From 7f4c41fc2c6ce55f8f1b87a5516573d99a9beec0 Mon Sep 17 00:00:00 2001
From: Rob Mensching <rob@firegiant.com>
Date: Mon, 19 Apr 2021 16:12:28 -0700
Subject: Prefer IReadOnlyCollection<> or IReadOnlyList<> over IEnumerable<>

Closes wixtoolset/issues#6422
---
 src/WixToolset.Core.Burn/Bind/BindBundleCommand.cs         |  4 ++--
 .../ExtensibilityServices/BurnBackendHelper.cs             |  2 +-
 .../ExtensionCacheManagerExtensionCommandLine.cs           |  2 +-
 .../ExtensibilityServices/WindowsInstallerBackendHelper.cs |  2 +-
 src/WixToolset.Core/Bind/ExtractEmbeddedFiles.cs           |  2 +-
 src/WixToolset.Core/Bind/ExtractEmbeddedFilesCommand.cs    |  2 +-
 src/WixToolset.Core/Bind/ResolveFieldsCommand.cs           |  2 +-
 src/WixToolset.Core/BindContext.cs                         | 14 +++++++-------
 src/WixToolset.Core/BindResult.cs                          |  4 ++--
 src/WixToolset.Core/Binder.cs                              |  2 +-
 src/WixToolset.Core/CommandLine/BuildCommand.cs            | 10 +++++-----
 src/WixToolset.Core/CommandLine/CompileCommand.cs          |  2 +-
 src/WixToolset.Core/CompileContext.cs                      |  2 +-
 src/WixToolset.Core/CompilerCore.cs                        |  2 +-
 src/WixToolset.Core/DecompileContext.cs                    |  2 +-
 src/WixToolset.Core/DecompileResult.cs                     |  2 +-
 src/WixToolset.Core/ExtensibilityServices/BackendHelper.cs |  2 +-
 .../ExtensibilityServices/ExtensionManager.cs              |  2 +-
 src/WixToolset.Core/LayoutContext.cs                       |  8 ++++----
 src/WixToolset.Core/LibraryContext.cs                      |  8 ++++----
 src/WixToolset.Core/LinkContext.cs                         |  7 +++----
 src/WixToolset.Core/PreprocessContext.cs                   |  4 ++--
 src/WixToolset.Core/PreprocessResult.cs                    |  2 +-
 src/WixToolset.Core/ResolveContext.cs                      | 10 +++++-----
 src/WixToolset.Core/ResolveFileResult.cs                   |  2 +-
 src/WixToolset.Core/ResolveResult.cs                       |  4 ++--
 src/WixToolset.Core/Resolver.cs                            |  2 +-
 .../ExamplePreprocessorExtensionAndCommandLine.cs          |  2 +-
 .../ExampleWindowsInstallerBackendExtension.cs             |  2 +-
 src/test/WixToolsetTest.CoreIntegration/LinkerFixture.cs   |  5 +++--
 30 files changed, 58 insertions(+), 58 deletions(-)

diff --git a/src/WixToolset.Core.Burn/Bind/BindBundleCommand.cs b/src/WixToolset.Core.Burn/Bind/BindBundleCommand.cs
index 37fc17f9..d8062008 100644
--- a/src/WixToolset.Core.Burn/Bind/BindBundleCommand.cs
+++ b/src/WixToolset.Core.Burn/Bind/BindBundleCommand.cs
@@ -73,9 +73,9 @@ namespace WixToolset.Core.Burn
 
         private IVariableResolver VariableResolver { get; }
 
-        public IEnumerable<IFileTransfer> FileTransfers { get; private set; }
+        public IReadOnlyCollection<IFileTransfer> FileTransfers { get; private set; }
 
-        public IEnumerable<ITrackedFile> TrackedFiles { get; private set; }
+        public IReadOnlyCollection<ITrackedFile> TrackedFiles { get; private set; }
 
         public WixOutput Wixout { get; private set; }
 
diff --git a/src/WixToolset.Core.Burn/ExtensibilityServices/BurnBackendHelper.cs b/src/WixToolset.Core.Burn/ExtensibilityServices/BurnBackendHelper.cs
index a4f37d10..e4d2b0c9 100644
--- a/src/WixToolset.Core.Burn/ExtensibilityServices/BurnBackendHelper.cs
+++ b/src/WixToolset.Core.Burn/ExtensibilityServices/BurnBackendHelper.cs
@@ -46,7 +46,7 @@ namespace WixToolset.Core.Burn.ExtensibilityServices
 
         public IResolvedDirectory CreateResolvedDirectory(string directoryParent, string name) => this.backendHelper.CreateResolvedDirectory(directoryParent, name);
 
