fish-shell/src/tokenizer.cpp

// A specialized tokenizer for tokenizing the fish language. In the future, the tokenizer should be
// extended to support marks, tokenizing multiple strings and disposing of unused string segments.
#include "config.h"  // IWYU pragma: keep

#include <fcntl.h>
#include <limits.h>
#include <unistd.h>
#include <cwchar>
#include <wctype.h>

#include <string>
#include <type_traits>

#include "common.h"
#include "fallback.h"  // IWYU pragma: keep
#include "future_feature_flags.h"
#include "tokenizer.h"
#include "wutil.h"  // IWYU pragma: keep

// _(s) is already wgettext(s).c_str(), so let's not convert back to wcstring
const wchar_t * tokenizer_get_error_message(tokenizer_error_t err) {
    switch (err) {
        case tokenizer_error_t::none:
            return L"";
        case tokenizer_error_t::unterminated_quote:
            return _(L"Unexpected end of string, quotes are not balanced");
        case tokenizer_error_t::unterminated_subshell:
            return _(L"Unexpected end of string, expecting ')'");
        case tokenizer_error_t::unterminated_slice:
            return _(L"Unexpected end of string, square brackets do not match");
        case tokenizer_error_t::unterminated_escape:
            return _(L"Unexpected end of string, incomplete escape sequence");
        case tokenizer_error_t::invalid_redirect:
            return _(L"Invalid input/output redirection");
        case tokenizer_error_t::invalid_pipe:
            return _(L"Cannot use stdin (fd 0) as pipe output");
        case tokenizer_error_t::closing_unopened_subshell:
            return _(L"Unexpected ')' for unopened parenthesis");
        case tokenizer_error_t::illegal_slice:
            return _(L"Unexpected '[' at this location");
        case tokenizer_error_t::closing_unopened_brace:
            return _(L"Unexpected '}' for unopened brace expansion");
        case tokenizer_error_t::unterminated_brace:
            return _(L"Unexpected end of string, incomplete parameter expansion");
        case tokenizer_error_t::expected_pclose_found_bclose:
            return _(L"Unexpected '}' found, expecting ')'");
        case tokenizer_error_t::expected_bclose_found_pclose:
            return _(L"Unexpected ')' found, expecting '}'");
    }
    assert(0 && "Unexpected tokenizer error");
    return nullptr;
}

// Whether carets redirect stderr.
static bool caret_redirs() { return !feature_test(features_t::stderr_nocaret); }

/// Return an error token and mark that we no longer have a next token.
tok_t tokenizer_t::call_error(tokenizer_error_t error_type, const wchar_t *token_start,
                              const wchar_t *error_loc) {
    assert(error_type != tokenizer_error_t::none && "tokenizer_error_t::none passed to call_error");
    assert(error_loc >= token_start && "Invalid error location");
    assert(this->buff >= token_start && "Invalid buff location");

    this->has_next = false;

    tok_t result;
    result.type = TOK_ERROR;
    result.error = error_type;
    result.offset = token_start - this->start;
    result.length = this->buff - token_start;
    result.error_offset = error_loc - token_start;
    return result;
}

tokenizer_t::tokenizer_t(const wchar_t *start, tok_flags_t flags) : buff(start), start(start) {
    assert(start != nullptr && "Invalid start");

    this->accept_unfinished = static_cast<bool>(flags & TOK_ACCEPT_UNFINISHED);
    this->show_comments = static_cast<bool>(flags & TOK_SHOW_COMMENTS);
    this->show_blank_lines = static_cast<bool>(flags & TOK_SHOW_BLANK_LINES);
}

bool tokenizer_t::next(struct tok_t *result) {
    assert(result != NULL);
    maybe_t<tok_t> tok = this->tok_next();
    if (!tok) {
        return false;
    }
    *result = std::move(*tok);
    return true;
}

