Now consistently uses the EOL processing ("\r" and "\r\n" convert to "\n")
and EOF processing (ensure "\n" before EOF) provided by next_char().
In particular the lexer can now correctly handle input that starts with CR.
By removing the 'E' code from the operator token encoding mini-language the
tokenising can be simplified. The 'E' code was only used for the !=
operator which is now handled as a special case; the optimisations for the
general case more than make up for the addition of this single, special
case. Furthermore, the . and ... operators can be handled in the same way
as != which reduces the code size a little further.
This simplification also removes a "goto".
Changes in code size for this patch are (measured in bytes):
bare-arm: -48
minimal x86: -64
unix x86-64: -112
unix nanbox: -64
stmhal: -48
cc3200: -48
esp8266: -76
This patch refactors the error handling in the lexer, to simplify it (ie
reduce code size).
A long time ago, when the lexer/parser/compiler were first written, the
lexer and parser were designed so they didn't use exceptions (ie nlr) to
report errors but rather returned an error code. Over time that has
gradually changed, the parser in particular has more and more ways of
raising exceptions. Also, the lexer never really handled all errors without
raising, eg there were some memory errors which could raise an exception
(and in these rare cases one would get a fatal nlr-not-handled fault).
This patch accepts the fact that the lexer can raise exceptions in some
cases and allows it to raise exceptions to handle all its errors, which are
for the most part just out-of-memory errors during construction of the
lexer. This makes the lexer a bit simpler, and also the persistent code
stuff is simplified.
What this means for users of the lexer is that calls to it must be wrapped
in a nlr handler. But all uses of the lexer already have such an nlr
handler for the parser (and compiler) so that doesn't put any extra burden
on the callers.
It's much more efficient in RAM and code size to do implicit literal string
concatenation in the lexer, as opposed to the compiler.
RAM usage is reduced because the concatenation can be done right away in the
tokeniser by just accumulating the string/bytes literals into the lexer's
vstr. Prior to this patch adjacent strings/bytes would create a parse tree
(one node per string/bytes) and then in the compiler a whole new chunk of
memory was allocated to store the concatenated string, which used more than
double the memory compared to just accumulating in the lexer.
This patch also significantly reduces code size:
bare-arm: -204
minimal: -204
unix x64: -328
stmhal: -208
esp8266: -284
cc3200: -224
Previous to this patch there was an explicit check for errors with line
continuation (where backslash was not immediately followed by a newline).
But this check is not necessary: if there is an error then the remaining
logic of the tokeniser will reject the backslash and correctly produce a
syntax error.
Since the table of keywords is sorted, we can use strcmp to do the search
and stop part way through the search if the comparison is less-than.
Because all tokens that are names are subject to this search, this
optimisation will improve the overall speed of the lexer when processing
a script.
The change also decreases code size by a little bit because we now use
strcmp instead of the custom str_strn_equal function.
Keywords only needs to be searched for if the token is a MP_TOKEN_NAME, so
we can move the seach to the part of the code that does the tokenising for
MP_TOKEN_NAME.
This provides mp_vfs_XXX functions (eg mount, open, listdir) which are
agnostic to the underlying filesystem type, and just require an object with
the relevant filesystem-like methods (eg .mount, .open, .listidr) which can
then be mounted.
These mp_vfs_XXX functions would typically be used by a port to implement
the "uos" module, and mp_vfs_open would be the builtin open function.
This feature is controlled by MICROPY_VFS, disabled by default.
This check always fails (ie chr0 is never EOF) because the callers of this
function never call it past the end of the input stream. And even if they
did it would be harmless because 1) reader.readbyte must continue to
return an EOF char if the stream is exhausted; 2) next_char would just
count the subsequent EOF's as characters worth 1 column.
If a port defines MICROPY_READER_POSIX or MICROPY_READER_FATFS then
lexer.c now provides an implementation of mp_lexer_new_from_file using
the mp_reader_new_file function.
Setting emit_dent=0 is unnecessary because arriving in that part of the
if-logic will guarantee that emit_dent is already zero.
The block to check indent_top(lex)>0 is unreachable because a newline is
always inserted an the end of the input stream, and hence dedents are
always processed before EOF.
The vstr.had_error flag was a relic from the very early days which assumed
that the malloc functions (eg m_new, m_renew) returned NULL if they failed
to allocate. But that's no longer the case: these functions will raise an
exception if they fail.
Since it was impossible for had_error to be set, this patch introduces no
change in behaviour.
An alternative option would be to change the malloc calls to the _maybe
variants, which return NULL instead of raising, but then a lot of code
will need to explicitly check if the vstr had an error and raise if it
did.
The code-size savings for this patch are, in bytes: bare-arm:188,
minimal:456, unix(NDEBUG,x86-64):368, stmhal:228, esp8266:360.
Tom Collins
Damien George