fix(parser): allow reserved words in argument position - #184
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bartlomieju merged 2 commits intoJul 23, 2026
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Reserved words (if/for/while/etc.) were rejected everywhere a bare word could appear, not just as a command name. This meant `echo for` failed to parse even though `for` is only meaningful as a command name. Per POSIX (XCU 2.4 "Reserved Words", grammar rule 7a), a reserved word is only recognized as such in command-name position (cmd_name). Argument words (cmd_suffix, rule 7b) are always plain WORDs, and quoting a reserved word anywhere suppresses recognition entirely. Move the reserved-word check out of the generic word parser and into a new parse_command_name_arg, used only for the first word of a simple command. This shell doesn't implement compound commands, so a bare reserved word as a command name is still rejected with a clear error instead of silently becoming a nonexistent command name. Fixes denoland#148
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Can you please sign the CLA? |
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@bartlomieju Done. LMK if you have any questions or feedback. |
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Fixes #148
Reserved words (
if,for,while,case, etc.) were rejected wherever a bare unquoted word could appear, not just as a command name. That meantecho forfailed to parse, even thoughforonly has any special meaning as the first word of a command.POSIX (XCU 2.4 "Reserved Words", and grammar rule 7a/7b) only recognizes a word as reserved when it's unquoted and sits in a "reserved word position" — most notably
cmd_name, the first word of a simple command. Argument words (cmd_suffix) are always plainWORDs, and quoting a reserved word anywhere, including command-name position, suppresses recognition entirely. This shell doesn't implementif/for/while/casecompound commands, so a bare reserved word as a command name is still rejected — but with a clear "Unsupported reserved word" error rather than silently becoming a nonexistent command name that fails at runtime.The fix moves the reserved-word check out of the generic word parser (which was applied to every word, argument or not) into a new
parse_command_name_arg, used only for the first word ofparse_command_args.Because the check previously lived in the shared word parser, this also loosens two positions beyond argument words that were incidentally caught by it: reserved words are now accepted as env var values (
FOO=if cmdpreviously failed with "Invalid environment variable value"; it now parses) and as redirect targets (echo hi > for,cat < in). Neither is a command name, so per POSIX neither should have been reserved-word-checked in the first place.Tested with a new
reserved_words_in_argument_positiontest covering: all reserved words as arguments (single and multiple), reserved words as arguments to arbitrary commands, env var values, word-boundary/substring cases, quoting (full and partial) in both command-name and argument position, rejection at every command-name position in a script (after;,&&,||,|, in subshells, across newlines), and case-sensitivity. Full existing test suite passes (cargo test,cargo fmt --check,cargo clippy --all-targets --all-features).This PR was prepared by an AI agent (Kiro) on behalf of @mrgrain. Human reviewed.