Implement builtin_printf in Rust

This implements builtin_printf in Rust.

fish-rust/src/builtins/mod.rs

@@ -7,6 +7,7 @@ pub mod contains;
 pub mod echo;
 pub mod emit;
 pub mod exit;
+pub mod printf;
 pub mod pwd;
 pub mod random;
 pub mod realpath;

fish-rust/src/builtins/printf.rs

@@ -0,0 +1,817 @@
+// printf - format and print data
+// Copyright (C) 1990-2007 Free Software Foundation, Inc.
+//
+// This program is free software; you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation; either version 2, or (at your option)
+// any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program; if not, write to the Free Software Foundation,
+// Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
+// Usage: printf format [argument...]
+//
+// A front end to the printf function that lets it be used from the shell.
+//
+// Backslash escapes:
+//
+// \" = double quote
+// \\ = backslash
+// \a = alert (bell)
+// \b = backspace
+// \c = produce no further output
+// \e = escape
+// \f = form feed
+// \n = new line
+// \r = carriage return
+// \t = horizontal tab
+// \v = vertical tab
+// \ooo = octal number (ooo is 1 to 3 digits)
+// \xhh = hexadecimal number (hhh is 1 to 2 digits)
+// \uhhhh = 16-bit Unicode character (hhhh is 4 digits)
+// \Uhhhhhhhh = 32-bit Unicode character (hhhhhhhh is 8 digits)
+//
+// Additional directive:
+//
+// %b = print an argument string, interpreting backslash escapes,
+//   except that octal escapes are of the form \0 or \0ooo.
+//
+// The `format' argument is re-used as many times as necessary
+// to convert all of the given arguments.
+//
+// David MacKenzie <djm@gnu.ai.mit.edu>
+
+// This file has been imported from source code of printf command in GNU Coreutils version 6.9.
+
+use libc::c_int;
+use num_traits;
+use std::result::Result;
+
+use crate::builtins::shared::{io_streams_t, STATUS_CMD_ERROR, STATUS_CMD_OK, STATUS_INVALID_ARGS};
+use crate::common::ENCODE_DIRECT_BASE;
+use crate::ffi::parser_t;
+use crate::locale::{get_numeric_locale, Locale};
+use crate::wchar::{wstr, WExt, WString, L};
+use crate::wutil::errors::Error;
+use crate::wutil::gettext::{wgettext, wgettext_fmt};
+use crate::wutil::wcstod::wcstod;
+use crate::wutil::wcstoi::{fish_wcstoi_partial, Options as WcstoiOpts};
+use crate::wutil::{sprintf, wstr_offset_in};
+use printf_compat::args::ToArg;
+use printf_compat::printf::sprintf_locale;
+
+/// \return true if \p c is an octal digit.
+fn is_octal_digit(c: char) -> bool {
+    ('0'..='7').contains(&c)
+}
+
+/// \return true if \p c is a decimal digit.
+fn iswdigit(c: char) -> bool {
+    c.is_ascii_digit()
+}
+
+/// \return true if \p c is a hexadecimal digit.
+fn iswxdigit(c: char) -> bool {
+    c.is_ascii_hexdigit()
+}
+
+struct builtin_printf_state_t<'a> {
+    // Out and err streams. Note this is a captured reference!
+    streams: &'a mut io_streams_t,
+
+    // The status of the operation.
+    exit_code: c_int,
+
+    // Whether we should stop outputting. This gets set in the case of an error, and also with the
+    // \c escape.
+    early_exit: bool,
+
+    // Our output buffer, so we don't write() constantly.
+    // Our strategy is simple:
+    // We print once per argument, and we flush the buffer before the error.
+    buff: WString,
+
+    // The locale, which affects printf output and also parsing of floats due to decimal separators.
+    locale: Locale,
+}
+
+/// Convert to a scalar type. \return the result of conversion, and the end of the converted string.
+/// On conversion failure, \p end is not modified.
+trait RawStringToScalarType: Copy + num_traits::Zero + std::convert::From<u32> {
+    /// Convert from a string to our self type.
+    /// \return the result of conversion, and the remainder of the string.
+    fn raw_string_to_scalar_type<'a>(
+        s: &'a wstr,
+        locale: &Locale,
+        end: &mut &'a wstr,
+    ) -> Result<Self, Error>;
+
+    /// Convert from a Unicode code point to this type.
+    /// This supports printf's ability to convert from char to scalar via a leading quote.
+    /// Try it:
+    ///     > printf "%f" "'a"
+    ///     97.000000
+    /// Wild stuff.
+    fn from_ord(c: char) -> Self {
+        let as_u32: u32 = c.into();
+        as_u32.into()
+    }
+}
+
+impl RawStringToScalarType for i64 {
+    fn raw_string_to_scalar_type<'a>(
+        s: &'a wstr,
+        _locale: &Locale,
+        end: &mut &'a wstr,
+    ) -> Result<Self, Error> {
+        let mut consumed = 0;
+        let res = fish_wcstoi_partial(s, WcstoiOpts::default(), &mut consumed);
+        *end = s.slice_from(consumed);
+        res
+    }
+}
+
+impl RawStringToScalarType for u64 {
+    fn raw_string_to_scalar_type<'a>(
+        s: &'a wstr,
+        _locale: &Locale,
+        end: &mut &'a wstr,
+    ) -> Result<Self, Error> {
+        let mut consumed = 0;
+        let res = fish_wcstoi_partial(
+            s,
+            WcstoiOpts {
+                wrap_negatives: true,
+                ..Default::default()
+            },
+            &mut consumed,
+        );
+        *end = s.slice_from(consumed);
+        res
+    }
+}
+
