Add support for causes with causes

lib/index.js

@@ -241,20 +241,28 @@ function createByline(state, stats) {
  */
 function createCauseLines(state, cause) {
   const lines = ['  ' + state.bold + '[cause]' + state.normalIntensity + ':']
-  /** @type {string | undefined} */
-  let stackValue
+  let foundReasonableCause = false
 
   if (cause !== null && typeof cause === 'object') {
-    stackValue =
+    const stackValue =
       ('stack' in cause ? String(cause.stack) : undefined) ||
       ('message' in cause ? String(cause.message) : undefined)
+
+    if (typeof stackValue === 'string') {
+      foundReasonableCause = true
+
+      const stackLines = stackValue.split(eol)
+      stackLines[0] = '    ' + stackLines[0]
+
+      lines.push(...stackLines)
+
+      if ('cause' in cause && cause.cause) {
+        lines.push(...createCauseLines(state, cause.cause))
+      }
+    }
   }
 
-  if (typeof stackValue === 'string') {
-    const stackLines = stackValue.split(eol)
-    stackLines[0] = '    ' + stackLines[0]
-    lines.push(...stackLines)
-  } else {
+  if (!foundReasonableCause) {
     lines.push('    ' + cause)
   }
 

test.js

@@ -50,6 +50,10 @@ try {
 }
 /* eslint-enable no-undef */
 
+// @ts-expect-error: it’s assigned.
+const causedCause = new Error('Boom!', {cause: exception})
+causedCause.stack = cleanStack(causedCause.stack, 3)
+
 test('reporter', async function () {
   const mod = await import('./index.js')
 
@@ -413,6 +417,30 @@ test('reporter', async function () {
     'should support a `message.cause`'
   )
 
+  file = new VFile()
+
+  file.message('Something failed terribly', {
+    cause: causedCause
+  })
+
+  assert.equal(
+    strip(reporter(file)),
+    [
+      ' warning Something failed terribly',
+      '  [cause]:',
+      '    Error: Boom!',
+      '    at test.js:1:1',
+      '    at ModuleJob.run (module_job:1:1)',
+      '  [cause]:',
+      '    ReferenceError: variable is not defined',
+      '    at test.js:1:1',
+      '    at ModuleJob.run (module_job:1:1)',
+      '',
+      '⚠ 1 warning'
+    ].join('\n'),
+    'should support a `message.cause`, w/ another cause'
+  )
+
   file = new VFile()
   let message = file.message('Something failed terribly')
   message.cause = 'Boom!'
@@ -442,7 +470,7 @@ test('reporter', async function () {
       '',
       '⚠ 1 warning'
     ].join('\n'),
-    'should support a `message.cause` set to a n object w/o stack'
+    'should support a `message.cause` set to an object w/o stack'
   )
 
   file = new VFile()
@@ -458,7 +486,7 @@ test('reporter', async function () {
       '',
       '⚠ 1 warning'
     ].join('\n'),
-    'should support a `message.cause` set to a n object w/o stack or message'
+    'should support a `message.cause` set to an object w/o stack or message'
   )
 
   /** @type {Text} */