From 75723d5c89e0ea958e440eef55aa715803ae32be Mon Sep 17 00:00:00 2001
From: JoostK <joost.koehoorn@gmail.com>
Date: Sun, 18 Nov 2018 21:14:48 +0100
Subject: [PATCH] feat(ivy): ngtsc support for static resolution of
 array.slice() (#27158)

For ngcc's processing of ES5 bundles, the spread syntax has been
downleveled from `[...ARRAY]` to become `ARRAY.slice()`. This commit
adds basic support for static resolution of such call.

PR Close #27158
---
 .../src/ngtsc/metadata/src/resolver.ts        | 30 ++++++++++++++++++-
 .../src/ngtsc/metadata/test/resolver_spec.ts  |  4 +++
 2 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/packages/compiler-cli/src/ngtsc/metadata/src/resolver.ts b/packages/compiler-cli/src/ngtsc/metadata/src/resolver.ts
index 7c5d0e7889..8223ed59b4 100644
--- a/packages/compiler-cli/src/ngtsc/metadata/src/resolver.ts
+++ b/packages/compiler-cli/src/ngtsc/metadata/src/resolver.ts
@@ -54,7 +54,7 @@ export function isDynamicValue(value: any): value is DynamicValue {
  * available statically.
  */
 export type ResolvedValue = number | boolean | string | null | undefined | Reference | EnumValue |
-    ResolvedValueArray | ResolvedValueMap | DynamicValue;
+    ResolvedValueArray | ResolvedValueMap | BuiltinFn | DynamicValue;
 
 /**
  * An array of `ResolvedValue`s.
@@ -81,6 +81,23 @@ export class EnumValue {
   constructor(readonly enumRef: Reference<ts.EnumDeclaration>, readonly name: string) {}
 }
 
+/**
+ * An implementation of a builtin function, such as `Array.prototype.slice`.
+ */
+export abstract class BuiltinFn { abstract evaluate(args: ResolvedValueArray): ResolvedValue; }
+
+class ArraySliceBuiltinFn extends BuiltinFn {
+  constructor(private lhs: ResolvedValueArray) { super(); }
+
+  evaluate(args: ResolvedValueArray): ResolvedValue {
+    if (args.length === 0) {
+      return this.lhs;
+    } else {
+      return DYNAMIC_VALUE;
+    }
+  }
+}
+
 /**
  * Tracks the scope of a function body, which includes `ResolvedValue`s for the parameters of that
  * body.
@@ -536,6 +553,8 @@ class StaticInterpreter {
     } else if (Array.isArray(lhs)) {
       if (rhs === 'length') {
         return lhs.length;
+      } else if (rhs === 'slice') {
+        return new ArraySliceBuiltinFn(lhs);
       }
       if (typeof rhs !== 'number' || !Number.isInteger(rhs)) {
         return DYNAMIC_VALUE;
@@ -571,6 +590,15 @@ class StaticInterpreter {
 
   private visitCallExpression(node: ts.CallExpression, context: Context): ResolvedValue {
     const lhs = this.visitExpression(node.expression, context);
+    if (isDynamicValue(lhs)) {
+      return DYNAMIC_VALUE;
+    }
+
+    // If the call refers to a builtin function, attempt to evaluate the function.
+    if (lhs instanceof BuiltinFn) {
+      return lhs.evaluate(node.arguments.map(arg => this.visitExpression(arg, context)));
+    }
+
     if (!(lhs instanceof Reference)) {
       throw new Error(`attempting to call something that is not a function: ${lhs}`);
     } else if (!isFunctionOrMethodReference(lhs)) {
diff --git a/packages/compiler-cli/src/ngtsc/metadata/test/resolver_spec.ts b/packages/compiler-cli/src/ngtsc/metadata/test/resolver_spec.ts
index 9886e719df..8a4ed0a3fd 100644
--- a/packages/compiler-cli/src/ngtsc/metadata/test/resolver_spec.ts
+++ b/packages/compiler-cli/src/ngtsc/metadata/test/resolver_spec.ts
@@ -118,6 +118,10 @@ describe('ngtsc metadata', () => {
   it('array `length` property access works',
      () => { expect(evaluate(`const a = [1, 2, 3];`, 'a[\'length\'] + 1')).toEqual(4); });
 
+  it('array `slice` function works', () => {
+    expect(evaluate(`const a = [1, 2, 3];`, 'a[\'slice\']()')).toEqual([1, 2, 3]);
+  });
+
   it('negation works', () => {
     expect(evaluate(`const x = 3;`, '!x')).toEqual(false);
     expect(evaluate(`const x = 3;`, '!!x')).toEqual(true);