Add ProcessStartOptions class with simplified path resolution by Copilot · Pull Request #124271 · dotnet/runtime

Copilot · 2026-02-11T13:33:48Z

Description

Adds ProcessStartOptions class providing explicit, simplified path resolution for process creation. Addresses security and predictability concerns with automatic directory probing.

Changes

API Surface

ProcessStartOptions(string fileName) - constructor resolves and validates executable paths
Properties: FileName, Arguments, Environment, WorkingDirectory, InheritedHandles, KillOnParentExit, CreateNewProcessGroup
Lazy-allocated collections (Arguments, Environment, InheritedHandles)
Environment populated from Environment.GetEnvironmentVariables() as Dictionary<string, string?>

Path Resolution Behavior

Windows: System32 directory → PATH. Current directory requires explicit .\ prefix.
Unix: PATH only. Current directory requires explicit ./ prefix.
Fully qualified paths (e.g., C:\path\file.exe) returned as-is
Rooted non-qualified paths (e.g., C:file.exe) normalized via Path.GetFullPath
Windows: .exe appended when filename lacks extension and path separators
Throws FileNotFoundException with localized message when resolution fails

Implementation Details

Reuses Environment.SystemDirectory instead of P/Invoke
Made Process.IsExecutable internal for shared use
Process.Unix retains original ResolvePath/FindProgramInPath for backward compatibility
ProcessStartOptions uses new simplified resolution

Tests

25 tests across 3 partial class files (base, Windows, Unix)
Theory-based tests for CWD resolution (positive: .\file, negative: file)
Platform-conditional tests (IsNotWindowsNanoServer, IsNotWindowsServerCore)
Path assertions use EndsWith and Path.GetFullPath() for cross-platform robustness

Example

// Resolves from PATH or System32
var options = new ProcessStartOptions("cmd");
Console.WriteLine(options.FileName); // C:\Windows\System32\cmd.exe

// Explicit current directory reference required
var local = new ProcessStartOptions(@".\myapp.exe");

// Lazy collections
options.Arguments.Add("/c");
options.Arguments.Add("echo test");
options.Environment["VAR"] = "value";

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.

Co-authored-by: adamsitnik <6011991+adamsitnik@users.noreply.github.com>

dotnet-policy-service · 2026-02-11T13:55:10Z

Tagging subscribers to this area: @dotnet/area-system-diagnostics-process
See info in area-owners.md if you want to be subscribed.

Co-authored-by: adamsitnik <6011991+adamsitnik@users.noreply.github.com>

adamsitnik

@copilot please address my feedback

src/libraries/System.Diagnostics.Process/tests/ProcessStartOptionsTests.cs

src/libraries/System.Diagnostics.Process/src/System/Diagnostics/ProcessStartOptions.cs

src/libraries/System.Diagnostics.Process/tests/ProcessStartOptionsTests.Unix.cs

Co-authored-by: adamsitnik <6011991+adamsitnik@users.noreply.github.com>

adamsitnik

@copilot address my feedback

src/libraries/System.Diagnostics.Process/src/System/Diagnostics/ProcessStartOptions.cs

Co-authored-by: adamsitnik <6011991+adamsitnik@users.noreply.github.com>

src/libraries/System.Diagnostics.Process/src/System/Diagnostics/ProcessStartOptions.cs

adamsitnik

@copilot please address my feedback

src/libraries/System.Diagnostics.Process/tests/ProcessStartOptionsTests.Unix.cs

src/libraries/System.Diagnostics.Process/tests/ProcessStartOptionsTests.Windows.cs

Co-authored-by: adamsitnik <6011991+adamsitnik@users.noreply.github.com>

src/libraries/System.Diagnostics.Process/src/System/Diagnostics/ProcessStartOptions.cs

- add comments - cache Environment.SystemDirectory - handle fully qualified paths on Windows

src/libraries/System.Diagnostics.Process/src/System/Diagnostics/ProcessStartOptions.cs

stephentoub · 2026-02-15T17:15:29Z

@copilot invoke the code-review skill and post your analysis/results as a comment on this pr

jkotas · 2026-02-15T17:27:38Z

src/libraries/System.Diagnostics.Process/src/System/Diagnostics/ProcessStartOptions.cs

+        // "Applications should not under any circumstances pass user-controlled input directly to CreateProcess;
+        // or, if they intend to do so (for passing user-originated parameters), they should be filling out the lpApplicationName parameter."
+        //
+        // We could either document that the FileName should never be user-controlled input or resolve it ourselves,


I do not understand this point. If we wanted to leave resolution of the file name to the OS, we could add the quotation marks around the file name as the official documentation suggests.

I think the main problem with leaving the resolution to the OS is that it would not work well with the current public API shape. We would not be able to provide the resolved path before the process starts as a public OS neutral API.

So I think the reasoning should be as follows:

We want to provide resolved path API

It means we need to have our own copy of the path resolution algorithm since there is no Windows OS API to do that.

Our own copy of the path resolution algorithm is not going to be equivalent to the Windows OS provided one since it is not fully documented.