+impl RawStringToScalarType for f64 {
+    fn raw_string_to_scalar_type<'a>(
+        s: &'a wstr,
+        locale: &Locale,
+        end: &mut &'a wstr,
+    ) -> Result<Self, Error> {
+        let mut consumed: usize = 0;
+        let mut result = wcstod(s, locale.decimal_point, &mut consumed);
+        if result.is_ok() && consumed == s.chars().count() {
+            *end = s.slice_from(consumed);
+            return result;
+        }
+        // The conversion using the user's locale failed. That may be due to the string not being a
+        // valid floating point value. It could also be due to the locale using different separator
+        // characters than the normal english convention. So try again by forcing the use of a locale
+        // that employs the english convention for writing floating point numbers.
+        consumed = 0;
+        result = wcstod(s, '.', &mut consumed);
+        if result.is_ok() {
+            *end = s.slice_from(consumed);
+        }
+        return result;
+    }
+}
+
+/// Convert a string to a scalar type.
+/// Use state.verify_numeric to report any errors.
+fn string_to_scalar_type<T: RawStringToScalarType>(
+    s: &wstr,
+    state: &mut builtin_printf_state_t,
+) -> T {
+    if s.char_at(0) == '"' || s.char_at(0) == '\'' {
+        // Note that if the string is really just a leading quote,
+        // we really do want to convert the "trailing nul".
+        T::from_ord(s.char_at(1))
+    } else {
+        let mut end = s;
+        let mval = T::raw_string_to_scalar_type(s, &state.locale, &mut end);
+        state.verify_numeric(s, end, mval.err());
+        mval.unwrap_or(T::zero())
+    }
+}
+
+/// For each character in str, set the corresponding boolean in the array to the given flag.
+fn modify_allowed_format_specifiers(ok: &mut [bool; 256], str: &str, flag: bool) {
+    for c in str.chars() {
+        ok[c as usize] = flag;
+    }
+}
+
+impl<'a> builtin_printf_state_t<'a> {
+    #[allow(clippy::partialeq_to_none)]
+    fn verify_numeric(&mut self, s: &wstr, end: &wstr, errcode: Option<Error>) {
+        // This check matches the historic `errcode != EINVAL` check from C++.
+        // Note that empty or missing values will be silently treated as 0.
+        if errcode != None && errcode != Some(Error::InvalidChar) && errcode != Some(Error::Empty) {
+            match errcode.unwrap() {
+                Error::Overflow => {
+                    self.fatal_error(sprintf!("%ls: %ls", s, wgettext!("Number out of range")));
+                }
+                Error::Empty => {
+                    self.fatal_error(sprintf!("%ls: %ls", s, wgettext!("Number was empty")));
+                }
+                Error::InvalidChar | Error::CharsLeft => {
+                    panic!("Unreachable");
+                }
+            }
+        } else if !end.is_empty() {
+            if s.as_ptr() == end.as_ptr() {
+                self.fatal_error(wgettext_fmt!("%ls: expected a numeric value", s));
+            } else {
+                // This isn't entirely fatal - the value should still be printed.
+                self.nonfatal_error(wgettext_fmt!(
+                    "%ls: value not completely converted (can't convert '%ls')",
+                    s,
+                    end
+                ));
+                // Warn about octal numbers as they can be confusing.
+                // Do it if the unconverted digit is a valid hex digit,
+                // because it could also be an "0x" -> "0" typo.
+                if s.char_at(0) == '0' && iswxdigit(end.char_at(0)) {
+                    self.nonfatal_error(wgettext_fmt!(
+                        "Hint: a leading '0' without an 'x' indicates an octal number"
+                    ));
+                }
+            }
+        }
+    }
+
+    /// Evaluate a printf conversion specification.  SPEC is the start of the directive, and CONVERSION
+    /// specifies the type of conversion.  SPEC does not include any length modifier or the
+    /// conversion specifier itself.  FIELD_WIDTH and PRECISION are the field width and
+    /// precision for '*' values, if HAVE_FIELD_WIDTH and HAVE_PRECISION are true, respectively.
+    /// ARGUMENT is the argument to be formatted.
+    #[allow(clippy::collapsible_else_if, clippy::too_many_arguments)]
+    fn print_direc(
+        &mut self,
+        spec: &wstr,
+        conversion: char,
+        have_field_width: bool,
+        field_width: i32,
+        have_precision: bool,
+        precision: i32,
+        argument: &wstr,
+    ) {
+        /// Printf macro helper which provides our locale.
+        macro_rules! sprintf_loc {
+            (
+            $fmt:expr, // format string of type &wstr
+            $($arg:expr),* // arguments
+            ) => {
+                sprintf_locale(
+                    $fmt,
+                    &self.locale,
+                    &[$($arg.to_arg()),*]
+                )
+            }
+        }
+
+        // Start with everything except the conversion specifier.
+        let mut fmt = spec.to_owned();
+
+        // Create a copy of the % directive, with a width modifier substituted for any
