Due to the above changes, it may not work with the existing build
configurations in cross-compilation (even if we can build without presym),
therefore revert it once (ref https://github.com/mruby/mruby/pull/5202#issuecomment-735412643). Sorry for the lack of consideration.
Previously, presym files were always created in `build/{presym,presym.inc}`.
However, this constraint is inconvenient because it is common to use
multiple build configurations and build targets in a single mruby tree.
Therefore, change to create presym file for each build target.
Chang to compare string length first.
### Benchmark
#### Code
* https://github.com/shuujii/mruby-presym_find-benchmark
#### Result
```console
Previous: 10.240772M i/s (25M times in 2.441222s)
New: 16.412985M i/s (25M times in 1.523184s)
```
* Output `GEN` log for generated files
* `MRBC` log is outputted one for each `mrbc` execution
#### Before this patch:
```console
CC src/array.c -> build/host/src/array.o
(snip)
GEN mrblib/*.rb -> build/host/mrblib/mrblib.c
MRBC mrblib/00class.rb
MRBC mrblib/10error.rb
(snip)
CC mrbgems/mruby-time/src/time.c -> build/host/mrbgems/mruby-time/src/time.o
MRBC mrbgems/mruby-time/mrblib/time.rb
(snip)
CC mrbgems/mruby-socket/test/sockettest.c -> build/host/mrbgems/mruby-socket/test/sockettest.o
MRBC mrbgems/mruby-socket/test/addrinfo.rb
MRBC mrbgems/mruby-socket/test/basicsocket.rb
(snip)
```
#### After this patch:
```console
GEN build/presym
GEN build/presym.inc
CC src/array.c -> build/host/src/array.o
(snip)
GEN mrblib/*.rb -> build/host/mrblib/mrblib.c
MRBC mrblib/00class.rb
mrblib/10error.rb
(snip)
CC mrbgems/mruby-time/src/time.c -> build/host/mrbgems/mruby-time/src/time.o
GEN build/host/mrbgems/mruby-time/gem_init.c
MRBC mrbgems/mruby-time/mrblib/time.rb
(snip)
CC mrbgems/mruby-socket/test/sockettest.c -> build/host/mrbgems/mruby-socket/test/sockettest.o
GEN build/host/mrbgems/mruby-socket/gem_test.c
MRBC mrbgems/mruby-socket/test/addrinfo.rb
MRBC mrbgems/mruby-socket/test/basicsocket.rb
(snip)
```
To be also able to build mruby without presym in the future. However,
`MRB_QSYM` has been removed and changed as follows:
### Example
| Type | Symbol | Previous Style | New Style |
|---------------------------|--------|------------------|----------------|
| Operator | & | MRB_QSYM(and) | MRB_OPSYM(and) |
| Class Variable | @@foo | MRB_QSYM(00_foo) | MRB_CVSYM(foo) |
| Instance Variable | @foo | MRB_QSYM(0_foo) | MRB_IVSYM(foo) |
| Method with Bang | foo! | MRB_QSYM(foo_b) | MRB_SYM_B(foo) |
| Method with Question mark | foo? | MRB_QSYM(foo_p) | MRB_SYM_Q(foo) |
| Mmethod with Equal | foo= | MRB_QSYM(foo_e) | MRB_SYM_E(foo) |
This change makes it possible to define, for example, `MRB_IVSYM(foo)` as
`mrb_intern_lit(mrb, "@" "foo")`, which is useful if we support building
without presym in the future.
When `rake -m` and so on are used to build in parallel, building may be
started before presym files are generated. Then, for example, the following
error occurs and this issue is fixed.
```console
In file included from /Users/shuujii/mruby/mruby/include/mruby.h:92:
/mruby/mruby/include/mruby/presym.h:16:10: fatal error: '../build/presym.inc' file not found
#include <../build/presym.inc>
^~~~~~~~~~~~~~~~~~~~~
```
* In explanation of mruby, the expression `build_config.rb` is frequently
used including official documents, so I think that it will not make sense
if the file is no longer used.
* The `MRUBY_TARGET` mechanism seems to have little improvement, so I don't
think it should be changed to avoid unnecessary confusion.
* `MRUBY_TARGET` and `MRuby.targets` represent somewhat different things,
so using the same term "target" is a bit confusing.
The mechanism that can be written short when using a file under
`build_config` (renamed from `target`) directory remains
(`build_config/${MRUBY_CONFIG}.rb` is used if the path specified
in `MRUBY_CONFIG` doesn't exist).
Files under `test/t` and `mrbgem/*/test` are for tests, not for actual
execution. So symbols in those files need not to be pre-allocated. This
change slightly reduce the memory consumption.
Where `QSYM` means quoted symbols, which cannot be represented C
symbols, so specify aliases instead.
- operators: name of the operation, e.g. add for `+`
- predicates: add `_p` suffix instead of `?`
- bang methods: add `_b` suffix instead of `!`
- instance variables: add `a_` prefix instead of `@`
- global variables: add `d_` prefix instead of `@`
- class variables: unsupported; don't use them
You have to specify `TARGET` to specify a configuration, e.g.
```
rake TARGET=host-debug all test
```
When you port `mruby` to a new configuration:
1. copy an existing configuration under `target` directory
2. modify the new configuration file
3. build using the new configuration
4. send PR if you please
KOBAYASHI Shuji