add 'extends' schema support and surface config chain diagnostics in VSCode

src/Bicep.Core/Configuration/BicepConfigurationChain.cs

@@ -3,6 +3,7 @@
 
 using System.Collections.Immutable;
 using Bicep.Core.Diagnostics;
+using Bicep.IO.Abstraction;
 
 namespace Bicep.Core.Configuration;
 
@@ -69,6 +70,17 @@ public IEnumerable<IDiagnostic> GetAllDiagnostics()
         return this.aggregatedDiagnostics.Value;
     }
 
+    /// <summary>
+    /// Returns diagnostics grouped by the config file URI they originated from.
+    /// Built-in default layers (no <see cref="IBicepConfiguration.ConfigFileUri"/>) are excluded.
+    /// </summary>
+    public DiagnosticsPerFile EnumerateDiagnosticsPerFile()
+        => this.layers
+            .Where(layer => !layer.IsBuiltIn)
+            .Select(layer => new KeyValuePair<IOUri, ImmutableArray<IDiagnostic>>(
+                layer.ConfigFileUri!,
+                layer.GetDiagnostics().ToImmutableArray()));
+
     /// <summary>
     /// The number of configuration files in the chain, including the built-in defaults.
     /// </summary>

src/Bicep.Core/Configuration/IBicepConfigurationChain.cs

@@ -17,6 +17,12 @@ public interface IBicepConfigurationChain
     /// </summary>
     IBicepConfiguration GetEffectiveConfiguration();
 
+    /// <summary>
+    /// Returns diagnostics grouped by the config file URI they originated from.
+    /// Only user-defined config files are included (built-in defaults are excluded).
+    /// </summary>
+    DiagnosticsPerFile EnumerateDiagnosticsPerFile();
+
     /// <summary>
     /// The number of configuration files in the chain.
     /// </summary>

src/Bicep.Core/Diagnostics/GlobalUsings.cs

@@ -0,0 +1,8 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+global using DiagnosticsPerFile =
+    System.Collections.Generic.IEnumerable<
+        System.Collections.Generic.KeyValuePair<
+            Bicep.IO.Abstraction.IOUri,
+            System.Collections.Immutable.ImmutableArray<Bicep.Core.Diagnostics.IDiagnostic>>>;

src/Bicep.LangServer.UnitTests/Configuration/BicepConfigChangeHandlerTests.cs

@@ -194,6 +194,42 @@ public void RefreshCompilationOfSourceFilesInWorkspace_WithEmptySourceFile_Shoul
             diagnostics.Should().BeNullOrEmpty();
         }
 
+        [TestMethod]
+        public void HandleBicepConfigOpenEvent_WithCyclicExtends_PublishesBCP454ToConfigFileUri()
+        {
+            var mockFileSystem = new MockFileSystem();
+            mockFileSystem.AddFile("/a/bicepconfig.json", """{ "extends": "./b/bicepconfig.json" }""");
+            mockFileSystem.AddFile("/a/b/bicepconfig.json", """{ "extends": "../bicepconfig.json" }""");
+
+            PublishDiagnosticsParams? receivedParams = null;
+            var document = BicepCompilationManagerHelper.CreateMockDocument(p => receivedParams = p);
+            ILanguageServerFacade server = BicepCompilationManagerHelper.CreateMockServer(document).Object;
+
+            var fileExplorer = new FileSystemFileExplorer(mockFileSystem);
+            var bicepConfigManager = new BicepConfigurationManager(fileExplorer);
+            var configurationManager = new ConfigurationManager(fileExplorer, bicepConfigManager);
+            var workspace = new ActiveSourceFileSet();
+            var bicepCompilationManager = new BicepCompilationManager(
+                server,
+                BicepCompilationManagerHelper.CreateEmptyCompilationProvider(configurationManager),
+                workspace,
+                BicepCompilationManagerHelper.CreateMockScheduler().Object,
+                new SourceFileFactory(configurationManager, BicepTestConstants.FeatureProviderFactory, BicepTestConstants.AuxiliaryFileCache, BicepTestConstants.FileExplorer),
+                BicepTestConstants.AuxiliaryFileCache);
+
+            var lifecycleManager = new BicepConfigLifecycleManager(
+                bicepCompilationManager,
+                configurationManager,
+                bicepConfigManager,
+                server);
+
+            var configUri = DocumentUri.From(InMemoryFileResolver.GetFileUri("/a/bicepconfig.json"));
+            lifecycleManager.HandleBicepConfigOpenEvent(configUri);
+
+            receivedParams.Should().NotBeNull();
+            receivedParams!.Diagnostics.Should().ContainSingle(d => d.Code!.Value.String == "BCP454");
+        }
+
         [TestMethod]
         public void RefreshCompilationOfSourceFilesInWorkspace_WithoutBicepConfigFile_ShouldUseDefaultConfigAndRefreshCompilation()
         {
@@ -246,7 +282,8 @@ private void RefreshCompilationOfSourceFilesInWorkspace(string bicepFileContents
 
