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py: Implement partial PEP-498 (f-string) support.

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This implements (most of) the PEP-498 spec for f-strings and is based on
https://github.com/micropython/micropython/pull/4998 by @klardotsh.

It is implemented in the lexer as a syntax translation to `str.format`:
  f"{a}" --> "{}".format(a)

It also supports:
  f"{a=}" --> "a={}".format(a)

This is done by extracting the arguments into a temporary vstr buffer,
then after the string has been tokenized, the lexer input queue is saved
and the contents of the temporary vstr buffer are injected into the lexer
instead.

There are four main limitations:
- raw f-strings (`fr` or `rf` prefixes) are not supported and will raise
  `SyntaxError: raw f-strings are not supported`.

- literal concatenation of f-strings with adjacent strings will fail
    "{}" f"{a}" --> "{}{}".format(a)    (str.format will incorrectly use
                                         the braces from the non-f-string)
    f"{a}" f"{a}" --> "{}".format(a) "{}".format(a) (cannot concatenate)

- PEP-498 requires the full parser to understand the interpolated
  argument, however because this entirely runs in the lexer it cannot
  resolve nested braces in expressions like
    f"{'}'}"

- The !r, !s, and !a conversions are not supported.

Includes tests and cpydiffs.

Signed-off-by: Jim Mussared <jim.mussared@gmail.com>
This commit is contained in:
Jim Mussared
2021-08-13 01:44:08 +10:00
committed by Damien George
parent 162bf3c5d8
commit 692d36d779
18 changed files with 292 additions and 8 deletions
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128
py/lexer.c
View File

