build: add task producing instrumented build for measuring code coverage

#5

package.json

@@ -5,6 +5,7 @@
   "scripts": {
     "dev": "node scripts/dev.js",
     "build": "tsc -noEmit -skipLibCheck && node scripts/esbuild.build.js production",
+    "build:coverage": "node scripts/esbuild.build.js coverage",
     "test:eslint": "eslint --cache --cache-location out/.eslintcache",
     "test:unit": "vitest --coverage"
   },
@@ -18,6 +19,7 @@
   "devDependencies": {
     "@eslint/js": "9.37.0",
     "@stylistic/eslint-plugin": "5.4.0",
+    "@types/istanbul-lib-instrument": "1.7.8",
     "@types/node": "24.6.2",
     "@vitest/coverage-v8": "3.2.4",
     "enquirer": "2.4.1",
@@ -26,6 +28,7 @@
     "eslint-plugin-perfectionist": "4.15.1",
     "eslint-plugin-wdio": "9.16.2",
     "globals": "16.4.0",
+    "istanbul-lib-instrument": "6.0.3",
     "obsidian": "1.10.0",
     "obsidian-utils": "0.10.2",
     "typescript": "5.9.3",

scripts/esbuild.build.js

@@ -5,21 +5,30 @@ import process from 'node:process'
 import esbuild from 'esbuild'
 
 import { sharedEsbuildConfig } from './esbuild.config.js'
+import { instrumentWithSourceMaps } from './utils/instrument.js'
 
 const config = sharedEsbuildConfig
 
 const prod = process.argv[2] === 'production'
+const coverage = process.argv[2] === 'coverage'
 
 const context = await esbuild.context({
   ...config,
   ...prod
     ? { minify: true, sourcemap: false }
     : {},
+  ...coverage
+    ? { minify: false, sourcemap: 'inline' }
+    : {},
 })
 
 if (prod) {
   await context.rebuild()
   process.exit(0)
+} else if (coverage) {
+  await context.rebuild()
+  instrumentWithSourceMaps('out/main.js', 'out/main.js')
+  process.exit(0)
 } else {
   await context.watch()
 }

scripts/utils/instrument.js

@@ -0,0 +1,47 @@
+// @ts-check
+import * as fs from 'node:fs'
+
+import { createInstrumenter } from 'istanbul-lib-instrument'
+
+/**
+ * Instrument a JavaScript file with Istanbul coverage instrumentation
+ * while preserving and remapping original sourcemaps
+ * @param {string} inputFile
+ * @param {string} outputFile
+ */
+export function instrumentWithSourceMaps(inputFile, outputFile) {
+  const code = fs.readFileSync(inputFile, 'utf8')
+
+  // Extract the original sourcemap from the bundled file
+  const sourceMapMatch
+    = code.match(/\/\/# sourceMappingURL=data:application\/json;base64,(.+)/)
+  if (!sourceMapMatch) throw new Error(`No sourcemap found in ${inputFile}`)
+
+  const sourceMapJson = Buffer.from(sourceMapMatch[1].trim(), 'base64').toString('utf8')
+  const originalSourceMap = JSON.parse(sourceMapJson)
+
+  const instrumenter = createInstrumenter({
+    esModules: false, // esbuild outputs Obsidian plugins as CommonJS
+    compact: false,
+    preserveComments: true,
+    produceSourceMap: true,
+    autoWrap: true,
+  })
+
+  const instrumentedCode = instrumenter.instrumentSync(
+    code,
+    inputFile,
+    originalSourceMap, // <- This is critical for sourcemaps remapping!
+  )
+  const sourceMap = instrumenter.lastSourceMap()
+
+  let output = instrumentedCode
+  if (!sourceMap) throw new Error('No source map found!')
+
+  const base64SourceMap = Buffer.from(JSON.stringify(sourceMap)).toString('base64')
+  output += `\n//# sourceMappingURL=data:application/json;base64,${base64SourceMap}`
+
+  fs.writeFileSync(outputFile, output, 'utf8')
+
+  console.log(`✓ Instrumented: ${inputFile} -> ${outputFile}`)
+}