             var workspace = new ActiveSourceFileSet();
             var fileExplorer = new FileSystemFileExplorer(mockFileSystem);
-            var configurationManager = new ConfigurationManager(fileExplorer, new BicepConfigurationManager(fileExplorer));
+            var bicepConfigManager = new BicepConfigurationManager(fileExplorer);
+            var configurationManager = new ConfigurationManager(fileExplorer, bicepConfigManager);
             var sourceFileFactory = new SourceFileFactory(configurationManager, BicepTestConstants.FeatureProviderFactory, BicepTestConstants.AuxiliaryFileCache, BicepTestConstants.FileExplorer);
             var bicepCompilationManager = new BicepCompilationManager(
                 server,
@@ -259,7 +296,9 @@ private void RefreshCompilationOfSourceFilesInWorkspace(string bicepFileContents
 
             var bicepConfigLifecycleManager = new BicepConfigLifecycleManager(
                 bicepCompilationManager,
-                configurationManager);
+                configurationManager,
+                bicepConfigManager,
+                server);
 
             bicepConfigLifecycleManager.RefreshCompilationOfSourceFilesInWorkspace();
 

src/Bicep.LangServer/BicepConfig/BicepConfigLifecycleManager.cs

@@ -2,21 +2,33 @@
 // Licensed under the MIT License.
 
 using Bicep.Core.Configuration;
+using Bicep.Core.Diagnostics;
 using Bicep.LanguageServer.Compilation;
+using Bicep.LanguageServer.Extensions;
 using OmniSharp.Extensions.LanguageServer.Protocol;
+using OmniSharp.Extensions.LanguageServer.Protocol.Document;
+using OmniSharp.Extensions.LanguageServer.Protocol.Models;
+using OmniSharp.Extensions.LanguageServer.Protocol.Server;
+using LspDiagnostic = OmniSharp.Extensions.LanguageServer.Protocol.Models.Diagnostic;
 
 namespace Bicep.LanguageServer.BicepConfig
 {
     public class BicepConfigLifecycleManager : IBicepConfigLifecycleManager
     {
         private readonly ICompilationManager compilationManager;
         private readonly ConfigurationManager configurationManager;
+        private readonly IBicepConfigurationManager bicepConfigurationManager;
+        private readonly ILanguageServerFacade server;
 
         public BicepConfigLifecycleManager(ICompilationManager compilationManager,
-                           ConfigurationManager configurationManager)
+                           ConfigurationManager configurationManager,
+                           IBicepConfigurationManager bicepConfigurationManager,
+                           ILanguageServerFacade server)
         {
             this.compilationManager = compilationManager;
             this.configurationManager = configurationManager;
+            this.bicepConfigurationManager = bicepConfigurationManager;
+            this.server = server;
         }
 
         public void RefreshCompilationOfSourceFilesInWorkspace()
@@ -29,6 +41,7 @@ public void RefreshCompilationOfSourceFilesInWorkspace()
         public void HandleBicepConfigOpenEvent(DocumentUri documentUri)
         {
             HandleBicepConfigOpenOrChangeEvent(documentUri);
+            PublishConfigDiagnostics(documentUri);
         }
 
         public void HandleBicepConfigChangeEvent(DocumentUri documentUri)
@@ -44,9 +57,68 @@ private void HandleBicepConfigOpenOrChangeEvent(DocumentUri documentUri)
             => configurationManager.RefreshConfigCacheEntry(documentUri.ToIOUri());
 
