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Running pkg-config multiple times can produce too many cflags, most
of them being dups. With this change, I rely on pkg-config itself to
discard dups properly - pkg-config(1) manpage says that "duplicate
flags are merged (maintaining proper ordering)".
Hierarchical processing makes cpp.req more susceptible to "once-only
header" optimization. To demonstrate the problem, I've implemented
some debugging facilities. Here is how <gtk/gtk.h> is processed.
$ cpp.req -vv /usr/include/gtk-2.0/gtk/gtk.h
[...]
Include gdk/gdk.h
+ Push /usr/include/gtk-2.0/gdk/gdk.h
Include gdk/gdkapplaunchcontext.h
+ Push /usr/include/gtk-2.0/gdk/gdkapplaunchcontext.h
Include gio/gio.h
! Push /usr/include/glib-2.0/gio/gio.h
Include gio/giotypes.h
Push /usr/include/glib-2.0/gio/giotypes.h
Include gio/gioenums.h
Push /usr/include/glib-2.0/gio/gioenums.h
Include glib-object.h
Push /usr/include/glib-2.0/glib-object.h
Include gobject/gbinding.h
Push /usr/include/glib-2.0/gobject/gbinding.h
Include glib.h
Push /usr/include/glib-2.0/glib.h
[...]
+ Push /usr/include/gtk-2.0/gtk/gtkdebug.h
Include glib.h
Pop
[...]
recovered glib.h -> /usr/include/glib-2.0/glib.h
recovered stdarg.h -> /usr/lib64/gcc/x86_64-alt-linux/4.5.3/include/stdarg.h
recovered time.h -> /usr/include/time.h
recovered glib-object.h -> /usr/include/glib-2.0/glib-object.h
In the output, "Include" lines annotate "#include" instructions which
are about to be processed by cpp; "Push" and "Pop" annotate actual
file operations performed by cpp. Technically, "Include" annotations
are enabled via -dI option which installs cb_include callback in
gcc/c-ppoutput.c; "Push" and "Pop" are triggered in the guts of the
libcpp library. The library has hardcoded optimization against repeated
inclusions. According to "info cpp", "It remembers when a header file
has a wrapper #ifndef. If a subsequent #include specifies that header,
and the macro in the #ifndef is still defined, it does not bother to
rescan the file at all." (See should_stack_file in libcpp/files.c.)
This means that, normally, each "Include" should be followed by a
corresponding "Push". However, due to "once-only header" optimization,
some includes are not followed by a push. This means that the file
has already been pushed, and it happens to use a wrapper #ifndef.
Note that, in the output, this is exactly the case with <glib2.h>.
Also note that, in the output, files internal to the package are marked
with "+" on the left. They are tracked down to the first non-packaged
file, which makes a dependency; these files are marked with "!". The
problem with <glib2.h> is then that it gets first included in an
external file. Later it is also included in an internal file, but
a "Push" is not triggered. And since the internal file is subordinate
to <gtk/gtk.h> and is not going to be processed on its own, the
dependency on <glib2.h> is lost.
To recover missing pushes, we have to associate each include with the
first-time push. In other words, we need a table which maintains a
(header -> filename) mapping; in the above example, the table will
contain (glib.h -> /usr/include/glib-2.0/glib.h). Using this table,
we can ascertain that each internal #include produced a result.
Now, this might still have some corner cases: includes with
non-canonical header names probably will not be recovered, and it is not
clear whether <foo.h> and "foo.h" should be processed differently.
It works well enough in simple cases, though.
I have to admit that cpp.req can be slow and often fails in an ugly
manner. To address these issues, this change introduces "hierarchical
processing". Consider the package libgtk+2-devel. Only a few header
files from this package can be included directly, and these files in
turn include other "private" headers which are protected against direct
inclusion. The idea is then that only those few files with the highest
rank have to be processed explicitly, and most of the "private" files
can be processed implicitly as they are included on behalf of
higher-ranking files.
To implement the idea, somehow we have to sort the files by their rank.
This probably has to involve some guesswork. However, assigning higher
ranks to shorter filenames seems to produce nice guesses. More precisely,
files are sorted by shorter directory names and then by shorter basenames.
Another possible criteria which is not currently implemented is also to
take into account the number of path components in a directory name.
The result is pretty amazing: the amount of time needed to process
libgtk+2-devel headers is reduced from 150s to 5s. Notably <gtk/gtk.h>
includes 241 packaged files. This is also due to other optimizations:
packaged files are excluded from dependencies early on, and each
required filename gets passed to FindPackage only once.
When plain cpp check fails, cpp.req tries to process the same file in
c++ mode, which requires c++ support to be installed. As result, when
c++ support is not installed, cpp.req clutter the log with vain attempts
to process files in c++ mode. This change reduces the noise by checking
whether c++ support is actually available.
Some header files have protection against being included into user
code directly. This means that, when processing such files, cpp
is going to fail, and some dependencies probably will be missing.
/usr/include/gtk-2.0/gtk/gtkaccessible.h:
20 #if defined(GTK_DISABLE_SINGLE_INCLUDES) && !defined (__GTK_H_INSIDE__) && !defined (GTK_COMPILATION)
21 #error "Only <gtk/gtk.h> can be included directly."
22 #endif
23
24 #ifndef __GTK_ACCESSIBLE_H__
25 #define __GTK_ACCESSIBLE_H__
26
27 #include <atk/atk.h>
28 #include <gtk/gtkwidget.h>
To remedy the problem, we should, as per the above example, process
gtk/gtk.h dependencies recursively. Dependencies which we now attribute
to gtk/gtk.h are: 1) files which are packaged within the same subpackage
- these dependencies will be optimized out later by rpm; 2) the first
file not packaged into this subpackage, which is atk/atk.h. Files below
atk/atk.h are not processed.
Packaged? Stack
+---------------------+
+ | gtk/gtk.h |
+---------------------+
+ | gtk/gtkaccessible.h | <- SPmark
+---------------------+
- | atk/atk.h |
+---------------------+
| ... |
Also note that packaged files in cpp output should not be identified by
filenames, since filenames in the output will be possibly non-canonical.
Therefore I use standard unix technique to identify files by (dev,ino).
/usr/include/boost/spirit/home/support/detail/lexer/containers/ptr_vector.hpp:
9 #include "../size_t.hpp"
