Re: [PATCH v3 01/15] scalar: create a rudimentary executable

> On Wed, Sep 8, 2021 at 12:24 PM Johannes Schindelin via GitGitGadget
> <gitgitgadget@gmail.com> wrote:
> >
> > From: Johannes Schindelin <johannes.schindelin@gmx.de>
> >
> > The idea of Scalar (https://github.com/microsoft/scalar), and before
> > that, of VFS for Git, has always been to prove that Git _can_ scale, and
> > to upstream whatever strategies have been demonstrated to help.
> >
> > With this patch, we start the journey from that C# project to move what
> > is left to Git's own `contrib/` directory, reimplementing it in pure C,
> > with the intention to facilitate integrating the functionality into core
> > Git all while maintaining backwards-compatibility for existing Scalar
> > users (which will be much easier when both live in the same worktree).
> > It was always to plan to contribute all of the proven strategies back to
> > core Git.
>
> s/always to plan/always the plan/
>
> > For example, while the virtual filesystem provided by VFS for Git helped
> > the team developing the Windows operating system to move onto Git, while
> > trying to upstream it we realized that it cannot be done: getting the
> > virtual filesystem to work (which we only managed to implement fully on
> > Windows, but not on, say, macOS or Linux), and the required server-side
> > support for the GVFS protocol, made this not quite feasible.
> >
> > The Scalar project learned from that and tackled the problem with
> > different tactics: instead of pretending to Git that the working
> > directory is fully populated, it _specifically_ teaches Git about
> > partial clone (which is based on VFS for Git's cache server), about
> > sparse checkout (which VFS for Git tried to do transparently, in the
> > file system layer), and regularly runs maintenance tasks to keep the
> > repository in a healthy state.
> >
> > With partial clone, sparse checkout and `git maintenance` having been
> > upstreamed, there is little left that `scalar.exe` does that which
> > `git.exe` cannot do. One such thing is that `scalar clone <url>` will
> > automatically set up a partial, sparse clone, and configure
> > known-helpful settings from the start.
>
> s/does that which/does which/

>
> > So let's bring this convenience into Git's tree.
> >
> > The idea here is that you can (optionally) build Scalar via
> >
> >         make -C contrib/scalar/Makefile
> >
> > This will build the `scalar` executable and put it into the
> > contrib/scalar/ subdirectory.
> >
> > The slightly awkward addition of the `contrib/scalar/*` bits to the
> > top-level `Makefile` are actually really required: we want to link to
> > `libgit.a`, which means that we will need to use the very same `CFLAGS`
> > and `LDFLAGS` as the rest of Git.
> >
> > An early development version of this patch tried to replicate all the
> > conditional code in `contrib/scalar/Makefile` (e.g. `NO_POLL`) just like
> > `contrib/svn-fe/Makefile` used to do before it was retired. It turned
> > out to be quite the whack-a-mole game: the SHA-1-related flags, the
> > flags enabling/disabling `compat/poll/`, `compat/regex/`,
> > `compat/win32mmap.c` & friends depending on the current platform... To
> > put it mildly: it was a major mess.
> >
> > Instead, this patch makes minimal changes to the top-level `Makefile` so
> > that the bits in `contrib/scalar/` can be compiled and linked, and
> > adds a `contrib/scalar/Makefile` that uses the top-level `Makefile` in a
> > most minimal way to do the actual compiling.
> >
> > Note: With this commit, we only establish the infrastructure, no
> > Scalar functionality is implemented yet; We will do that incrementally
> > over the next few commits.
