{{or obj.a obj.b obj.c obj.d}}', {
+      strictMode: true,
+      scope: () => ({ obj }),
+    });
+
+    this.renderComponent(compiled);
+    this.assertHTML('2');
+    assert.verifySteps(
+      ['a', 'b', 'c'],
+      'd not evaluated because obj.c was the last to be evaluated and short-circuited'
+    );
+  }
+
   @test
   'explicit scope'() {
     let a = false;

packages/@glimmer/runtime/lib/helpers/and.ts

@@ -1,13 +1,26 @@
 import { DEBUG } from '@glimmer/env';
+import type { CapturedArguments } from '@glimmer/interfaces';
 import { toBool } from '@glimmer/global-context';
+import { createComputeRef, valueForRef } from '@glimmer/reference';
 
-export const and = (...args: unknown[]) => {
-  if (DEBUG && args.length < 2) {
-    throw new Error(`\`and\` expects at least two arguments, but received ${args.length}.`);
-  }
+import { internalHelper } from './internal-helper';
 
-  for (let i = 0; i < args.length; i++) {
-    if (!toBool(args[i])) return args[i];
+export const and = internalHelper(({ positional }: CapturedArguments) => {
+  if (DEBUG && positional.length < 2) {
+    throw new Error(`\`and\` expects at least two arguments, but received ${positional.length}.`);
   }
-  return args[args.length - 1];
-};
+
+  return createComputeRef(
+    () => {
+      let last: unknown;
+      for (let i = 0; i < positional.length; i++) {
+        let arg = positional[i];
+        last = arg ? valueForRef(arg) : arg;
+        if (!toBool(last)) return last;
+      }
+      return last;
+    },
+    null,
+    'and'
+  );
+});

packages/@glimmer/runtime/lib/helpers/or.ts

@@ -1,13 +1,26 @@
 import { DEBUG } from '@glimmer/env';
+import type { CapturedArguments } from '@glimmer/interfaces';
 import { toBool } from '@glimmer/global-context';
+import { createComputeRef, valueForRef } from '@glimmer/reference';
 
-export const or = (...args: unknown[]) => {
-  if (DEBUG && args.length < 2) {
-    throw new Error(`\`or\` expects at least two arguments, but received ${args.length}.`);
-  }
+import { internalHelper } from './internal-helper';
 
-  for (let i = 0; i < args.length; i++) {
-    if (toBool(args[i])) return args[i];
+export const or = internalHelper(({ positional }: CapturedArguments) => {
+  if (DEBUG && positional.length < 2) {
+    throw new Error(`\`or\` expects at least two arguments, but received ${positional.length}.`);
   }
-  return args[args.length - 1];
-};
+
+  return createComputeRef(
+    () => {
+      let last: unknown;
+      for (let i = 0; i < positional.length; i++) {
+        let arg = positional[i];
+        last = arg ? valueForRef(arg) : arg;
+        if (toBool(last)) return last;
+      }
+      return last;
+    },
+    null,
+    'or'
+  );
+});