         public void HandleBicepConfigSaveEvent(DocumentUri documentUri)
-            => configurationManager.RefreshConfigCacheEntry(documentUri.ToIOUri());
+        {
+            configurationManager.RefreshConfigCacheEntry(documentUri.ToIOUri());
+            PublishConfigDiagnostics(documentUri);
+        }
 
         public void HandleBicepConfigCloseEvent(DocumentUri documentUri)
-            => configurationManager.RemoveConfigCacheEntry(documentUri.ToIOUri());
+        {
+            configurationManager.RemoveConfigCacheEntry(documentUri.ToIOUri());
+
+            // Clear squiggles when the file is closed.
+            server.TextDocument.PublishDiagnostics(new PublishDiagnosticsParams
+            {
+                Uri = documentUri,
+                Diagnostics = new Container<LspDiagnostic>()
+            });
+        }
+
+        private void PublishConfigDiagnostics(DocumentUri documentUri)
+        {
+            var chain = bicepConfigurationManager.GetConfigurationChain(documentUri.ToIOUri());
+
+            // Always publish to documentUri first — covers chain-level errors (cycle, too deep)
+            // stored on the built-in fallback layer, and clears stale squiggles on the active file.
+            var effectiveDiagnostics = chain.GetEffectiveConfiguration().GetDiagnostics();
+            server.TextDocument.PublishDiagnostics(new PublishDiagnosticsParams
+            {
+                Uri = documentUri,
+                Diagnostics = new Container<LspDiagnostic>(effectiveDiagnostics.Select(d => new LspDiagnostic
+                {
+                    Severity = ToLspSeverity(d.Level),
+                    Code = new DiagnosticCode(d.Code),
+                    Message = d.Message,
+                    Range = new OmniSharp.Extensions.LanguageServer.Protocol.Models.Range(0, 0, 0, 0),
+                    Source = "bicep"
+                }))
+            });
+
+            // Publish diagnostics for every user-layer config file in the chain — including empty
+            // arrays so the client clears stale squiggles for files that no longer have errors.
+            foreach (var (fileUri, diagnostics) in chain.EnumerateDiagnosticsPerFile())
+            {
+                server.TextDocument.PublishDiagnostics(new PublishDiagnosticsParams
+                {
+                    Uri = DocumentUri.From(fileUri.ToUri()),
+                    Diagnostics = new Container<LspDiagnostic>(diagnostics.Select(d => new LspDiagnostic
+                    {
+                        Severity = ToLspSeverity(d.Level),
+                        Code = new DiagnosticCode(d.Code),
+                        Message = d.Message,
+                        Range = new OmniSharp.Extensions.LanguageServer.Protocol.Models.Range(0, 0, 0, 0),
+                        Source = "bicep"
+                    }))
+                });
+            }
+        }
+
+        private static DiagnosticSeverity ToLspSeverity(DiagnosticLevel level) => level switch
+        {
+            DiagnosticLevel.Error => DiagnosticSeverity.Error,
+            DiagnosticLevel.Warning => DiagnosticSeverity.Warning,
+            DiagnosticLevel.Info => DiagnosticSeverity.Information,
+            _ => DiagnosticSeverity.Hint
+        };
     }
 }

src/Bicep.LangServer/IServiceCollectionExtensions.cs

@@ -54,6 +54,7 @@ BicepLangServerOptions bicepLangServerOptions
         .AddSingleton<IModuleRestoreScheduler, ModuleRestoreScheduler>()
         .AddSingleton<IAzResourceProvider, AzResourceProvider>()
         .AddSingleton<IBicepConfigLifecycleManager, BicepConfigLifecycleManager>()
+        .AddSingleton<IBicepConfigurationManager, BicepConfigurationManager>()
         .AddSingleton<IDeploymentCollectionProvider, DeploymentCollectionProvider>()
         .AddSingleton<IDeploymentOperationsCache, DeploymentOperationsCache>()
         .AddSingleton<IDeploymentFileCompilationCache, DeploymentFileCompilationCache>()

src/vscode-bicep/resources/configuration/bicepconfig.schema.json

@@ -157,6 +157,11 @@
   "type": "object",
   "default": {},
   "properties": {
+    "extends": {
+      "title": "Extends",
+      "description": "Relative path to a base bicepconfig.json to inherit settings from. Absolute paths are not allowed.",
+      "type": "string"
+    },
     "cloud": {
       "title": "Cloud",
       "type": "object",