-        public IEnumerable<ITrackedFile> ExtractEmbeddedFiles(IEnumerable<IExpectedExtractFile> embeddedFiles) => this.backendHelper.ExtractEmbeddedFiles(embeddedFiles);
+        public IReadOnlyList<ITrackedFile> ExtractEmbeddedFiles(IEnumerable<IExpectedExtractFile> embeddedFiles) => this.backendHelper.ExtractEmbeddedFiles(embeddedFiles);
 
         public string GenerateIdentifier(string prefix, params string[] args) => this.backendHelper.GenerateIdentifier(prefix, args);
 
diff --git a/src/WixToolset.Core.ExtensionCache/ExtensionCacheManagerExtensionCommandLine.cs b/src/WixToolset.Core.ExtensionCache/ExtensionCacheManagerExtensionCommandLine.cs
index 76587830..2a603adf 100644
--- a/src/WixToolset.Core.ExtensionCache/ExtensionCacheManagerExtensionCommandLine.cs
+++ b/src/WixToolset.Core.ExtensionCache/ExtensionCacheManagerExtensionCommandLine.cs
@@ -21,7 +21,7 @@ namespace WixToolset.Core.ExtensionCache
 
         private IServiceProvider ServiceProvider { get; }
 
-        public override IEnumerable<ExtensionCommandLineSwitch> CommandLineSwitches => new ExtensionCommandLineSwitch[]
+        public override IReadOnlyCollection<ExtensionCommandLineSwitch> CommandLineSwitches => new ExtensionCommandLineSwitch[]
         {
             new ExtensionCommandLineSwitch { Switch = "extension", Description = "Manage extension cache." },
         };
diff --git a/src/WixToolset.Core.WindowsInstaller/ExtensibilityServices/WindowsInstallerBackendHelper.cs b/src/WixToolset.Core.WindowsInstaller/ExtensibilityServices/WindowsInstallerBackendHelper.cs
index ca1cd0e3..8305b5e6 100644
--- a/src/WixToolset.Core.WindowsInstaller/ExtensibilityServices/WindowsInstallerBackendHelper.cs
+++ b/src/WixToolset.Core.WindowsInstaller/ExtensibilityServices/WindowsInstallerBackendHelper.cs
@@ -37,7 +37,7 @@ namespace WixToolset.Core.WindowsInstaller.ExtensibilityServices
 
         public IResolvedDirectory CreateResolvedDirectory(string directoryParent, string name) => this.backendHelper.CreateResolvedDirectory(directoryParent, name);
 
-        public IEnumerable<ITrackedFile> ExtractEmbeddedFiles(IEnumerable<IExpectedExtractFile> embeddedFiles) => this.backendHelper.ExtractEmbeddedFiles(embeddedFiles);
+        public IReadOnlyList<ITrackedFile> ExtractEmbeddedFiles(IEnumerable<IExpectedExtractFile> embeddedFiles) => this.backendHelper.ExtractEmbeddedFiles(embeddedFiles);
 
         public string GenerateIdentifier(string prefix, params string[] args) => this.backendHelper.GenerateIdentifier(prefix, args);
 
diff --git a/src/WixToolset.Core/Bind/ExtractEmbeddedFiles.cs b/src/WixToolset.Core/Bind/ExtractEmbeddedFiles.cs
index 35c8a2f0..a0798e62 100644
--- a/src/WixToolset.Core/Bind/ExtractEmbeddedFiles.cs
+++ b/src/WixToolset.Core/Bind/ExtractEmbeddedFiles.cs
@@ -50,7 +50,7 @@ namespace WixToolset.Core.Bind
             return extractPath;
         }
 