/// Tests if this character can be a part of a string. The redirect ^ is allowed unless it's the
/// first character. Hash (#) starts a comment if it's the first character in a token; otherwise it
/// is considered a string character. See issue #953.
static bool tok_is_string_character(wchar_t c, bool is_first) {
    switch (c) {
        case L'\0':
        case L' ':
        case L'\n':
        case L'|':
        case L'\t':
        case L';':
        case L'\r':
        case L'<':
        case L'>':
        case L'&': {
            // Unconditional separators.
            return false;
        }
        case L'^': {
            // Conditional separator.
            return !caret_redirs() || !is_first;
        }
        default: { return true; }
    }
}

/// Quick test to catch the most common 'non-magical' characters, makes read_string slightly faster
/// by adding a fast path for the most common characters. This is obviously not a suitable
/// replacement for iswalpha.
static inline int myal(wchar_t c) { return (c >= L'a' && c <= L'z') || (c >= L'A' && c <= L'Z'); }

namespace tok_modes {
enum {
    regular_text = 0,         // regular text
    subshell = 1 << 0,        // inside of subshell parentheses
    array_brackets = 1 << 1,  // inside of array brackets
    curly_braces = 1 << 2,
    char_escape = 1 << 3,
};
}
using tok_mode_t = uint32_t;

/// Read the next token as a string.
tok_t tokenizer_t::read_string() {
    tok_mode_t mode{tok_modes::regular_text};
    std::vector<int> paran_offsets;
    std::vector<int> brace_offsets;
    std::vector<char> expecting;
    int slice_offset = 0;
    const wchar_t *const buff_start = this->buff;
    bool is_first = true;

    while (true) {
        wchar_t c = *this->buff;
#if false
        wcstring msg = L"Handling 0x%x (%lc)";
        tok_mode mode_begin = mode;
#endif

        if (c == L'\0') {
            break;
        }

        // Make sure this character isn't being escaped before anything else
        if ((mode & tok_modes::char_escape) == tok_modes::char_escape) {
            mode &= ~(tok_modes::char_escape);
            // and do nothing more
        } else if (myal(c)) {
            // Early exit optimization in case the character is just a letter,
            // which has no special meaning to the tokenizer, i.e. the same mode continues.
        }

        // Now proceed with the evaluation of the token, first checking to see if the token
        // has been explicitly ignored (escaped).
        else if (c == L'\\') {
            mode |= tok_modes::char_escape;
        } else if (c == L'(') {
            paran_offsets.push_back(this->buff - this->start);
            expecting.push_back(L')');
            mode |= tok_modes::subshell;
        } else if (c == L'{') {
            brace_offsets.push_back(this->buff - this->start);
            expecting.push_back(L'}');
            mode |= tok_modes::curly_braces;
        } else if (c == L')') {
            if (expecting.size() > 0 && expecting.back() == L'}') {
                return this->call_error(tokenizer_error_t::expected_bclose_found_pclose,
                                        this->start, this->buff);
            }
            switch (paran_offsets.size()) {
                case 0:
                    return this->call_error(tokenizer_error_t::closing_unopened_subshell,
                                            this->start, this->buff);
                case 1:
                    mode &= ~(tok_modes::subshell);
                default:
                    paran_offsets.pop_back();
            }
            expecting.pop_back();
        } else if (c == L'}') {
            if (expecting.size() > 0 && expecting.back() == L')') {
                return this->call_error(tokenizer_error_t::expected_pclose_found_bclose,
                                        this->start, this->buff);
            }
            switch (brace_offsets.size()) {
                case 0:
                    return this->call_error(tokenizer_error_t::closing_unopened_brace, this->buff,
                                            this->start + wcslen(this->start));
                case 1:
                    mode &= ~(tok_modes::curly_braces);
                default:
                    brace_offsets.pop_back();
            }
            expecting.pop_back();
        } else if (c == L'[') {
            if (this->buff != buff_start) {
                mode |= tok_modes::array_brackets;
                slice_offset = this->buff - this->start;
            } else {
                // This is actually allowed so the test operator `[` can be used as the head of a
                // command
            }
        }
        // Only exit bracket mode if we are in bracket mode.
        // Reason: `]` can be a parameter, e.g. last parameter to `[` test alias.
        // e.g. echo $argv[([ $x -eq $y ])] # must not end bracket mode on first bracket
        else if (c == L']' && ((mode & tok_modes::array_brackets) == tok_modes::array_brackets)) {
            mode &= ~(tok_modes::array_brackets);
        } else if (c == L'\'' || c == L'"') {
            const wchar_t *end = quote_end(this->buff);
            if (end) {
                this->buff = end;
            } else {
                const wchar_t *error_loc = this->buff;
                this->buff += std::wcslen(this->buff);
                if ((!this->accept_unfinished)) {
                    return this->call_error(tokenizer_error_t::unterminated_quote, buff_start,
                                            error_loc);
                }
                break;
            }
        } else if (mode == tok_modes::regular_text && !tok_is_string_character(c, is_first)) {
            break;
        }

