Add support for case function

src/Runner.Worker/ActionManifestManager.cs

@@ -316,6 +316,7 @@ private TemplateContext CreateTemplateContext(
                 Schema = _actionManifestSchema,
                 // TODO: Switch to real tracewriter for cutover
                 TraceWriter = new GitHub.Actions.WorkflowParser.ObjectTemplating.EmptyTraceWriter(),
+                AllowCaseFunction = false,
             };
 
             // Expression values from execution context

src/Runner.Worker/ActionManifestManagerLegacy.cs

@@ -315,6 +315,7 @@ private TemplateContext CreateTemplateContext(
                     maxBytes: 10 * 1024 * 1024),
                 Schema = _actionManifestSchema,
                 TraceWriter = executionContext.ToTemplateTraceWriter(),
+                AllowCaseFunction = false,
             };
 
             // Expression values from execution context

src/Sdk/DTExpressions2/Expressions2/ExpressionConstants.cs

@@ -9,6 +9,7 @@ internal static class ExpressionConstants
     {
         static ExpressionConstants()
         {
+            AddFunction<Case>("case", 3, Byte.MaxValue);
             AddFunction<Contains>("contains", 2, 2);
             AddFunction<EndsWith>("endsWith", 2, 2);
             AddFunction<Format>("format", 1, Byte.MaxValue);

src/Sdk/DTExpressions2/Expressions2/ExpressionParser.cs

@@ -17,9 +17,10 @@ public IExpressionNode CreateTree(
             String expression,
             ITraceWriter trace,
             IEnumerable<INamedValueInfo> namedValues,
-            IEnumerable<IFunctionInfo> functions)
+            IEnumerable<IFunctionInfo> functions,
+            Boolean allowCaseFunction = true)
         {
-            var context = new ParseContext(expression, trace, namedValues, functions);
+            var context = new ParseContext(expression, trace, namedValues, functions, allowCaseFunction);
             context.Trace.Info($"Parsing expression: <{expression}>");
             return CreateTree(context);
         }
@@ -349,6 +350,10 @@ private static void FlushTopEndParameters(ParseContext context)
             {
                 throw new ParseException(ParseExceptionKind.TooManyParameters, token: @operator, expression: context.Expression);
             }
+            else if (functionInfo.Name.Equals("case", StringComparison.OrdinalIgnoreCase) && function.Parameters.Count % 2 == 0)
+            {
+                throw new ParseException(ParseExceptionKind.EvenParameters, token: @operator, expression: context.Expression);
+            }
         }
 
         /// <summary>
@@ -411,13 +416,20 @@ private static Boolean TryGetFunctionInfo(
             String name,
             out IFunctionInfo functionInfo)
         {
+            if (String.Equals(name, "case", StringComparison.OrdinalIgnoreCase) && !context.AllowCaseFunction)
+            {
+                functionInfo = null;
+                return false;
+            }
+
             return ExpressionConstants.WellKnownFunctions.TryGetValue(name, out functionInfo) ||
                 context.ExtensionFunctions.TryGetValue(name, out functionInfo);
         }
 
         private sealed class ParseContext
         {
             public Boolean AllowUnknownKeywords;
+            public Boolean AllowCaseFunction;
             public readonly String Expression;
             public readonly Dictionary<String, IFunctionInfo> ExtensionFunctions = new Dictionary<String, IFunctionInfo>(StringComparer.OrdinalIgnoreCase);
             public readonly Dictionary<String, INamedValueInfo> ExtensionNamedValues = new Dictionary<String, INamedValueInfo>(StringComparer.OrdinalIgnoreCase);
@@ -433,7 +445,8 @@ public ParseContext(
                 ITraceWriter trace,
                 IEnumerable<INamedValueInfo> namedValues,
                 IEnumerable<IFunctionInfo> functions,
-                Boolean allowUnknownKeywords = false)
+                Boolean allowUnknownKeywords = false,
+                Boolean allowCaseFunction = true)
             {
                 Expression = expression ?? String.Empty;
                 if (Expression.Length > ExpressionConstants.MaxLength)
@@ -454,6 +467,7 @@ public ParseContext(
 
