Add support for dotnet file.cs (without explicit run subcommand)

documentation/general/dotnet-run-file.md

@@ -87,6 +87,8 @@ File-based programs are processed by `dotnet run` equivalently to project-based
 For example, the remaining command-line arguments after the first argument (the target path) are passed through to the target app
 (except for the arguments recognized by `dotnet run` unless they are after the `--` separator).
 
+`dotnet path.cs` is a shortcut for `dotnet run path.cs` provided that `path.cs` exists and has `.cs` file extension.
+
 ## Entry points
 
 If a file is given to `dotnet run`, it has to be an *entry-point file*, otherwise an error is reported.
@@ -233,28 +235,24 @@ Along with `#:`, the language also ignores `#!` which could be then used for [sh
 Console.WriteLine("Hello");
 ```
 
-It might be beneficial to also ship `dotnet-run` binary
-(or `dotnet-run-file` that would only work with file-based programs, not project-based ones, perhaps simply named `cs`)
-because some shells do not support multiple command-line arguments in the shebang
+Some shells do not support multiple command-line arguments in the shebang
 which is needed if one wants to use `/usr/bin/env` to find the `dotnet` executable
-(although `-S` argument can be sometimes used to enable multiple argument support):
+(although `-S` argument can be sometimes used to enable multiple argument support),
+so `dotnet file.cs` instead of `dotnet run file.cs` should be used in shebangs:
 
 ```cs
 #!/usr/bin/env dotnet run
 // ^ Might not work in all shells. "dotnet run" might be passed as a single argument to "env".
 ```
 ```cs
-#!/usr/bin/env dotnet-run
+#!/usr/bin/env dotnet
 // ^ Should work in all shells.
 ```
 ```cs
 #!/usr/bin/env -S dotnet run
-// ^ Workaround in some shells.
+// ^ Works in some shells.
 ```
 
-We could also consider making `dotnet file.cs` work because `dotnet file.dll` also works today
-but that would require changes to the native dotnet host.
-
 ## Other commands
 
 We can consider supporting other commands like `dotnet build`, `dotnet pack`, `dotnet watch`.

src/Cli/dotnet/Program.cs

@@ -4,6 +4,7 @@
 using System.CommandLine;
 using System.Diagnostics;
 using Microsoft.DotNet.Cli.CommandFactory;
+using Microsoft.DotNet.Cli.Commands.Run;
 using Microsoft.DotNet.Cli.Commands.Workload;
 using Microsoft.DotNet.Cli.Extensions;
 using Microsoft.DotNet.Cli.ShellShim;
@@ -123,7 +124,10 @@ internal static int ProcessArgs(string[] args, TimeSpan startupTime, ITelemetry
         ParseResult parseResult;
         using (new PerformanceMeasurement(performanceData, "Parse Time"))
         {
-            parseResult = Parser.Instance.Parse(args);
+            // If we get C# file path as the first argument, parse as `dotnet run file.cs`.
+            parseResult = args is [{ } filePath, ..] && VirtualProjectBuildingCommand.IsValidEntryPointPath(filePath)
+                ? Parser.Instance.Parse(["run", .. args])
+                : Parser.Instance.Parse(args);
 
             // Avoid create temp directory with root permission and later prevent access in non sudo
             // This method need to be run very early before temp folder get created

test/dotnet.Tests/CommandTests/Run/RunFileTests.cs

@@ -112,6 +112,22 @@ public void FilePath(string? path, bool differentCasing)
         }
     }
 
+    /// <summary>
+    /// <c>dotnet file.cs</c> is equivalent to <c>dotnet run file.cs</c>.
+    /// </summary>
+    [Fact]
+    public void FilePath_WithoutRun()
+    {
+        var testInstance = _testAssetsManager.CreateTestDirectory();
+        File.WriteAllText(Path.Join(testInstance.Path, "Program.cs"), s_program);
+
+        new DotnetCommand(Log, "Program.cs")
+            .WithWorkingDirectory(testInstance.Path)
+            .Execute()
+            .Should().Pass()
+            .And.HaveStdOut("Hello from Program");
+    }
+
     /// <summary>
     /// Casing of the argument is used for the output binary name.
     /// </summary>