#if false
        if (mode != mode_begin) {
            msg.append(L": mode 0x%x -> 0x%x\n");
        } else {
            msg.push_back(L'\n');
        }
        debug(0, msg.c_str(), c, c, int(mode_begin), int(mode));
#endif

        this->buff++;
        is_first = false;
    }

    if ((!this->accept_unfinished) && (mode != tok_modes::regular_text)) {
        tok_t error;
        if ((mode & tok_modes::char_escape) == tok_modes::char_escape) {
            error = this->call_error(tokenizer_error_t::unterminated_escape, buff_start,
                                     this->buff - 1);
        } else if ((mode & tok_modes::array_brackets) == tok_modes::array_brackets) {
            error = this->call_error(tokenizer_error_t::unterminated_slice, buff_start,
                                     this->start + slice_offset);
        } else if ((mode & tok_modes::subshell) == tok_modes::subshell) {
            assert(paran_offsets.size() > 0);
            size_t offset_of_open_paran = paran_offsets.back();

            error = this->call_error(tokenizer_error_t::unterminated_subshell, buff_start,
                                     this->start + offset_of_open_paran);
        } else if ((mode & tok_modes::curly_braces) == tok_modes::curly_braces) {
            assert(brace_offsets.size() > 0);
            size_t offset_of_open_brace = brace_offsets.back();

            error = this->call_error(tokenizer_error_t::unterminated_brace, buff_start,
                                     this->start + offset_of_open_brace);
        }
        return error;
    }

    tok_t result;
    result.type = TOK_STRING;
    result.offset = buff_start - this->start;
    result.length = this->buff - buff_start;
    return result;
}

// Reads a redirection or an "fd pipe" (like 2>|) from a string.
// Returns the parsed pipe or redirection, or none() on error.
struct parsed_redir_or_pipe_t {
    // Number of characters consumed.
    size_t consumed{0};

    // The token type, always either TOK_PIPE or TOK_REDIRECT.
    token_type type{TOK_REDIRECT};

    // The redirection mode if the type is TOK_REDIRECT.
    redirection_type_t redirection_mode{redirection_type_t::overwrite};

    // The redirected fd, or -1 on overflow.
    int fd{0};
};

static maybe_t<parsed_redir_or_pipe_t> read_redirection_or_fd_pipe(const wchar_t *buff) {
    bool errored = false;
    parsed_redir_or_pipe_t result;
    size_t idx = 0;

    // Determine the fd. This may be specified as a prefix like '2>...' or it may be implicit like
    // '>' or '^'. Try parsing out a number; if we did not get any digits then infer it from the
    // first character. Watch out for overflow.
    long long big_fd = 0;
    for (; iswdigit(buff[idx]); idx++) {
        // Note that it's important we consume all the digits here, even if it overflows.
        if (big_fd <= INT_MAX) big_fd = big_fd * 10 + (buff[idx] - L'0');
    }

    result.fd = (big_fd > INT_MAX ? -1 : static_cast<int>(big_fd));

    if (idx == 0) {
        // We did not find a leading digit, so there's no explicit fd. Infer it from the type.
        switch (buff[idx]) {
            case L'>': {
                result.fd = STDOUT_FILENO;
                break;
            }
            case L'<': {
                result.fd = STDIN_FILENO;
                break;
            }
            case L'^': {
                if (caret_redirs()) {
                    result.fd = STDERR_FILENO;
                } else {
                    errored = true;
                }
                break;
            }
            default: {
                errored = true;
                break;
            }
        }
    }