-        public IEnumerable<ExpectedExtractFile> GetExpectedEmbeddedFiles()
+        public IReadOnlyList<ExpectedExtractFile> GetExpectedEmbeddedFiles()
         {
             var files = new List<ExpectedExtractFile>();
 
diff --git a/src/WixToolset.Core/Bind/ExtractEmbeddedFilesCommand.cs b/src/WixToolset.Core/Bind/ExtractEmbeddedFilesCommand.cs
index 981a991f..ec2d8896 100644
--- a/src/WixToolset.Core/Bind/ExtractEmbeddedFilesCommand.cs
+++ b/src/WixToolset.Core/Bind/ExtractEmbeddedFilesCommand.cs
@@ -17,7 +17,7 @@ namespace WixToolset.Core.Bind
             this.FilesWithEmbeddedFiles = embeddedFiles;
         }
 
-        public IEnumerable<ITrackedFile> TrackedFiles { get; private set; }
+        public IReadOnlyList<ITrackedFile> TrackedFiles { get; private set; }
 
         private IBackendHelper BackendHelper { get; }
 
diff --git a/src/WixToolset.Core/Bind/ResolveFieldsCommand.cs b/src/WixToolset.Core/Bind/ResolveFieldsCommand.cs
index 2738ac6c..794208e5 100644
--- a/src/WixToolset.Core/Bind/ResolveFieldsCommand.cs
+++ b/src/WixToolset.Core/Bind/ResolveFieldsCommand.cs
@@ -36,7 +36,7 @@ namespace WixToolset.Core.Bind
 
         public bool AllowUnresolvedVariables { private get; set; }
 
-        public IEnumerable<DelayedField> DelayedFields { get; private set; }
+        public IReadOnlyCollection<DelayedField> DelayedFields { get; private set; }
 
         public void Execute()
         {
diff --git a/src/WixToolset.Core/BindContext.cs b/src/WixToolset.Core/BindContext.cs
index 09454824..052382f1 100644
--- a/src/WixToolset.Core/BindContext.cs
+++ b/src/WixToolset.Core/BindContext.cs
@@ -18,7 +18,7 @@ namespace WixToolset.Core
 
         public IServiceProvider ServiceProvider { get; }
 
-        public IEnumerable<BindPath> BindPaths { get; set; }
+        public IReadOnlyCollection<BindPath> BindPaths { get; set; }
 
         public string BurnStubPath { get; set; }
 
@@ -28,15 +28,15 @@ namespace WixToolset.Core
 
         public CompressionLevel? DefaultCompressionLevel { get; set; }
 
-        public IEnumerable<IDelayedField> DelayedFields { get; set; }
+        public IReadOnlyCollection<IDelayedField> DelayedFields { get; set; }
 
-        public IEnumerable<IExpectedExtractFile> ExpectedEmbeddedFiles { get; set; }
+        public IReadOnlyCollection<IExpectedExtractFile> ExpectedEmbeddedFiles { get; set; }
 
-        public IEnumerable<IBinderExtension> Extensions { get; set; }
+        public IReadOnlyCollection<IBinderExtension> Extensions { get; set; }
 
-        public IEnumerable<IFileSystemExtension> FileSystemExtensions { get; set; }
+        public IReadOnlyCollection<IFileSystemExtension> FileSystemExtensions { get; set; }
 
-        public IEnumerable<string> Ices { get; set; }
+        public IReadOnlyCollection<string> Ices { get; set; }
 
         public string IntermediateFolder { get; set; }
 
@@ -54,7 +54,7 @@ namespace WixToolset.Core
 
         public int? ResolvedLcid { get; set; }
 
-        public IEnumerable<string> SuppressIces { get; set; }
+        public IReadOnlyCollection<string> SuppressIces { get; set; }
 
         public bool SuppressValidation { get; set; }
 
diff --git a/src/WixToolset.Core/BindResult.cs b/src/WixToolset.Core/BindResult.cs
index 4edade7a..9785484c 100644
--- a/src/WixToolset.Core/BindResult.cs
+++ b/src/WixToolset.Core/BindResult.cs
@@ -11,9 +11,9 @@ namespace WixToolset.Core
     {
         private bool disposed;
 
-        public IEnumerable<IFileTransfer> FileTransfers { get; set; }
+        public IReadOnlyCollection<IFileTransfer> FileTransfers { get; set; }
 