+        // existing integer length modifier.
+        match conversion {
+            'x' | 'X' | 'd' | 'i' | 'o' | 'u' => {
+                fmt.push_str("ll");
+            }
+            'a' | 'e' | 'f' | 'g' | 'A' | 'E' | 'F' | 'G' => {
+                fmt.push_str("L");
+            }
+            's' | 'c' => {
+                fmt.push_str("l");
+            }
+            _ => {}
+        }
+
+        // Append the conversion itself.
+        fmt.push(conversion);
+
+        // Rebind as a ref.
+        let fmt: &wstr = &fmt;
+        match conversion {
+            'd' | 'i' => {
+                let arg: i64 = string_to_scalar_type(argument, self);
+                if !have_field_width {
+                    if !have_precision {
+                        self.append_output_str(sprintf_loc!(fmt, arg));
+                    } else {
+                        self.append_output_str(sprintf_loc!(fmt, precision, arg));
+                    }
+                } else {
+                    if !have_precision {
+                        self.append_output_str(sprintf_loc!(fmt, field_width, arg));
+                    } else {
+                        self.append_output_str(sprintf_loc!(fmt, field_width, precision, arg));
+                    }
+                }
+            }
+            'o' | 'u' | 'x' | 'X' => {
+                let arg: u64 = string_to_scalar_type(argument, self);
+                if !have_field_width {
+                    if !have_precision {
+                        self.append_output_str(sprintf_loc!(fmt, arg));
+                    } else {
+                        self.append_output_str(sprintf_loc!(fmt, precision, arg));
+                    }
+                } else {
+                    if !have_precision {
+                        self.append_output_str(sprintf_loc!(fmt, field_width, arg));
+                    } else {
+                        self.append_output_str(sprintf_loc!(fmt, field_width, precision, arg));
+                    }
+                }
+            }
+
+            'a' | 'A' | 'e' | 'E' | 'f' | 'F' | 'g' | 'G' => {
+                let arg: f64 = string_to_scalar_type(argument, self);
+                if !have_field_width {
+                    if !have_precision {
+                        self.append_output_str(sprintf_loc!(fmt, arg));
+                    } else {
+                        self.append_output_str(sprintf_loc!(fmt, precision, arg));
+                    }
+                } else {
+                    if !have_precision {
+                        self.append_output_str(sprintf_loc!(fmt, field_width, arg));
+                    } else {
+                        self.append_output_str(sprintf_loc!(fmt, field_width, precision, arg));
+                    }
+                }
+            }
+
+            'c' => {
+                if !have_field_width {
+                    self.append_output_str(sprintf_loc!(fmt, argument.char_at(0)));
+                } else {
+                    self.append_output_str(sprintf_loc!(fmt, field_width, argument.char_at(0)));
+                }
+            }
+
+            's' => {
+                if !have_field_width {
+                    if !have_precision {
+                        self.append_output_str(sprintf_loc!(fmt, argument));
+                    } else {
+                        self.append_output_str(sprintf_loc!(fmt, precision, argument));
+                    }
+                } else {
+                    if !have_precision {
+                        self.append_output_str(sprintf_loc!(fmt, field_width, argument));
+                    } else {
+                        self.append_output_str(sprintf_loc!(fmt, field_width, precision, argument));
+                    }
+                }
+            }
+
+            _ => {
+                panic!("unexpected opt: {}", conversion);
+            }
+        }
+    }
+
+    /// Print the text in FORMAT, using ARGV for arguments to any `%' directives.
+    /// Return the number of elements of ARGV used.
+    fn print_formatted(&mut self, format: &wstr, mut argv: &[&wstr]) -> usize {
+        let mut argc = argv.len();
+        let save_argc = argc; /* Preserve original value.  */
+        let mut f: &wstr; /* Pointer into `format'.  */
+        let mut direc_start: &wstr; /* Start of % directive.  */
+        let mut direc_length: usize; /* Length of % directive.  */
+        let mut have_field_width: bool; /* True if FIELD_WIDTH is valid.  */
+        let mut field_width: c_int = 0; /* Arg to first '*'.  */
+        let mut have_precision: bool; /* True if PRECISION is valid.  */
+        let mut precision = 0; /* Arg to second '*'.  */
+        let mut ok = [false; 256]; /* ok['x'] is true if %x is allowed.  */
+
+        // N.B. this was originally written as a loop like so:
+        //    for (f = format; *f != L'\0'; ++f) {
+        // so we emulate that.
+        f = format;
+        let mut first = true;
+        loop {
+            if !first {
+                f = &f[1..];
+            }
+            first = false;