    // Either way we should have ended on the redirection character itself like '>'.
    // Don't allow an fd with a caret redirection - see #1873
    wchar_t redirect_char = buff[idx++];  // note increment of idx
    if (redirect_char == L'>' || (redirect_char == L'^' && idx == 1 && caret_redirs())) {
        result.redirection_mode = redirection_type_t::overwrite;
        if (buff[idx] == redirect_char) {
            // Doubled up like ^^ or >>. That means append.
            result.redirection_mode = redirection_type_t::append;
            idx++;
        }
    } else if (redirect_char == L'<') {
        result.redirection_mode = redirection_type_t::input;
    } else {
        // Something else.
        errored = true;
    }

    // Bail on error.
    if (errored) {
        return none();
    }

    // Optional characters like & or ?, or the pipe char |.
    wchar_t opt_char = buff[idx];
    if (opt_char == L'&') {
        result.redirection_mode = redirection_type_t::fd;
        idx++;
    } else if (opt_char == L'?') {
        result.redirection_mode = redirection_type_t::noclob;
        idx++;
    } else if (opt_char == L'|') {
        // So the string looked like '2>|'. This is not a redirection - it's a pipe! That gets
        // handled elsewhere.
        result.type = TOK_PIPE;
        idx++;
    }

    result.consumed = idx;
    return result;
}

maybe_t<redirection_type_t> redirection_type_for_string(const wcstring &str, int *out_fd) {
    auto v = read_redirection_or_fd_pipe(str.c_str());
    // Redirections only, no pipes.
    if (!v || v->type != TOK_REDIRECT || v->fd < 0) return none();
    if (out_fd) *out_fd = v->fd;
    return v->redirection_mode;
}

int fd_redirected_by_pipe(const wcstring &str) {
    // Hack for the common case.
    if (str == L"|") {
        return STDOUT_FILENO;
    }
    auto v = read_redirection_or_fd_pipe(str.c_str());
    return (v && v->type == TOK_PIPE) ? v->fd : -1;
}

int oflags_for_redirection_type(redirection_type_t type) {
    switch (type) {
        case redirection_type_t::append: {
            return O_CREAT | O_APPEND | O_WRONLY;
        }
        case redirection_type_t::overwrite: {
            return O_CREAT | O_WRONLY | O_TRUNC;
        }
        case redirection_type_t::noclob: {
            return O_CREAT | O_EXCL | O_WRONLY;
        }
        case redirection_type_t::input: {
            return O_RDONLY;
        }
        case redirection_type_t::fd:
        default: {
            return -1;
        }
    }
}

/// Test if a character is whitespace. Differs from iswspace in that it does not consider a newline
/// to be whitespace.
static bool iswspace_not_nl(wchar_t c) {
    switch (c) {
        case L' ':
        case L'\t':
        case L'\r':
            return true;
        case L'\n':
            return false;
        default:
            return iswspace(c);
    }
}

maybe_t<tok_t> tokenizer_t::tok_next() {
    if (!this->has_next) {
        return none();
    }

    // Consume non-newline whitespace. If we get an escaped newline, mark it and continue past it.
    bool preceding_escaped_nl = false;
    for (;;) {
        if (this->buff[0] == L'\\' && this->buff[1] == L'\n') {
            this->buff += 2;
            this->continue_line_after_comment = true;
            preceding_escaped_nl = true;
        } else if (iswspace_not_nl(this->buff[0])) {
            this->buff++;
        } else {
            break;
        }
    }

    while (*this->buff == L'#') {
        // We have a comment, walk over the comment.
        const wchar_t *comment_start = this->buff;
        while (this->buff[0] != L'\n' && this->buff[0] != L'\0') this->buff++;
        size_t comment_len = this->buff - comment_start;

        // If we are going to continue after the comment, skip any trailing newline.
        if (this->buff[0] == L'\n' && this->continue_line_after_comment) this->buff++;

        // Maybe return the comment.
        if (this->show_comments) {
            tok_t result;
            result.type = TOK_COMMENT;
            result.offset = comment_start - this->start;
            result.length = comment_len;
            result.preceding_escaped_nl = preceding_escaped_nl;
            return result;
        }
        while (iswspace_not_nl(this->buff[0])) this->buff++;
    }

