Allow reading file-based app from stdin (#49348)

Author: jjonescz

documentation/general/dotnet-run-file.md

@@ -65,7 +65,11 @@ For example, the remaining command-line arguments after the first argument (the
 (except for the arguments recognized by `dotnet run` unless they are after the `--` separator)
 and working directory is not changed (e.g., `cd /x/ && dotnet run /y/file.cs` runs the program in directory `/x/`).
 
-`dotnet path.cs` is a shortcut for `dotnet run path.cs` provided that `path.cs` is a valid [target path](#target-path).
+If a dash (`-`) is given instead of the target path (i.e., `dotnet run -`), the C# file to be executed is read from the standard input.
+In this case, the current working directory is not used to search for other files (launch profiles, other sources in case of multi-file apps);
+the compilation consists solely of the single file read from the standard input.
+
+`dotnet path.cs` is a shortcut for `dotnet run path.cs` provided that `path.cs` is a valid [target path](#target-path) (`dotnet -` is currently not supported).
 
 ### Other commands
 
@@ -247,10 +251,6 @@ This section outlines potential future enhancements and alternatives considered.
 
 We could allow folders as the target path in the future (e.g., `dotnet run ./my-app/`).
 
-An option like `dotnet run --cs-from-stdin` could read the C# file from standard input.
-In this case, the current working directory would not be used to search for project or other C# files;
-the compilation would consist solely of the single file read from standard input.
-
 Similarly, it could be possible to specify the whole C# source text in a command-line argument
 like `dotnet run --cs-code 'Console.WriteLine("Hi")'`.
 

src/Cli/dotnet/Commands/CliCommandStrings.resx

@@ -1535,6 +1535,10 @@ Tool '{1}' (version '{2}') was successfully installed. Entry is added to the man
     <value>Cannot combine option '{0}' and '{1}'.</value>
     <comment>{0} and {1} are option names like '--no-build'.</comment>
   </data>
+  <data name="InvalidOptionForStdin" xml:space="preserve">
+    <value>Cannot specify option '{0}' when also using '-' to read the file from standard input.</value>
+    <comment>{0} is an option name like '--no-build'.</comment>
+  </data>
   <data name="NoBinaryLogBecauseUpToDate" xml:space="preserve">
     <value>Warning: Binary log option was specified but build will be skipped because output is up to date, specify '--no-cache' to force build.</value>
     <comment>{Locked="--no-cache"}</comment>

src/Cli/dotnet/Commands/Run/Api/RunApiCommand.cs

@@ -95,7 +95,8 @@ public override RunApiOutput Execute()
 
             var runCommand = new RunCommand(
                 noBuild: false,
-                projectFileOrDirectory: null,
+                projectFileFullPath: null,
+                entryPointFileFullPath: EntryPointFileFullPath,
                 launchProfile: null,
                 noLaunchProfile: false,
                 noLaunchProfileArguments: false,
@@ -104,7 +105,8 @@ public override RunApiOutput Execute()
                 interactive: false,
                 verbosity: VerbosityOptions.quiet,
                 restoreArgs: [],
-                args: [EntryPointFileFullPath],
+                args: [],
+                readCodeFromStdin: false,
                 environmentVariables: ReadOnlyDictionary<string, string>.Empty);
 
             runCommand.TryGetLaunchProfileSettingsIfNeeded(out var launchSettings);

src/Cli/dotnet/Commands/Run/RunCommand.cs

@@ -3,6 +3,7 @@
 
 using System.Collections.Immutable;
 using System.CommandLine;
+using System.CommandLine.Parsing;
 using System.Diagnostics;
 using Microsoft.Build.Evaluation;
 using Microsoft.Build.Exceptions;
@@ -22,11 +23,6 @@ public class RunCommand
 {
     public bool NoBuild { get; }
 
-    /// <summary>
-    /// Value of the <c>--project</c> option.
-    /// </summary>
-    public string? ProjectFileOrDirectory { get; }
-
     /// <summary>
     /// Full path to a project file to run.
     /// <see langword="null"/> if running without a project file
@@ -39,6 +35,13 @@ public class RunCommand
     /// </summary>
     public string? EntryPointFileFullPath { get; }
 
