[release/10.0] Allow tools to run on projects targeting multiple frameworks (#37301)

Fixes #37230

Author: AndriySvyryd

src/dotnet-ef/Project.cs

@@ -85,6 +85,11 @@ public static Project FromFile(
         var exitCode = Exe.Run("dotnet", args, handleOutput: line => output.AppendLine(line));
         if (exitCode != 0)
         {
+            if (framework == null && HasMultipleTargetFrameworks(file))
+            {
+                throw new CommandException(Resources.MultipleTargetFrameworks);
+            }
+
             throw new CommandException(Resources.GetMetadataFailed);
         }
 
@@ -131,6 +136,21 @@ private record class ProjectMetadata
         public Dictionary<string, Dictionary<string, string>[]> Items { get; set; } = null!;
     }
 
+    private static bool HasMultipleTargetFrameworks(string file)
+    {
+        var args = new List<string> { "msbuild", "/getProperty:TargetFrameworks", file };
+
+        var output = new StringBuilder();
+        var exitCode = Exe.Run("dotnet", args, handleOutput: line => output.AppendLine(line));
+        if (exitCode != 0)
+        {
+            return false;
+        }
+
+        var outputString = output.ToString();
+        return !string.IsNullOrWhiteSpace(outputString);
+    }
+
     private static void CopyBuildHost(
         Dictionary<string, string>[] runtimeCopyLocalItems,
         string targetDir)

src/dotnet-ef/Properties/Resources.Designer.cs

@@ -264,6 +264,9 @@
   <data name="MultipleStartupProjects" xml:space="preserve">
     <value>More than one project was found in the current working directory. Use the --startup-project option.</value>
   </data>
+  <data name="MultipleTargetFrameworks" xml:space="preserve">
+    <value>The project targets multiple frameworks. Use the --framework option to specify which target framework to use.</value>
+  </data>
   <data name="NamespaceDescription" xml:space="preserve">
     <value>The namespace to use. Matches the directory by default.</value>
   </data>

src/dotnet-ef/Properties/Resources.resx

@@ -66,7 +66,11 @@ protected override int Execute(string[] _)
         Reporter.WriteVerbose(Resources.UsingProject(projectFile));
         Reporter.WriteVerbose(Resources.UsingStartupProject(startupProjectFile));
 
-        var project = Project.FromFile(projectFile);
+        var project = Project.FromFile(
+            projectFile,
+            _framework!.Value(),
+            _configuration!.Value(),
+            _runtime!.Value());
         var startupProject = Project.FromFile(
             startupProjectFile,
             _framework!.Value(),