+            if f.is_empty() {
+                break;
+            }
+
+            match f.char_at(0) {
+                '%' => {
+                    direc_start = f;
+                    f = &f[1..];
+                    direc_length = 1;
+                    have_field_width = false;
+                    have_precision = false;
+                    if f.char_at(0) == '%' {
+                        self.append_output('%');
+                        continue;
+                    }
+                    if f.char_at(0) == 'b' {
+                        // FIXME: Field width and precision are not supported for %b, even though POSIX
+                        // requires it.
+                        if argc > 0 {
+                            self.print_esc_string(argv[0]);
+                            argv = &argv[1..];
+                            argc -= 1;
+                        }
+                        continue;
+                    }
+
+                    modify_allowed_format_specifiers(&mut ok, "aAcdeEfFgGiosuxX", true);
+                    let mut continue_looking_for_flags = true;
+                    while continue_looking_for_flags {
+                        match f.char_at(0) {
+                            'I' | '\'' => {
+                                modify_allowed_format_specifiers(&mut ok, "aAceEosxX", false);
+                            }
+
+                            '-' | '+' | ' ' => {
+                                // pass
+                            }
+
+                            '#' => {
+                                modify_allowed_format_specifiers(&mut ok, "cdisu", false);
+                            }
+
+                            '0' => {
+                                modify_allowed_format_specifiers(&mut ok, "cs", false);
+                            }
+
+                            _ => {
+                                continue_looking_for_flags = false;
+                            }
+                        }
+                        if continue_looking_for_flags {
+                            f = &f[1..];
+                            direc_length += 1;
+                        }
+                    }
+
+                    if f.char_at(0) == '*' {
+                        f = &f[1..];
+                        direc_length += 1;
+                        if argc > 0 {
+                            let width: i64 = string_to_scalar_type(argv[0], self);
+                            if (c_int::MIN as i64) <= width && width <= (c_int::MAX as i64) {
+                                field_width = width as c_int;
+                            } else {
+                                self.fatal_error(wgettext_fmt!(
+                                    "invalid field width: %ls",
+                                    argv[0]
+                                ));
+                            }
+                            argv = &argv[1..];
+                            argc -= 1;
+                        } else {
+                            field_width = 0;
+                        }
+                        have_field_width = true;
+                    } else {
+                        while iswdigit(f.char_at(0)) {
+                            f = &f[1..];
+                            direc_length += 1;
+                        }
+                    }
+
+                    if f.char_at(0) == '.' {
+                        f = &f[1..];
+                        direc_length += 1;
+                        modify_allowed_format_specifiers(&mut ok, "c", false);
+                        if f.char_at(0) == '*' {
+                            f = &f[1..];
+                            direc_length += 1;
+                            if argc > 0 {
+                                let prec: i64 = string_to_scalar_type(argv[0], self);
+                                if prec < 0 {
+                                    // A negative precision is taken as if the precision were omitted,
+                                    // so -1 is safe here even if prec < INT_MIN.
+                                    precision = -1;
+                                } else if (c_int::MAX as i64) < prec {
+                                    self.fatal_error(wgettext_fmt!(
+                                        "invalid precision: %ls",
+                                        argv[0]
+                                    ));
+                                } else {
+                                    precision = prec as c_int;
+                                }
+                                argv = &argv[1..];
+                                argc -= 1;
+                            } else {
+                                precision = 0;
+                            }
+                            have_precision = true;
+                        } else {
+                            while iswdigit(f.char_at(0)) {
+                                f = &f[1..];
+                                direc_length += 1;
+                            }
+                        }
+                    }
+