+    /// <summary>
+    /// Whether <c>dotnet run -</c> is being executed.
+    /// In that case, <see cref="EntryPointFileFullPath"/> points to a temporary file
+    /// containing all text read from the standard input.
+    /// </summary>
+    public bool ReadCodeFromStdin { get; }
+
     public string[] Args { get; set; }
     public bool NoRestore { get; }
     public bool NoCache { get; }
@@ -63,7 +66,8 @@ public class RunCommand
 
     public RunCommand(
         bool noBuild,
-        string? projectFileOrDirectory,
+        string? projectFileFullPath,
+        string? entryPointFileFullPath,
         string? launchProfile,
         bool noLaunchProfile,
         bool noLaunchProfileArguments,
@@ -73,12 +77,16 @@ public RunCommand(
         VerbosityOptions? verbosity,
         string[] restoreArgs,
         string[] args,
+        bool readCodeFromStdin,
         IReadOnlyDictionary<string, string> environmentVariables)
     {
+        Debug.Assert(projectFileFullPath is null ^ entryPointFileFullPath is null);
+        Debug.Assert(!readCodeFromStdin || entryPointFileFullPath is not null);
+
         NoBuild = noBuild;
-        ProjectFileOrDirectory = projectFileOrDirectory;
-        ProjectFileFullPath = DiscoverProjectFilePath(projectFileOrDirectory, ref args, out string? entryPointFileFullPath);
+        ProjectFileFullPath = projectFileFullPath;
         EntryPointFileFullPath = entryPointFileFullPath;
+        ReadCodeFromStdin = readCodeFromStdin;
         LaunchProfile = launchProfile;
         NoLaunchProfile = noLaunchProfile;
         NoLaunchProfileArguments = noLaunchProfileArguments;
@@ -117,6 +125,7 @@ public int Execute()
 
             if (EntryPointFileFullPath is not null)
             {
+                Debug.Assert(!ReadCodeFromStdin);
                 projectFactory = CreateVirtualCommand().PrepareProjectInstance().CreateProjectInstance;
             }
         }
@@ -180,7 +189,7 @@ internal bool TryGetLaunchProfileSettingsIfNeeded(out ProjectLaunchSettingsModel
             return true;
         }
 
-        var launchSettingsPath = TryFindLaunchSettings(ProjectFileFullPath ?? EntryPointFileFullPath!);
+        var launchSettingsPath = ReadCodeFromStdin ? null : TryFindLaunchSettings(ProjectFileFullPath ?? EntryPointFileFullPath!);
         if (!File.Exists(launchSettingsPath))
         {
             if (!string.IsNullOrEmpty(LaunchProfile))
@@ -437,7 +446,7 @@ private static void ThrowUnableToRunError(ProjectInstance project)
                     project.GetPropertyValue("OutputType")));
     }
 
-    private static string? DiscoverProjectFilePath(string? projectFileOrDirectoryPath, ref string[] args, out string? entryPointFilePath)
+    private static string? DiscoverProjectFilePath(string? projectFileOrDirectoryPath, bool readCodeFromStdin, ref string[] args, out string? entryPointFilePath)
     {
         bool emptyProjectOption = false;
         if (string.IsNullOrWhiteSpace(projectFileOrDirectoryPath))
@@ -453,7 +462,7 @@ private static void ThrowUnableToRunError(ProjectInstance project)
         // If no project exists in the directory and no --project was given,
         // try to resolve an entry-point file instead.
         entryPointFilePath = projectFilePath is null && emptyProjectOption
-            ? TryFindEntryPointFilePath(ref args)
+            ? TryFindEntryPointFilePath(readCodeFromStdin, ref args)
             : null;
 
         if (entryPointFilePath is null && projectFilePath is null)
@@ -480,16 +489,27 @@ private static void ThrowUnableToRunError(ProjectInstance project)
             return projectFiles[0];
         }
 
