fix(keybinds): parse niri configs with leading-underscore identifiers (#2646)

DMS reads the niri config with kdl-go, which rejects '_' as the first
character of a bare identifier ("unexpected character _") even though niri's
own parser and the KDL spec accept it. The common trigger is the
`_JAVA_AWT_WM_NONREPARENTING "1"` environment node (the standard Java /
tiling-WM fix). When the parse aborts, `dms keybinds show` returns nothing and
the Keyboard Shortcuts UI shows no binds at all.

Extend the existing preprocessor approach (the brace fix from #2230) with
quoteLeadingUnderscoreIdents, which double-quotes bare identifiers that begin
with '_' before the text reaches kdl-go. The scan is string/comment aware and
only touches a leading '_' at a token boundary, so mid-identifier underscores
(XDG_CURRENT_DESKTOP) and underscores inside strings/comments are left alone.
Token boundaries include the ends of block comments and KDL slashdash (/-), so
a node abutting a comment with no whitespace is handled too. This is safe
because the niri parser only dispatches on fixed node/section names that never
start with '_', so re-quoting such a name cannot change what DMS reads.

Refs #2230

core/internal/keybinds/providers/niri_parser.go

@@ -51,7 +51,7 @@ type NiriParser struct {
 }
 
 func parseKDL(data []byte) (*document.Document, error) {
-	return kdl.Parse(strings.NewReader(normalizeKDLBraces(string(data))))
+	return kdl.Parse(strings.NewReader(normalizeKDLBraces(quoteLeadingUnderscoreIdents(string(data)))))
 }
 
 func normalizeKDLBraces(input string) string {
@@ -94,6 +94,93 @@ func normalizeKDLBraces(input string) string {
 	return sb.String()
 }
 
+// quoteLeadingUnderscoreIdents wraps bare KDL identifiers that begin with '_'
+// in double quotes. kdl-go rejects '_' as the first character of a bare
+// identifier (e.g. the common `_JAVA_AWT_WM_NONREPARENTING "1"` environment
+// node), even though niri's own parser and the KDL spec accept it — so without
+// this the whole config fails to parse and no keybinds load. Quoting lets
+// kdl-go parse it; this is safe because the niri parser only dispatches on
+// fixed node/section names (binds, recent-windows, include, ...) that never
+// start with '_', so re-quoting such a name cannot change what DMS reads.
+// Underscores elsewhere in an identifier (XDG_CURRENT_DESKTOP) are left
+// untouched, and underscores inside strings or comments are skipped. Only a
+// leading '_' is handled; other start characters kdl-go over-rejects (e.g. '.'
+// or '?') do not occur in niri configs.
+func quoteLeadingUnderscoreIdents(input string) string {
+	var sb strings.Builder
+	sb.Grow(len(input))
+
+	var prev byte
+	n := len(input)
+	for i := 0; i < n; {
+		c := input[i]
+
+		switch {
+		case c == '"':
+			end := findStringEnd(input, i)
+			sb.WriteString(input[i:end])
+			prev = '"'
+			i = end
+		case c == '/' && i+1 < n && input[i+1] == '/':
+			end := findLineCommentEnd(input, i)
+			sb.WriteString(input[i:end])
+			prev = '\n'
+			i = end
+		case c == '/' && i+1 < n && input[i+1] == '*':
+			end := findBlockCommentEnd(input, i)
+			sb.WriteString(input[i:end])
+			prev = ' '
+			i = end
+		case c == '/' && i+1 < n && input[i+1] == '-':
+			// KDL slashdash: /- comments out the next node/value. Keep the
+			// marker but treat what follows as a fresh token start, so a
+			// slashdashed leading-underscore node (e.g. `/-_FOO "1"`) still
+			// gets quoted instead of crashing kdl-go.
+			sb.WriteByte('/')
+			sb.WriteByte('-')
+			prev = ' '
+			i += 2
+		case c == '_' && isIdentBoundary(prev):
+			end := scanBareIdent(input, i)
+			sb.WriteByte('"')
+			sb.WriteString(input[i:end])
+			sb.WriteByte('"')
+			prev = '"'
+			i = end
+		default:
+			sb.WriteByte(c)
+			prev = c
+			i++
+		}
+	}
+
+	return sb.String()
+}
+
+// isIdentBoundary reports whether the previously emitted byte ends a token, so
+// that a following '_' starts a fresh bare identifier rather than sitting in
+// the middle of one.
+func isIdentBoundary(prev byte) bool {
+	switch prev {
+	case 0, ' ', '\t', '\n', '\r', '{', '}', ';', '=', '(', ')', ',':
+		return true
+	}
+	return false
+}
+
+// scanBareIdent returns the index just past the bare identifier starting at
+// start, stopping at whitespace or any KDL delimiter.
+func scanBareIdent(s string, start int) int {
+	n := len(s)
+	for i := start; i < n; i++ {
+		switch s[i] {
+		case ' ', '\t', '\n', '\r', '"', '{', '}', '(', ')', ';', '=', ',', '/', '\\', '<', '>', '[', ']':
+			return i
+		}
+	}
+	return n
+}
+
 func findStringEnd(s string, start int) int {
 	n := len(s)
 	for i := start + 1; i < n; {