+                    while matches!(f.char_at(0), 'l' | 'L' | 'h' | 'j' | 't' | 'z') {
+                        f = &f[1..];
+                    }
+
+                    let conversion = f.char_at(0);
+                    if (conversion as usize) > 0xFF || !ok[conversion as usize] {
+                        self.fatal_error(wgettext_fmt!(
+                            "%.*ls: invalid conversion specification",
+                            wstr_offset_in(f, direc_start) + 1,
+                            direc_start
+                        ));
+                        return 0;
+                    }
+
+                    let mut argument = L!("");
+                    if argc > 0 {
+                        argument = argv[0];
+                        argv = &argv[1..];
+                        argc -= 1;
+                    }
+                    self.print_direc(
+                        &direc_start[..direc_length],
+                        f.char_at(0),
+                        have_field_width,
+                        field_width,
+                        have_precision,
+                        precision,
+                        argument,
+                    );
+                }
+                '\\' => {
+                    let consumed_minus_1 = self.print_esc(f, false);
+                    f = &f[consumed_minus_1..]; // Loop increment will add 1.
+                }
+
+                c => {
+                    self.append_output(c);
+                }
+            }
+        }
+        save_argc - argc
+    }
+
+    fn nonfatal_error<Str: AsRef<wstr>>(&mut self, errstr: Str) {
+        let errstr = errstr.as_ref();
+        // Don't error twice.
+        if self.early_exit {
+            return;
+        }
+
+        // If we have output, write it so it appears first.
+        if !self.buff.is_empty() {
+            self.streams.out.append(&self.buff);
+            self.buff.clear();
+        }
+
+        self.streams.err.append(errstr);
+        if !errstr.ends_with('\n') {
+            self.streams.err.append1('\n');
+        }
+
+        // We set the exit code to error, because one occurred,
+        // but we don't do an early exit so we still print what we can.
+        self.exit_code = STATUS_CMD_ERROR.unwrap();
+    }
+
+    fn fatal_error<Str: AsRef<wstr>>(&mut self, errstr: Str) {
+        let errstr = errstr.as_ref();
+
+        // Don't error twice.
+        if self.early_exit {
+            return;
+        }
+
+        // If we have output, write it so it appears first.
+        if !self.buff.is_empty() {
+            self.streams.out.append(&self.buff);
+            self.buff.clear();
+        }
+
+        self.streams.err.append(errstr);
+        if !errstr.ends_with('\n') {
+            self.streams.err.append1('\n');
+        }
+
+        self.exit_code = STATUS_CMD_ERROR.unwrap();
+        self.early_exit = true;
+    }
+
+    /// Print a \ escape sequence starting at ESCSTART.
+    /// Return the number of characters in the string, *besides the backslash*.
+    /// That is this is ONE LESS than the number of characters consumed.
+    /// If octal_0 is nonzero, octal escapes are of the form \0ooo, where o
+    /// is an octal digit; otherwise they are of the form \ooo.
+    fn print_esc(&mut self, escstart: &wstr, octal_0: bool) -> usize {
+        assert!(escstart.char_at(0) == '\\');
+        let mut p = &escstart[1..];
+        let mut esc_value = 0; /* Value of \nnn escape. */
+        let mut esc_length; /* Length of \nnn escape. */
+        if p.char_at(0) == 'x' {
+            // A hexadecimal \xhh escape sequence must have 1 or 2 hex. digits.
+            p = &p[1..];
+            esc_length = 0;
+            while esc_length < 2 && iswxdigit(p.char_at(0)) {
+                esc_value = esc_value * 16 + p.char_at(0).to_digit(16).unwrap();
+                esc_length += 1;
+                p = &p[1..];
+            }
+            if esc_length == 0 {
+                self.fatal_error(wgettext!("missing hexadecimal number in escape"));
+            }
+            self.append_output(
+                char::from_u32(ENCODE_DIRECT_BASE + esc_value % 256)
+                    .expect("Escape should be encodeable"),
+            );
+        } else if is_octal_digit(p.char_at(0)) {
+            // Parse \0ooo (if octal_0 && *p == L'0') or \ooo (otherwise). Allow \ooo if octal_0 && *p
+            // != L'0'; this is an undocumented extension to POSIX that is compatible with Bash 2.05b.
+            // Wrap mod 256, which matches historic behavior.
+            esc_length = 0;
+            if octal_0 && p.char_at(0) == '0' {
+                p = &p[1..];
+            }
+            while esc_length < 3 && is_octal_digit(p.char_at(0)) {
+                esc_value = esc_value * 8 + p.char_at(0).to_digit(8).unwrap();
+                esc_length += 1;
+                p = &p[1..];
+            }
+            self.append_output(
+                char::from_u32(ENCODE_DIRECT_BASE + esc_value % 256)
+                    .expect("Escape should be encodeable"),
+            );
