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Allow await expressions in optional chaining and nullish coalescing #497

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Jan 1, 2020
Merged

Allow await expressions in optional chaining and nullish coalescing #497

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46 changes: 46 additions & 0 deletions src/HelperManager.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -54,6 +54,15 @@ const HELPERS = {
}
}
`,
asyncNullishCoalesce: `
async function asyncNullishCoalesce(lhs, rhsFn) {
if (lhs != null) {
return lhs;
} else {
return await rhsFn();
}
}
`,
optionalChain: `
function optionalChain(ops) {
let lastAccessLHS = undefined;
Expand All @@ -77,12 +86,41 @@ const HELPERS = {
return value;
}
`,
asyncOptionalChain: `
async function asyncOptionalChain(ops) {
let lastAccessLHS = undefined;
let value = ops[0];
let i = 1;
while (i < ops.length) {
const op = ops[i];
const fn = ops[i + 1];
i += 2;
if ((op === 'optionalAccess' || op === 'optionalCall') && value == null) {
return undefined;
}
if (op === 'access' || op === 'optionalAccess') {
lastAccessLHS = value;
value = await fn(value);
} else if (op === 'call' || op === 'optionalCall') {
value = await fn((...args) => value.call(lastAccessLHS, ...args));
lastAccessLHS = undefined;
}
}
return value;
}
`,
optionalChainDelete: `
function optionalChainDelete(ops) {
const result = OPTIONAL_CHAIN_NAME(ops);
return result == null ? true : result;
}
`,
asyncOptionalChainDelete: `
async function asyncOptionalChainDelete(ops) {
const result = await ASYNC_OPTIONAL_CHAIN_NAME(ops);
return result == null ? true : result;
}
`,
};

export class HelperManager {
Expand All @@ -104,11 +142,19 @@ export class HelperManager {
if (this.helperNames.optionalChainDelete) {
this.getHelperName("optionalChain");
}
if (this.helperNames.asyncOptionalChainDelete) {
this.getHelperName("asyncOptionalChain");
}
for (const [baseName, helperCodeTemplate] of Object.entries(HELPERS)) {
const helperName = this.helperNames[baseName];
let helperCode = helperCodeTemplate;
if (baseName === "optionalChainDelete") {
helperCode = helperCode.replace("OPTIONAL_CHAIN_NAME", this.helperNames.optionalChain!);
} else if (baseName === "asyncOptionalChainDelete") {
helperCode = helperCode.replace(
"ASYNC_OPTIONAL_CHAIN_NAME",
this.helperNames.asyncOptionalChain!,
);
}
if (helperName) {
resultCode += " ";
Expand Down
22 changes: 20 additions & 2 deletions src/TokenProcessor.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,7 @@ import {HelperManager} from "./HelperManager";
import {Token} from "./parser/tokenizer";
import {ContextualKeyword} from "./parser/tokenizer/keywords";
import {TokenType, TokenType as tt} from "./parser/tokenizer/types";
import isAsyncOperation from "./util/isAsyncOperation";

export interface TokenProcessorSnapshot {
resultCode: string;
Expand Down Expand Up @@ -206,15 +207,32 @@ export default class TokenProcessor {

