Enhance fish shell completions with static+dynamic hybrid generation by slang25 · Pull Request #53716 · dotnet/sdk

slang25 · 2026-04-06T18:07:33Z

Summary

Replace the fish shell provider's simple dynamic one-liner (complete -f -c dotnet -a "(dotnet complete (commandline -cp))") with a full static+dynamic completion generator, matching the approach taken by the Bash, Zsh, and PowerShell providers.
The generated script uses a state-machine that walks the tokenized command line to determine the current subcommand context, then emits static completions for subcommands, options (including all aliases), and positional arguments — falling back to dynamic complete calls where IsDynamic is set.
Add 6 snapshot tests for the fish provider covering generic, option, subcommand, nested subcommand, dynamic, and static option value scenarios.

Test plan

All 21 StaticCompletions tests pass (15 existing + 6 new fish tests)
Manual verification with a fish shell and a real dotnet binary

🤖 Generated with Claude Code

Replace the fish shell provider's simple dynamic one-liner with a full static+dynamic completion generator, matching the approach taken by the Bash, Zsh, and PowerShell providers. The generated script uses a state-machine that walks the tokenized command line to determine the current subcommand context, then emits static completions for subcommands, options, and positional arguments — falling back to dynamic complete calls where IsDynamic is set. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

baronfel · 2026-04-06T18:09:45Z

HECK YEAH! Thanks for sending this, I'll try to review this afternoon.

Copilot

Pull request overview

This PR upgrades the Fish shell completions generator from a simple dynamic invocation to a hybrid static+dynamic generator (similar in spirit to the existing Bash/Zsh/PowerShell providers), and adds snapshot coverage for the new output.

Changes:

Replaced Fish completion generation with a state-machine driven script that emits static completions and falls back to dynamic completions for IsDynamic symbols.
Added Fish snapshot tests covering generic, options/subcommands, nested subcommands, dynamic completions, and static option values.
Updated Verify configuration to treat .fish snapshot files as text.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 2 comments.

File	Description
test/System.CommandLine.StaticCompletions.Tests/VerifyConfiguration.cs	Registers `.fish` as a text extension for snapshot verification.
test/System.CommandLine.StaticCompletions.Tests/FishShellProviderTests.cs	Adds Fish provider snapshot tests.
src/System.CommandLine.StaticCompletions/shells/FishShellProvider.cs	Implements the new static+dynamic Fish completion script generator.
test/System.CommandLine.StaticCompletions.Tests/snapshots/fish/*.verified.fish	Adds the expected Fish completion script snapshots for the new tests.

Copilot · 2026-04-06T18:14:04Z

+    /// Uses fish's commandline builtin to get completed tokens and the current partial word.
+    /// </summary>
+    private static void WriteTokenization(IndentedTextWriter writer)
+    {
+        // -opc: tokenize, cut at cursor, only completed tokens (excludes current partial word)
+        writer.WriteLine("set -l tokens (commandline -opc)");
+        // -ct: the current token being completed (may be empty or partial)
+        writer.WriteLine("set -l current (commandline -ct)");


The generated fish script assigns current from commandline -ct but never uses it anywhere in the output. Consider removing this line (or using current to filter/short-circuit) to avoid dead code in the generated completion function.

Suggested change

/// Uses fish's commandline builtin to get completed tokens and the current partial word.

/// </summary>

private static void WriteTokenization(IndentedTextWriter writer)

{

// -opc: tokenize, cut at cursor, only completed tokens (excludes current partial word)

writer.WriteLine("set -l tokens (commandline -opc)");

// -ct: the current token being completed (may be empty or partial)

writer.WriteLine("set -l current (commandline -ct)");

/// Uses fish's commandline builtin to get completed tokens up to the cursor.

/// </summary>

private static void WriteTokenization(IndentedTextWriter writer)

{

// -opc: tokenize, cut at cursor, only completed tokens

writer.WriteLine("set -l tokens (commandline -opc)");

Copilot · 2026-04-06T18:14:04Z

+            // Subcommand transitions
+            foreach (var sub in visibleSubs)
+            {
+                var subStateId = states.First(s => s.cmd == sub).id;
+                var names = string.Join(" ", sub.Names());
+                writer.WriteLine($"case {names}");
+                writer.Indent++;
+                writer.WriteLine($"set state {subStateId}");
+                writer.Indent--;
+            }


WriteStateWalker resolves each subcommand’s state id via states.First(...) inside nested loops, making generation O(n^2) in the number of commands. For large command graphs (e.g., dotnet), consider building a Dictionary<Command,int> once (e.g., when collecting states) and using it for O(1) lookups.

