Use target rather than expression type as narrowing base case

src/Bicep.Core.IntegrationTests/ScenarioTests.cs

@@ -6258,4 +6258,39 @@ public void Recursive_types_generate_diagnostics_where_referenced()
             ("BCP062", DiagnosticLevel.Error, """The referenced declaration with name "invalidRecursiveObjectType" is not valid."""),
         ]);
     }
+
+    // https://github.com/Azure/bicep/issues/15114
+    [TestMethod]
+    public void Test_Issue15114()
+    {
+        var result = CompilationHelper.Compile("""
+            param recoverDeleted bool
+
+            resource KeyVaultResource 'Microsoft.KeyVault/vaults@2023-07-01' = {
+              name: 'vault'
+              location: resourceGroup().location
+              properties: recoverDeleted
+                ? {
+                  createMode: 'recover'
+                  sku: {
+                    name: 'standard'
+                    family: 'A'
+                  }
+                  tenantId: tenant().tenantId
+                }
+                : {
+                  createMode: 'default'
+                  sku: {
+                    name: 'standard'
+                    family: 'A'
+                  }
+                  tenantId: tenant().tenantId
+                }
+            }
+
+            output keyvaultUri string = KeyVaultResource.properties.vaultUri
+            """);
+
+        result.ExcludingLinterDiagnostics().Should().NotHaveAnyDiagnostics();
+    }
 }

src/Bicep.Core.Samples/Files/baselines/Functions_LF/main.symbols.bicep

@@ -23,13 +23,13 @@ func objReturnType(name string) object => {
 
 func arrayReturnType(name string) array => [
 //@[21:025) Local name. Type: string. Declaration start char: 21, length: 11
-//@[05:020) Function arrayReturnType. Type: string => [string]. Declaration start char: 0, length: 53
+//@[05:020) Function arrayReturnType. Type: string => [any]. Declaration start char: 0, length: 53
   name
 ]
 
 func asdf(name string) array => [
 //@[10:014) Local name. Type: string. Declaration start char: 10, length: 11
-//@[05:009) Function asdf. Type: string => ['asdf', string]. Declaration start char: 0, length: 51
+//@[05:009) Function asdf. Type: string => [any, any]. Declaration start char: 0, length: 51
   'asdf'
   name
 ]
@@ -43,10 +43,10 @@ func typedArg(input string[]) positiveInt => length(input)
 //@[05:013) Function typedArg. Type: string[] => int. Declaration start char: 0, length: 58
 
 func barTest() array => ['abc', 'def']
-//@[05:012) Function barTest. Type: () => ['abc', 'def']. Declaration start char: 0, length: 38
+//@[05:012) Function barTest. Type: () => [any, any]. Declaration start char: 0, length: 38
 func fooTest() array => map(barTest(), a => 'Hello ${a}!')
 //@[39:040) Local a. Type: any. Declaration start char: 39, length: 1
-//@[05:012) Function fooTest. Type: () => string[]. Declaration start char: 0, length: 58
+//@[05:012) Function fooTest. Type: () => array. Declaration start char: 0, length: 58
 
 output fooValue array = fooTest()
 //@[07:015) Output fooValue. Type: array. Declaration start char: 0, length: 33

src/Bicep.Core.Samples/Files/baselines/InvalidFunctions_LF/main.symbols.bicep

@@ -1,9 +1,9 @@
 func useRuntimeFunction() string => reference('foo').bar
-//@[05:23) Function useRuntimeFunction. Type: () => any. Declaration start char: 0, length: 56
+//@[05:23) Function useRuntimeFunction. Type: () => string. Declaration start char: 0, length: 56
 
 func missingArgType(input) string => input
 //@[20:25) Local input. Type: any. Declaration start char: 20, length: 5
-//@[05:19) Function missingArgType. Type: any => any. Declaration start char: 0, length: 42
+//@[05:19) Function missingArgType. Type: any => string. Declaration start char: 0, length: 42
 
 func missingOutputType(input string) => input
 //@[23:28) Local input. Type: string. Declaration start char: 23, length: 12
@@ -35,7 +35,7 @@ func argLengthMismatch(a string, b string, c string) array => ([a, b, c])
 //@[23:24) Local a. Type: string. Declaration start char: 23, length: 8
 //@[33:34) Local b. Type: string. Declaration start char: 33, length: 8
 //@[43:44) Local c. Type: string. Declaration start char: 43, length: 8
-//@[05:22) Function argLengthMismatch. Type: (string, string, string) => string[]. Declaration start char: 0, length: 73
+//@[05:22) Function argLengthMismatch. Type: (string, string, string) => array. Declaration start char: 0, length: 73
 var sdf = argLengthMismatch('asdf')
 //@[04:07) Variable sdf. Type: error. Declaration start char: 0, length: 35
 
@@ -58,7 +58,7 @@ type validStringLiteralUnion = 'foo'|'bar'|'baz'
 func invalidArgs(a validStringLiteralUnion, b string) string => a
 //@[17:18) Local a. Type: 'bar' | 'baz' | 'foo'. Declaration start char: 17, length: 25
 //@[44:45) Local b. Type: string. Declaration start char: 44, length: 8
-//@[05:16) Function invalidArgs. Type: (('bar' | 'baz' | 'foo'), string) => ('bar' | 'baz' | 'foo'). Declaration start char: 0, length: 65
+//@[05:16) Function invalidArgs. Type: (('bar' | 'baz' | 'foo'), string) => string. Declaration start char: 0, length: 65
 func invalidOutput() validStringLiteralUnion => 'foo'
 //@[05:18) Function invalidOutput. Type: () => 'foo'. Declaration start char: 0, length: 53
 