-        public IEnumerable<ITrackedFile> TrackedFiles { get; set; }
+        public IReadOnlyCollection<ITrackedFile> TrackedFiles { get; set; }
 
         public WixOutput Wixout { get; set; }
 
diff --git a/src/WixToolset.Core/Binder.cs b/src/WixToolset.Core/Binder.cs
index 090b5d32..204ab6ee 100644
--- a/src/WixToolset.Core/Binder.cs
+++ b/src/WixToolset.Core/Binder.cs
@@ -58,7 +58,7 @@ namespace WixToolset.Core
 
             var backendFactories = extensionManager.GetServices<IBackendFactory>();
 
-            var entrySection = context.IntermediateRepresentation.Sections[0];
+            var entrySection = context.IntermediateRepresentation.Sections.First();
 
             foreach (var factory in backendFactories)
             {
diff --git a/src/WixToolset.Core/CommandLine/BuildCommand.cs b/src/WixToolset.Core/CommandLine/BuildCommand.cs
index 59aa2f1f..5f618b81 100644
--- a/src/WixToolset.Core/CommandLine/BuildCommand.cs
+++ b/src/WixToolset.Core/CommandLine/BuildCommand.cs
@@ -216,7 +216,7 @@ namespace WixToolset.Core.CommandLine
             }
         }
 
-        private IEnumerable<Intermediate> CompilePhase(IDictionary<string, string> preprocessorVariables, IEnumerable<SourceFile> sourceFiles, CancellationToken cancellationToken)
+        private IReadOnlyList<Intermediate> CompilePhase(IDictionary<string, string> preprocessorVariables, IEnumerable<SourceFile> sourceFiles, CancellationToken cancellationToken)
         {
             var intermediates = new List<Intermediate>();
 
@@ -257,7 +257,7 @@ namespace WixToolset.Core.CommandLine
             return intermediates;
         }
 
-        private Intermediate LibraryPhase(IEnumerable<Intermediate> intermediates, IEnumerable<Localization> localizations, bool bindFiles, IEnumerable<IBindPath> bindPaths, CancellationToken cancellationToken)
+        private Intermediate LibraryPhase(IReadOnlyCollection<Intermediate> intermediates, IReadOnlyCollection<Localization> localizations, bool bindFiles, IReadOnlyCollection<IBindPath> bindPaths, CancellationToken cancellationToken)
         {
             var context = this.ServiceProvider.GetService<ILibraryContext>();
             context.BindFiles = bindFiles;
@@ -302,7 +302,7 @@ namespace WixToolset.Core.CommandLine
             return linker.Link(context);
         }
 
-        private void BindPhase(Intermediate output, IEnumerable<Localization> localizations, IEnumerable<string> filterCultures, string cabCachePath, IEnumerable<IBindPath> bindPaths, CancellationToken cancellationToken)
+        private void BindPhase(Intermediate output, IReadOnlyCollection<Localization> localizations, IReadOnlyCollection<string> filterCultures, string cabCachePath, IReadOnlyCollection<IBindPath> bindPaths, CancellationToken cancellationToken)
         {
             var intermediateFolder = this.IntermediateFolder;
             if (String.IsNullOrEmpty(intermediateFolder))
@@ -405,7 +405,7 @@ namespace WixToolset.Core.CommandLine
             return Array.Empty<Intermediate>();
         }
 
-        private IEnumerable<Localization> LoadLocalizationFiles(IEnumerable<string> locFiles, IDictionary<string, string> preprocessorVariables, CancellationToken cancellationToken)
+        private IReadOnlyList<Localization> LoadLocalizationFiles(IEnumerable<string> locFiles, IDictionary<string, string> preprocessorVariables, CancellationToken cancellationToken)
         {
             var localizations = new List<Localization>();
             var parser = this.ServiceProvider.GetService<ILocalizationParser>();
@@ -787,7 +787,7 @@ namespace WixToolset.Core.CommandLine
                 return Data.OutputType.Unknown;
             }
 
