Add this.exists() and this.existingResource() as an experimental feature

docs/experimental-features.md

@@ -74,6 +74,20 @@ Allows the ARM template layer to use a new schema to represent resources as an o
 ### `testFramework`
 
 Should be enabled in tandem with `assertions` experimental feature flag for expected functionality. Allows you to author client-side, offline unit-test test blocks that reference Bicep files and mock deployment parameters in a separate `test.bicep` file using the new `test` keyword. Test blocks can be run with the command *bicep test <filepath_to_file_with_test_blocks>* which runs all `assert` statements in the Bicep files referenced by the test blocks. For more information, see [Bicep Experimental Test Framework](https://github.com/Azure/bicep/issues/11967).
+### `thisNamespace`
+
+Enables the `this` namespace for accessing the current resource instance. The `this` namespace is only discoverable in resource bodies. Currently, `this.exists()` and `this.existingResource()` are available for usage. `this.exists()` returns a bool indicating the existence of the current resource. `this.existingResource()` returns null if the resource does not exist and returns the full resource if the resource exists. (Note: This feature will not work until the backend service support has been deployed) 
+```
+resource usingThis 'Microsoft...' = {
+  name: 'example'
+  location: 'eastus'
+  properties: {
+    property1: this.exists() ? 'resource exists' : 'resource does not exist'
+    property2: this.existingResource().?properties.?property2
+    property3: this.existingResource().?tags
+  }
+}
+```
 
 ### `userDefinedConstraints`
 

src/Bicep.Core.UnitTests/Configuration/ConfigurationManagerTests.cs

@@ -113,7 +113,8 @@ public void GetBuiltInConfiguration_NoParameter_ReturnsBuiltInConfigurationWithA
           "desiredStateConfiguration": false,
           "userDefinedConstraints": false,
           "deployCommands": false,
-          "multilineStringInterpolation": false
+          "multilineStringInterpolation": false,
+          "thisNamespace": false
         },
         "formatting": {
           "indentKind": "Space",
@@ -197,7 +198,8 @@ public void GetBuiltInConfiguration_DisableAllAnalyzers_ReturnsBuiltInConfigurat
           "desiredStateConfiguration": false,
           "userDefinedConstraints": false,
           "deployCommands": false,
-          "multilineStringInterpolation": false
+          "multilineStringInterpolation": false,
+          "thisNamespace": false
         },
         "formatting": {
           "indentKind": "Space",
@@ -303,7 +305,8 @@ public void GetBuiltInConfiguration_DisableAnalyzers_ReturnsBuiltInConfiguration
           "desiredStateConfiguration": false,
           "userDefinedConstraints": false,
           "deployCommands": false,
-          "multilineStringInterpolation": false
+          "multilineStringInterpolation": false,
+          "thisNamespace": false
         },
         "formatting": {
           "indentKind": "Space",
@@ -390,7 +393,8 @@ public void GetBuiltInConfiguration_EnableExperimentalFeature_ReturnsBuiltInConf
                 DesiredStateConfiguration: false,
                 UserDefinedConstraints: false,
                 DeployCommands: false,
-                MultilineStringInterpolation: false);
+                MultilineStringInterpolation: false,
+                ThisNamespace: false);
 
             configuration.WithExperimentalFeaturesEnabled(experimentalFeaturesEnabled).Should().HaveContents(/*lang=json,strict*/ """
             {
@@ -475,7 +479,8 @@ public void GetBuiltInConfiguration_EnableExperimentalFeature_ReturnsBuiltInConf
                 "desiredStateConfiguration": false,
                 "userDefinedConstraints": false,
                 "deployCommands": false,
-                "multilineStringInterpolation": false
+                "multilineStringInterpolation": false,
+                "thisNamespace": false
             },
             "formatting": {
                 "indentKind": "Space",
@@ -827,7 +832,8 @@ public void GetConfiguration_ValidCustomConfiguration_OverridesBuiltInConfigurat
                     "desiredStateConfiguration": false,
                     "userDefinedConstraints": false,
                     "deployCommands": false,
-                    "multilineStringInterpolation": false
+                    "multilineStringInterpolation": false,
+                    "thisNamespace": false
                   },
                   "formatting": {
                     "indentKind": "Space",

src/Bicep.Core.UnitTests/Features/FeatureProviderOverrides.cs

@@ -26,7 +26,8 @@ public record FeatureProviderOverrides(
     bool? DesiredStateConfigurationEnabled = default,
     bool? UserDefinedConstraintsEnabled = default,
     bool? DeployCommandsEnabled = default,
-    bool? MultilineStringInterpolationEnabled = default)
+    bool? MultilineStringInterpolationEnabled = default,
+    bool? ThisNamespaceEnabled = default)
 {
     public FeatureProviderOverrides(
         TestContext testContext,
@@ -47,7 +48,8 @@ public FeatureProviderOverrides(
         bool? DesiredStateConfigurationEnabled = default,
         bool? UserDefinedConstraintsEnabled = default,
         bool? DeployCommandsEnabled = default,
-        bool? MultilineStringInterpolationEnabled = default) : this(
+        bool? MultilineStringInterpolationEnabled = default,
+        bool? ThisNamespaceEnabled = default) : this(
             FileHelper.GetCacheRootDirectory(testContext),
             RegistryEnabled,
             SymbolicNameCodegenEnabled,
@@ -66,6 +68,7 @@ public FeatureProviderOverrides(
             DesiredStateConfigurationEnabled,
             UserDefinedConstraintsEnabled,
             DeployCommandsEnabled,
-            MultilineStringInterpolationEnabled)
+            MultilineStringInterpolationEnabled,
+            ThisNamespaceEnabled)
     { }
 }

src/Bicep.Core.UnitTests/Features/OverriddenFeatureProvider.cs

@@ -50,4 +50,6 @@ public OverriddenFeatureProvider(IFeatureProvider features, FeatureProviderOverr
     public bool DeployCommandsEnabled => overrides.DeployCommandsEnabled ?? features.DeployCommandsEnabled;
 
     public bool MultilineStringInterpolationEnabled => overrides.MultilineStringInterpolationEnabled ?? features.MultilineStringInterpolationEnabled;
+
+    public bool ThisNamespaceEnabled => overrides.ThisNamespaceEnabled ?? features.ThisNamespaceEnabled;
 }

src/Bicep.Core.UnitTests/Semantics/Namespaces/AzNamespaceTests.cs

@@ -1,14 +1,17 @@
 // Copyright (c) Microsoft Corporation.
 // Licensed under the MIT License.
 
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using Bicep.Core.Diagnostics;
 using Bicep.Core.Semantics;
 using Bicep.Core.Semantics.Namespaces;
 using Bicep.Core.TypeSystem;
 using Bicep.Core.TypeSystem.Types;
+using Bicep.Core.UnitTests.Assertions;
 using Bicep.Core.UnitTests.Utils;
 using FluentAssertions;
+using FluentAssertions.Execution;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 
 namespace Bicep.Core.UnitTests.Semantics.Namespaces