Handle types in first and last functions

src/Bicep.Core.IntegrationTests/Scenarios/ScopeTests.cs

@@ -187,7 +187,7 @@ param postgreSqlServerId string
 ]
 
 resource postgreSQL 'Microsoft.DBForPostgreSQL/servers@2017-12-01' existing = {
-  name: last(split(postgreSqlServerId, '/'))
+  name: last(split(postgreSqlServerId, '/'))!
   resource database 'databases' = [for (item, index) in PSQL_DATABASES: {
     name: item.database.name
     properties: {

src/Bicep.Core.Samples/Files/user_submitted/201/cloud-shell-vnet/main.bicep

@@ -241,7 +241,7 @@ resource privateDnsZoneARecord 'Microsoft.Network/privateDnsZones/A@2020-01-01'
     ttl: 3600
     aRecords: [
       {
-        ipv4Address: first(first(privateEndpoint.properties.customDnsConfigs).ipAddresses)
+        ipv4Address: first(first(privateEndpoint.properties.customDnsConfigs)!.ipAddresses)!
       }
     ]
   }

src/Bicep.Core.Samples/Files/user_submitted/201/private-aks-cluster/aks.bicep

@@ -157,7 +157,7 @@ var aadProfileConfiguration = {
   tenantID: aadProfileTenantId
 }
 
-var virtualNetworkName = last(split(virtualNetworkId, '/'))
+var virtualNetworkName = last(split(virtualNetworkId, '/'))!
 
 resource virtualNetwork 'Microsoft.Network/virtualNetworks@2020-08-01' existing = {
   name: virtualNetworkName

src/Bicep.Core.Samples/Files/user_submitted/201/private-aks-cluster/jumpbox.bicep

@@ -81,8 +81,8 @@ var linuxConfiguration = {
   provisionVMAgent: true
 }
 
-var virtualNetworkName = last(split(virtualNetworkId, '/'))
-var logAnalyticsWorkspaceName = last(split(logAnalyticsWorkspaceId, '/'))
+var virtualNetworkName = last(split(virtualNetworkId, '/'))!
+var logAnalyticsWorkspaceName = last(split(logAnalyticsWorkspaceId, '/'))!
 
 resource logAnalyticsWorkspace 'Microsoft.OperationalInsights/workspaces@2020-10-01' existing = {
   name: logAnalyticsWorkspaceName

src/Bicep.Core.Samples/Files/user_submitted/201/vm-windows-with-custom-script-extension/main.bicep

@@ -250,7 +250,7 @@ var virtualMachineExtensionCustomScript = {
   fileUris: [
     virtualMachineExtensionCustomScriptUri
   ]
-  commandToExecute: 'powershell -ExecutionPolicy Unrestricted -File ./${last(split(virtualMachineExtensionCustomScriptUri, '/'))}'
+  commandToExecute: 'powershell -ExecutionPolicy Unrestricted -File ./${last(split(virtualMachineExtensionCustomScriptUri, '/'))!}'
 }
 
 resource vmext 'Microsoft.Compute/virtualMachines/extensions@2020-06-01' = {

src/Bicep.Core.Samples/Files/user_submitted/201/wvd-create-hostpool/modules/managedDisks-customimagevm.bicep

@@ -125,7 +125,7 @@ param aadJoin bool = false
 param intune bool = false
 
 var emptyArray = []
-var domain_var = ((domain == '') ? last(split(administratorAccountUsername, '@')) : domain)
+var domain_var = ((domain == '') ? last(split(administratorAccountUsername, '@'))! : domain)
 var storageAccountType = rdshVMDiskType
 var newNsgName = '${rdshPrefix}nsg-${guidValue}'
 var nsgId = (createNetworkSecurityGroup ? resourceId('Microsoft.Network/networkSecurityGroups', newNsgName) : networkSecurityGroupId)

src/Bicep.Core.Samples/Files/user_submitted/201/wvd-create-hostpool/modules/managedDisks-customvhdvm.bicep