We take it as an opportunity to clean up the legacy baggage to have simpler, easier to understand and more secure filename resolution algorithm that is consistent across OSes and aligned with other modern platforms.

I do not understand this point. If we wanted to leave resolution of the file name to the OS, we could add the quotation marks around the file name as the official documentation suggests.

This was also my understanding, but the feedback I got from the Windows Team made me believe we should not be doing this.

We take it as an opportunity to clean up the legacy baggage to have simpler, easier to understand and more secure filename resolution algorithm that is consistent across OSes and aligned with other modern platforms.

I agree it's great opportunity and timing (Preview 2?). However, which parts exactly do we want to give up on?

no current directory probing

For CWD, we could just explicitly demand the ".\here.exe" syntax.

no process .exe path probing

It's a valid scenario, but the users can use Path.Combine(Path.GetDirectoryName(Environment.ProcessPath), "name") API to build such path quickly (assuming Environment.ProcessPath does not return null).

no legacy Windows directory probing, etc.

Just to be sure, by legacy you don't mean C:\Windows\System32 (returned by Environment.ProcessPath, contains "cmd.exe" etc), but C:\Windows\System?

stephentoub · 2026-02-15T18:22:01Z

@copilot?

adamsitnik

@copilot Please address my feedback

src/libraries/Common/src/Interop/Windows/Kernel32/Interop.GetWindowsDirectoryW.cs

src/libraries/System.Diagnostics.Process/src/System/Diagnostics/Process.Unix.cs

src/libraries/System.Diagnostics.Process/src/System/Diagnostics/ProcessStartOptions.cs

src/libraries/System.Diagnostics.Process/tests/ProcessStartOptionsTests.Unix.cs

src/libraries/System.Diagnostics.Process/tests/ProcessStartOptionsTests.Windows.cs

Co-authored-by: adamsitnik <6011991+adamsitnik@users.noreply.github.com>

adamsitnik · 2026-02-16T08:43:53Z

@copilot address all of my feedback, not only some parts of it

… explicit ./ Co-authored-by: adamsitnik <6011991+adamsitnik@users.noreply.github.com>

Co-authored-by: adamsitnik <6011991+adamsitnik@users.noreply.github.com>

Copilot

Pull request overview

Copilot reviewed 12 out of 12 changed files in this pull request and generated 2 comments.

Copilot · 2026-02-16T15:00:43Z

src/libraries/System.Diagnostics.Process/src/System/Diagnostics/ProcessStartOptions.cs

+            if (path != null)
+            {
+                path = Path.Combine(path, filename);
+                if (File.Exists(path))
+                {
+                    return path;
+                }


Environment.SystemDirectory is a non-nullable string property that always returns a value. The null check on line 247 is unnecessary and violates the coding guideline to trust C# null annotations and avoid null checks when the type system indicates a value cannot be null.

Suggested change

if (path != null)

{

path = Path.Combine(path, filename);

if (File.Exists(path))

{

return path;

}

path = Path.Combine(path, filename);

if (File.Exists(path))

{

return path;

src/libraries/System.Diagnostics.Process/tests/ProcessStartOptionsTests.Unix.cs

Initial plan

4f3f950

Copilot AI assigned Copilot and adamsitnik Feb 11, 2026

Copilot started work on behalf of adamsitnik February 11, 2026 13:34 View session

Add ProcessStartOptions class with path resolution and tests

92de299

Co-authored-by: adamsitnik <6011991+adamsitnik@users.noreply.github.com>

github-actions bot added the area-System.Diagnostics.Process label Feb 11, 2026

Copilot AI and others added 3 commits February 11, 2026 14:07

Fix build errors and test failures in ProcessStartOptions

0c9d3e2

Co-authored-by: adamsitnik <6011991+adamsitnik@users.noreply.github.com>

Improve code comments based on review feedback

794a8a2

Co-authored-by: adamsitnik <6011991+adamsitnik@users.noreply.github.com>

Fix exception documentation and add caching comment

a1b3426

Co-authored-by: adamsitnik <6011991+adamsitnik@users.noreply.github.com>

Copilot AI changed the title ~~[WIP] Add ProcessStartOptions class to System.Diagnostics namespace~~ Add ProcessStartOptions class with platform-aware path resolution Feb 11, 2026

Copilot AI requested a review from adamsitnik February 11, 2026 14:16

Copilot finished work on behalf of adamsitnik February 11, 2026 14:16

adamsitnik reviewed Feb 11, 2026

View reviewed changes

Copilot started work on behalf of adamsitnik February 11, 2026 15:51 View session

Address PR feedback: use Process.ResolvePath, fix tests, add null checks

10ff95a

Co-authored-by: adamsitnik <6011991+adamsitnik@users.noreply.github.com>

Copilot AI requested a review from adamsitnik February 11, 2026 16:10

Copilot finished work on behalf of adamsitnik February 11, 2026 16:10

adamsitnik reviewed Feb 11, 2026

View reviewed changes

src/libraries/System.Diagnostics.Process/src/System/Diagnostics/ProcessStartOptions.cs Outdated Show resolved Hide resolved

