Look for TargetFramework being set in C# file

Author: normj

src/Amazon.Lambda.Tools/Commands/DeployFunctionCommand.cs

@@ -257,7 +257,7 @@ protected override async Task<bool> PerformActionAsync()
                     {
                         if (Utilities.IsSingleFileCSharpFile(projectLocation))
                         {
-                            targetFramework = LambdaUtilities.DetermineTargetFrameworkForSingleFile(lambdaRuntime);
+                            targetFramework = LambdaUtilities.DetermineTargetFrameworkForSingleFile(projectLocation, lambdaRuntime);
                         }
                         else
                         {

src/Amazon.Lambda.Tools/Commands/PackageCommand.cs

@@ -233,7 +233,7 @@ protected override async Task<bool> PerformActionAsync()
                 {
                     if (Utilities.IsSingleFileCSharpFile(projectLocation))
                     {
-                        targetFramework = LambdaUtilities.DetermineTargetFrameworkForSingleFile(null);
+                        targetFramework = LambdaUtilities.DetermineTargetFrameworkForSingleFile(projectLocation, null);
                     }
                     else
                     {

src/Amazon.Lambda.Tools/LambdaUtilities.cs

@@ -1,22 +1,22 @@
-using System;
+using Amazon.Common.DotNetCli.Tools;
+using Amazon.Lambda.Model;
+using Amazon.S3;
+using Amazon.S3.Model;
+using Amazon.SecurityToken;
+using Newtonsoft.Json;
+using Newtonsoft.Json.Linq;
+using System;
 using System.Collections.Generic;
 using System.IO;
 using System.Linq;
+using System.Runtime.InteropServices;
 using System.Text.Json;
-using YamlDotNet.RepresentationModel;
-using Newtonsoft.Json;
-using Newtonsoft.Json.Linq;
-using System.Xml.Linq;
-using Amazon.Common.DotNetCli.Tools;
-
-using Amazon.Lambda.Model;
-using Amazon.S3;
-using Amazon.S3.Model;
+using System.Text.RegularExpressions;
 using System.Threading.Tasks;
+using System.Xml.Linq;
 using System.Xml.XPath;
+using YamlDotNet.RepresentationModel;
 using Environment = System.Environment;
-using Amazon.SecurityToken;
-using System.Runtime.InteropServices;
 
 namespace Amazon.Lambda.Tools
 {
@@ -83,16 +83,45 @@ public static string DetermineLambdaRuntimeFromTargetFramework(string targetFram
             return kvp.Key;
         }
 
-        public static string DetermineTargetFrameworkForSingleFile(string lambdaRuntime)
+        public static string DetermineTargetFrameworkForSingleFile(string filePath, string lambdaRuntime)
         {
-            string targetFramework;
+            return DetermineTargetFrameworkForSingleFile(File.ReadAllLines(filePath), lambdaRuntime);
+        }
+
+        public static string DetermineTargetFrameworkForSingleFile(string[] lines, string lambdaRuntime)
+        {
+            string targetFramework = null;
             if (lambdaRuntime != null && _lambdaRuntimeToDotnetFramework.TryGetValue(lambdaRuntime, out targetFramework))
             {
                 return targetFramework;
             }
 
-            // TODO: Figure out what to do when we don't have a lambdaRuntime to base it on.
-            targetFramework = "net10.0";
+            // Look for an in-file directive that starts with "#:property" and contains "TargetFramework=<value>"
+            // Allow extra spaces but the directive must begin with "#:property". Extract the value after '='.
+            if (lines != null && lines.Length > 0)
+            {
+                // Pattern explanation:
+                // ^\s*           -> optional leading whitespace
+                // #\s*:\s*property -> literal "#", optional spaces, ":", optional spaces, "property"
+                // \s+            -> at least one space (separates property from key)
+                // TargetFramework -> literal key
+                // \s*=\s*        -> equals with optional surrounding spaces
+                // (\S+)          -> capture the value (non-whitespace sequence)
+                var directiveRegex = new Regex(@"^\s*#\s*:\s*property\s+TargetFramework\s*=\s*(\S+)", RegexOptions.IgnoreCase);
+
+                foreach (var rawLine in lines)
+                {
+                    if (string.IsNullOrWhiteSpace(rawLine))
+                        continue;
+
+                    var m = directiveRegex.Match(rawLine);
+                    if (m.Success && m.Groups.Count > 1)
+                    {
+                        targetFramework = m.Groups[1].Value.Trim();
+                        break;
+                    }
+                }
+            }
 
             return targetFramework;
         }

test/Amazon.Lambda.Tools.Test/LambdaSingleFilePackageTests.cs

@@ -298,5 +298,53 @@ public void GetSolutionDirectoryWithExplicitSolutionDirectory()
             var solutionDirectory = Utilities.GetSolutionDirectoryFullPath(Environment.CurrentDirectory, projectLocation, givenSolutionDirectory);
             Assert.Equal(givenSolutionDirectory, solutionDirectory);
         }
+
+        [Fact]
+        public void DetermineTargetFrameworkForSingleFile_FindsExactDirective()
+        {
+            var lines = new[] { "#:property TargetFramework=net10.0" };
+            var result = LambdaUtilities.DetermineTargetFrameworkForSingleFile(lines, null);
+            Assert.Equal("net10.0", result);
+        }
+
+        [Fact]
+        public void DetermineTargetFrameworkForSingleFile_FindsDirectiveWithExtraSpaces()
+        {
+            var lines = new[] { "#:property   TargetFramework=net11.0" };
+            var result = LambdaUtilities.DetermineTargetFrameworkForSingleFile(lines, null);
+            Assert.Equal("net11.0", result);
+        }
+
+        [Fact]
+        public void DetermineTargetFrameworkForSingleFile_FindsDirectiveWithSpacesAroundEquals()
+        {
+            var lines = new[] { "#:property TargetFramework =   net12.0" };
+            var result = LambdaUtilities.DetermineTargetFrameworkForSingleFile(lines, null);
+            Assert.Equal("net12.0", result);
+        }
+
+        [Fact]
+        public void DetermineTargetFrameworkForSingleFile_CommentedOut()
+        {
+            var lines = new[] { "//#:property TargetFramework=NET13.0" };
+            var result = LambdaUtilities.DetermineTargetFrameworkForSingleFile(lines, null);
+            Assert.Null(result);
+        }
+
+        [Fact]
+        public void DetermineTargetFrameworkForSingleFile_WithLambdaRuntime()
+        {
+            var lines = new[] { "// Nothing to see here" };
+            var result = LambdaUtilities.DetermineTargetFrameworkForSingleFile(lines, "dotnet10");
+            Assert.Equal("net10.0", result);
+        }
+
+        [Fact]
+        public void DetermineTargetFrameworkForSingleFile_NoDirectiveReturnsNull()
+        {
+            var lines = new[] { "// just a comment", "using System;" };
+            var result = LambdaUtilities.DetermineTargetFrameworkForSingleFile(lines, null);
+            Assert.Null(result);
+        }
     }
 }