@@ -125,7 +125,7 @@ param aadJoin bool = false
 param intune bool = false
 
 var emptyArray = []
-var domain_var = ((domain == '') ? last(split(administratorAccountUsername, '@')) : domain)
+var domain_var = ((domain == '') ? last(split(administratorAccountUsername, '@'))! : domain)
 var storageAccountType = rdshVMDiskType
 var imageName_var = '${rdshPrefix}image'
 var newNsgName = '${rdshPrefix}nsg-${guidValue}'

src/Bicep.Core.Samples/Files/user_submitted/201/wvd-create-hostpool/modules/managedDisks-galleryvm.bicep

@@ -125,7 +125,7 @@ param aadJoin bool = false
 param intune bool = false
 
 var emptyArray = []
-var domain_var = ((domain == '') ? last(split(administratorAccountUsername, '@')) : domain)
+var domain_var = ((domain == '') ? last(split(administratorAccountUsername, '@'))! : domain)
 var storageAccountType = rdshVMDiskType
 var newNsgName = '${rdshPrefix}nsg-${guidValue}'
 var nsgId = (createNetworkSecurityGroup ? resourceId('Microsoft.Network/networkSecurityGroups', newNsgName) : networkSecurityGroupId)

src/Bicep.Core.Samples/Files/user_submitted/201/wvd-create-hostpool/modules/unmanagedDisks-customvhdvm.bicep

@@ -125,7 +125,7 @@ param aadJoin bool = false
 param intune bool = false
 
 var emptyArray = []
-var domain_var = ((domain == '') ? last(split(administratorAccountUsername, '@')) : domain)
+var domain_var = ((domain == '') ? last(split(administratorAccountUsername, '@'))! : domain)
 var storageAccountName = split(split(vmImageVhdUri, '/')[2], '.')[0]
 var storageaccount = concat(resourceId(storageAccountResourceGroupName, 'Microsoft.Storage/storageAccounts', storageAccountName))
 var newNsgName = '${rdshPrefix}nsg-${guidValue}'

src/Bicep.Core.UnitTests/TypeSystem/FunctionResolverTests.cs

@@ -146,6 +146,20 @@ public void ShouldNotFlatten(TypeSymbol typeToFlatten, params string[] diagnosti
                 .Should().HaveDiagnostics(diagnosticMessages.Select(message => ("BCP309", DiagnosticLevel.Error, message)));
         }
 
+        [DataTestMethod]
+        [DynamicData(nameof(GetFirstTestCases), DynamicDataSourceType.Method)]
+        public void FirstReturnsCorrectType(TypeSymbol inputArrayType, TypeSymbol expected)
+        {
+            TypeValidator.AreTypesAssignable(EvaluateFunction("first", new List<TypeSymbol> { inputArrayType }, new[] { new FunctionArgumentSyntax(TestSyntaxFactory.CreateArray(Enumerable.Empty<SyntaxBase>())) }).Type, expected).Should().BeTrue();
+        }
+
+        [DataTestMethod]
+        [DynamicData(nameof(GetLastTestCases), DynamicDataSourceType.Method)]
+        public void LastReturnsCorrectType(TypeSymbol inputArrayType, TypeSymbol expected)
+        {
+            TypeValidator.AreTypesAssignable(EvaluateFunction("last", new List<TypeSymbol> { inputArrayType }, new[] { new FunctionArgumentSyntax(TestSyntaxFactory.CreateArray(Enumerable.Empty<SyntaxBase>())) }).Type, expected).Should().BeTrue();
+        }
+
         private FunctionResult EvaluateFunction(string functionName, IList<TypeSymbol> argumentTypes, FunctionArgumentSyntax[] arguments)
         {
             var matches = GetMatches(functionName, argumentTypes, out _, out _);
@@ -227,6 +241,64 @@ private static IEnumerable<object[]> GetFlattenNegativeTestCases() => new[]
             },
         };
 