+        } else if "\"\\abcefnrtv".contains(p.char_at(0)) {
+            self.print_esc_char(p.char_at(0));
+            p = &p[1..];
+        } else if p.char_at(0) == 'u' || p.char_at(0) == 'U' {
+            let esc_char: char = p.char_at(0);
+            p = &p[1..];
+            let mut uni_value = 0;
+            let exp_esc_length = if esc_char == 'u' { 4 } else { 8 };
+            for esc_length in 0..exp_esc_length {
+                if !iswxdigit(p.char_at(0)) {
+                    // Escape sequence must be done. Complain if we didn't get anything.
+                    if esc_length == 0 {
+                        self.fatal_error(wgettext!("Missing hexadecimal number in Unicode escape"));
+                    }
+                    break;
+                }
+                uni_value = uni_value * 16 + p.char_at(0).to_digit(16).unwrap();
+                p = &p[1..];
+            }
+            // N.B. we assume __STDC_ISO_10646__.
+            if uni_value > 0x10FFFF {
+                self.fatal_error(wgettext_fmt!(
+                    "Unicode character out of range: \\%c%0*x",
+                    esc_char,
+                    exp_esc_length,
+                    uni_value
+                ));
+            } else {
+                // TODO-RUST: if uni_value is a surrogate, we need to encode it using our PUA scheme.
+                if let Some(c) = char::from_u32(uni_value) {
+                    self.append_output(c);
+                } else {
+                    self.fatal_error(wgettext!("Invalid code points not yet supported by printf"));
+                }
+            }
+        } else {
+            self.append_output('\\');
+            if !p.is_empty() {
+                self.append_output(p.char_at(0));
+                p = &p[1..];
+            }
+        }
+        return wstr_offset_in(p, escstart) - 1;
+    }
+
+    /// Print string str, evaluating \ escapes.
+    fn print_esc_string(&mut self, mut str: &wstr) {
+        // Emulating the following loop: for (; *str; str++)
+        while !str.is_empty() {
+            let c = str.char_at(0);
+            if c == '\\' {
+                let consumed_minus_1 = self.print_esc(str, false);
+                str = &str[consumed_minus_1..];
+            } else {
+                self.append_output(c);
+            }
+            str = &str[1..];
+        }
+    }
+
+    /// Output a single-character \ escape.
+    fn print_esc_char(&mut self, c: char) {
+        match c {
+            'a' => {
+                // alert
+                self.append_output('\x07'); // \a
+            }
+            'b' => {
+                // backspace
+                self.append_output('\x08'); // \b
+            }
+            'c' => {
+                // cancel the rest of the output
+                self.early_exit = true;
+            }
+            'e' => {
+                // escape
+                self.append_output('\x1B');
+            }
+            'f' => {
+                // form feed
+                self.append_output('\x0C'); // \f
+            }
+            'n' => {
+                // new line
+                self.append_output('\n');
+            }
+            'r' => {
+                // carriage return
+                self.append_output('\r');
+            }
+            't' => {
+                // horizontal tab
+                self.append_output('\t');
+            }
+            'v' => {
+                // vertical tab
+                self.append_output('\x0B'); // \v
+            }
+            _ => {
+                self.append_output(c);
+            }
+        }
+    }
+
+    fn append_output(&mut self, c: char) {
+        // Don't output if we're done.
+        if self.early_exit {
+            return;
+        }
+
+        self.buff.push(c);
+    }
+
+    fn append_output_str<Str: AsRef<wstr>>(&mut self, s: Str) {
+        // Don't output if we're done.
+        if self.early_exit {
+            return;
+        }
+
+        self.buff.push_utfstr(&s);
+    }
+}
+
+/// The printf builtin.
+pub fn printf(
+    _parser: &mut parser_t,
+    streams: &mut io_streams_t,
+    argv: &mut [&wstr],
+) -> Option<c_int> {
+    let mut argc = argv.len();
+
+    // Rebind argv as immutable slice (can't rearrange its elements), skipping the command name.
+    let mut argv: &[&wstr] = &argv[1..];
+    argc -= 1;
+    if argc < 1 {
+        return STATUS_INVALID_ARGS;
+    }
+
+    let mut state = builtin_printf_state_t {
+        streams,
+        exit_code: STATUS_CMD_OK.unwrap(),
+        early_exit: false,
+        buff: WString::new(),
+        locale: get_numeric_locale(),
+    };
+    let format = argv[0];
+    argc -= 1;
+    argv = &argv[1..];
+    loop {
+        let args_used = state.print_formatted(format, argv);
+        argc -= args_used;
+        argv = &argv[args_used..];
+        if !state.buff.is_empty() {
+            state.streams.out.append(&state.buff);
+            state.buff.clear();
+        }
+        if !(args_used > 0 && argc > 0 && !state.early_exit) {
+            break;
+        }
+    }
+    return Some(state.exit_code);
+}

