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.

With the previous patch combining 3 emit functions into 1, it now makes
sense to also combine the corresponding VM opcodes, which is what this
patch does.  This eliminates 2 opcodes which simplifies the VM and reduces
code size, in bytes: bare-arm:44, minimal:64, unix(NDEBUG,x86-64):272,
stmhal:92, esp8266:200.  Profiling (with a simple script that creates many
list/dict/set comprehensions) shows no measurable change in performance.

The 3 kinds of comprehensions are similar enough that merging their emit
functions reduces code size.  Decreases in code size in bytes are:
bare-arm:24, minimal:96, unix(NDEBUG,x86-64):328, stmhal:80, esp8266:76.

A port now just needs to define FROZEN_DIR var and add $(BUILD)/frozen.c
to SRC_C to support frozen modules.

bool(None) has a fast path in mp_obj_is_true so doesn't need to be
handled in none_unary_op.  The only caveat is that subclassing may
bypass the mp_obj_is_true function, but actually you aren't allowed to
subclass classes that have singleton instances like NoneType (see
https://mail.python.org/pipermail/python-dev/2002-March/020822.html for
reference on this point).

py/makeqstrdefs.py declares that it works with python 2.6 however the
syntax used to initialise of a set with values was only added in python
2.7. This leads to build failures when the host system doesn't have
python 2.7 or newer.

Instead of using the new syntax pass a list of initial values through
set() to achieve the same result. This should work for python versions
from at least 2.6 onwards.

Helped-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Chris Packham <judge.packham@gmail.com>

Tested on a STM32F7DISCO at 216MHz.  All tests generating code (inlineasm,
native, viper) now pass, except pybnative/while.py, but that's because
there is no LED(2).

This new config option allows to control whether MicroPython uses its own
internal printf or not (if not, an external one should be linked in).
Accompanying this new option is the inclusion of lib/utils/printf.c in the
core list of source files, so that ports no longer need to include it
themselves.

Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>

Arguments of an unknown type cannot be skipped and continuing to parse a
format string after encountering an unknown format specifier leads to
undefined behaviour.  This patch helps to find use of unsupported formats.

The idea is that all ports can use these helper methods and only need to
provide initialisation of the SPI bus, as well as a single transfer
function.  The coding pattern follows the stream protocol and helper
methods.

Or alternatively, refer to an exact library file, not just phony target
"lib".

This rename was missed in the previous patch.

Also at _t to mp_exc_stack pre-declaration in struct typedef.

Saves a few bytes of code size.

As per CPython.

There can be stray pointers in memory blocks that are not properly zero'd
after allocation.  This patch adds a new config option to always zero all
allocated memory (via gc_alloc and gc_realloc) and hence help to eliminate
stray pointers.

See issue #2195.

Disable by default, enable in unix port.

In current state `mp_get_stream_raise` assumes that `self_in` is an object
and always performs a pointer derefence which may cause a segfault.

This function shall throw an exception whenever `self_in` does not implement
a stream protocol, that includes qstr's and numbers.

fixes #2331

See issue #2264.

The machine_ptr_t type is long obsolete as the type of mp_obj_t is now
defined by the object representation, ie by MICROPY_OBJ_REPR.  So just use
void* explicitly for the typedef of mp_obj_t.

If a port wants to use something different then they should define a new
object representation.

This patch does further refactoring using the new mp_raise_TypeError
and mp_raise_ValueError functions.

Only tuple, namedtuple and attrtuple use the tuple_cmp_helper function,
and they all have getiter=mp_obj_tuple_getiter, so the check here is only
to ensure that the self object is consistent.  Hence use mp_check_self.

Checks for number of args removes where guaranteed by function descriptor,
self checking is replaced with mp_check_self(). In few cases, exception
is raised instead of assert.

Indended to replace raw asserts in bunch of files. Expands to empty
if MICROPY_BUILTIN_METHOD_CHECK_SELF_ARG is defined, otehrwise by
default still to assert, though a particular port may define it to
something else.

Introduce mp_raise_msg(), mp_raise_ValueError(), mp_raise_TypeError()
instead of previous pattern nlr_raise(mp_obj_new_exception_msg(...)).
Save few bytes on each call, which are many.

Similar to existing MP_NOINLINE.

Default is disabled, enabled for unix port. Saves 600 bytes on x86.

To filter out even prototypes of mp_stream_posix_*() functions, which
require POSIX types like ssize_t & off_t, which may be not available in
some ports.

Helpful when porting existing C libraries to MicroPython. abort()ing in
embedded environment isn't a good idea, so when compiling such library,
-Dabort=abort_ option can be given to redirect standard abort() to this
"safe" version.

Previoussly such read() and write() methods were used by modussl_axtls,
move to py/stream for reuse.