+        private static IEnumerable<object[]> GetFirstTestCases() => new[]
+        {
+            // first(resourceGroup[]) -> resourceGroup
+            new object[] { 
+                new TypedArrayType(LanguageConstants.CreateResourceScopeReference(ResourceScope.ResourceGroup), default),
+                TypeHelper.CreateTypeUnion(LanguageConstants.Null, LanguageConstants.CreateResourceScopeReference(ResourceScope.ResourceGroup))
+            },
+            // first(['test', 3]) -> 'test'
+            new object[] {
+                new TupleType("['test', 3]",
+                    ImmutableArray.Create<ITypeReference>(
+                        new StringLiteralType("test"),
+                        new IntegerLiteralType(3)
+                    ),
+                default),
+                new StringLiteralType("test")
+            },
+            // first([resourceGroup, subscription]) => resourceGroup
+            new object[] {
+                new TupleType("[resourceGroup, subscription]",
+                    ImmutableArray.Create<ITypeReference>(
+                        LanguageConstants.CreateResourceScopeReference(ResourceScope.ResourceGroup),
+                        LanguageConstants.CreateResourceScopeReference(ResourceScope.Subscription)
+                    ),
+                default),
+                LanguageConstants.CreateResourceScopeReference(ResourceScope.ResourceGroup)
+            }
+        };
+
+        private static IEnumerable<object[]> GetLastTestCases() => new[]
+        {
+            // last(resourceGroup[]) -> resourceGroup
+            new object[] { 
+                new TypedArrayType(LanguageConstants.CreateResourceScopeReference(ResourceScope.ResourceGroup), default),
+                TypeHelper.CreateTypeUnion(LanguageConstants.Null, LanguageConstants.CreateResourceScopeReference(ResourceScope.ResourceGroup))
+            },
+            // last(['test', 3]) -> 3
+            new object[] {
+                new TupleType("['test', 3]",
+                    ImmutableArray.Create<ITypeReference>(
+                        new StringLiteralType("test"),
+                        new IntegerLiteralType(3)
+                    ),
+                default),
+                new IntegerLiteralType(3)
+            },
+            // last([resourceGroup, subscription]) => subscription
+            new object[] {
+                new TupleType("[resourceGroup, subscription]",
+                    ImmutableArray.Create<ITypeReference>(
+                        LanguageConstants.CreateResourceScopeReference(ResourceScope.ResourceGroup),
+                        LanguageConstants.CreateResourceScopeReference(ResourceScope.Subscription)
+                    ),
+                default),
+                LanguageConstants.CreateResourceScopeReference(ResourceScope.Subscription)
+            }
+        };
+
         private static IEnumerable<object[]> GetLiteralTransformations()
         {
             FunctionArgumentSyntax ToFunctionArgumentSyntax(object argument) => argument switch
@@ -240,18 +312,19 @@ private static IEnumerable<object[]> GetLiteralTransformations()
                 _ => throw new NotImplementedException($"Unable to transform {argument} to a literal syntax node.")
             };
 
-            TypeSymbol ToTypeLiteral(object argument) => argument switch
+            TypeSymbol ToTypeLiteral(object? argument) => argument switch
             {
                 string str => new StringLiteralType(str),
                 string[] strArray => new TupleType($"[{string.Join(", ", strArray.Select(str => $"'{str}'"))}]", strArray.Select(str => new StringLiteralType(str)).ToImmutableArray<ITypeReference>(), default),
                 int intVal => new IntegerLiteralType(intVal),
                 int[] intArray => new TupleType("", intArray.Select(@int => new IntegerLiteralType(@int)).ToImmutableArray<ITypeReference>(), default),
                 bool boolVal => new BooleanLiteralType(boolVal),
                 bool[] boolArray => new TupleType("", boolArray.Select(@bool => new BooleanLiteralType(@bool)).ToImmutableArray<ITypeReference>(), default),
+                null => LanguageConstants.Null,
                 _ => throw new NotImplementedException($"Unable to transform {argument} to a type literal.")
             };
 