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

@@ -279,11 +279,11 @@ static object[] Row(TypeSymbol sourceType, TypeSymbol targetType, TypeSymbol exp
                 // A source type whose domain is disjoint from the domain of the target should error and not narrow
                 Row(TypeFactory.CreateStringType(minLength: 10),
                     TypeFactory.CreateStringType(maxLength: 9),
-                    TypeFactory.CreateStringType(minLength: 10),
+                    TypeFactory.CreateStringType(maxLength: 9),
                     ("BCP332", DiagnosticLevel.Error, "The provided value (whose length will always be greater than or equal to 10) is too long to assign to a target for which the maximum allowable length is 9.")),
                 Row(TypeFactory.CreateStringType(maxLength: 9),
                     TypeFactory.CreateStringType(minLength: 10),
-                    TypeFactory.CreateStringType(maxLength: 9),
+                    TypeFactory.CreateStringType(minLength: 10),
                     ("BCP333", DiagnosticLevel.Error, "The provided value (whose length will always be less than or equal to 9) is too short to assign to a target for which the minimum allowable length is 10.")),
                 Row(TypeFactory.CreateStringLiteralType("0123456789"),
                     TypeFactory.CreateStringType(maxLength: 9),
@@ -369,19 +369,19 @@ static object[] Row(TypeSymbol sourceType, TypeSymbol targetType, TypeSymbol exp
                 // A source type whose domain is disjoint from the domain of the target should error and not narrow
                 Row(TypeFactory.CreateIntegerType(minValue: 10),
                     TypeFactory.CreateIntegerType(maxValue: 9),
-                    TypeFactory.CreateIntegerType(minValue: 10),
+                    TypeFactory.CreateIntegerType(maxValue: 9),
                     ("BCP327", DiagnosticLevel.Error, "The provided value (which will always be greater than or equal to 10) is too large to assign to a target for which the maximum allowable value is 9.")),
                 Row(TypeFactory.CreateIntegerType(maxValue: 9),
                     TypeFactory.CreateIntegerType(minValue: 10),
-                    TypeFactory.CreateIntegerType(maxValue: 9),
+                    TypeFactory.CreateIntegerType(minValue: 10),
                     ("BCP328", DiagnosticLevel.Error, "The provided value (which will always be less than or equal to 9) is too small to assign to a target for which the minimum allowable value is 10.")),
                 Row(TypeFactory.CreateIntegerLiteralType(10),
                     TypeFactory.CreateIntegerType(maxValue: 9),
-                    TypeFactory.CreateIntegerLiteralType(10),
+                    TypeFactory.CreateIntegerType(maxValue: 9),
                     ("BCP327", DiagnosticLevel.Error, "The provided value (which will always be greater than or equal to 10) is too large to assign to a target for which the maximum allowable value is 9.")),
                 Row(TypeFactory.CreateIntegerLiteralType(9),
                     TypeFactory.CreateIntegerType(minValue: 10),
-                    TypeFactory.CreateIntegerLiteralType(9),
+                    TypeFactory.CreateIntegerType(minValue: 10),
                     ("BCP328", DiagnosticLevel.Error, "The provided value (which will always be less than or equal to 9) is too small to assign to a target for which the minimum allowable value is 10.")),
                 Row(TypeFactory.CreateIntegerType(minValue: 10, validationFlags: TypeSymbolValidationFlags.AllowLooseAssignment),
                     TypeFactory.CreateIntegerLiteralType(9),

src/Bicep.Core/TypeSystem/TypeValidator.cs

@@ -362,7 +362,7 @@ private TypeSymbol NarrowType(TypeValidatorConfig config, SyntaxBase expression,
                 return NarrowLambdaType(config, sourceLambda, targetLambdaType);
             }
 
-            return expressionType;
+            return targetType;
         }
 
         private static SyntaxBase UnwrapIfConditionBody(SyntaxBase expression) => expression switch
@@ -457,7 +457,7 @@ private TypeSymbol NarrowIntegerAssignmentType(TypeValidatorConfig config, Synta
                     return expressionIntegerLiteral;
             }
 
-            return expressionType;
+            return targetType;
         }
 
         private TypeSymbol NarrowIntegerLiteralAssignmentType(TypeValidatorConfig config, SyntaxBase expression, TypeSymbol expressionType, IntegerLiteralType targetType)
@@ -548,7 +548,7 @@ private TypeSymbol NarrowStringAssignmentType(TypeValidatorConfig config, Syntax
                     return expressionStringLiteral;
             }
 
-            return expressionType;
+            return targetType;
         }
 
         private TypeSymbol NarrowStringLiteralAssignmentType(TypeValidatorConfig config, SyntaxBase expression, TypeSymbol expressionType, StringLiteralType targetType)
@@ -1049,7 +1049,7 @@ static TypeSymbol RemoveImplicitNull(TypeSymbol type, bool typeWasPreserved)
             // we should not return the parse errors however because they will get double collected
             if (this.parsingErrorLookup.Contains(expression))
             {
-                return targetType;
+                return null;
             }
 
             if (expressionType is ObjectType expressionObjectType)