4b49907ce7
Mark issues #02 (backtick lexing/parsing), #03 (command execution runtime), and #04 (argv parsing) as resolved. Add new issues for configuration (#08), programmable prompt (#09), and interactive command execution (#10).
115 lines
4.5 KiB
Markdown
115 lines
4.5 KiB
Markdown
# Issue #10 — Interactive command execution
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## Problem
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All backtick commands redirect stdout/stderr to pipes and capture output into a table `{code, stdout, stderr}`. Interactive programs lose their tty connection:
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```lua
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`bash` -- launches bash but it can't read/write the terminal
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`vim foo` -- screen is blank, no input works
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```
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A real shell needs to hand the terminal to a child process and wait for it to finish.
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## What interactive execution means
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The child process inherits all three file descriptors (stdin, stdout, stderr) directly from the parent. The parent `waitpid()`s until the child exits. The terminal behaves as if lush isn't there — the child owns it.
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## Syntax
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### Option A: `!` prefix (recommended starting point)
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A `!` token marks a command as interactive. The command string extends to end-of-line (no closing delimiter needed):
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```lua
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!bash
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!vim foo.lua
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!ssh user@host
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```
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`!` doesn't conflict with Lua syntax (`not` is the logical-not keyword). Supports `${}` interpolation like backticks:
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```lua
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local f = "foo.lua"
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!vim ${f}
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```
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### Option B: Bare-word REPL fallback (separate issue?)
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If a line fails to parse as Lua, interpret it as an interactive command:
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```
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> vim foo.lua -- not valid Lua, runs interactively
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> ls -la -- same
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> local x = 1 -- valid Lua, runs as Lua
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```
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Only applies in the REPL, not scripts. Could be combined with Option A. Touches `lua.c` (REPL loop) rather than the lexer/parser, so may warrant its own issue.
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### Option C: Built-in function
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```lua
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exec("bash")
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exec("vim", "foo.lua")
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```
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No new syntax. Could serve as the low-level primitive that `!` compiles down to.
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## Return value
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Interactive commands return the exit code as a plain integer:
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```lua
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local code = !bash
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assert(type(code) == "number")
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```
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No stdout/stderr to capture — they go to the terminal. Returning an integer (not a table) clearly distinguishes interactive from captured commands.
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When used as a statement (no assignment), the return value is discarded.
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## Runtime implementation
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Add `luaB_interactive` to `lcmd.c`, registered as `__interactive` global:
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- `fork()` without creating any pipes
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- Child: `execvp()` directly (inherits parent's stdin/stdout/stderr)
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- Parent: ignore `SIGINT`/`SIGQUIT` (so Ctrl-C goes to child, not lush), then `waitpid()` and return exit code as integer
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- Child: restore `SIG_DFL` for `SIGINT`/`SIGQUIT` before `execvp()`
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- Reuses existing `parse_argv()` for command string tokenization
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## Lexer changes (if using `!` prefix)
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- Add `TK_ICMD` and `TK_ICMD_INTERP` tokens to enum in `llex.h`
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- Add `in_icmd` flag to `LexState` (mirrors `in_command` for backticks)
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- `read_icmd_body()`: like `read_command_body()` but terminates on newline/EOF instead of closing backtick
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- `read_icmd()`: skips leading whitespace after `!`, then calls `read_icmd_body()`
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- `luaX_readicmdcont()`: continuation reader after `${}` interpolation (mirrors `luaX_readcommandcont()`)
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- Handle `!` case in `llex()` switch: when `!` is followed by a non-`=` character at statement position, read as interactive command
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## Parser changes (if using `!` prefix)
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- Add `interactiveexp()` in `lparser.c` — mirrors `commandexp()` but compiles to `__interactive(cmdstring)` instead of `__command(cmdstring)`
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- Add `TK_ICMD` / `TK_ICMD_INTERP` cases in `simpleexp()`
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- Both simple and interpolated forms follow the same pattern as backtick commands
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## Open questions
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- Which syntax option(s) to pursue? Could start with `!` prefix and add others later.
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- Job control: should `Ctrl-Z` suspend the child and return to lush? Requires `tcsetpgrp()` / process group work. Probably defer to a later issue.
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- Should bare-word REPL fallback (Option B) be a separate issue?
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- `PATH` lookup: `execvp` already searches `PATH`, so this should just work.
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- Should `!` support multi-line commands (e.g. with `\` continuation)? Probably not — keep it simple.
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## Files touched
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| File | Description |
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|------|-------------|
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| `lcmd.c` | Add `luaB_interactive` — fork/exec without pipes, return exit code |
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| `lcmd.h` | Declare `luaB_interactive` |
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| `linit.c` | Register `__interactive` global in `opencommand()` |
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| `llex.h` | Add `TK_ICMD`, `TK_ICMD_INTERP` tokens; `in_icmd` flag on `LexState`; declare `luaX_readicmdcont()` |
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| `llex.c` | Add `read_icmd_body()`, `read_icmd()`, `luaX_readicmdcont()`; handle `!` in `llex()` |
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| `lparser.c` | Add `interactiveexp()`; handle `TK_ICMD`/`TK_ICMD_INTERP` in `simpleexp()` |
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| `lua.c` | *(Only if doing Option B)* REPL fallback logic in `loadline()` |
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