    // We made it past the comments and ate any trailing newlines we wanted to ignore.
    this->continue_line_after_comment = false;
    size_t start_pos = this->buff - this->start;

    tok_t result;
    result.offset = start_pos;
    switch (*this->buff) {
        case L'\0': {
            this->has_next = false;
            return none();
        }
        case L'\r':  // carriage-return
        case L'\n':  // newline
        case L';': {
            result.type = TOK_END;
            result.length = 1;
            this->buff++;
            // Hack: when we get a newline, swallow as many as we can. This compresses multiple
            // subsequent newlines into a single one.
            if (!this->show_blank_lines) {
                while (*this->buff == L'\n' || *this->buff == 13 /* CR */ || *this->buff == ' ' ||
                       *this->buff == '\t') {
                    this->buff++;
                }
            }
            break;
        }
        case L'&': {
            if (this->buff[1] == L'&') {
                result.type = TOK_ANDAND;
                result.length = 2;
                this->buff += 2;
            } else {
                result.type = TOK_BACKGROUND;
                result.length = 1;
                this->buff++;
            }
            break;
        }
        case L'|': {
            if (this->buff[1] == L'|') {
                result.type = TOK_OROR;
                result.length = 2;
                this->buff += 2;
            } else {
                result.type = TOK_PIPE;
                result.redirected_fd = 1;
                result.length = 1;
                this->buff++;
            }
            break;
        }
        case L'>':
        case L'<': {
            // There's some duplication with the code in the default case below. The key difference
            // here is that we must never parse these as a string; a failed redirection is an error!
            auto redir_or_pipe = read_redirection_or_fd_pipe(this->buff);
            if (!redir_or_pipe || redir_or_pipe->fd < 0) {
                return this->call_error(tokenizer_error_t::invalid_redirect, this->buff,
                                        this->buff);
            }
            result.type = redir_or_pipe->type;
            result.redirected_fd = redir_or_pipe->fd;
            result.length = redir_or_pipe->consumed;
            this->buff += redir_or_pipe->consumed;
            break;
        }
        default: {
            // Maybe a redirection like '2>&1', maybe a pipe like 2>|, maybe just a string.
            const wchar_t *error_location = this->buff;
            maybe_t<parsed_redir_or_pipe_t> redir_or_pipe;
            if (iswdigit(*this->buff) || (*this->buff == L'^' && caret_redirs())) {
                redir_or_pipe = read_redirection_or_fd_pipe(this->buff);
            }

            if (redir_or_pipe && redir_or_pipe->consumed > 0) {
                // It looks like a redirection or a pipe. But we don't support piping fd 0. Note
                // that fd 0 may be -1, indicating overflow; but we don't treat that as a tokenizer
                // error.
                if (redir_or_pipe->type == TOK_PIPE && redir_or_pipe->fd == 0) {
                    return this->call_error(tokenizer_error_t::invalid_pipe, error_location,
                                            error_location);
                }
                result.type = redir_or_pipe->type;
                result.redirected_fd = redir_or_pipe->fd;
                result.length = redir_or_pipe->consumed;
                this->buff += redir_or_pipe->consumed;
            } else {
                // Not a redirection or pipe, so just a string.
                result = this->read_string();
            }
            break;
        }
    }
    result.preceding_escaped_nl = preceding_escaped_nl;
    return result;
}

wcstring tok_first(const wcstring &str) {
    tokenizer_t t(str.c_str(), 0);
    tok_t token;
    if (t.next(&token) && token.type == TOK_STRING) {
        return t.text_of(token);
    }
    return {};
}

bool move_word_state_machine_t::consume_char_punctuation(wchar_t c) {
    enum { s_always_one = 0, s_rest, s_whitespace_rest, s_whitespace, s_alphanumeric, s_end };

