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perf(@ngtools/webpack): reduce repeat path mapping analysis during re…
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…solution

The internal TypeScript path mapping Webpack resolver plugin is used to adjust module resolution during builds via the TypeScript configuration `paths` option. Prior to a build, the `paths` option is now preprocessed to limit the amount of analysis that is needed within each individual module resolution attempt during a build. Since module resolution attempts can occur frequently during a build, this change offers the potential to reduce the total cost of module resolution especially for applications with a large amount of configured path mappings.
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@clydin @filipesilva
clydin authored and filipesilva committed Aug 23, 2021
1 parent 4f91816 commit 7928b18
Showing 1 changed file with 137 additions and 91 deletions.
228 changes: 137 additions & 91 deletions packages/ngtools/webpack/src/paths-plugin.ts
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Expand Up @@ -7,7 +7,7 @@
*/

import * as path from 'path';
import { CompilerOptions, MapLike } from 'typescript';
import { CompilerOptions } from 'typescript';
import type { Configuration } from 'webpack';

// eslint-disable-next-line @typescript-eslint/no-empty-interface
Expand All @@ -16,21 +16,98 @@ export interface TypeScriptPathsPluginOptions extends Pick<CompilerOptions, 'pat
// Extract Resolver type from Webpack types since it is not directly exported
type Resolver = Exclude<Exclude<Configuration['resolve'], undefined>['resolver'], undefined>;

interface PathPattern {
starIndex: number;
prefix: string;
suffix?: string;
potentials: { hasStar: boolean; prefix: string; suffix?: string }[];
}

export class TypeScriptPathsPlugin {
constructor(private options?: TypeScriptPathsPluginOptions) {}
private baseUrl?: string;
private patterns?: PathPattern[];

constructor(options?: TypeScriptPathsPluginOptions) {
if (options) {
this.update(options);
}
}

/**
* Update the plugin with new path mapping option values.
* The options will also be preprocessed to reduce the overhead of individual resolve actions
* during a build.
*
* @param options The `paths` and `baseUrl` options from TypeScript's `CompilerOptions`.
*/
update(options: TypeScriptPathsPluginOptions): void {
this.options = options;
this.baseUrl = options.baseUrl;
this.patterns = undefined;

if (options.paths) {
for (const [pattern, potentials] of Object.entries(options.paths)) {
// Ignore any entries that would not result in a new mapping
if (potentials.length === 0 || potentials.every((potential) => potential === '*')) {
continue;
}

const starIndex = pattern.indexOf('*');
let prefix = pattern;
let suffix;
if (starIndex > -1) {
prefix = pattern.slice(0, starIndex);
if (starIndex < pattern.length - 1) {
suffix = pattern.slice(starIndex + 1);
}
}

this.patterns ??= [];
this.patterns.push({
starIndex,
prefix,
suffix,
potentials: potentials.map((potential) => {
const potentialStarIndex = potential.indexOf('*');
if (potentialStarIndex === -1) {
return { hasStar: false, prefix: potential };
}

return {
hasStar: true,
prefix: potential.slice(0, potentialStarIndex),
suffix:
potentialStarIndex < potential.length - 1
? potential.slice(potentialStarIndex + 1)
: undefined,
};
}),
});
}

// Sort patterns so that exact matches take priority then largest prefix match
this.patterns?.sort((a, b) => {
if (a.starIndex === -1) {
return -1;
} else if (b.starIndex === -1) {
return 1;
} else {
return b.starIndex - a.starIndex;
}
});
}
}

apply(resolver: Resolver): void {
const target = resolver.ensureHook('resolve');

// To support synchronous resolvers this hook cannot be promise based.
// Webpack supports synchronous resolution with `tap` and `tapAsync` hooks.
resolver.getHook('described-resolve').tapAsync(
'TypeScriptPathsPlugin',
// eslint-disable-next-line @typescript-eslint/no-explicit-any
(request: any, resolveContext, callback) => {
if (!this.options) {
// Preprocessing of the options will ensure that `patterns` is either undefined or has elements to check
if (!this.patterns) {
callback();

return;
Expand All @@ -50,39 +127,45 @@ export class TypeScriptPathsPlugin {
}

// Only work on Javascript/TypeScript issuers.
if (!request.context.issuer || !request.context.issuer.match(/\.[jt]sx?$/)) {
if (!request.context.issuer || !request.context.issuer.match(/\.[cm]?[jt]sx?$/)) {
callback();

