feat: enhance warning messages about unanalyzable config field

packages/next/build/analysis/extract-const-value.ts

@@ -53,7 +53,7 @@ export function extractExportedConstValue(
         decl.id.value === exportedName &&
         decl.init
       ) {
-        return extractValue(decl.init)
+        return extractValue(decl.init, [exportedName])
       }
     }
   }
@@ -109,10 +109,38 @@ function isTemplateLiteral(node: Node): node is TemplateLiteral {
   return node.type === 'TemplateLiteral'
 }
 
-export class UnsupportedValueError extends Error {}
+export class UnsupportedValueError extends Error {
+  /** @example `config.runtime[0].value` */
+  path?: string
+
+  constructor(message: string, paths?: string[]) {
+    super(message)
+
+    // Generating "path" that looks like "config.runtime[0].value"
+    let codePath: string | undefined
+    if (paths) {
+      codePath = ''
+      for (const path of paths) {
+        if (path[0] === '[') {
+          // "array" + "[0]"
+          codePath += path
+        } else {
+          if (codePath === '') {
+            codePath = path
+          } else {
+            // "object" + ".key"
+            codePath += `.${path}`
+          }
+        }
+      }
+    }
+
+    this.path = codePath
+  }
+}
 export class NoSuchDeclarationError extends Error {}
 
-function extractValue(node: Node): any {
+function extractValue(node: Node, path?: string[]): any {
   if (isNullLiteral(node)) {
     return null
   } else if (isBooleanLiteral(node)) {
@@ -132,19 +160,26 @@ function extractValue(node: Node): any {
       case 'undefined':
         return undefined
       default:
-        throw new UnsupportedValueError()
+        throw new UnsupportedValueError(
+          `Unknown identifier "${node.value}"`,
+          path
+        )
     }
   } else if (isArrayExpression(node)) {
     // e.g. [1, 2, 3]
     const arr = []
-    for (const elem of node.elements) {
+    for (let i = 0, len = node.elements.length; i < len; i++) {
+      const elem = node.elements[i]
       if (elem) {
         if (elem.spread) {
           // e.g. [ ...a ]
-          throw new UnsupportedValueError()
+          throw new UnsupportedValueError(
+            'Unsupported spread operator in the Array Expression',
+            path
+          )
         }
 
-        arr.push(extractValue(elem.expression))
+        arr.push(extractValue(elem.expression, path && [...path, `[${i}]`]))
       } else {
         // e.g. [1, , 2]
         //         ^^
@@ -158,7 +193,10 @@ function extractValue(node: Node): any {
     for (const prop of node.properties) {
       if (!isKeyValueProperty(prop)) {
         // e.g. { ...a }
-        throw new UnsupportedValueError()
+        throw new UnsupportedValueError(
+          'Unsupported spread operator in the Object Expression',
+          path
+        )
       }
 
       let key
@@ -169,18 +207,24 @@ function extractValue(node: Node): any {
         // e.g. { "a": 1, "b": 2 }
         key = prop.key.value
       } else {
-        throw new UnsupportedValueError()
+        throw new UnsupportedValueError(
+          `Unsupported key type "${prop.key.type}" in the Object Expression`,
+          path
+        )
       }
 
-      obj[key] = extractValue(prop.value)
+      obj[key] = extractValue(prop.value, path && [...path, key])
     }
 
     return obj
   } else if (isTemplateLiteral(node)) {
     // e.g. `abc`
     if (node.expressions.length !== 0) {
       // TODO: should we add support for `${'e'}d${'g'}'e'`?
-      throw new UnsupportedValueError()
+      throw new UnsupportedValueError(
+        'Unsupported template literal with expressions',
+        path
+      )
     }
 
     // When TemplateLiteral has 0 expressions, the length of quasis is always 1.
@@ -196,6 +240,9 @@ function extractValue(node: Node): any {
 
     return cooked ?? raw
   } else {
-    throw new UnsupportedValueError()
+    throw new UnsupportedValueError(
+      `Unsupported node type "${node.type}"`,
+      path
+    )
   }
 }

packages/next/build/analysis/get-page-static-info.ts

@@ -48,7 +48,7 @@ export async function getPageStaticInfo(params: {
       config = extractExportedConstValue(swcAST, 'config')
     } catch (e) {
       if (e instanceof UnsupportedValueError) {
-        warnAboutUnsupportedValue(pageFilePath, page)
+        warnAboutUnsupportedValue(pageFilePath, page, e)
       }
       // `export config` doesn't exist, or other unknown error throw by swc, silence them
     }
@@ -235,15 +235,23 @@ let warnedAboutExperimentalEdgeApiFunctions = false
 const warnedUnsupportedValueMap = new Map<string, boolean>()
 function warnAboutUnsupportedValue(
   pageFilePath: string,
-  page: string | undefined
+  page: string | undefined,
+  error: UnsupportedValueError
 ) {
   if (warnedUnsupportedValueMap.has(pageFilePath)) {
     return
   }
+
   Log.warn(
-    `You have exported a \`config\` field in ${
-      page ? `route "${page}"` : `"${pageFilePath}"`
-    } that Next.js can't recognize, so it will be ignored. See: https://nextjs.org/docs/messages/invalid-page-config`
+    `Next.js can't recognize the exported \`config\` field in ` +
+      (page ? `route "${page}"` : `"${pageFilePath}"`) +
+      ':\n' +
+      error.message +
+      (error.path ? ` at "${error.path}"` : '') +
+      '.\n' +
+      'The default config will be used instead.\n' +
+      'Read More - https://nextjs.org/docs/messages/invalid-page-config'
   )
+
   warnedUnsupportedValueMap.set(pageFilePath, true)
 }

test/production/exported-runtimes-value-validation/index.test.ts

@@ -23,11 +23,87 @@ describe('Exported runtimes value validation', () => {
       { stdout: true, stderr: true }
     )
 