                 LexicalAnalyzer = new LexicalAnalyzer(Expression);
                 AllowUnknownKeywords = allowUnknownKeywords;
+                AllowCaseFunction = allowCaseFunction;
             }
 
             private class NoOperationTraceWriter : ITraceWriter

src/Sdk/DTExpressions2/Expressions2/ParseException.cs

@@ -29,6 +29,9 @@ internal ParseException(ParseExceptionKind kind, Token token, String expression)
                 case ParseExceptionKind.TooManyParameters:
                     description = "Too many parameters supplied";
                     break;
+                case ParseExceptionKind.EvenParameters:
+                    description = "Even number of parameters supplied, requires an odd number of parameters";
+                    break;
                 case ParseExceptionKind.UnexpectedEndOfExpression:
                     description = "Unexpected end of expression";
                     break;

src/Sdk/DTExpressions2/Expressions2/ParseExceptionKind.cs

@@ -6,6 +6,7 @@ internal enum ParseExceptionKind
         ExceededMaxLength,
         TooFewParameters,
         TooManyParameters,
+        EvenParameters,
         UnexpectedEndOfExpression,
         UnexpectedSymbol,
         UnrecognizedFunction,

src/Sdk/DTExpressions2/Expressions2/Sdk/Functions/Case.cs

@@ -0,0 +1,45 @@
+#nullable disable // Consider removing in the future to minimize likelihood of NullReferenceException; refer https://learn.microsoft.com/en-us/dotnet/csharp/nullable-references
+
+using System;
+using GitHub.Actions.Expressions.Data;
+
+namespace GitHub.DistributedTask.Expressions2.Sdk.Functions
+{
+    internal sealed class Case : Function
+    {
+        protected sealed override Object EvaluateCore(
+            EvaluationContext context,
+            out ResultMemory resultMemory)
+        {
+            resultMemory = null;
+            // Validate argument count - must be odd (pairs of predicate-result plus default)
+            if (Parameters.Count % 2 == 0)
+            {
+                throw new InvalidOperationException("case requires an odd number of arguments");
+            }
+
+            // Evaluate predicate-result pairs
+            for (var i = 0; i < Parameters.Count - 1; i += 2)
+            {
+                var predicate = Parameters[i].Evaluate(context);
+
+                // Predicate must be a boolean
+                if (predicate.Kind != ValueKind.Boolean)
+                {
+                    throw new InvalidOperationException("case predicate must evaluate to a boolean value");
+                }
+
+                // If predicate is true, return the corresponding result
+                if ((Boolean)predicate.Value)
+                {
+                    var result = Parameters[i + 1].Evaluate(context);
+                    return result.Value;
+                }
+            }
+
+            // No predicate matched, return default (last argument)
+            var defaultResult = Parameters[Parameters.Count - 1].Evaluate(context);
+            return defaultResult.Value;
+        }
+    }
+}

src/Sdk/DTObjectTemplating/ObjectTemplating/TemplateContext.cs

@@ -86,6 +86,12 @@ internal IDictionary<String, Object> State
 
         internal ITraceWriter TraceWriter { get; set; }
 
+        /// <summary>
+        /// Gets or sets a value indicating whether the case expression function is allowed.
+        /// Defaults to true. Set to false to disable the case function.
+        /// </summary>
+        internal Boolean AllowCaseFunction { get; set; } = true;
+
         private IDictionary<String, Int32> FileIds
         {
             get

src/Sdk/DTObjectTemplating/ObjectTemplating/Tokens/TemplateToken.cs

@@ -57,7 +57,7 @@ protected StringToken EvaluateStringToken(
             var originalBytes = context.Memory.CurrentBytes;
             try
             {
-                var tree = new ExpressionParser().CreateTree(expression, null, context.GetExpressionNamedValues(), context.ExpressionFunctions);
+                var tree = new ExpressionParser().CreateTree(expression, null, context.GetExpressionNamedValues(), context.ExpressionFunctions, allowCaseFunction: context.AllowCaseFunction);
                 var options = new EvaluationOptions
                 {
                     MaxMemory = context.Memory.MaxBytes,
@@ -94,7 +94,7 @@ protected SequenceToken EvaluateSequenceToken(
             var originalBytes = context.Memory.CurrentBytes;
             try
             {
-                var tree = new ExpressionParser().CreateTree(expression, null, context.GetExpressionNamedValues(), context.ExpressionFunctions);
+                var tree = new ExpressionParser().CreateTree(expression, null, context.GetExpressionNamedValues(), context.ExpressionFunctions, allowCaseFunction: context.AllowCaseFunction);
                 var options = new EvaluationOptions
                 {
                     MaxMemory = context.Memory.MaxBytes,
@@ -123,7 +123,7 @@ protected MappingToken EvaluateMappingToken(
             var originalBytes = context.Memory.CurrentBytes;
             try
             {
-                var tree = new ExpressionParser().CreateTree(expression, null, context.GetExpressionNamedValues(), context.ExpressionFunctions);
+                var tree = new ExpressionParser().CreateTree(expression, null, context.GetExpressionNamedValues(), context.ExpressionFunctions, allowCaseFunction: context.AllowCaseFunction);
                 var options = new EvaluationOptions
                 {
                     MaxMemory = context.Memory.MaxBytes,
@@ -152,7 +152,7 @@ protected TemplateToken EvaluateTemplateToken(
             var originalBytes = context.Memory.CurrentBytes;
             try
             {
-                var tree = new ExpressionParser().CreateTree(expression, null, context.GetExpressionNamedValues(), context.ExpressionFunctions);
+                var tree = new ExpressionParser().CreateTree(expression, null, context.GetExpressionNamedValues(), context.ExpressionFunctions, allowCaseFunction: context.AllowCaseFunction);
                 var options = new EvaluationOptions
                 {
                     MaxMemory = context.Memory.MaxBytes,