private appendTokenPrefix(): void {
const token = this.currentToken();
if (token.numNullishCoalesceStarts || token.isOptionalChainStart) {
token.isAsyncOperation = isAsyncOperation(this);
}
if (token.numNullishCoalesceStarts) {
for (let i = 0; i < token.numNullishCoalesceStarts; i++) {
this.resultCode += this.helperManager.getHelperName("nullishCoalesce");
if (token.isAsyncOperation) {
this.resultCode += "await ";
this.resultCode += this.helperManager.getHelperName("asyncNullishCoalesce");
} else {
this.resultCode += this.helperManager.getHelperName("nullishCoalesce");
}
this.resultCode += "(";
}
}
if (token.isOptionalChainStart) {
if (token.isAsyncOperation) {
this.resultCode += "await ";
}
if (this.tokenIndex > 0 && this.tokenAtRelativeIndex(-1).type === tt._delete) {
this.resultCode += this.helperManager.getHelperName("optionalChainDelete");
if (token.isAsyncOperation) {
this.resultCode += this.helperManager.getHelperName("asyncOptionalChainDelete");
} else {
this.resultCode += this.helperManager.getHelperName("optionalChainDelete");
}
} else if (token.isAsyncOperation) {
this.resultCode += this.helperManager.getHelperName("asyncOptionalChain");
} else {
this.resultCode += this.helperManager.getHelperName("optionalChain");
}
Expand Down
8 changes: 8 additions & 0 deletions src/parser/tokenizer/index.ts
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Expand Up @@ -94,6 +94,7 @@ export class Token {
this.contextualKeyword = state.contextualKeyword;
this.start = state.start;
this.end = state.end;
this.scopeDepth = state.scopeDepth;
this.isType = state.isType;
this.identifierRole = null;
this.shadowsGlobal = false;
Expand All @@ -105,17 +106,22 @@ export class Token {
this.isOptionalChainStart = false;
this.isOptionalChainEnd = false;
this.subscriptStartIndex = null;
this.nullishStartIndex = null;
}

type: TokenType;
contextualKeyword: ContextualKeyword;
start: number;
end: number;
scopeDepth: number;
isType: boolean;
identifierRole: IdentifierRole | null;
// Initially false for all tokens, then may be computed in a follow-up step that does scope
// analysis.
shadowsGlobal: boolean;
// Initially false for all tokens, but may be set during transform to mark it as containing an
// await operation.
isAsyncOperation: boolean;
contextId: number | null;
// For assignments, the index of the RHS. For export tokens, the end of the export.
rhsEndIndex: number | null;
Expand All @@ -132,6 +138,8 @@ export class Token {
// Tag for `.`, `?.`, `[`, `?.[`, `(`, and `?.(` to denote the "root" token for this
// subscript chain. This can be used to determine if this chain is an optional chain.
subscriptStartIndex: number | null;
// Tag for `??` operators to denote the root token for this nullish coalescing call.
nullishStartIndex: number | null;
}

// ## Tokenizer
Expand Down
3 changes: 3 additions & 0 deletions src/parser/traverser/expression.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -209,6 +209,9 @@ function parseExprOp(startTokenIndex: number, minPrec: number, noIn: boolean): v
if (prec > minPrec) {
const op = state.type;
next();
if (op === tt.nullishCoalescing) {
state.tokens[state.tokens.length - 1].nullishStartIndex = startTokenIndex;
}

const rhsStartTokenIndex = state.tokens.length;
parseMaybeUnary();
Expand Down
10 changes: 9 additions & 1 deletion src/transformers/OptionalChainingNullishTransformer.ts
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Expand Up @@ -19,7 +19,12 @@ export default class OptionalChainingNullishTransformer extends Transformer {

process(): boolean {
if (this.tokens.matches1(tt.nullishCoalescing)) {
this.tokens.replaceTokenTrimmingLeftWhitespace(", () =>");
const token = this.tokens.currentToken();
if (this.tokens.tokens[token.nullishStartIndex!].isAsyncOperation) {
this.tokens.replaceTokenTrimmingLeftWhitespace(", async () =>");
} else {
this.tokens.replaceTokenTrimmingLeftWhitespace(", () =>");
}
return true;
}
if (this.tokens.matches1(tt._delete)) {
Expand All @@ -46,6 +51,9 @@ export default class OptionalChainingNullishTransformer extends Transformer {
} else {
arrowStartSnippet = `${param} => ${param}`;
}
if (this.tokens.tokens[chainStart].isAsyncOperation) {
arrowStartSnippet = `async ${arrowStartSnippet}`;
}
if (
this.tokens.matches2(tt.questionDot, tt.parenL) ||
this.tokens.matches2(tt.questionDot, tt.lessThan)
Expand Down
38 changes: 38 additions & 0 deletions src/util/isAsyncOperation.ts
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Original file line number Diff line number Diff line change
@@ -0,0 +1,38 @@
import {ContextualKeyword} from "../parser/tokenizer/keywords";
import TokenProcessor from "../TokenProcessor";