-        static string? TryFindEntryPointFilePath(ref string[] args)
+        static string? TryFindEntryPointFilePath(bool readCodeFromStdin, ref string[] args)
         {
-            if (args is not [{ } arg, ..] ||
-                !VirtualProjectBuildingCommand.IsValidEntryPointPath(arg))
+            if (args is not [{ } arg, ..])
             {
                 return null;
             }
 
+            if (!readCodeFromStdin)
+            {
+                if (VirtualProjectBuildingCommand.IsValidEntryPointPath(arg))
+                {
+                    arg = Path.GetFullPath(arg);
+                }
+                else
+                {
+                    return null;
+                }
+            }
+
             args = args[1..];
-            return Path.GetFullPath(arg);
+            return arg;
         }
     }
 
@@ -521,9 +541,44 @@ public static RunCommand FromParseResult(ParseResult parseResult)
             restoreArgs.AddRange(binLogArgs);
         }
 
+        // Only consider `-` to mean "read code from stdin" if it is before double dash `--`
+        // (otherwise it should be fowarded to the target application as its command-line argument).
+        bool readCodeFromStdin = nonBinLogArgs is ["-", ..] &&
+            parseResult.Tokens.TakeWhile(static t => t.Type != TokenType.DoubleDash)
+                .Any(static t => t is { Type: TokenType.Argument, Value: "-" });
+
+        string? projectOption = parseResult.GetValue(RunCommandParser.ProjectOption);
+
+        string[] args = [.. nonBinLogArgs];
+        string? projectFilePath = DiscoverProjectFilePath(projectOption, readCodeFromStdin, ref args, out string? entryPointFilePath);
+
+        bool noBuild = parseResult.HasOption(RunCommandParser.NoBuildOption);
+
+        if (readCodeFromStdin && entryPointFilePath != null)
+        {
+            Debug.Assert(projectFilePath is null && entryPointFilePath is "-");
+
+            if (noBuild)
+            {
+                throw new GracefulException(CliCommandStrings.InvalidOptionForStdin, RunCommandParser.NoBuildOption.Name);
+            }
+
+            // If '-' is specified as the input file, read all text from stdin into a temporary file and use that as the entry point.
+            entryPointFilePath = Path.GetTempFileName();
+            using (var stdinStream = Console.OpenStandardInput())
+            using (var fileStream = File.OpenWrite(entryPointFilePath))
+            {
+                stdinStream.CopyTo(fileStream);
+            }
+
+            Debug.Assert(nonBinLogArgs[0] == "-");
+            nonBinLogArgs[0] = entryPointFilePath;
+        }
+
         var command = new RunCommand(
-            noBuild: parseResult.HasOption(RunCommandParser.NoBuildOption),
-            projectFileOrDirectory: parseResult.GetValue(RunCommandParser.ProjectOption),
+            noBuild: noBuild,
+            projectFileFullPath: projectFilePath,
+            entryPointFileFullPath: entryPointFilePath,
             launchProfile: parseResult.GetValue(RunCommandParser.LaunchProfileOption) ?? string.Empty,
             noLaunchProfile: parseResult.HasOption(RunCommandParser.NoLaunchProfileOption),
             noLaunchProfileArguments: parseResult.HasOption(RunCommandParser.NoLaunchProfileArgumentsOption),
@@ -532,7 +587,8 @@ public static RunCommand FromParseResult(ParseResult parseResult)
             interactive: parseResult.GetValue(RunCommandParser.InteractiveOption),
             verbosity: parseResult.HasOption(CommonOptions.VerbosityOption) ? parseResult.GetValue(CommonOptions.VerbosityOption) : null,
             restoreArgs: [.. restoreArgs],
-            args: [.. nonBinLogArgs],
+            args: args,
+            readCodeFromStdin: readCodeFromStdin,
             environmentVariables: parseResult.GetValue(CommonOptions.EnvOption) ?? ImmutableDictionary<string, string>.Empty
         );