> >
> > Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
> > ---
> >  Makefile                  |  8 ++++++++
> >  contrib/scalar/.gitignore |  2 ++
> >  contrib/scalar/Makefile   | 34 ++++++++++++++++++++++++++++++++++
> >  contrib/scalar/scalar.c   | 36 ++++++++++++++++++++++++++++++++++++
> >  4 files changed, 80 insertions(+)
> >  create mode 100644 contrib/scalar/.gitignore
> >  create mode 100644 contrib/scalar/Makefile
> >  create mode 100644 contrib/scalar/scalar.c
> >
> > diff --git a/Makefile b/Makefile
> > index c3565fc0f8f..2d5c822f7a8 100644
> > --- a/Makefile
> > +++ b/Makefile
> > @@ -2447,6 +2447,10 @@ endif
> >  .PHONY: objects
> >  objects: $(OBJECTS)
> >
> > +SCALAR_SOURCES := contrib/scalar/scalar.c
> > +SCALAR_OBJECTS := $(SCALAR_SOURCES:c=o)
> > +OBJECTS += $(SCALAR_OBJECTS)
> > +
> >  dep_files := $(foreach f,$(OBJECTS),$(dir $f).depend/$(notdir $f).d)
> >  dep_dirs := $(addsuffix .depend,$(sort $(dir $(OBJECTS))))
> >
> > @@ -2586,6 +2590,10 @@ $(REMOTE_CURL_PRIMARY): remote-curl.o http.o http-walker.o GIT-LDFLAGS $(GITLIBS
> >         $(QUIET_LINK)$(CC) $(ALL_CFLAGS) -o $@ $(ALL_LDFLAGS) $(filter %.o,$^) \
> >                 $(CURL_LIBCURL) $(EXPAT_LIBEXPAT) $(LIBS)
> >
> > +contrib/scalar/scalar$X: $(SCALAR_OBJECTS) GIT-LDFLAGS $(GITLIBS)
> > +       $(QUIET_LINK)$(CC) $(ALL_CFLAGS) -o $@ $(ALL_LDFLAGS) \
> > +               $(filter %.o,$^) $(LIBS)
> > +
> >  $(LIB_FILE): $(LIB_OBJS)
> >         $(QUIET_AR)$(RM) $@ && $(AR) $(ARFLAGS) $@ $^
> >
> > diff --git a/contrib/scalar/.gitignore b/contrib/scalar/.gitignore
> > new file mode 100644
> > index 00000000000..ff3d47e84d0
> > --- /dev/null
> > +++ b/contrib/scalar/.gitignore
> > @@ -0,0 +1,2 @@
> > +/*.exe
> > +/scalar
> > diff --git a/contrib/scalar/Makefile b/contrib/scalar/Makefile
> > new file mode 100644
> > index 00000000000..40c03ad10e1
> > --- /dev/null
> > +++ b/contrib/scalar/Makefile
> > @@ -0,0 +1,34 @@
> > +QUIET_SUBDIR0  = +$(MAKE) -C # space to separate -C and subdir
> > +QUIET_SUBDIR1  =
> > +
> > +ifneq ($(findstring s,$(MAKEFLAGS)),s)
> > +ifndef V
> > +       QUIET_SUBDIR0  = +@subdir=
> > +       QUIET_SUBDIR1  = ;$(NO_SUBDIR) echo '   ' SUBDIR $$subdir; \
> > +                        $(MAKE) $(PRINT_DIR) -C $$subdir
> > +else
> > +       export V
> > +endif
> > +endif
> > +
> > +all:
> > +
> > +include ../../config.mak.uname
> > +-include ../../config.mak.autogen
> > +-include ../../config.mak
> > +
> > +TARGETS = scalar$(X) scalar.o
> > +GITLIBS = ../../common-main.o ../../libgit.a ../../xdiff/lib.a
> > +
> > +all: scalar$X
> > +
> > +$(GITLIBS):
> > +       $(QUIET_SUBDIR0)../.. $(QUIET_SUBDIR1) $(subst ../../,,$@)
> > +
> > +$(TARGETS): $(GITLIBS) scalar.c
> > +       $(QUIET_SUBDIR0)../.. $(QUIET_SUBDIR1) $(patsubst %,contrib/scalar/%,$@)
> > +
> > +clean:
> > +       $(RM) $(TARGETS)
> > +
> > +.PHONY: all clean FORCE
> > diff --git a/contrib/scalar/scalar.c b/contrib/scalar/scalar.c
> > new file mode 100644
> > index 00000000000..7cff29e0fcd
> > --- /dev/null
> > +++ b/contrib/scalar/scalar.c
> > @@ -0,0 +1,36 @@
> > +/*
> > + * The Scalar command-line interface.
> > + */
> > +
> > +#include "cache.h"
> > +#include "gettext.h"
> > +#include "parse-options.h"
> > +
> > +static struct {
> > +       const char *name;
> > +       int (*fn)(int, const char **);
> > +} builtins[] = {
> > +       { NULL, NULL},
> > +};
> > +
> > +int cmd_main(int argc, const char **argv)
> > +{
> > +       struct strbuf scalar_usage = STRBUF_INIT;
> > +       int i;
> > +
> > +       if (argc > 1) {
> > +               argv++;
> > +               argc--;
> > +
> > +               for (i = 0; builtins[i].name; i++)
> > +                       if (!strcmp(builtins[i].name, argv[0]))
> > +                               return !!builtins[i].fn(argc, argv);
> > +       }
> > +
> > +       strbuf_addstr(&scalar_usage,
> > +                     N_("scalar <command> [<options>]\n\nCommands:\n"));
> > +       for (i = 0; builtins[i].name; i++)
> > +               strbuf_addf(&scalar_usage, "\t%s\n", builtins[i].name);
> > +
> > +       usage(scalar_usage.buf);
> > +}
> > --
> > gitgitgadget
> >
>