-            public IEnumerable<string> CalculateFilterCultures()
+            public IReadOnlyList<string> CalculateFilterCultures()
             {
                 var result = new List<string>();
 
diff --git a/src/WixToolset.Core/CommandLine/CompileCommand.cs b/src/WixToolset.Core/CommandLine/CompileCommand.cs
index 54d1b6f1..6e31b241 100644
--- a/src/WixToolset.Core/CommandLine/CompileCommand.cs
+++ b/src/WixToolset.Core/CommandLine/CompileCommand.cs
@@ -42,7 +42,7 @@ namespace WixToolset.Core.CommandLine
 
         private Platform Platform { get; }
 
-        public IEnumerable<string> IncludeSearchPaths { get; }
+        public IReadOnlyCollection<string> IncludeSearchPaths { get; }
 
         public bool ShowLogo => throw new NotImplementedException();
 
diff --git a/src/WixToolset.Core/CompileContext.cs b/src/WixToolset.Core/CompileContext.cs
index 2aeb3998..d84d7aac 100644
--- a/src/WixToolset.Core/CompileContext.cs
+++ b/src/WixToolset.Core/CompileContext.cs
@@ -21,7 +21,7 @@ namespace WixToolset.Core
 
         public string CompilationId { get; set; }
 
-        public IEnumerable<ICompilerExtension> Extensions { get; set; }
+        public IReadOnlyCollection<ICompilerExtension> Extensions { get; set; }
 
         public Platform Platform { get; set; }
 
diff --git a/src/WixToolset.Core/CompilerCore.cs b/src/WixToolset.Core/CompilerCore.cs
index 8705cacd..727084eb 100644
--- a/src/WixToolset.Core/CompilerCore.cs
+++ b/src/WixToolset.Core/CompilerCore.cs
@@ -1048,7 +1048,7 @@ namespace WixToolset.Core
         {
             var section = new IntermediateSection(id, type, compilationId);
 
-            this.intermediate.Sections.Add(section);
+            this.intermediate.AddSection(section);
 
             return section;
         }
diff --git a/src/WixToolset.Core/DecompileContext.cs b/src/WixToolset.Core/DecompileContext.cs
index 056785d6..a7ec03fd 100644
--- a/src/WixToolset.Core/DecompileContext.cs
+++ b/src/WixToolset.Core/DecompileContext.cs
@@ -22,7 +22,7 @@ namespace WixToolset.Core
 
         public OutputType DecompileType { get; set; }
 
-        public IEnumerable<IDecompilerExtension> Extensions { get; set; }
+        public IReadOnlyCollection<IDecompilerExtension> Extensions { get; set; }
 
         public string ExtractFolder { get; set; }
 
diff --git a/src/WixToolset.Core/DecompileResult.cs b/src/WixToolset.Core/DecompileResult.cs
index 8c9285ba..fc24cab7 100644
--- a/src/WixToolset.Core/DecompileResult.cs
+++ b/src/WixToolset.Core/DecompileResult.cs
@@ -11,7 +11,7 @@ namespace WixToolset.Core
     {
         public XDocument Document { get; set; }
 
-        public IEnumerable<string> ExtractedFilePaths { get; set; }
+        public IReadOnlyCollection<string> ExtractedFilePaths { get; set; }
 
         public Platform? Platform { get; set; }
     }
diff --git a/src/WixToolset.Core/ExtensibilityServices/BackendHelper.cs b/src/WixToolset.Core/ExtensibilityServices/BackendHelper.cs
index 539cec78..cfa78623 100644
--- a/src/WixToolset.Core/ExtensibilityServices/BackendHelper.cs
+++ b/src/WixToolset.Core/ExtensibilityServices/BackendHelper.cs
@@ -73,7 +73,7 @@ namespace WixToolset.Core.ExtensibilityServices
             };
         }
 
-        public IEnumerable<ITrackedFile> ExtractEmbeddedFiles(IEnumerable<IExpectedExtractFile> embeddedFiles)
+        public IReadOnlyList<ITrackedFile> ExtractEmbeddedFiles(IEnumerable<IExpectedExtractFile> embeddedFiles)
         {
             var command = new ExtractEmbeddedFilesCommand(this, embeddedFiles);
             command.Execute();
diff --git a/src/WixToolset.Core/ExtensibilityServices/ExtensionManager.cs b/src/WixToolset.Core/ExtensibilityServices/ExtensionManager.cs
index 31184c33..2340ed9e 100644
--- a/src/WixToolset.Core/ExtensibilityServices/ExtensionManager.cs
+++ b/src/WixToolset.Core/ExtensibilityServices/ExtensionManager.cs
@@ -94,7 +94,7 @@ namespace WixToolset.Core.ExtensibilityServices
             }
         }
 