src/Sdk/DTPipelines/Pipelines/ObjectTemplating/PipelineTemplateConverter.cs

@@ -663,7 +663,7 @@ private static String ConvertToIfCondition(
             var node = default(ExpressionNode);
             try
             {
-                node = expressionParser.CreateTree(condition, null, namedValues, functions) as ExpressionNode;
+                node = expressionParser.CreateTree(condition, null, namedValues, functions, allowCaseFunction: context.AllowCaseFunction) as ExpressionNode;
             }
             catch (Exception ex)
             {

src/Sdk/Expressions/ExpressionConstants.cs

@@ -10,6 +10,7 @@ public static class ExpressionConstants
     {
         static ExpressionConstants()
         {
+            AddFunction<Case>("case", 3, Byte.MaxValue);
             AddFunction<Contains>("contains", 2, 2);
             AddFunction<EndsWith>("endsWith", 2, 2);
             AddFunction<Format>("format", 1, Byte.MaxValue);

src/Sdk/Expressions/ExpressionParser.cs

@@ -17,9 +17,10 @@ public IExpressionNode CreateTree(
             String expression,
             ITraceWriter trace,
             IEnumerable<INamedValueInfo> namedValues,
-            IEnumerable<IFunctionInfo> functions)
+            IEnumerable<IFunctionInfo> functions,
+            Boolean allowCaseFunction = true)
         {
-            var context = new ParseContext(expression, trace, namedValues, functions);
+            var context = new ParseContext(expression, trace, namedValues, functions, allowCaseFunction: allowCaseFunction);
             context.Trace.Info($"Parsing expression: <{expression}>");
             return CreateTree(context);
         }
@@ -349,6 +350,10 @@ private static void FlushTopEndParameters(ParseContext context)
             {
                 throw new ParseException(ParseExceptionKind.TooManyParameters, token: @operator, expression: context.Expression);
             }
+            else if (functionInfo.Name.Equals("case", StringComparison.OrdinalIgnoreCase) && function.Parameters.Count % 2 == 0)
+            {
+                throw new ParseException(ParseExceptionKind.EvenParameters, token: @operator, expression: context.Expression);
+            }
         }
 
         /// <summary>
@@ -411,13 +416,20 @@ private static Boolean TryGetFunctionInfo(
             String name,
             out IFunctionInfo functionInfo)
         {
+            if (String.Equals(name, "case", StringComparison.OrdinalIgnoreCase) && !context.AllowCaseFunction)
+            {
+                functionInfo = null;
+                return false;
+            }
+
             return ExpressionConstants.WellKnownFunctions.TryGetValue(name, out functionInfo) ||
                 context.ExtensionFunctions.TryGetValue(name, out functionInfo);
         }
 
         private sealed class ParseContext
         {
             public Boolean AllowUnknownKeywords;
+            public Boolean AllowCaseFunction;
             public readonly String Expression;
             public readonly Dictionary<String, IFunctionInfo> ExtensionFunctions = new Dictionary<String, IFunctionInfo>(StringComparer.OrdinalIgnoreCase);
             public readonly Dictionary<String, INamedValueInfo> ExtensionNamedValues = new Dictionary<String, INamedValueInfo>(StringComparer.OrdinalIgnoreCase);
@@ -433,7 +445,8 @@ public ParseContext(
                 ITraceWriter trace,
                 IEnumerable<INamedValueInfo> namedValues,
                 IEnumerable<IFunctionInfo> functions,
-                Boolean allowUnknownKeywords = false)
+                Boolean allowUnknownKeywords = false,
+                Boolean allowCaseFunction = true)
             {
                 Expression = expression ?? String.Empty;
                 if (Expression.Length > ExpressionConstants.MaxLength)
@@ -454,6 +467,7 @@ public ParseContext(
 