-    expect(result).toMatchObject({
-      code: 0,
-      stderr: expect.stringContaining(
-        `You have exported a \`config\` field in route "/" that Next.js can't recognize, so it will be ignored`
-      ),
-    })
+    console.log(result.stderr, result.stdout)
+
+    // The build should still succeed with invalid config being ignored
+    expect(result.code).toBe(0)
+
+    // Template Literal with Expressions
+    expect(result.stderr).toEqual(
+      expect.stringContaining(
+        'Next.js can\'t recognize the exported `config` field in route "/template-literal-with-expressions"'
+      )
+    )
+    expect(result.stderr).toEqual(
+      expect.stringContaining(
+        'Unsupported template literal with expressions at "config.runtime".'
+      )
+    )
+    // Binary Expression
+    expect(result.stderr).toEqual(
+      expect.stringContaining(
+        'Next.js can\'t recognize the exported `config` field in route "/binary-expression"'
+      )
+    )
+    expect(result.stderr).toEqual(
+      expect.stringContaining(
+        'Unsupported node type "BinaryExpression" at "config.runtime"'
+      )
+    )
+    // Spread Operator within Object Expression
+    expect(result.stderr).toEqual(
+      expect.stringContaining(
+        'Next.js can\'t recognize the exported `config` field in route "/object-spread-operator"'
+      )
+    )
+    expect(result.stderr).toEqual(
+      expect.stringContaining(
+        'Unsupported spread operator in the Object Expression at "config.runtime"'
+      )
+    )
+    // Spread Operator within Array Expression
+    expect(result.stderr).toEqual(
+      expect.stringContaining(
+        'Next.js can\'t recognize the exported `config` field in route "/array-spread-operator"'
+      )
+    )
+    expect(result.stderr).toEqual(
+      expect.stringContaining(
+        'Unsupported spread operator in the Array Expression at "config.runtime"'
+      )
+    )
+    // Unknown Identifier
+    expect(result.stderr).toEqual(
+      expect.stringContaining(
+        'Next.js can\'t recognize the exported `config` field in route "/invalid-identifier"'
+      )
+    )
+    expect(result.stderr).toEqual(
+      expect.stringContaining(
+        'Unknown identifier "runtime" at "config.runtime".'
+      )
+    )
+    // Unknown Expression Type
+    expect(result.stderr).toEqual(
+      expect.stringContaining(
+        'Next.js can\'t recognize the exported `config` field in route "/unsupported-value-type"'
+      )
+    )
+    expect(result.stderr).toEqual(
+      expect.stringContaining(
+        'Unsupported node type "CallExpression" at "config.runtime"'
+      )
+    )
+    // Unknown Object Key
+    expect(result.stderr).toEqual(
+      expect.stringContaining(
+        'Next.js can\'t recognize the exported `config` field in route "/unsupported-object-key"'
+      )
+    )
+    expect(result.stderr).toEqual(
+      expect.stringContaining(
+        'Unsupported key type "Computed" in the Object Expression at "config.runtime"'
+      )
+    )
   })
 })

test/production/exported-runtimes-value-validation/unsupported-syntax/app/pages/array-spread-operator.js

@@ -0,0 +1,7 @@
+export default function Page() {
+  return <p>hello world</p>
+}
+
+export const config = {
+  runtime: [...['nodejs']],
+}

test/production/exported-runtimes-value-validation/unsupported-syntax/app/pages/binary-expression.js

@@ -0,0 +1,7 @@
+export default function Page() {
+  return <p>hello world</p>
+}
+
+export const config = {
+  runtime: 1 + 1 > 2,
+}

test/production/exported-runtimes-value-validation/unsupported-syntax/app/pages/invalid-identifier.js

@@ -0,0 +1,9 @@
+export default function Page() {
+  return <p>hello world</p>
+}
+
+const runtime = Symbol('runtime')
+
+export const config = {
+  runtime: runtime,
+}

test/production/exported-runtimes-value-validation/unsupported-syntax/app/pages/object-spread-operator.js

@@ -0,0 +1,7 @@
+export default function Page() {
+  return <p>hello world</p>
+}
+
+export const config = {
+  runtime: { ...{ a: 'b' } },
+}

test/production/exported-runtimes-value-validation/unsupported-syntax/app/pages/unsupported-object-key.js

@@ -0,0 +1,9 @@
+export default function Page() {
+  return <p>hello world</p>
+}
+
+export const config = {
+  runtime: {
+    [Symbol('nodejs')]: true,
+  },
+}

test/production/exported-runtimes-value-validation/unsupported-syntax/app/pages/unsupported-value-type.js

@@ -0,0 +1,7 @@
+export default function Page() {
+  return <p>hello world</p>
+}
+
+export const config = {
+  runtime: Symbol('nodejs'),
+}