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fix(tmux): expand short format aliases in tmux compat #3206

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fix(tmux): expand short format aliases in tmux compat #3206

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56 changes: 55 additions & 1 deletion CLI/cmux.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -11550,13 +11550,66 @@ struct CMUXCLI {
return nil
}

private let tmuxShortFormatAliases: [Character: String] = [
"D": "pane_id",
"F": "window_flags",
"I": "window_index",
"P": "pane_index",
"S": "session_name",
"W": "window_name"
]

private func tmuxExpandShortFormatAliases(
_ format: String,
context: [String: String]
) -> String {
guard format.contains("#") else { return format }

var rendered = ""
rendered.reserveCapacity(format.count)
var index = format.startIndex
while index < format.endIndex {
let character = format[index]
guard character == "#" else {
rendered.append(character)
index = format.index(after: index)
continue
}

let nextIndex = format.index(after: index)
guard nextIndex < format.endIndex else {
rendered.append(character)
break
}

let nextCharacter = format[nextIndex]
if nextCharacter == "#" {
rendered.append("##")
index = format.index(after: nextIndex)
continue
}

if let key = tmuxShortFormatAliases[nextCharacter],
let value = context[key] {
rendered.append(value)
index = format.index(after: nextIndex)
continue
}

rendered.append(character)
index = nextIndex
}

return rendered
}

private func tmuxRenderFormat(
_ format: String?,
context: [String: String],
fallback: String
) -> String {
guard let format, !format.isEmpty else { return fallback }
var rendered = format
var rendered = tmuxExpandShortFormatAliases(format, context: context)
for (key, value) in context {
rendered = rendered.replacingOccurrences(of: "#{\(key)}", with: value)
}
Expand All @@ -11578,6 +11631,7 @@ struct CMUXCLI {
let canonicalWorkspaceId = try resolveWorkspaceId(workspaceId, client: client)
var context: [String: String] = [
"session_name": "cmux",
"window_flags": "*",
"window_id": "@\(canonicalWorkspaceId)",
"window_uuid": canonicalWorkspaceId
]
Expand Down
45 changes: 44 additions & 1 deletion daemon/remote/cmd/cmuxd-remote/tmux_compat.go
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Original file line number Diff line number Diff line change
Expand Up @@ -168,11 +168,54 @@ func parseTmuxArgs(args []string, valueFlags, boolFlags []string) *tmuxParsed {

var tmuxFormatVarRe = regexp.MustCompile(`#\{[^}]+\}`)

var tmuxShortFormatAliases = map[byte]string{
'D': "pane_id",
'F': "window_flags",
'I': "window_index",
'P': "pane_index",
'S': "session_name",
'W': "window_name",
}

func tmuxExpandShortFormatAliases(format string, context map[string]string) string {
if format == "" {
return format
}

var builder strings.Builder
builder.Grow(len(format))
for i := 0; i < len(format); i++ {
ch := format[i]
if ch != '#' || i+1 >= len(format) {
builder.WriteByte(ch)
continue
}

next := format[i+1]
if next == '#' {
builder.WriteString("##")
i++
continue
}
if key, ok := tmuxShortFormatAliases[next]; ok {
if value, exists := context[key]; exists {
builder.WriteString(value)
i++
continue
}
}
Comment on lines +200 to +206

@greptile-apps greptile-apps Bot Apr 28, 2026

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P2 Known alias but missing context key silently passes through

When a recognized alias (e.g. #I) appears in the format string but its context key (window_index) is absent from the map, the # is emitted and the loop advances to the alias letter, which is then emitted on the next iteration — reproducing the original #I literally. This passthrough is reasonable, but it diverges slightly from real tmux which would render an empty string. A brief comment clarifying the intended behavior would help future readers distinguish a deliberate design choice from a bug.


builder.WriteByte(ch)
}

return builder.String()
}

func tmuxRenderFormat(format string, context map[string]string, fallback string) string {
if format == "" {
return fallback
}
rendered := format
rendered := tmuxExpandShortFormatAliases(format, context)
for key, value := range context {
rendered = strings.ReplaceAll(rendered, "#{"+key+"}", value)
}
Expand Down
14 changes: 11 additions & 3 deletions daemon/remote/cmd/cmuxd-remote/tmux_compat_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -68,9 +68,14 @@ func TestParseTmuxArgsClusteredValueFlag(t *testing.T) {

func TestTmuxRenderFormat(t *testing.T) {
ctx := map[string]string{
"pane_id": "%abc123",
"pane_width": "80",
"window_id": "@ws1",
"session_name": "cmux",
"pane_id": "%abc123",
"pane_index": "2",
"pane_width": "80",
"window_flags": "*",
"window_id": "@ws1",
"window_index": "4",
"window_name": "editor",
}