@@ -62,6 +62,12 @@ STATIC bool is_char_or3(mp_lexer_t *lex, byte c1, byte c2, byte c3) {
return lex->chr0 == c1 || lex->chr0 == c2 || lex->chr0 == c3;
}
#if MICROPY_PY_FSTRINGS
STATIC bool is_char_or4(mp_lexer_t *lex, byte c1, byte c2, byte c3, byte c4) {
return lex->chr0 == c1 || lex->chr0 == c2 || lex->chr0 == c3 || lex->chr0 == c4;
}
#endif
STATIC bool is_char_following(mp_lexer_t *lex, byte c) {
return lex->chr1 == c;
}
@@ -105,7 +111,13 @@ STATIC bool is_following_odigit(mp_lexer_t *lex) {
STATIC bool is_string_or_bytes(mp_lexer_t *lex) {
return is_char_or(lex, '\'', '\"')
#if MICROPY_PY_FSTRINGS
|| (is_char_or4(lex, 'r', 'u', 'b', 'f') && is_char_following_or(lex, '\'', '\"'))
|| (((is_char_and(lex, 'r', 'f') || is_char_and(lex, 'f', 'r'))
&& is_char_following_following_or(lex, '\'', '\"')))
#else
|| (is_char_or3(lex, 'r', 'u', 'b') && is_char_following_or(lex, '\'', '\"'))
#endif
|| ((is_char_and(lex, 'r', 'b') || is_char_and(lex, 'b', 'r'))
&& is_char_following_following_or(lex, '\'', '\"'));
}
@@ -132,9 +144,35 @@ STATIC void next_char(mp_lexer_t *lex) {
++lex->column;
}
// shift the input queue forward
lex->chr0 = lex->chr1;
lex->chr1 = lex->chr2;
lex->chr2 = lex->reader.readbyte(lex->reader.data);
// and add the next byte from either the fstring args or the reader
#if MICROPY_PY_FSTRINGS
if (lex->fstring_args_idx) {
// if there are saved chars, then we're currently injecting fstring args
if (lex->fstring_args_idx < lex->fstring_args.len) {
lex->chr2 = lex->fstring_args.buf[lex->fstring_args_idx++];
} else {
// no more fstring arg bytes
lex->chr2 = '\0';
}
if (lex->chr0 == '\0') {
// consumed all fstring data, restore saved input queue
lex->chr0 = lex->chr0_saved;
lex->chr1 = lex->chr1_saved;
lex->chr2 = lex->chr2_saved;
// stop consuming fstring arg data
vstr_reset(&lex->fstring_args);
lex->fstring_args_idx = 0;
}
} else
#endif
{
lex->chr2 = lex->reader.readbyte(lex->reader.data);
}
if (lex->chr1 == '\r') {
// CR is a new line, converted to LF
@@ -272,7 +310,7 @@ STATIC bool get_hex(mp_lexer_t *lex, size_t num_digits, mp_uint_t *result) {
return true;
}
STATIC void parse_string_literal(mp_lexer_t *lex, bool is_raw) {
STATIC void parse_string_literal(mp_lexer_t *lex, bool is_raw, bool is_fstring) {
// get first quoting character
char quote_char = '\'';
if (is_char(lex, '\"')) {
@@ -293,12 +331,57 @@ STATIC void parse_string_literal(mp_lexer_t *lex, bool is_raw) {
}
size_t n_closing = 0;
#if MICROPY_PY_FSTRINGS
if (is_fstring) {
// assume there's going to be interpolation, so prep the injection data
// fstring_args_idx==0 && len(fstring_args)>0 means we're extracting the args.
// only when fstring_args_idx>0 will we consume the arg data
// note: lex->fstring_args will be empty already (it's reset when finished)
vstr_add_str(&lex->fstring_args, ".format(");
}
#endif
while (!is_end(lex) && (num_quotes > 1 || !is_char(lex, '\n')) && n_closing < num_quotes) {
if (is_char(lex, quote_char)) {
n_closing += 1;
vstr_add_char(&lex->vstr, CUR_CHAR(lex));
} else {
n_closing = 0;
#if MICROPY_PY_FSTRINGS
while (is_fstring && is_char(lex, '{')) {
next_char(lex);
if (is_char(lex, '{')) {
// "{{" is passed through unchanged to be handled by str.format
vstr_add_byte(&lex->vstr, '{');
next_char(lex);
} else {
// remember the start of this argument (if we need it for f'{a=}').
size_t i = lex->fstring_args.len;
// extract characters inside the { until we reach the
// format specifier or closing }.
// (MicroPython limitation) note: this is completely unaware of
// Python syntax and will not handle any expression containing '}' or ':'.
// e.g. f'{"}"}' or f'{foo({})}'.
while (!is_end(lex) && !is_char_or(lex, ':', '}')) {
// like the default case at the end of this function, stay 8-bit clean
vstr_add_byte(&lex->fstring_args, CUR_CHAR(lex));
next_char(lex);
}
if (lex->fstring_args.buf[lex->fstring_args.len - 1] == '=') {
// if the last character of the arg was '=', then inject "arg=" before the '{'.
// f'{a=}' --> 'a={}'.format(a)
vstr_add_strn(&lex->vstr, lex->fstring_args.buf + i, lex->fstring_args.len - i);
// remove the trailing '='
lex->fstring_args.len--;
}
// comma-separate args
vstr_add_byte(&lex->fstring_args, ',');
}
vstr_add_byte(&lex->vstr, '{');
}
#endif
if (is_char(lex, '\\')) {
next_char(lex);
unichar c = CUR_CHAR(lex);
@@ -451,6 +534,23 @@ STATIC bool skip_whitespace(mp_lexer_t *lex, bool stop_at_newline) {
}
void mp_lexer_to_next(mp_lexer_t *lex) {
#if MICROPY_PY_FSTRINGS
if (lex->fstring_args.len && lex->fstring_args_idx == 0) {
// moving onto the next token means the literal string is complete.
// switch into injecting the format args.
vstr_add_byte(&lex->fstring_args, ')');
lex->chr0_saved = lex->chr0;
lex->chr1_saved = lex->chr1;
lex->chr2_saved = lex->chr2;
lex->chr0 = lex->fstring_args.buf[0];
lex->chr1 = lex->fstring_args.buf[1];
lex->chr2 = lex->fstring_args.buf[2];
// we've already extracted 3 chars, but setting this non-zero also
// means we'll start consuming the fstring data
lex->fstring_args_idx = 3;
}
#endif
// start new token text
vstr_reset(&lex->vstr);
@@ -506,6 +606,7 @@ void mp_lexer_to_next(mp_lexer_t *lex) {
do {
// parse type codes
bool is_raw = false;
bool is_fstring = false;
mp_token_kind_t kind = MP_TOKEN_STRING;
int n_char = 0;
if (is_char(lex, 'u')) {
@@ -524,7 +625,25 @@ void mp_lexer_to_next(mp_lexer_t *lex) {
kind = MP_TOKEN_BYTES;
n_char = 2;
}
#if MICROPY_PY_FSTRINGS
if (is_char_following(lex, 'f')) {
// raw-f-strings unsupported, immediately return (invalid) token.
lex->tok_kind = MP_TOKEN_FSTRING_RAW;
break;
}
#endif
}
#if MICROPY_PY_FSTRINGS
else if (is_char(lex, 'f')) {
if (is_char_following(lex, 'r')) {
// raw-f-strings unsupported, immediately return (invalid) token.
lex->tok_kind = MP_TOKEN_FSTRING_RAW;
break;
}
n_char = 1;
is_fstring = true;
}
#endif
// Set or check token kind
if (lex->tok_kind == MP_TOKEN_END) {
@@ -543,7 +662,7 @@ void mp_lexer_to_next(mp_lexer_t *lex) {
}
// Parse the literal
parse_string_literal(lex, is_raw);
parse_string_literal(lex, is_raw, is_fstring);
// Skip whitespace so we can check if there's another string following
skip_whitespace(lex, true);
@@ -703,6 +822,9 @@ mp_lexer_t *mp_lexer_new(qstr src_name, mp_reader_t reader) {
lex->num_indent_level = 1;
lex->indent_level = m_new(uint16_t, lex->alloc_indent_level);
vstr_init(&lex->vstr, 32);
#if MICROPY_PY_FSTRINGS
vstr_init(&lex->fstring_args, 0);
#endif
// store sentinel for first indentation level
lex->indent_level[0] = 0;

