Show user-friendly diagnostic for Info.plist decode error

Author: Kyle-Ye

Sources/SwiftDocC/Infrastructure/Workspace/DataProviderBundleDiscovery.swift

@@ -52,13 +52,13 @@ extension DocumentationWorkspaceDataProvider where Self: FileSystemProvider {
     ///           a ``DocumentationBundle/PropertyListError`` error if the bundle's Info.plist file is invalid.
     /// - Returns: The new documentation bundle.
     private func createBundle(_ directory: FSNode.Directory, _ bundleChildren: [FSNode], options: BundleDiscoveryOptions) throws -> DocumentationBundle {
-        let info: DocumentationBundle.Info
-        
-        var infoPlistData: Data?
+        let infoPlistData: Data?
         if let infoPlistRef = findInfoPlist(bundleChildren) {
             infoPlistData = try contentsOfURL(infoPlistRef.url)
+        } else {
+            infoPlistData = nil
         }
-        info = try DocumentationBundle.Info(from: infoPlistData, bundleDiscoveryOptions: options)
+        let info = try DocumentationBundle.Info(from: infoPlistData, bundleDiscoveryOptions: options)
 
         let markupFiles = findMarkupFiles(bundleChildren, recursive: true).map { $0.url }
         let miscResources = findNonMarkupFiles(bundleChildren, recursive: true).map { $0.url }

Sources/SwiftDocC/Infrastructure/Workspace/DocumentationBundle+Info.swift

@@ -64,11 +64,16 @@ extension DocumentationBundle {
 
         enum Error: DescribedError {
             case wrongType(expected: Any.Type, actual: Any.Type)
+            case plistDecodingError(_ context: DecodingError.Context)
 
             var errorDescription: String {
                 switch self {
                 case .wrongType(let expected, let actual):
                     return "Expected '\(expected)', but found '\(actual)'."
+                case .plistDecodingError(let context):
+                    let message = "Unable to decode Info.plist file. Verify that it is correctly formed."
+                    let verboseMessage = ((context.underlyingError as? NSError)?.userInfo["NSDebugDescription"] as? String) ?? context.debugDescription
+                    return [message, verboseMessage].joined(separator: " ")
                 }
             }
         }
@@ -86,10 +91,15 @@ extension DocumentationBundle {
                     propertyListDecoder.userInfo[.bundleDiscoveryOptions] = options
                 }
 
-                self = try propertyListDecoder.decode(
-                    DocumentationBundle.Info.self,
-                    from: infoPlist
-                )
+                do {
+                    self = try propertyListDecoder.decode(
+                        DocumentationBundle.Info.self,
+                        from: infoPlist
+                    )
+                } catch DecodingError.dataCorrupted(let context) {
+                    throw Error.plistDecodingError(context)
+                }
+                
             } else {
                 try self.init(with: nil, bundleDiscoveryOptions: options)
             }

Tests/SwiftDocCTests/Infrastructure/DocumentationBundleInfoTests.swift

@@ -284,4 +284,50 @@ class DocumentationBundleInfoTests: XCTestCase {
             try DocumentationBundle.Info(bundleDiscoveryOptions: bundleDiscoveryOptions)
         )
     }
+    
+    func testDataCorruptedPlist() throws {
+        let valueMissingInvaildPlist = """
+        <plist version="1.0">
+        <dict>
+          <key>CDDefaultCodeListingLanguage</key>
+          <string>swift</string>
+          <key>CFBundleName</key>
+          <string>Example</string>
+          <key>CFBundleDisplayName</key>
+          <string>Example</string>
+          <key>CFBundleIdentifier</key>
+          <string>org.swift.docc.example</string>
+          <key>CFBundleDevelopmentRegion</key>
+          <string>en</string>
+          <key>CFBundleIconName</key>
+          <string>DocumentationIcon</string>
+          <key>CFBundleIconFile</key>
+          <string>DocumentationIcon</string>
+          <key>CFBundlePackageType</key>
+          <string>DOCS</string>
+          <key>CFBundleShortVersionString</key>
+          <string>0.1.0</string>
+          <key>CFBundleVersion</key>
+          <string>0.1.0</string>
+          <key>CDAppleDefaultAvailability</key>
+        </dict>
+        </plist>
+        """
+        
+        let valueMissingInvaildPlistData = Data(valueMissingInvaildPlist.utf8)
+        XCTAssertThrowsError(
+            try DocumentationBundle.Info(from: valueMissingInvaildPlistData),
+            "Info.plist decode didn't throw as expected"
+        ) { error in
+            XCTAssertTrue(error is DocumentationBundle.Info.Error)
+            let errorTypeChecking: Bool
+            if case DocumentationBundle.Info.Error.plistDecodingError(_) = error {
+                errorTypeChecking = true
+            } else {
+                errorTypeChecking = false
+            }
+            XCTAssertTrue(errorTypeChecking)
+            XCTAssertEqual(error.localizedDescription, "Unable to decode Info.plist file. Verify that it is correctly formed. Value missing for key inside <dict> at line 24")
+        }
+    }
 }