Handle options with arity > 1 (bounded and unbounded) in the fish shell state walker and option value completions. Fix fish seq warning when token count is less than 2 by guarding the scan-back loop. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

…kups Address review feedback: remove dead `set -l current` variable from generated fish script, and replace O(n²) states.First() lookups with a pre-built Dictionary<Command, int> for O(1) state ID resolution. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Copilot

Pull request overview

Copilot reviewed 12 out of 12 changed files in this pull request and generated 4 comments.

Copilot · 2026-04-08T18:53:31Z

+    // Options with MaximumNumberOfValues at or above this threshold are treated as unbounded
+    // (i.e. consume tokens until an option-like token is encountered).
+    // System.CommandLine uses 100_000 as its internal sentinel for ZeroOrMore/OneOrMore.
+    private const int UnboundedArityThreshold = 100;


UnboundedArityThreshold is set to 100, but the comment indicates System.CommandLine uses 100_000 as the sentinel for unbounded arities (ZeroOrMore/OneOrMore). With the current value, any option with a bounded max >99 will be treated as unbounded, which can change parsing/completion behavior. Consider using the actual sentinel (or a check keyed specifically to the unbounded sentinel) so large-but-bounded arities stay bounded.

Suggested change

private const int UnboundedArityThreshold = 100;

private const int UnboundedArityThreshold = 100_000;

Copilot · 2026-04-08T18:53:32Z

+        writer.WriteLine("if string match -q -- '-*' $next");
+        writer.Indent++;
+        writer.WriteLine("break");
+        writer.Indent--;


The multi-value skip loop stops when the next token matches -*. This will incorrectly stop consuming values for legitimate option values that start with - (e.g., negative numbers like -1, or strings beginning with a dash), causing the state machine to mis-parse the command line. Consider checking whether the next token is actually one of the known option names for the current command context (and handling -- end-of-options) instead of using a prefix heuristic.

Suggested change

writer.WriteLine("if string match -q -- '-*' $next");

writer.Indent++;

writer.WriteLine("break");

writer.Indent--;

writer.WriteLine("if test \"$next\" = \"--\"");

writer.Indent++;

writer.WriteLine("break");

writer.Indent--;

writer.WriteLine("else if string match -rq -- '^--.+|^-[^0-9].*' $next");

writer.Indent++;

writer.WriteLine("break");

writer.Indent--;

Copilot · 2026-04-08T18:53:32Z

+        // Scan backward through tokens to find the nearest option (token starting with -)
+        writer.WriteLine("set -l opt_index 0");
+        writer.WriteLine("if test (count $tokens) -ge 2");
+        writer.Indent++;
+        writer.WriteLine("for j in (seq (count $tokens) -1 2)");
+        writer.Indent++;
+        writer.WriteLine("if string match -q -- '-*' $tokens[$j]");
+        writer.Indent++;
+        writer.WriteLine("set opt_index $j");
+        writer.WriteLine("break");
+        writer.Indent--;
+        writer.WriteLine("end");
+        writer.Indent--;
+        writer.WriteLine("end");
+        writer.Indent--;
+        writer.WriteLine("end");


Option-value completion scans backward for the nearest token matching -* to decide which option we're completing. This can misidentify negative numeric values (or other dash-prefixed values) as the "current option", which will suppress/alter completions incorrectly. Consider restricting the scan to tokens that match known option names in the current state (and treating -- as an end-of-options marker).

Suggested change

// Scan backward through tokens to find the nearest option (token starting with -)

writer.WriteLine("set -l opt_index 0");

writer.WriteLine("if test (count $tokens) -ge 2");

writer.Indent++;

writer.WriteLine("for j in (seq (count $tokens) -1 2)");

writer.Indent++;

writer.WriteLine("if string match -q -- '-*' $tokens[$j]");

writer.Indent++;

writer.WriteLine("set opt_index $j");

writer.WriteLine("break");

writer.Indent--;

writer.WriteLine("end");

writer.Indent--;

writer.WriteLine("end");

writer.Indent--;

writer.WriteLine("end");

// Scan backward through tokens to find the nearest known value-taking option for the current state.