11
py/lexer.h
View File

@@ -44,6 +44,10 @@ typedef enum _mp_token_kind_t {
MP_TOKEN_INVALID,
MP_TOKEN_DEDENT_MISMATCH,
MP_TOKEN_LONELY_STRING_OPEN,
#if MICROPY_PY_FSTRINGS
MP_TOKEN_MALFORMED_FSTRING,
MP_TOKEN_FSTRING_RAW,
#endif
MP_TOKEN_NEWLINE,
MP_TOKEN_INDENT,
@@ -158,6 +162,9 @@ typedef struct _mp_lexer_t {
mp_reader_t reader; // stream source
unichar chr0, chr1, chr2; // current cached characters from source
#if MICROPY_PY_FSTRINGS
unichar chr0_saved, chr1_saved, chr2_saved; // current cached characters from alt source
#endif
size_t line; // current source line
size_t column; // current source column
@@ -173,6 +180,10 @@ typedef struct _mp_lexer_t {
size_t tok_column; // token source column
mp_token_kind_t tok_kind; // token kind
vstr_t vstr; // token data
#if MICROPY_PY_FSTRINGS
vstr_t fstring_args; // extracted arguments to pass to .format()
size_t fstring_args_idx; // how many bytes of fstring_args have been read
#endif
} mp_lexer_t;
mp_lexer_t *mp_lexer_new(qstr src_name, mp_reader_t reader);

5
py/mpconfig.h
View File

@@ -875,6 +875,11 @@ typedef double mp_float_t;
#define MICROPY_PY_ASYNC_AWAIT (1)
#endif
// Support for literal string interpolation, f-strings (see PEP 498, Python 3.6+)
#ifndef MICROPY_PY_FSTRINGS
#define MICROPY_PY_FSTRINGS (0)
#endif
// Support for assignment expressions with := (see PEP 572, Python 3.8+)
#ifndef MICROPY_PY_ASSIGN_EXPR
#define MICROPY_PY_ASSIGN_EXPR (1)

8
py/parse.c
View File

@@ -1152,6 +1152,14 @@ mp_parse_tree_t mp_parse(mp_lexer_t *lex, mp_parse_input_kind_t input_kind) {
} else if (lex->tok_kind == MP_TOKEN_DEDENT_MISMATCH) {
exc = mp_obj_new_exception_msg(&mp_type_IndentationError,
MP_ERROR_TEXT("unindent doesn't match any outer indent level"));
#if MICROPY_PY_FSTRINGS
} else if (lex->tok_kind == MP_TOKEN_MALFORMED_FSTRING) {
exc = mp_obj_new_exception_msg(&mp_type_SyntaxError,
MP_ERROR_TEXT("malformed f-string"));
} else if (lex->tok_kind == MP_TOKEN_FSTRING_RAW) {
exc = mp_obj_new_exception_msg(&mp_type_SyntaxError,
MP_ERROR_TEXT("raw f-strings are not supported"));
#endif
} else {
exc = mp_obj_new_exception_msg(&mp_type_SyntaxError,
MP_ERROR_TEXT("invalid syntax"));