/**
* Determine whether this optional chain or nullish coalescing operation has any await statements in
* it. If so, we'll need to transpile to an async operation.
*
* We compute this by walking the length of the operation and returning true if we see an await
* keyword used as a real await (rather than an object key or property access). Nested optional
* chain/nullish operations need to be tracked but don't silence await, but a nested async function
* (or any other nested scope) will make the await not count.
*/
export default function isAsyncOperation(tokens: TokenProcessor): boolean {
let index = tokens.currentIndex();
let depth = 0;
const startToken = tokens.currentToken();
do {
const token = tokens.tokens[index];
if (token.isOptionalChainStart) {
depth++;
}
if (token.isOptionalChainEnd) {
depth--;
}
depth += token.numNullishCoalesceStarts;
depth -= token.numNullishCoalesceEnds;

if (
token.contextualKeyword === ContextualKeyword._await &&
token.identifierRole == null &&
token.scopeDepth === startToken.scopeDepth
) {
return true;
}
index += 1;
} while (depth > 0 && index < tokens.tokens.length);
return false;
}
30 changes: 15 additions & 15 deletions test/index-test.ts
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Expand Up @@ -13,21 +13,21 @@ if (foo) {
{transforms: ["jsx", "imports"]},
),
`\
Location Label Raw contextualKeyword isType identifierRole shadowsGlobal contextId rhsEndIndex isExpression numNullishCoalesceStarts numNullishCoalesceEnds isOptionalChainStart isOptionalChainEnd subscriptStartIndex
1:1-1:3 if if 0 0 0
1:4-1:5 ( ( 0 0 0
1:5-1:8 name foo 0 0 0 0
1:8-1:9 ) ) 0 0 0
1:10-1:11 { { 0 0 0
2:3-2:10 name console 0 0 0 0
2:10-2:11 . . 0 0 0 5
2:11-2:14 name log 0 0 0
2:14-2:15 ( ( 0 1 0 0 5
2:15-2:29 string 'Hello world!' 0 0 0
2:29-2:30 ) ) 0 1 0 0
2:30-2:31 ; ; 0 0 0
3:1-3:2 } } 0 0 0
3:2-3:2 eof 0 0 0 `,
Location Label Raw contextualKeyword scopeDepth isType identifierRole shadowsGlobal contextId rhsEndIndex isExpression numNullishCoalesceStarts numNullishCoalesceEnds isOptionalChainStart isOptionalChainEnd subscriptStartIndex nullishStartIndex
1:1-1:3 if if 0 0 0 0
1:4-1:5 ( ( 0 0 0 0
1:5-1:8 name foo 0 0 0 0 0
1:8-1:9 ) ) 0 0 0 0
1:10-1:11 { { 0 1 0 0
2:3-2:10 name console 0 1 0 0 0
2:10-2:11 . . 0 1 0 0 5
2:11-2:14 name log 0 1 0 0
2:14-2:15 ( ( 0 1 1 0 0 5
2:15-2:29 string 'Hello world!' 0 1 0 0
2:29-2:30 ) ) 0 1 1 0 0
2:30-2:31 ; ; 0 1 0 0
3:1-3:2 } } 0 1 0 0
3:2-3:2 eof 0 0 0 0 `,
);
});
});
13 changes: 13 additions & 0 deletions test/prefixes.ts
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Expand Up @@ -19,6 +19,8 @@ var enterModule = require('react-hot-loader').enterModule; enterModule && enterM
})();`;
export const NULLISH_COALESCE_PREFIX = ` function _nullishCoalesce(lhs, rhsFn) { \
if (lhs != null) { return lhs; } else { return rhsFn(); } }`;
export const ASYNC_NULLISH_COALESCE_PREFIX = ` async function _asyncNullishCoalesce(lhs, rhsFn) { \
if (lhs != null) { return lhs; } else { return await rhsFn(); } }`;
export const OPTIONAL_CHAIN_PREFIX = ` function _optionalChain(ops) { \
let lastAccessLHS = undefined; let value = ops[0]; let i = 1; \
while (i < ops.length) { \
Expand All @@ -28,5 +30,16 @@ if (op === 'access' || op === 'optionalAccess') { lastAccessLHS = value; value =
else if (op === 'call' || op === 'optionalCall') { \
value = fn((...args) => value.call(lastAccessLHS, ...args)); lastAccessLHS = undefined; \
} } return value; }`;
export const ASYNC_OPTIONAL_CHAIN_PREFIX = ` async function _asyncOptionalChain(ops) { \
let lastAccessLHS = undefined; let value = ops[0]; let i = 1; \
while (i < ops.length) { \
const op = ops[i]; const fn = ops[i + 1]; i += 2; \
if ((op === 'optionalAccess' || op === 'optionalCall') && value == null) { return undefined; } \
if (op === 'access' || op === 'optionalAccess') { lastAccessLHS = value; value = await fn(value); } \
else if (op === 'call' || op === 'optionalCall') { \
value = await fn((...args) => value.call(lastAccessLHS, ...args)); lastAccessLHS = undefined; \
} } return value; }`;
export const OPTIONAL_CHAIN_DELETE_PREFIX = ` function _optionalChainDelete(ops) { \
const result = _optionalChain(ops); return result == null ? true : result; }`;
export const ASYNC_OPTIONAL_CHAIN_DELETE_PREFIX = ` async function _asyncOptionalChainDelete(ops) { \
const result = await _asyncOptionalChain(ops); return result == null ? true : result; }`;
67 changes: 67 additions & 0 deletions test/sucrase-test.ts
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@@ -1,4 +1,7 @@
import {
ASYNC_NULLISH_COALESCE_PREFIX,
ASYNC_OPTIONAL_CHAIN_DELETE_PREFIX,
ASYNC_OPTIONAL_CHAIN_PREFIX,
ESMODULE_PREFIX,
IMPORT_DEFAULT_PREFIX,
NULLISH_COALESCE_PREFIX,
Expand Down Expand Up @@ -1025,4 +1028,68 @@ describe("sucrase", () => {
{transforms: []},
);
});