// Stop scanning if we encounter the end-of-options marker.

writer.WriteLine("set -l opt_index 0");

writer.WriteLine("if test (count $tokens) -ge 2");

writer.Indent++;

writer.WriteLine("switch $state");

writer.Indent++;

foreach (var (stateId, cmd) in states)

{

var valueOptions = cmd.HierarchicalOptions()

.Where(o => !o.Hidden && !o.IsFlag())

.ToArray();

if (valueOptions.Length == 0)

continue;

writer.WriteLine($"case {stateId}");

writer.Indent++;

writer.WriteLine("for j in (seq (count $tokens) -1 2)");

writer.Indent++;

writer.WriteLine("if test $tokens[$j] = '--'");

writer.Indent++;

writer.WriteLine("break");

writer.Indent--;

writer.WriteLine("end");

writer.WriteLine("switch $tokens[$j]");

writer.Indent++;

foreach (var option in valueOptions)

{

var names = string.Join(" ", option.Names());

writer.WriteLine($"case {names}");

writer.Indent++;

writer.WriteLine("set opt_index $j");

writer.WriteLine("break");

writer.Indent--;

}

writer.Indent--;

writer.WriteLine("end");

writer.Indent--;

writer.WriteLine("end");

writer.Indent--;

}

writer.Indent--;

writer.WriteLine("end");

writer.Indent--;

writer.WriteLine("end");

Copilot · 2026-04-08T18:53:32Z

+            foreach (var sub in visibleSubs)
+            {
+                var subStateId = stateIdByCommand[sub];
+                var names = string.Join(" ", sub.Names());
+                writer.WriteLine($"case {names}");
+                writer.Indent++;


Fish switch/case patterns are glob patterns. Emitting raw command/option names into case clauses (e.g., case {names}) can cause unexpected matches if a name contains glob metacharacters like *, ?, or []. Consider escaping fish glob metacharacters when generating case patterns so symbol names are treated literally.

Change UnboundedArityThreshold from 100 to 100_000 to match the actual sentinel value used by System.CommandLine for ZeroOrMore/OneOrMore. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

baronfel · 2026-04-09T14:25:25Z

/backport to release/10.0.3xx

github-actions · 2026-04-09T14:25:39Z

Started backporting to release/10.0.3xx (link to workflow run)

Copilot AI review requested due to automatic review settings April 6, 2026 18:07

Copilot started reviewing on behalf of slang25 April 6, 2026 18:08 View session

Copilot AI reviewed Apr 6, 2026

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baronfel approved these changes Apr 7, 2026

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Comment thread src/System.CommandLine.StaticCompletions/shells/FishShellProvider.cs Outdated

baronfel force-pushed the slang25/fish-static-completions branch from 6fb5dca to 2320bab Compare April 8, 2026 14:04

slang25 force-pushed the slang25/fish-static-completions branch from 2320bab to 1977339 Compare April 8, 2026 17:39

baronfel added the Document for new feature label Apr 8, 2026

baronfel added this to the 11.0.1xx milestone Apr 8, 2026

baronfel enabled auto-merge (squash) April 8, 2026 17:42

auto-merge was automatically disabled April 8, 2026 18:40
Head branch was pushed to by a user without write access

slang25 requested a review from Copilot April 8, 2026 18:48

Copilot started reviewing on behalf of slang25 April 8, 2026 18:49 View session

Copilot AI reviewed Apr 8, 2026

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Use exact System.CommandLine sentinel for unbounded arity threshold

9ab7886

Change UnboundedArityThreshold from 100 to 100_000 to match the actual sentinel value used by System.CommandLine for ZeroOrMore/OneOrMore. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

baronfel enabled auto-merge (squash) April 8, 2026 20:12

baronfel merged commit d043492 into dotnet:main Apr 8, 2026
22 of 24 checks passed

github-actions Bot mentioned this pull request Apr 9, 2026

[release-notes] .NET 11 Preview 3 jeffhandley/dotnet-core-release-notes#4

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github-actions Bot mentioned this pull request Apr 9, 2026

[release/10.0.3xx] Enhance fish shell completions with static+dynamic hybrid generation #53779

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dotnet-maestro Bot mentioned this pull request Apr 10, 2026

[main] Source code updates from dotnet/sdk dotnet/dotnet#5968

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Enhance fish shell completions with static+dynamic hybrid generation#53716

Enhance fish shell completions with static+dynamic hybrid generation#53716
baronfel merged 4 commits intodotnet:mainfrom
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	private const int UnboundedArityThreshold = 100;
	private const int UnboundedArityThreshold = 100_000;

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slang25 commented Apr 6, 2026

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