tests := []struct {
Expand All @@ -80,6 +85,9 @@ func TestTmuxRenderFormat(t *testing.T) {
}{
{"#{pane_id}", "fallback", "%abc123"},
{"#{pane_id}:#{pane_width}", "", "%abc123:80"},
{"#S:#I.#P #W", "", "cmux:4.2 editor"},
{"#F #D", "", "* %abc123"},
{"##S #S", "", "##S cmux"},
{"#{unknown_var}", "fallback", "fallback"},
{"", "fallback", "fallback"},
{"#{pane_id} #{pane_width} #{window_id}", "", "%abc123 80 @ws1"},
Expand Down
4 changes: 4 additions & 0 deletions tests_v2/test_tmux_compat_matrix.py
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Original file line number Diff line number Diff line change
Expand Up @@ -269,6 +269,10 @@ def main() -> int:
shown = _run_cli(cli, ["display-message", "-p", msg])
_must(msg in shown.stdout, f"display-message -p should print message: {shown.stdout!r}")

short_aliases = _run_cli(cli, ["display-message", "-p", "#S:#I.#P #W"])
_must(short_aliases.stdout.strip() == f"cmux:0.0 {ws}",
f"display-message short aliases should expand: {short_aliases.stdout!r}")
Comment on lines +273 to +274

@greptile-apps greptile-apps Bot Apr 28, 2026

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P1 #W asserted against workspace UUID instead of workspace title

ws is the UUID returned by c.new_workspace(), but #W expands to window_name, which is set from the workspace's title field (see tmuxFormatContext in tmux_compat.go, line ~259). By this point in the test the workspace has been renamed to title = f"tmux-title-{stamp}", so #W would expand to that renamed title — not the UUID — causing this assertion to always fail.

Suggested change
_must(short_aliases.stdout.strip() == f"cmux:0.0 {ws}",
f"display-message short aliases should expand: {short_aliases.stdout!r}")
short_aliases = _run_cli(cli, ["display-message", "-p", "#S:#I.#P #W"])
_must(short_aliases.stdout.strip() == f"cmux:0.0 {title}",
f"display-message short aliases should expand: {short_aliases.stdout!r}")

Comment on lines +272 to +274

@greptile-apps greptile-apps Bot Apr 28, 2026

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P2 Hardcoded window_index=0 and pane_index=0 are fragile

The assertion "cmux:0.0 {title}" assumes #I (window_index) is 0 and #P (pane_index) is also 0. Window index depends on the order workspaces are listed by the daemon, which can be affected by pre-existing workspaces. Pane index after break-pane / join-pane / swap-pane operations may also not be 0. Consider reading back the actual index values from display-message #{window_index} and #{pane_index} and interpolating them into the expected string, or at least asserting that #S and #W expand correctly in isolation.

Comment on lines +272 to +274

@coderabbitai coderabbitai Bot Apr 28, 2026

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⚠️ Potential issue | 🟠 Major

Avoid hard-coding dynamic tmux context values in this regression assertion.

At Line 184 the test renames the window, and #I/#P/#W depend on current runtime context. Asserting cmux:0.0 {ws} makes this check brittle and can fail despite correct short-alias expansion.

Suggested fix 
-        short_aliases = _run_cli(cli, ["display-message", "-p", "#S:`#I`.#P `#W`"])
-        _must(short_aliases.stdout.strip() == f"cmux:0.0 {ws}",
-              f"display-message short aliases should expand: {short_aliases.stdout!r}")
+        long_form = _run_cli(
+            cli,
+            ["display-message", "-p", "#{session_name}:#{window_index}.#{pane_index} #{window_name}"],
+        )
+        short_aliases = _run_cli(cli, ["display-message", "-p", "#S:`#I`.#P `#W`"])
+        _must(
+            short_aliases.stdout.strip() == long_form.stdout.strip(),
+            f"display-message short aliases should match long-form render: short={short_aliases.stdout!r} long={long_form.stdout!r}",
+        )
🤖 Prompt for AI Agents 
Verify each finding against the current code and only fix it if needed.

In `@tests_v2/test_tmux_compat_matrix.py` around lines 272 - 274, The assertion
hard-codes dynamic tmux context values; update the check around short_aliases
(result of _run_cli) so it doesn't require fixed indices. Instead parse or
regex-match short_aliases.stdout.strip(): verify the part after the space equals
the expected window name variable ws, and verify the prefix matches the pattern
"cmux:<number>.<number>" (e.g., with a regex like r"^cmux:\d+\.\d+$" applied to
the first token). Use the existing _must helper to assert both conditions
against short_aliases.stdout.strip() so the test no longer depends on exact
runtime `#I/`#P values.


print("PASS: tmux compatibility matrix commands are wired and tested")
return 0

Expand Down