Fix a few minor warnings (#449)

* Resolve deprecation warning in test for a renamed SwiftDocC property

* Resolve warning about inferred type for an empty array literal

* Resolve another deprecation warning in test for a renamed SwiftDocC property

* Resolve warning about comparing non-optional value to nil

* Resolve another warning about comparing non-optional value to nil

Since the filter has no effect the second `count > 1` check is redundant

Author: d-ronnqvist

Sources/SwiftDocC/Model/Rendering/Symbol/AvailabilityRenderMetadataItem.swift

@@ -1,7 +1,7 @@
 /*
  This source file is part of the Swift.org open source project
 
- Copyright (c) 2021 Apple Inc. and the Swift project authors
+ Copyright (c) 2021-2023 Apple Inc. and the Swift project authors
  Licensed under Apache License v2.0 with Runtime Library Exception
 
  See https://swift.org/LICENSE.txt for license information
@@ -141,11 +141,8 @@ public struct AvailabilityRenderItem: Codable, Hashable, Equatable {
     }
 
     init?(_ availability: Metadata.Availability, current: PlatformVersion?) {
-        if availability.introduced == nil {
-            // FIXME: Deprecated/Beta markings need platform versions to display properly in Swift-DocC-Render (rdar://56897597)
-            // Fill in the appropriate values here when that's fixed (https://github.com/apple/swift-docc/issues/441)
-            return nil
-        }
+        // FIXME: Deprecated/Beta markings need platform versions to display properly in Swift-DocC-Render (rdar://56897597)
+        // Fill in the appropriate values here when that's fixed (https://github.com/apple/swift-docc/issues/441)
 
         let platformName = PlatformName(metadataPlatform: availability.platform)
         name = platformName?.displayName

Sources/SwiftDocC/Semantics/DirectiveInfrastructure/AutomaticDirectiveConvertible.swift

@@ -1,7 +1,7 @@
 /*
  This source file is part of the Swift.org open source project
 
- Copyright (c) 2022 Apple Inc. and the Swift project authors
+ Copyright (c) 2022-2023 Apple Inc. and the Swift project authors
  Licensed under Apache License v2.0 with Runtime Library Exception
 
  See https://swift.org/LICENSE.txt for license information
@@ -239,7 +239,7 @@ extension AutomaticDirectiveConvertible {
 
                 guard let parsedDirective = parsedDirective else {
                     if childDirective.storedAsArray && !childDirective.storedAsOptional {
-                        childDirective.setValue(on: self, to: [parsedDirective].compactMap { $0 })
+                        childDirective.setValue(on: self, to: [DirectiveConvertible.Type]())
                     }
 
                     continue

Sources/SwiftDocC/Semantics/Metadata/Metadata.swift

@@ -150,39 +150,36 @@ public final class Metadata: Semantic, AutomaticDirectiveConvertible {
 
         let categorizedAvailability = Dictionary(grouping: availability, by: \.platform)
 
-        for availabilityAttrs in categorizedAvailability.values {
-            guard availabilityAttrs.count > 1 else {
+        for duplicateIntroduced in categorizedAvailability.values {
+            guard duplicateIntroduced.count > 1 else {
                 continue
             }
+            
+            for availability in duplicateIntroduced {
+                let diagnostic = Diagnostic(
+                    source: availability.originalMarkup.nameLocation?.source,
+                    severity: .warning,
+                    range: availability.originalMarkup.range,
+                    identifier: "org.swift.docc.\(Metadata.Availability.self).DuplicateIntroduced",
+                    summary: "Duplicate \(Metadata.Availability.directiveName.singleQuoted) directive with 'introduced' argument",
+                    explanation: """
+                    A documentation page can only contain a single 'introduced' version for each platform.
+                    """
+                )
 
-            let duplicateIntroduced = availabilityAttrs.filter({ $0.introduced != nil })
-            if duplicateIntroduced.count > 1 {
-                for avail in duplicateIntroduced {
-                    let diagnostic = Diagnostic(
-                        source: avail.originalMarkup.nameLocation?.source,
-                        severity: .warning,
-                        range: avail.originalMarkup.range,
-                        identifier: "org.swift.docc.\(Metadata.Availability.self).DuplicateIntroduced",
-                        summary: "Duplicate \(Metadata.Availability.directiveName.singleQuoted) directive with 'introduced' argument",
-                        explanation: """
-                        A documentation page can only contain a single 'introduced' version for each platform.
-                        """
-                    )
-
-                    guard let range = avail.originalMarkup.range else {
-                        problems.append(Problem(diagnostic: diagnostic))
-                        continue
-                    }
+                guard let range = availability.originalMarkup.range else {
+                    problems.append(Problem(diagnostic: diagnostic))
+                    continue
+                }
 
-                    let solution = Solution(
-                        summary: "Remove extraneous \(Metadata.Availability.directiveName.singleQuoted) directive",
-                        replacements: [
-                            Replacement(range: range, replacement: "")
-                        ]
-                    )
+                let solution = Solution(
+                    summary: "Remove extraneous \(Metadata.Availability.directiveName.singleQuoted) directive",
+                    replacements: [
+                        Replacement(range: range, replacement: "")
+                    ]
+                )
 
-                    problems.append(Problem(diagnostic: diagnostic, possibleSolutions: [solution]))
-                }
+                problems.append(Problem(diagnostic: diagnostic, possibleSolutions: [solution]))
             }
         }