    bool consumed = false;
    while (state != s_end && !consumed) {
        switch (state) {
            case s_always_one: {
                // Always consume the first character.
                consumed = true;
                if (iswspace(c)) {
                    state = s_whitespace;
                } else {
                    // Don't allow switching type (ws->nonws) after non-whitespace.
                    state = s_rest;
                }
                break;
            }
            case s_rest: {
                if (iswspace(c)) {
                    // Consume only trailing whitespace.
                    state = s_whitespace_rest;
                } else if (iswalnum(c)) {
                    // Consume only alnums.
                    state = s_alphanumeric;
                } else {
                    consumed = false;
                    state = s_end;
                }
                break;
            }
            case s_whitespace_rest:
            case s_whitespace: {
                // "whitespace" consumes whitespace and switches to alnums,
                // "whitespace_rest" only consumes whitespace.
                if (iswspace(c)) {
                    // Consumed whitespace.
                    consumed = true;
                } else {
                    state = state == s_whitespace ? s_alphanumeric : s_end;
                }
                break;
            }
            case s_alphanumeric: {
                if (iswalnum(c)) {
                    consumed = true;  // consumed alphanumeric
                } else {
                    state = s_end;
                }
                break;
            }
            case s_end:
            default: { break; }
        }
    }
    return consumed;
}

bool move_word_state_machine_t::is_path_component_character(wchar_t c) {
    // Always treat separators as first. All this does is ensure that we treat ^ as a string
    // character instead of as stderr redirection, which I hypothesize is usually what is desired.
    return tok_is_string_character(c, true) && !std::wcschr(L"/={,}'\"", c);
}

bool move_word_state_machine_t::consume_char_path_components(wchar_t c) {
    enum {
        s_initial_punctuation,
        s_whitespace,
        s_separator,
        s_slash,
        s_path_component_characters,
        s_end
    };

    // std::fwprintf(stdout, L"state %d, consume '%lc'\n", state, c);
    bool consumed = false;
    while (state != s_end && !consumed) {
        switch (state) {
            case s_initial_punctuation: {
                if (!is_path_component_character(c)) {
                    consumed = true;
                }
                state = s_whitespace;
                break;
            }
            case s_whitespace: {
                if (iswspace(c)) {
                    consumed = true;  // consumed whitespace
                } else if (c == L'/' || is_path_component_character(c)) {
                    state = s_slash;  // path component
                } else {
                    state = s_separator;  // path separator
                }
                break;
            }
            case s_separator: {
                if (!iswspace(c) && !is_path_component_character(c)) {
                    consumed = true;  // consumed separator
                } else {
                    state = s_end;
                }
                break;
            }
            case s_slash: {
                if (c == L'/') {
                    consumed = true;  // consumed slash
                } else {
                    state = s_path_component_characters;
                }
                break;
            }
            case s_path_component_characters: {
                if (is_path_component_character(c)) {
                    consumed = true;  // consumed string character except slash
                } else {
                    state = s_end;
                }
                break;
            }
            case s_end:
            default: { break; }
        }
    }
    return consumed;
}

bool move_word_state_machine_t::consume_char_whitespace(wchar_t c) {
    enum { s_always_one = 0, s_blank, s_graph, s_end };

    bool consumed = false;
    while (state != s_end && !consumed) {
        switch (state) {
            case s_always_one: {
                consumed = true;  // always consume the first character
                state = s_blank;
                break;
            }
            case s_blank: {
                if (iswblank(c)) {
                    consumed = true;  // consumed whitespace
                } else {
                    state = s_graph;
                }
                break;
            }
            case s_graph: {
                if (iswgraph(c)) {
                    consumed = true;  // consumed printable non-space
                } else {
                    state = s_end;
                }
                break;
            }
            case s_end:
            default: { break; }
        }
    }
    return consumed;
}

bool move_word_state_machine_t::consume_char(wchar_t c) {
    switch (style) {
        case move_word_style_punctuation: {
            return consume_char_punctuation(c);
        }
        case move_word_style_path_components: {
            return consume_char_path_components(c);
        }
        case move_word_style_whitespace: {
            return consume_char_whitespace(c);
        }
    }

    DIE("should not reach this statement");  // silence some compiler errors about not returning
}

move_word_state_machine_t::move_word_state_machine_t(move_word_style_t syl)
    : state(0), style(syl) {}

void move_word_state_machine_t::reset() { state = 0; }