console: print promise details (#4524)

4 files changed, 74 insertions, 1 deletions

diff --git a/cli/js/globals.ts b/cli/js/globals.ts
index 87ff13b22..e5b7ff85a 100644
--- a/cli/js/globals.ts
+++ b/cli/js/globals.ts
@@ -2,6 +2,7 @@
 
 import * as blob from "./web/blob.ts";
 import * as consoleTypes from "./web/console.ts";
+import * as promiseTypes from "./web/promise.ts";
 import * as customEvent from "./web/custom_event.ts";
 import * as domTypes from "./web/dom_types.ts";
 import * as domFile from "./web/dom_file.ts";
@@ -102,6 +103,18 @@ declare global {
 
     formatError: (e: Error) => string;
 
+    /**
+     * Get promise details as two elements array.
+     *
+     * First element is the `PromiseState`.
+     * If promise isn't pending, second element would be the result of the promise.
+     * Otherwise, second element would be undefined.
+     *
+     * Throws `TypeError` if argument isn't a promise
+     *
+     */
+    getPromiseDetails<T>(promise: Promise<T>): promiseTypes.PromiseDetails<T>;
+
     decode(bytes: Uint8Array): string;
     encode(text: string): Uint8Array;
   }
diff --git a/cli/js/tests/console_test.ts b/cli/js/tests/console_test.ts
index c49c941f4..88902f84b 100644
--- a/cli/js/tests/console_test.ts
+++ b/cli/js/tests/console_test.ts
@@ -580,6 +580,27 @@ unitTest(function consoleTestStringifyIterable() {
   );
 });
 
+unitTest(async function consoleTestStringifyPromises(): Promise<void> {
+  const pendingPromise = new Promise((_res, _rej) => {});
+  assertEquals(stringify(pendingPromise), "Promise { <pending> }");
+
+  const resolvedPromise = new Promise((res, _rej) => {
+    res("Resolved!");
+  });
+  assertEquals(stringify(resolvedPromise), `Promise { "Resolved!" }`);
+
+  let rejectedPromise;
+  try {
+    rejectedPromise = new Promise((_, rej) => {
+      rej(Error("Whoops"));
+    });
+    await rejectedPromise;
+  } catch (err) {}
+  const strLines = stringify(rejectedPromise).split("\n");
+  assertEquals(strLines[0], "Promise {");
+  assertEquals(strLines[1], " <rejected> Error: Whoops");
+});
+
 unitTest(function consoleTestWithCustomInspector(): void {
   class A {
     [customInspect](): string {
diff --git a/cli/js/web/console.ts b/cli/js/web/console.ts
index a9b4d53be..3a274e086 100644
--- a/cli/js/web/console.ts
+++ b/cli/js/web/console.ts
@@ -4,6 +4,7 @@ import { TextEncoder } from "./text_encoding.ts";
 import { File, stdout } from "../files.ts";
 import { cliTable } from "./console_table.ts";
 import { exposeForTest } from "../internals.ts";
+import { PromiseState } from "./promise.ts";
 
 type ConsoleContext = Set<unknown>;
 type InspectOptions = Partial<{
@@ -28,6 +29,8 @@ const CHAR_LOWERCASE_O = 111; /* o */
 const CHAR_UPPERCASE_O = 79; /* O */
 const CHAR_LOWERCASE_C = 99; /* c */
 
+const PROMISE_STRING_BASE_LENGTH = 12;
+
 export class CSI {
   static kClear = "\x1b[1;1H";
   static kClearScreenDown = "\x1b[0J";
@@ -442,7 +445,34 @@ function createNumberWrapperString(value: Number): string {
 
 /* eslint-enable @typescript-eslint/ban-types */
 
-// TODO: Promise, requires v8 bindings to get info
+function createPromiseString(
+  value: Promise<unknown>,
+  ctx: ConsoleContext,
+  level: number,
+  maxLevel: number
+): string {
+  const [state, result] = Deno.core.getPromiseDetails(value);
+
+  if (state === PromiseState.Pending) {
+    return "Promise { <pending> }";
+  }
+
+  const prefix = state === PromiseState.Fulfilled ? "" : "<rejected> ";
+
+  const str = `${prefix}${stringifyWithQuotes(
+    result,
+    ctx,
+    level + 1,
+    maxLevel
+  )}`;
+
+  if (str.length + PROMISE_STRING_BASE_LENGTH > LINE_BREAKING_LENGTH) {
+    return `Promise {\n${" ".repeat(level + 1)}${str}\n}`;
+  }
+
+  return `Promise { ${str} }`;
+}
+
 // TODO: Proxy
 
 function createRawObjectString(
@@ -531,6 +561,8 @@ function createObjectString(
     return createBooleanWrapperString(value);
   } else if (value instanceof String) {
     return createStringWrapperString(value);
+  } else if (value instanceof Promise) {
+    return createPromiseString(value, ...args);
   } else if (value instanceof RegExp) {
     return createRegExpString(value);
   } else if (value instanceof Date) {
diff --git a/cli/js/web/promise.ts b/cli/js/web/promise.ts
new file mode 100644
index 000000000..b00c0786f
--- /dev/null
+++ b/cli/js/web/promise.ts
@@ -0,0 +1,7 @@
+export enum PromiseState {
+  Pending = 0,
+  Fulfilled = 1,
+  Rejected = 2,
+}
+
+export type PromiseDetails<T> = [PromiseState, T | undefined];