                 LexicalAnalyzer = new LexicalAnalyzer(Expression);
                 AllowUnknownKeywords = allowUnknownKeywords;
+                AllowCaseFunction = allowCaseFunction;
             }
 
             private class NoOperationTraceWriter : ITraceWriter
@@ -468,4 +482,4 @@ public void Verbose(String message)
             }
         }
     }
-}
+}

src/Sdk/Expressions/ParseException.cs

@@ -29,6 +29,9 @@ internal ParseException(ParseExceptionKind kind, Token token, String expression)
                 case ParseExceptionKind.TooManyParameters:
                     description = "Too many parameters supplied";
                     break;
+                case ParseExceptionKind.EvenParameters:
+                    description = "Even number of parameters supplied, requires an odd number of parameters";
+                    break;
                 case ParseExceptionKind.UnexpectedEndOfExpression:
                     description = "Unexpected end of expression";
                     break;

src/Sdk/Expressions/ParseExceptionKind.cs

@@ -6,6 +6,7 @@ internal enum ParseExceptionKind
         ExceededMaxLength,
         TooFewParameters,
         TooManyParameters,
+        EvenParameters,
         UnexpectedEndOfExpression,
         UnexpectedSymbol,
         UnrecognizedFunction,

src/Sdk/Expressions/Sdk/Functions/Case.cs

@@ -0,0 +1,45 @@
+#nullable disable // Consider removing in the future to minimize likelihood of NullReferenceException; refer https://learn.microsoft.com/en-us/dotnet/csharp/nullable-references
+
+using System;
+using GitHub.Actions.Expressions.Data;
+
+namespace GitHub.Actions.Expressions.Sdk.Functions
+{
+    internal sealed class Case : Function
+    {
+        protected sealed override Object EvaluateCore(
+            EvaluationContext context,
+            out ResultMemory resultMemory)
+        {
+            resultMemory = null;
+            // Validate argument count - must be odd (pairs of predicate-result plus default)
+            if (Parameters.Count % 2 == 0)
+            {
+                throw new InvalidOperationException("case requires an odd number of arguments");
+            }
+
+            // Evaluate predicate-result pairs
+            for (var i = 0; i < Parameters.Count - 1; i += 2)
+            {
+                var predicate = Parameters[i].Evaluate(context);
+
+                // Predicate must be a boolean
+                if (predicate.Kind != ValueKind.Boolean)
+                {
+                    throw new InvalidOperationException("case predicate must evaluate to a boolean value");
+                }
+
+                // If predicate is true, return the corresponding result
+                if ((Boolean)predicate.Value)
+                {
+                    var result = Parameters[i + 1].Evaluate(context);
+                    return result.Value;
+                }
+            }
+
+            // No predicate matched, return default (last argument)
+            var defaultResult = Parameters[Parameters.Count - 1].Evaluate(context);
+            return defaultResult.Value;
+        }
+    }
+}

src/Sdk/WorkflowParser/Conversion/WorkflowTemplateConverter.cs

@@ -1775,7 +1775,7 @@ private static BasicExpressionToken ConvertToIfCondition(
             var node = default(ExpressionNode);
             try
             {
-                node = expressionParser.CreateTree(condition, null, namedValues, functions) as ExpressionNode;
+                node = expressionParser.CreateTree(condition, null, namedValues, functions, allowCaseFunction: context.AllowCaseFunction) as ExpressionNode;
             }
             catch (Exception ex)
             {

src/Sdk/WorkflowParser/ObjectTemplating/TemplateContext.cs

@@ -113,6 +113,12 @@ public IDictionary<String, Object> State
         /// </summary>
         internal Boolean StrictJsonParsing { get; set; }
 
+        /// <summary>
+        /// Gets or sets a value indicating whether the case expression function is allowed.
+        /// Defaults to true. Set to false to disable the case function.
+        /// </summary>
+        internal Boolean AllowCaseFunction { get; set; } = true;
+
         internal ITraceWriter TraceWriter { get; set; }
 
         private IDictionary<String, Int32> FileIds