feat(generate:entrypoints): Support output filename customization (#2…

…0593)

Adds new flags to the `generate:entrypoints` command that allow
customization of the filename used for each `ApiLevel`. These flags are
combined with the existing prefix/suffix flags to build the final file
names. For example, consider the following command:

```
flub generate entrypoints --outDir ./api-report --outFilePrefix {@unscopedPackageName}- --outFileAlpha legacy --outFileBeta b
 --outFilePublic p
```

Running that command on the tree package will output the following
files:

```
INFO:   Generating api-report/tree-p.d.ts
INFO:   Generating api-report/tree-b.d.ts
INFO:   Generating api-report/tree-legacy.d.ts
```

build-tools/packages/build-cli/docs/generate.md

@@ -218,15 +218,18 @@ Generates type declaration entrypoints for Fluid Framework API levels (/alpha, /
 
 ```
 USAGE
-  $ flub generate entrypoints [-v | --quiet] [--mainEntrypoint <value>] [--outDir <value>] [--outFilePrefix <value>]
-    [--outFileSuffix <value>]
+  $ flub generate entrypoints [-v | --quiet] [--mainEntrypoint <value>] [--outDir <value>] [--outFileAlpha <value>]
+    [--outFileBeta <value>] [--outFilePublic <value>] [--outFilePrefix <value>] [--outFileSuffix <value>]
 
 FLAGS
   --mainEntrypoint=<value>  [default: ./src/index.ts] Main entrypoint file containing all untrimmed exports.
   --outDir=<value>          [default: ./lib] Directory to emit entrypoint declaration files.
+  --outFileAlpha=<value>    [default: alpha] Base file name for alpha entrypoint declaration files.
+  --outFileBeta=<value>     [default: beta] Base file name for beta entrypoint declaration files.
   --outFilePrefix=<value>   File name prefix for emitting entrypoint declaration files. Pattern of
                             '{@unscopedPackageName}' within value will be replaced with the unscoped name of this
                             package.
+  --outFilePublic=<value>   [default: public] Base file name for public entrypoint declaration files.
   --outFileSuffix=<value>   [default: .d.ts] File name suffix including extension for emitting entrypoint declaration
                             files.
 

build-tools/packages/build-cli/src/commands/generate/entrypoints.ts

@@ -44,6 +44,18 @@ export default class GenerateEntrypointsCommand extends BaseCommand<
 			default: "./lib",
 			exists: true,
 		}),
+		outFileAlpha: Flags.string({
+			description: "Base file name for alpha entrypoint declaration files.",
+			default: ApiLevel.alpha,
+		}),
+		outFileBeta: Flags.string({
+			description: "Base file name for beta entrypoint declaration files.",
+			default: ApiLevel.beta,
+		}),
+		outFilePublic: Flags.string({
+			description: "Base file name for public entrypoint declaration files.",
+			default: ApiLevel.public,
+		}),
 		outFilePrefix: Flags.string({
 			description: `File name prefix for emitting entrypoint declaration files. Pattern of '${unscopedPackageNameString}' within value will be replaced with the unscoped name of this package.`,
 			default: "",
@@ -57,11 +69,28 @@ export default class GenerateEntrypointsCommand extends BaseCommand<
 	};
 
 	public async run(): Promise<void> {
-		const { mainEntrypoint, outFileSuffix } = this.flags;
+		const { mainEntrypoint, outFileSuffix, outFileAlpha, outFileBeta, outFilePublic } =
+			this.flags;
 
 		return generateEntrypoints(
 			mainEntrypoint,
 			{ pathPrefix: await getOutPathPrefix(this.flags), pathSuffix: outFileSuffix },
+			(level: Exclude<ApiLevel, typeof ApiLevel.internal>): string => {
+				switch (level) {
+					case ApiLevel.alpha: {
+						return outFileAlpha;
+					}
+					case ApiLevel.beta: {
+						return outFileBeta;
+					}
+					case ApiLevel.public: {
+						return outFilePublic;
+					}
+					default: {
+						this.error(`Unexpected ApiLevel value: ${level}`, { exit: 1 });
+					}
+				}
+			},
 			this.logger,
 		);
 	}
@@ -114,11 +143,13 @@ const generatedHeader: string = `/*!
  * THIS IS AN AUTOGENERATED FILE. DO NOT EDIT THIS FILE DIRECTLY.
  * Generated by "flub generate entrypoints" in @fluidframework/build-tools.
  */
+
 `;
 
 async function generateEntrypoints(
 	mainEntrypoint: string,
 	{ pathPrefix, pathSuffix }: { pathPrefix: string; pathSuffix: string },
+	getApiLevelDisplayName: (level: Exclude<ApiLevel, typeof ApiLevel.internal>) => string,
 	log: CommandLogger,
 ): Promise<void> {
 	/**
@@ -182,7 +213,7 @@ async function generateEntrypoints(
 			namedExports[namedExports.length - 1].trailingTrivia = "\n";
 		}
 
-		const outFile = `${pathPrefix}${apiLevel}${pathSuffix}`;
+		const outFile = `${pathPrefix}${getApiLevelDisplayName(apiLevel)}${pathSuffix}`;
 		log.info(`\tGenerating ${outFile}`);
 		const sourceFile = project.createSourceFile(outFile, undefined, {
 			overwrite: true,