Copilot started work on behalf of adamsitnik February 11, 2026 17:07 View session

Refactor: ProcessStartOptions.ResolvePath as main impl, Process calls it

fc0fd30

Co-authored-by: adamsitnik <6011991+adamsitnik@users.noreply.github.com>

Copilot AI requested a review from adamsitnik February 11, 2026 17:18

Copilot finished work on behalf of adamsitnik February 11, 2026 17:18

address my own feedback

f687eb8

adamsitnik reviewed Feb 11, 2026

View reviewed changes

src/libraries/System.Diagnostics.Process/src/System/Diagnostics/ProcessStartOptions.cs Show resolved Hide resolved

adamsitnik reviewed Feb 11, 2026

View reviewed changes

Copilot started work on behalf of adamsitnik February 11, 2026 18:40 View session

adamsitnik requested a review from GrabYourPitchforks February 11, 2026 18:42

Simplify Windows tests: remove ConditionalFact, fix nested try-finally

5459ec9

Co-authored-by: adamsitnik <6011991+adamsitnik@users.noreply.github.com>

Copilot AI requested a review from adamsitnik February 11, 2026 18:49

stephentoub reviewed Feb 14, 2026

View reviewed changes

src/libraries/System.Diagnostics.Process/src/System/Diagnostics/ProcessStartOptions.cs Show resolved Hide resolved

jkotas reviewed Feb 15, 2026

View reviewed changes

src/libraries/System.Diagnostics.Process/src/System/Diagnostics/ProcessStartOptions.cs Outdated Show resolved Hide resolved

jkotas reviewed Feb 15, 2026

View reviewed changes

src/libraries/System.Diagnostics.Process/src/System/Diagnostics/ProcessStartOptions.cs Outdated Show resolved Hide resolved

jkotas reviewed Feb 15, 2026

View reviewed changes

src/libraries/System.Diagnostics.Process/src/System/Diagnostics/ProcessStartOptions.cs Show resolved Hide resolved

address code review feedback:

bf02bd9

- add comments - cache Environment.SystemDirectory - handle fully qualified paths on Windows

jkotas reviewed Feb 15, 2026

View reviewed changes

src/libraries/System.Diagnostics.Process/src/System/Diagnostics/ProcessStartOptions.cs Outdated Show resolved Hide resolved

jkotas reviewed Feb 15, 2026

View reviewed changes

build-analysis bot mentioned this pull request Feb 15, 2026

crossgen2 failing on Linux Arm32 intermittently #124007

Open

adamsitnik reviewed Feb 16, 2026

View reviewed changes

Copilot started work on behalf of adamsitnik February 16, 2026 08:21 View session

Remove executable directory probing per code review feedback

e778275

Co-authored-by: adamsitnik <6011991+adamsitnik@users.noreply.github.com>

auto-merge was automatically disabled February 16, 2026 08:32
Head branch was pushed to by a user without write access

Copilot finished work on behalf of adamsitnik February 16, 2026 08:34

Copilot AI requested a review from adamsitnik February 16, 2026 08:34

Copilot started work on behalf of adamsitnik February 16, 2026 10:26 View session

Copilot AI and others added 2 commits February 16, 2026 10:43

Simplify path resolution: remove CWD and Windows dir probing, require…

168ddf6

… explicit ./ Co-authored-by: adamsitnik <6011991+adamsitnik@users.noreply.github.com>

Restore Process.Unix.cs ResolvePath for backward compatibility

200d9f4

Co-authored-by: adamsitnik <6011991+adamsitnik@users.noreply.github.com>

Copilot AI changed the title ~~Add ProcessStartOptions class with platform-aware path resolution~~ Add ProcessStartOptions class with simplified path resolution Feb 16, 2026

Copilot finished work on behalf of adamsitnik February 16, 2026 10:49

adamsitnik added 3 commits February 16, 2026 14:22

address my own feedback, fix the tests

ec3f354

update comments, minor cleanup

bdd6301

changes after reading everything again

02905f0

adamsitnik requested review from Copilot, jkotas and stephentoub February 16, 2026 14:54

Copilot started reviewing on behalf of adamsitnik February 16, 2026 14:55 View session

Copilot AI reviewed Feb 16, 2026

View reviewed changes

Conversation

Copilot AI commented Feb 11, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Description

Changes

Example

Uh oh!

dotnet-policy-service bot commented Feb 11, 2026

Uh oh!

adamsitnik left a comment

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

adamsitnik left a comment

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Uh oh!

adamsitnik left a comment

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

stephentoub commented Feb 15, 2026

Uh oh!

jkotas Feb 15, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

adamsitnik Feb 16, 2026

Choose a reason for hiding this comment

Uh oh!

stephentoub commented Feb 15, 2026

Uh oh!

adamsitnik left a comment

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

adamsitnik commented Feb 16, 2026

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

Pull request overview

Uh oh!

Copilot AI Feb 16, 2026

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Reviewers

Assignees

Copilot AI commented Feb 11, 2026 •

edited

Loading

jkotas Feb 15, 2026 •

edited

Loading