return;
}

// Relative or absolute requests are not mapped
if (originalRequest.startsWith('.') || originalRequest.startsWith('/')) {
callback();

return;
}

// Ignore all webpack special requests
if (originalRequest.startsWith('!!')) {
callback();
switch (originalRequest[0]) {
case '.':
case '/':
// Relative or absolute requests are not mapped
callback();

return;
return;
case '!':
// Ignore all webpack special requests
if (originalRequest.length > 1 && originalRequest[1] === '!') {
callback();

return;
}
break;
}

const replacements = findReplacements(originalRequest, this.options.paths || {});
// A generator is used to limit the amount of replacements that need to be created.
// For example, if the first one resolves, any others are not needed and do not need
// to be created.
const replacements = findReplacements(originalRequest, this.patterns);

const tryResolve = () => {
const potential = replacements.shift();
if (!potential) {
const next = replacements.next();
if (next.done) {
callback();

return;
}

const potentialRequest = {
...request,
request: path.resolve(this.options?.baseUrl || '', potential),
request: path.resolve(this.baseUrl ?? '', next.value),
typescriptPathMapped: true,
};

Expand Down Expand Up @@ -110,89 +193,52 @@ export class TypeScriptPathsPlugin {
}
}

function findReplacements(originalRequest: string, paths: MapLike<string[]>): string[] {
function* findReplacements(
originalRequest: string,
patterns: PathPattern[],
): IterableIterator<string> {
// check if any path mapping rules are relevant
const pathMapOptions = [];
for (const pattern in paths) {
// get potentials and remove duplicates; JS Set maintains insertion order
const potentials = Array.from(new Set(paths[pattern]));
if (potentials.length === 0) {
// no potential replacements so skip
continue;
}
for (const { starIndex, prefix, suffix, potentials } of patterns) {
let partial;

// can only contain zero or one
const starIndex = pattern.indexOf('*');
if (starIndex === -1) {
if (pattern === originalRequest) {
pathMapOptions.push({
starIndex,
partial: '',
potentials,
});
}
} else if (starIndex === 0 && pattern.length === 1) {
if (potentials.length === 1 && potentials[0] === '*') {
// identity mapping -> noop
continue;
// No star means an exact match is required
if (prefix === originalRequest) {
partial = '';
}
pathMapOptions.push({
starIndex,
partial: originalRequest,
potentials,
});
} else if (starIndex === pattern.length - 1) {
if (originalRequest.startsWith(pattern.slice(0, -1))) {
pathMapOptions.push({
starIndex,
partial: originalRequest.slice(pattern.length - 1),
potentials,
});
} else if (starIndex === 0 && !suffix) {
// Everything matches a single wildcard pattern ("*")
partial = originalRequest;
} else if (!suffix) {
// No suffix means the star is at the end of the pattern
if (originalRequest.startsWith(prefix)) {
partial = originalRequest.slice(prefix.length);
}
} else {
const [prefix, suffix] = pattern.split('*');
// Star was in the middle of the pattern
if (originalRequest.startsWith(prefix) && originalRequest.endsWith(suffix)) {
pathMapOptions.push({
starIndex,
partial: originalRequest.slice(prefix.length).slice(0, -suffix.length),
potentials,
});
partial = originalRequest.substring(prefix.length, originalRequest.length - suffix.length);
}
}
}

if (pathMapOptions.length === 0) {
return [];
}

// exact matches take priority then largest prefix match
pathMapOptions.sort((a, b) => {
if (a.starIndex === -1) {
return -1;
} else if (b.starIndex === -1) {
return 1;
} else {
return b.starIndex - a.starIndex;
// If request was not matched, move on to the next pattern
if (partial === undefined) {
continue;
}
});

const replacements: string[] = [];
pathMapOptions.forEach((option) => {
for (const potential of option.potentials) {
let replacement;
const starIndex = potential.indexOf('*');
if (starIndex === -1) {
replacement = potential;
} else if (starIndex === potential.length - 1) {
replacement = potential.slice(0, -1) + option.partial;
} else {
const [prefix, suffix] = potential.split('*');
replacement = prefix + option.partial + suffix;

// Create the full replacement values based on the original request and the potentials
// for the successfully matched pattern.
for (const { hasStar, prefix, suffix } of potentials) {
let replacement = prefix;

if (hasStar) {
replacement += partial;
if (suffix) {
replacement += suffix;
}
}

replacements.push(replacement);
yield replacement;
}
});

return replacements;
}
}

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