fixes#24434
In https://github.com/nim-lang/Nim/pull/24432
```nim
let ex = "NIM_EXTERNC N_NIMCALL(void, nimLoadProcs$1)(void) {$2}$N$N" %
[(i.ord - '0'.ord).rope, extract(el)]
```
```nim
procs.addDeclWithVisibility(ExternC):
procs.addProcHeader(ccNimCall, "nimLoadProcs" & $(i.ord - '0'.ord), "void", cProcParams())
```
extern "C" makes a function-name in C++ have C linkage; it should be
effaced with C compiler
Follows up #24423, needed more refactoring than I expected, sorry for
ugly diff.
With this pretty much all of the raw C code generating parts of the
codegen are abstracted into the cbuilder API (to my knowledge at least).
The current design of NIFC does not implement everything the codegen
generates, such things have mostly not been adapted, they are the
following along with how I'm guessing they could be implemented:
* C++ specific codegen: Maybe a dialect of NIFC for generating C++?
* `codegenDecl` pragma: Could be passed as a pragma to NIFC
* C macros, currently only used for line info IIRC i.e. `nimln_(123)`:
Just inline them when generating NIFC
* Other C defines & `#line`: Maybe as NIFC directives or line infos?
* There is also [this
`#ifndef`](21420d8b09/compiler/cgen.nim (L2249))
when generating headers but NIFC shouldn't need it
* `alignof`/`offsetof`: Is in `cbuilder` but not implemented in NIFC,
should be easy
For now we can disable C++ and the `codegenDecl` pragma when generating
NIFC but since cbuilder is mostly designed to generate NIFC as a flag
when booting the compiler, this hinders the ability to run the CI
against NIFC. Maybe we could also make cbuilder able to generate both C
and NIFC at runtime, this would be a large refactor but wouldn't be too
difficult.
Other missing abstractions before being able to generate NIFC are:
* Primitive types and symbols i.e. `int`, `void*`, `NI`, `NIM_NULL` are
currently still constant string literals, `NU8`, `NU16` etc are also
sometimes generated like `"NU" & $bits`.
* NIFC identifiers, i.e. adding `.c` to imported symbols and properly
mangling generated ones. Not sure how difficult this is going to be.
The lower half of cgen contains the main proc and HCR init code which
cause a large diff, so they are excluded from this PR. In general things
like generated defines, line directives, the stacktrace macros (`nimfr_`
etc) are also not done, since there are not exact equivalents for these
in NIFC (NIFC does generate line directives but based on the NIF line
info mechanism).
Not all uses of switch statements are implemented, `genCaseGeneric` and
`genIfForCaseUntil` still exist. The main purpose is to finish
`ccgreset` and `ccgtrav`.
Doing this early is useful so we can move the indentation logic into
`Builder` itself rather than mix it with the block logic in `ccgstmts`
(the `if` statements in #24381 have not been indented properly either).
However it also means `Builder` is now used for code that still
generates raw C code, so the diff won't be as clean when these get
updated.
C++ member procs are not implemented, and `codegenDecl` in general is
also not adapted, although it had to be included in the generation of
proc params for simplicity. Guessing `codegenDecl` and C++ stuff are
supposed to map to pragmas on NIFC, or are just not supported.
Different from `intLiteral`, we add procs that just try to generate
integer values, assuming they're not an edge case like `<= low(int32)`
or `> high(int32)`.
The only remaining explicit use of `typedef` in the codegen (from my
search) is in `addForwardStructFormat` which from what I understand
won't do anything in NIFC.
The remaining followup from #24259. A body for building the type doesn't
seem necessary here since the types with array fields are generally
atomic/already built from `getTypeDescAux`.
follows up #24259
This is the remaining missing use of `StructInitializer` in
`getDefaultValue` after #24259 and #24302. The only remaining direct C
code in getDefaultValue is [this
line](922f7dfd71/compiler/ccgexprs.nim (L3525))
which creates a global array variable, which isn't implemented yet. Next
steps would be all remaining variable and `typedef` declarations, then
hopefully we can move on to general statements and expressions.
`StructInitializer` is now used for most braced initializers in the C
generation, mostly in `genBracedInit`, `getNullValueAux`,
`getDefaultValue`. The exceptions are:
* the default case branch initializer for objects uses C99 designated
initializers with field names, which are not implemented for
`StructInitializer` yet (`siNamedStruct`)
* the uses in `ccgliterals` are untouched so all of ccgliterals can be
done separately and in 1 go
There is one case where `genBracedInit` does not use cbuilder, which is
the global literal variable for openarrays. The reason for this is
simply that variables with C array type are not implemented, which I
thought would be best to leave out of this PR.
For the simplicity of the implementation, code in `getNullValueAuxT`
that reset the initializer back to its initial state if the `Sup` field
did not have any fields itself, is now disabled. This was so the
compiler does not generate `{}` for the Sup field, i.e. `{{}}`, but
every call to `getNullValueAuxT` still generates `{}` if the struct
doesn't have any fields, so I don't know if it really breaks anything.
The case where the Sup field doesn't have any fields but the struct does
also would have generated `{{}, field}`.
Worst case, we can implement either the "resetting" or just disable the
generation of the `Sup` field if there are no fields total. But a better
fix might be to always generate `{0}` if the struct has no fields, in
line with the `char dummy` field that gets added for all objects with no
fields. This doesn't seem necessary for now but might be for the NIFC
output, in which case we can probably keep the logic contained inside
cbuilder (if no fields generated for `siOrderedStruct`/`siNamedStruct`,
we add a `0` for the `dummy` field). This would stipulate that all uses
of struct initializers are exhaustive for every field in structs.
The only remaining use of `struct` after this is in
`genConstSeq`/`genConstSeqV2` which use `genBracedInit`, I figured these
should be done in the PR that adapts `genBracedInit` in general to
cbuilder.
`cbuilder` is now split into `cbuilderbase`, `cbuilderexprs`,
`cbuilderdecls`, with all the struct builder code up to this point going
in `cbuilderdecls`.
Variable builders are added, with local, global and constant variables
implemented, but not threadvars.
A builder for struct (braced) initializers is added. The field names
have to be passed to build each field (so they can be used in `oconstr`
in nifc), but they're not used in the output code if a flag
`orderCompliant` is enabled, which means the initializer list is
generated in order of the built fields. The version which uses the names
on C is not implemented (C99 designated initializers), so this flag has
to be enabled for now.
The struct builders now generate the struct as an inline expression if a
name isn't provided rather than a statement. This means we can now use
`addSimpleStruct` etc for the type of fields, but we can't replace
`addFieldWithStructType` because of `#pragma pack(pop)`.
Doc comments are added to every usable proc but may still not be
sufficient.
