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remove `clap` dependency :tada:
update the book installation instructions
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space.
Fixes #1947.
There are two separate issues here: First, the change in comp.rs ensures
that we don't round up the amount of storage to the alignment of the
bitfield. That generates the "expected" output in #1947
(`__BindgenBitfieldUnit<[u8; 3], u16>`).
But that's still not enough to fix that test-case because
__BindgenBitfieldUnit would be aligned and have padding, and Rust won't
put the extra field in the padding.
In order to ensure the bitfield starts at the right alignment, but that
Rust can put stuff in the extra field, we need to make a breaking change
and split the generated fields in two: One preceding that guarantees
alignment, and the actual storage, bit-aligned.
This keeps the existing behavior while fixing that test-case.
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Individual bitfields are still limited to at most 64 bits, but this
restriction can be weakened when Rust supports u128.
This implements issue #816.
Usage notes:
* Since common code is added to each generated binding, a program which uses
more than one binding may need to work around the duplication by including
each binding in its own module.
* The values created by bitfield allocation unit constructors can be assigned
directly to the corresponding struct fields with no need for transmutation.
Implementation notes:
__BindgenBitfieldUnit represents a bitfield allocation unit using a Storage
type accessible as a slice of u8. The alignment of the unit is inherited from
an Align type by virtue of the field:
align: [Align; 0],
The position of this field in the struct is irrelevant.
The alignment of the Storage type is intended to be no larger than the
alignment of the Align type, which will be true if the Storage type is, for
example, an array of u8.
Although the double underscore (__) prefix is reserved for implementations of
C++, there are precedents for this convention elsewhere in bindgen and so the
convention is adopted here too.
Acknowledgement:
Thanks to @fitzgen for an initial implementation of __BindgenBitfieldUnit and
code to integrate it into bindgen.
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