-            object[] CreateRow(object returnedLiteral, string functionName, params object[] argumentLiterals)
+            object[] CreateRow(object? returnedLiteral, string functionName, params object[] argumentLiterals)
             {
                 var argumentLiteralSyntaxes = argumentLiterals.Select(ToFunctionArgumentSyntax).ToArray();
                 var argumentTypeLiterals = argumentLiterals.Select(ToTypeLiteral).ToList();
@@ -298,7 +371,9 @@ object[] CreateRow(object returnedLiteral, string functionName, params object[]
                 CreateRow(new[] { "pop" }, "intersection", new[] { "fizz", "buzz", "pop" }, new[] { "snap", "crackle", "pop" }),
                 CreateRow(new[] { "fizz", "buzz", "pop" }, "union", new[] { "fizz", "buzz" }, new[] { "pop" }),
                 CreateRow("fizz", "first", new[] { new[] { "fizz", "buzz", "pop" } }),
+                CreateRow(null, "first", new[] { Array.Empty<string>() }),
                 CreateRow("pop", "last", new[] { new[] { "fizz", "buzz", "pop" } }),
+                CreateRow(null, "last", new[] { Array.Empty<string>() }),
                 CreateRow(0, "indexOf", new[] { "fizz", "buzz", "pop", "fizz" }, "fizz"),
                 CreateRow(3, "lastIndexOf", new[] { "fizz", "buzz", "pop", "fizz" }, "fizz"),
                 CreateRow(1, "min", new[] { 10, 4, 1, 6 }),

src/Bicep.Core/Semantics/Namespaces/SystemNamespaceType.cs

@@ -280,8 +280,15 @@ private static IEnumerable<FunctionOverload> GetSystemOverloads(IFeatureProvider
                 .Build();
 
             yield return new FunctionOverloadBuilder("first")
-                // TODO even with non-literal types, some type arithmetic could be performed
-                .WithReturnResultBuilder(TryDeriveLiteralReturnType("first", LanguageConstants.Any), LanguageConstants.Any)
+                .WithReturnResultBuilder((binder, fileResolver, diagnostics, arguments, argumentTypes) =>
+                {
+                    return new(argumentTypes[0] switch 
+                    {
+                        TupleType tupleType => tupleType.Items.FirstOrDefault()?.Type ?? LanguageConstants.Null,
+                        ArrayType arrayType => TypeHelper.CreateTypeUnion(LanguageConstants.Null, arrayType.Item.Type),
+                        _ => LanguageConstants.Any
+                    });
+                }, LanguageConstants.Any)
                 .WithGenericDescription(FirstDescription)
                 .WithDescription("Returns the first element of the array.")
                 .WithRequiredParameter("array", LanguageConstants.Array, "The value to retrieve the first element.")
@@ -295,8 +302,15 @@ private static IEnumerable<FunctionOverload> GetSystemOverloads(IFeatureProvider
                 .Build();
 
             yield return new FunctionOverloadBuilder("last")
-                // TODO even with non-literal types, some type arithmetic could be performed
-                .WithReturnResultBuilder(TryDeriveLiteralReturnType("last", LanguageConstants.Any), LanguageConstants.Any)
+                .WithReturnResultBuilder((binder, fileResolver, diagnostics, arguments, argumentTypes) =>
+                {
+                    return new(argumentTypes[0] switch 
+                    {
+                        TupleType tupleType => tupleType.Items.LastOrDefault()?.Type ?? LanguageConstants.Null,
+                        ArrayType arrayType => TypeHelper.CreateTypeUnion(LanguageConstants.Null, arrayType.Item.Type),
+                        _ => LanguageConstants.Any
+                    });
+                }, LanguageConstants.Any)
                 .WithGenericDescription(LastDescription)
                 .WithDescription("Returns the last element of the array.")
                 .WithRequiredParameter("array", LanguageConstants.Array, "The value to retrieve the last element.")