-        public IEnumerable<T> GetServices<T>() where T : class
+        public IReadOnlyCollection<T> GetServices<T>() where T : class
         {
             if (!this.loadedExtensionsByType.TryGetValue(typeof(T), out var extensions))
             {
diff --git a/src/WixToolset.Core/LayoutContext.cs b/src/WixToolset.Core/LayoutContext.cs
index deb5057f..4b8c7b99 100644
--- a/src/WixToolset.Core/LayoutContext.cs
+++ b/src/WixToolset.Core/LayoutContext.cs
@@ -17,13 +17,13 @@ namespace WixToolset.Core
 
         public IServiceProvider ServiceProvider { get; }
 
-        public IEnumerable<ILayoutExtension> Extensions { get; set; }
+        public IReadOnlyCollection<ILayoutExtension> Extensions { get; set; }
 
-        public IEnumerable<IFileSystemExtension> FileSystemExtensions { get; set; }
+        public IReadOnlyCollection<IFileSystemExtension> FileSystemExtensions { get; set; }
 
-        public IEnumerable<IFileTransfer> FileTransfers { get; set; }
+        public IReadOnlyCollection<IFileTransfer> FileTransfers { get; set; }
 
-        public IEnumerable<ITrackedFile> TrackedFiles { get; set; }
+        public IReadOnlyCollection<ITrackedFile> TrackedFiles { get; set; }
 
         public string IntermediateFolder { get; set; }
 
diff --git a/src/WixToolset.Core/LibraryContext.cs b/src/WixToolset.Core/LibraryContext.cs
index 62d4e70c..e701cadf 100644
--- a/src/WixToolset.Core/LibraryContext.cs
+++ b/src/WixToolset.Core/LibraryContext.cs
@@ -23,15 +23,15 @@ namespace WixToolset.Core
 
         public bool BindFiles { get; set; }
 
-        public IEnumerable<IBindPath> BindPaths { get; set; }
+        public IReadOnlyCollection<IBindPath> BindPaths { get; set; }
 
-        public IEnumerable<ILibrarianExtension> Extensions { get; set; }
+        public IReadOnlyCollection<ILibrarianExtension> Extensions { get; set; }
 
         public string LibraryId { get; set; }
 
-        public IEnumerable<Localization> Localizations { get; set; }
+        public IReadOnlyCollection<Localization> Localizations { get; set; }
 
-        public IEnumerable<Intermediate> Intermediates { get; set; }
+        public IReadOnlyCollection<Intermediate> Intermediates { get; set; }
 
         public CancellationToken CancellationToken { get; set; }
     }
diff --git a/src/WixToolset.Core/LinkContext.cs b/src/WixToolset.Core/LinkContext.cs
index 528d0f0f..b99bb9c4 100644
--- a/src/WixToolset.Core/LinkContext.cs
+++ b/src/WixToolset.Core/LinkContext.cs
@@ -8,7 +8,6 @@ namespace WixToolset.Core
     using WixToolset.Data;
     using WixToolset.Extensibility;
     using WixToolset.Extensibility.Data;
-    using WixToolset.Extensibility.Services;
 
     internal class LinkContext : ILinkContext
     {
@@ -19,13 +18,13 @@ namespace WixToolset.Core
 
         public IServiceProvider ServiceProvider { get; }
 
-        public IEnumerable<ILinkerExtension> Extensions { get; set; }
+        public IReadOnlyCollection<ILinkerExtension> Extensions { get; set; }
 