fish-rust/src/builtins/shared.rs

@@ -1,4 +1,4 @@
-use crate::builtins::wait;
+use crate::builtins::{printf, wait};
 use crate::ffi::{self, parser_t, wcharz_t, Repin, RustBuiltin};
 use crate::wchar::{self, wstr, L};
 use crate::wchar_ffi::{c_str, empty_wstring};
@@ -45,7 +45,9 @@ pub const STATUS_CMD_OK: Option<c_int> = Some(0);
 /// The status code used for failure exit in a command (but not if the args were invalid).
 pub const STATUS_CMD_ERROR: Option<c_int> = Some(1);
 
-/// A handy return value for invalid args.
+/// The status code used for invalid arguments given to a command. This is distinct from valid
+/// arguments that might result in a command failure. An invalid args condition is something
+/// like an unrecognized flag, missing or too many arguments, an invalid integer, etc.
 pub const STATUS_INVALID_ARGS: Option<c_int> = Some(2);
 
 /// A wrapper around output_stream_t.
@@ -61,6 +63,11 @@ impl output_stream_t {
     pub fn append<Str: AsRef<wstr>>(&mut self, s: Str) -> bool {
         self.ffi().append1(c_str!(s))
     }
+
+    /// Append a char.
+    pub fn append1(&mut self, c: char) -> bool {
+        self.append(wstr::from_char_slice(&[c]))
+    }
 }
 