it("correctly transforms async functions using await in an optional chain", () => {
assertResult(
`
async function foo() {
a?.b(await f())
}
`,
`${ASYNC_OPTIONAL_CHAIN_PREFIX}
async function foo() {
await _asyncOptionalChain([a, 'optionalAccess', async _ => _.b, 'call', async _2 => _2(await f())])
}
`,
{transforms: []},
);
});

it("does not mistake an unrelated await keyword for an async optional chain", () => {
assertResult(
`
function foo() {
a?.b(async () => await f())
}
`,
`${OPTIONAL_CHAIN_PREFIX}
function foo() {
_optionalChain([a, 'optionalAccess', _ => _.b, 'call', _2 => _2(async () => await f())])
}
`,
{transforms: []},
);
});

it("correctly transforms async functions using await in an optional chain deletion", () => {
assertResult(
`
async function foo() {
delete a?.[await f()];
}
`,
`${ASYNC_OPTIONAL_CHAIN_PREFIX}${ASYNC_OPTIONAL_CHAIN_DELETE_PREFIX}
async function foo() {
await _asyncOptionalChainDelete([a, 'optionalAccess', async _ => _[await f()]]);
}
`,
{transforms: []},
);
});

it("correctly transforms async functions using await in nullish coalescing", () => {
assertResult(
`
async function foo() {
return a ?? await b();
}
`,
`${ASYNC_NULLISH_COALESCE_PREFIX}
async function foo() {
return await _asyncNullishCoalesce(a, async () => await b());
}
`,
{transforms: []},
);
});
});