-        public IEnumerable<IExtensionData> ExtensionData { get; set; }
+        public IReadOnlyCollection<IExtensionData> ExtensionData { get; set; }
 
         public OutputType ExpectedOutputType { get; set; }
 
-        public IEnumerable<Intermediate> Intermediates { get; set; }
+        public IReadOnlyCollection<Intermediate> Intermediates { get; set; }
 
         public ISymbolDefinitionCreator SymbolDefinitionCreator { get; set; }
 
diff --git a/src/WixToolset.Core/PreprocessContext.cs b/src/WixToolset.Core/PreprocessContext.cs
index 0b735a7c..986045ff 100644
--- a/src/WixToolset.Core/PreprocessContext.cs
+++ b/src/WixToolset.Core/PreprocessContext.cs
@@ -18,11 +18,11 @@ namespace WixToolset.Core
 
         public IServiceProvider ServiceProvider { get; }
 
-        public IEnumerable<IPreprocessorExtension> Extensions { get; set; }
+        public IReadOnlyCollection<IPreprocessorExtension> Extensions { get; set; }
 
         public Platform Platform { get; set; }
 
-        public IEnumerable<string> IncludeSearchPaths { get; set; }
+        public IReadOnlyCollection<string> IncludeSearchPaths { get; set; }
 
         public string SourcePath { get; set; }
 
diff --git a/src/WixToolset.Core/PreprocessResult.cs b/src/WixToolset.Core/PreprocessResult.cs
index 7126f049..83b29a90 100644
--- a/src/WixToolset.Core/PreprocessResult.cs
+++ b/src/WixToolset.Core/PreprocessResult.cs
@@ -10,6 +10,6 @@ namespace WixToolset.Core
     {
         public XDocument Document { get; set; }
 
-        public IEnumerable<IIncludedFile> IncludedFiles { get; set; }
+        public IReadOnlyCollection<IIncludedFile> IncludedFiles { get; set; }
     }
 }
diff --git a/src/WixToolset.Core/ResolveContext.cs b/src/WixToolset.Core/ResolveContext.cs
index 185b556c..638c8079 100644
--- a/src/WixToolset.Core/ResolveContext.cs
+++ b/src/WixToolset.Core/ResolveContext.cs
@@ -19,19 +19,19 @@ namespace WixToolset.Core
 
         public IServiceProvider ServiceProvider { get; }
 
-        public IEnumerable<IBindPath> BindPaths { get; set; }
+        public IReadOnlyCollection<IBindPath> BindPaths { get; set; }
 
-        public IEnumerable<IResolverExtension> Extensions { get; set; }
+        public IReadOnlyCollection<IResolverExtension> Extensions { get; set; }
 
-        public IEnumerable<IExtensionData> ExtensionData { get; set; }
+        public IReadOnlyCollection<IExtensionData> ExtensionData { get; set; }
 
-        public IEnumerable<string> FilterCultures { get; set; }
+        public IReadOnlyCollection<string> FilterCultures { get; set; }
 
         public string IntermediateFolder { get; set; }
 
         public Intermediate IntermediateRepresentation { get; set; }
 
-        public IEnumerable<Localization> Localizations { get; set; }
+        public IReadOnlyCollection<Localization> Localizations { get; set; }
 
         public IVariableResolver VariableResolver { get; set; }
 
diff --git a/src/WixToolset.Core/ResolveFileResult.cs b/src/WixToolset.Core/ResolveFileResult.cs
index 12b31d54..f6e201d4 100644
--- a/src/WixToolset.Core/ResolveFileResult.cs
+++ b/src/WixToolset.Core/ResolveFileResult.cs
@@ -9,6 +9,6 @@ namespace WixToolset.Core
     {
         public string Path { get; set; }
 
-        public IEnumerable<string> CheckedPaths { get; set; }
+        public IReadOnlyCollection<string> CheckedPaths { get; set; }
     }
 }
diff --git a/src/WixToolset.Core/ResolveResult.cs b/src/WixToolset.Core/ResolveResult.cs
index 38b432b0..fa8e09b7 100644
--- a/src/WixToolset.Core/ResolveResult.cs
+++ b/src/WixToolset.Core/ResolveResult.cs
@@ -14,9 +14,9 @@ namespace WixToolset.Core
 
         public int? PackageLcid { get; set; }
 
-        public IEnumerable<IDelayedField> DelayedFields { get; set; }
+        public IReadOnlyCollection<IDelayedField> DelayedFields { get; set; }
 
