improvement(fluid-build): Ignore some tsconfig fields when determining incremental build

build-tools/packages/build-tools/package.json

@@ -53,6 +53,7 @@
 		"ignore": "^5.3.2",
 		"json5": "^2.2.3",
 		"lodash.isequal": "^4.5.0",
+		"microdiff": "^1.5.0",
 		"multimatch": "^5.0.0",
 		"picocolors": "^1.1.1",
 		"picomatch": "^2.3.1",

build-tools/packages/build-tools/src/fluidBuild/tasks/leaf/leafTask.ts

@@ -28,6 +28,7 @@ import { Task, TaskExec } from "../task";
 
 const { log } = defaultLogger;
 const traceTaskTrigger = registerDebug("fluid-build:task:trigger");
+const traceTaskTriggerDebug = registerDebug("fluid-build:task:trigger:debug");
 const traceTaskCheck = registerDebug("fluid-build:task:check");
 const traceTaskInitDep = registerDebug("fluid-build:task:init:dep");
 const traceTaskInitWeight = registerDebug("fluid-build:task:init:weight");
@@ -435,6 +436,11 @@ export abstract class LeafTask extends Task {
 		traceTaskTrigger(msg);
 	}
 
+	protected traceTriggerDebug(reason: string) {
+		const msg = `${this.nameColored}: [${reason}]`;
+		traceTaskTriggerDebug(msg);
+	}
+
 	protected traceError(msg: string) {
 		traceError(`${this.nameColored}: ${msg}`);
 	}

build-tools/packages/build-tools/src/fluidBuild/tasks/leaf/tscTask.ts

@@ -3,11 +3,13 @@
  * Licensed under the MIT License.
  */
 
-import * as assert from "node:assert";
+import assert from "node:assert";
 import { type BigIntStats, type Stats, existsSync, lstatSync } from "node:fs";
 import { readFile } from "node:fs/promises";
 import path from "node:path";
+
 import isEqual from "lodash.isequal";
+import diff from "microdiff";
 import * as tsTypes from "typescript";
 
 import { TscUtil, getTscUtils } from "../../tscUtils";
@@ -258,12 +260,37 @@ export class TscTask extends LeafTask {
 			path.resolve,
 		);
 
+		// The following code checks that the cached buildInfo options -- that is, the tsconfig options used to build
+		// originally -- match the current tsconfig. If they don't match, then the cache is outdated and a rebuild is
+		// needed.
+		//
+		// However, there are some tsconfig settings that don't seem to be cached in the tsbuildinfo. This makes any builds
+		// including these settings always fail this check. We special-case the properties in this set -- any differences in
+		// those fields are ignored.
+		//
+		// IMPORTANT: This is a somewhat unsafe action. Technically speaking, we don't know for sure the incremental build
+		// status when there is ANY difference between these settings. Thus the safest thing to do is to assume a rebuild is
+		// needed, Projects using these ignored settings may exhibit strange incremental build behavior.
+		//
+		// For that reason, this behavior must be enabled using the _FLUID_BUILD_ENABLE_IGNORE_TSC_OPTIONS_
+		// environment variable. To enable ignoring these settings, set the environment variable to "1".
+		const tsConfigOptionsIgnored: Set<string> =
+			process.env._FLUID_BUILD_ENABLE_IGNORE_TSC_OPTIONS_ === "1"
+				? new Set(["allowJs", "checkJs"])
+				: new Set();
+
+		for (const ignoredOption of tsConfigOptionsIgnored) {
+			// Delete the ignored option if it exists on the object
+			if (ignoredOption in tsBuildInfoOptions) {
+				this.traceTrigger(`ignoring tsBuildInfoOption: '${ignoredOption}'`);
+				delete tsBuildInfoOptions[ignoredOption];
+			}
+		}
+
 		if (!isEqual(configOptions, tsBuildInfoOptions)) {
-			this.traceTrigger(`ts option changed ${configFileFullPath}`);
-			this.traceTrigger("Config:");
-			this.traceTrigger(JSON.stringify(configOptions, undefined, 2));
-			this.traceTrigger("BuildInfo:");
-			this.traceTrigger(JSON.stringify(tsBuildInfoOptions, undefined, 2));
+			this.traceTrigger(`ts option changed in '${configFileFullPath}'`);
+			this.traceTrigger("Diff:");
+			this.traceTrigger(JSON.stringify(diff(configOptions, tsBuildInfoOptions), undefined, 2));
 			return false;
 		}
 		return true;