 // Convenience wrappers around C++ io_streams_t.
@@ -132,6 +139,7 @@ pub fn run_builtin(
         RustBuiltin::Realpath => super::realpath::realpath(parser, streams, args),
         RustBuiltin::Return => super::r#return::r#return(parser, streams, args),
         RustBuiltin::Wait => wait::wait(parser, streams, args),
+        RustBuiltin::Printf => printf::printf(parser, streams, args),
     }
 }
 

fish-rust/src/common.rs

@@ -107,6 +107,16 @@ impl<T, F: FnOnce(&mut T)> Drop for ScopeGuard<T, F> {
         unsafe { ManuallyDrop::drop(&mut self.captured) };
     }
 }
+// These are in the Unicode private-use range. We really shouldn't use this
+// range but have little choice in the matter given how our lexer/parser works.
+// We can't use non-characters for these two ranges because there are only 66 of
+// them and we need at least 256 + 64.
+//
+// Note: We don't use the highest 8 bit range (0xF800 - 0xF8FF) because we know
+// of at least one use of a codepoint in that range: the Apple symbol (0xF8FF)
+// on Mac OS X. See http://www.unicode.org/faq/private_use.html.
+pub const ENCODE_DIRECT_BASE: u32 = 0xF600;
+pub const ENCODE_DIRECT_END: u32 = ENCODE_DIRECT_BASE + 256;
 
 /// A scoped manager to save the current value of some variable, and optionally set it to a new
 /// value. When dropped, it restores the variable to its old value.

fish-rust/src/wchar_ext.rs

@@ -153,6 +153,13 @@ pub trait WExt {
     /// Access the chars of a WString or wstr.
     fn as_char_slice(&self) -> &[char];
 
+    /// Return a char slice from a *char index*.
+    /// This is different from Rust string slicing, which takes a byte index.
+    fn slice_from(&self, start: usize) -> &wstr {
+        let chars = self.as_char_slice();
+        wstr::from_char_slice(&chars[start..])
+    }
+
     /// \return the char at an index.
     /// If the index is equal to the length, return '\0'.
     /// If the index exceeds the length, then panic.

fish-rust/src/wutil/mod.rs

@@ -46,6 +46,25 @@ pub fn join_strings(strs: &[&wstr], sep: char) -> WString {
     result
 }
 
+/// Given that \p cursor is a pointer into \p base, return the offset in characters.
+/// This emulates C pointer arithmetic:
+///    `wstr_offset_in(cursor, base)` is equivalent to C++ `cursor - base`.
+pub fn wstr_offset_in(cursor: &wstr, base: &wstr) -> usize {
+    let cursor = cursor.as_slice();
+    let base = base.as_slice();
+    // cursor may be a zero-length slice at the end of base,
+    // which base.as_ptr_range().contains(cursor.as_ptr()) will reject.
+    let base_range = base.as_ptr_range();
+    let curs_range = cursor.as_ptr_range();
+    assert!(
+        base_range.start <= curs_range.start && curs_range.end <= base_range.end,
+        "cursor should be a subslice of base"
+    );
+    let offset = unsafe { cursor.as_ptr().offset_from(base.as_ptr()) };
+    assert!(offset >= 0, "offset should be non-negative");
+    offset as usize
+}
+
 #[test]
 fn test_join_strings() {
     use crate::wchar::L;
@@ -56,3 +75,13 @@ fn test_join_strings() {
         "foo/bar/baz"
     );
 }
+
+#[test]
+fn test_wstr_offset_in() {
+    use crate::wchar::L;
+    let base = L!("hello world");
+    assert_eq!(wstr_offset_in(&base[6..], base), 6);
+    assert_eq!(wstr_offset_in(&base[0..], base), 0);
+    assert_eq!(wstr_offset_in(&base[6..], &base[6..]), 0);
+    assert_eq!(wstr_offset_in(&base[base.len()..], base), base.len());
+}

src/builtin.cpp

@@ -557,6 +557,9 @@ static maybe_t<RustBuiltin> try_get_rust_builtin(const wcstring &cmd) {
     if (cmd == L"wait") {
         return RustBuiltin::Wait;
     }
+    if (cmd == L"printf") {
+        return RustBuiltin::Printf;
+    }
     if (cmd == L"return") {
         return RustBuiltin::Return;
     }

src/builtin.h

@@ -116,6 +116,7 @@ enum RustBuiltin : int32_t {
     Echo,
     Emit,
     Exit,
+    Printf,
     Pwd,
     Random,
     Realpath,