-        public IEnumerable<IExpectedExtractFile> ExpectedEmbeddedFiles { get; set; }
+        public IReadOnlyCollection<IExpectedExtractFile> ExpectedEmbeddedFiles { get; set; }
 
         public Intermediate IntermediateRepresentation { get; set; }
     }
diff --git a/src/WixToolset.Core/Resolver.cs b/src/WixToolset.Core/Resolver.cs
index f4cb2fd6..e93f8e1b 100644
--- a/src/WixToolset.Core/Resolver.cs
+++ b/src/WixToolset.Core/Resolver.cs
@@ -77,7 +77,7 @@ namespace WixToolset.Core
 
             var filesWithEmbeddedFiles = new ExtractEmbeddedFiles();
 
-            IEnumerable<DelayedField> delayedFields;
+            IReadOnlyCollection<DelayedField> delayedFields;
             {
                 var command = new ResolveFieldsCommand();
                 command.Messaging = this.Messaging;
diff --git a/src/test/Example.Extension/ExamplePreprocessorExtensionAndCommandLine.cs b/src/test/Example.Extension/ExamplePreprocessorExtensionAndCommandLine.cs
index 49f68de5..7244798a 100644
--- a/src/test/Example.Extension/ExamplePreprocessorExtensionAndCommandLine.cs
+++ b/src/test/Example.Extension/ExamplePreprocessorExtensionAndCommandLine.cs
@@ -12,7 +12,7 @@ namespace Example.Extension
     {
         private string exampleValueFromCommandLine;
 
-        public IEnumerable<ExtensionCommandLineSwitch> CommandLineSwitches => throw new NotImplementedException();
+        public IReadOnlyCollection<ExtensionCommandLineSwitch> CommandLineSwitches => throw new NotImplementedException();
 
         public ExamplePreprocessorExtensionAndCommandLine()
         {
diff --git a/src/test/Example.Extension/ExampleWindowsInstallerBackendExtension.cs b/src/test/Example.Extension/ExampleWindowsInstallerBackendExtension.cs
index 87b7855c..afccc56f 100644
--- a/src/test/Example.Extension/ExampleWindowsInstallerBackendExtension.cs
+++ b/src/test/Example.Extension/ExampleWindowsInstallerBackendExtension.cs
@@ -9,7 +9,7 @@ namespace Example.Extension
 
     internal class ExampleWindowsInstallerBackendExtension : BaseWindowsInstallerBackendBinderExtension
     {
-        public override IEnumerable<TableDefinition> TableDefinitions => ExampleTableDefinitions.All;
+        public override IReadOnlyCollection<TableDefinition> TableDefinitions => ExampleTableDefinitions.All;
 
         public override bool TryProcessSymbol(IntermediateSection section, IntermediateSymbol symbol, WindowsInstallerData output, TableDefinitionCollection tableDefinitions)
         {
diff --git a/src/test/WixToolsetTest.CoreIntegration/LinkerFixture.cs b/src/test/WixToolsetTest.CoreIntegration/LinkerFixture.cs
index 676d7d87..cfe4d3f1 100644
--- a/src/test/WixToolsetTest.CoreIntegration/LinkerFixture.cs
+++ b/src/test/WixToolsetTest.CoreIntegration/LinkerFixture.cs
@@ -3,6 +3,7 @@
 
 namespace WixToolsetTest.CoreIntegration
 {
+    using System;
     using System.IO;
     using System.Linq;
     using WixBuildTools.TestSupport;
@@ -29,8 +30,8 @@ namespace WixToolsetTest.CoreIntegration
 
             var creator = serviceProvider.GetService<ISymbolDefinitionCreator>();
             var context = serviceProvider.GetService<ILinkContext>();
-            context.Extensions = Enumerable.Empty<WixToolset.Extensibility.ILinkerExtension>();
-            context.ExtensionData = Enumerable.Empty<WixToolset.Extensibility.IExtensionData>();
+            context.Extensions = Array.Empty<WixToolset.Extensibility.ILinkerExtension>();
+            context.ExtensionData = Array.Empty<WixToolset.Extensibility.IExtensionData>();
             context.Intermediates = new[] { intermediate1, intermediate2 };
             context.SymbolDefinitionCreator = creator;
 
-- 
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