Documentation: Split public/private documentation

The API reference pages generated by Doxygen are comprehensive, but
therefore quite overwhelming for application developers who will
likely never need to use the majority of the library's objects. To
reduce the complexity of the documentation, split it into two runs of
doxygen.

The first run of doxygen is for the public API. We pass a specific list
of source files to parse, which is built from the arrays of public
headers and sources in meson build files. This ensures that we only
generate the documentation for code from those files.

A custom Python script is needed to add the list of input files to
Doxyfile, as several of the objects included in the header and source
array are custom_tgt objects, which can't be handled as strings to
populate a variable in the configuration data.

The headers defining the Extensible and Object classes (class.h and
object.h respectively), as well as the corresponding source files, are
excluded from the public API documentation despite being referenced in
the meson public headers and sources arrays. This is due to the fact
that public API classes inherit from Extensible and Object, making the
Extensible and Object classes part of the public ABI. Those two base
classes are however implementation details and must not be accessed
directly by application code.

The second run of doxygen is for the internal API. This contains
documentation for all of the library's objects as it currently does.
This set will now be output into build/Documentation/internal-api-html.

Signed-off-by: Daniel Scally <dan.scally@ideasonboard.com>
Co-developed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Daniel Scally <dan.scally@ideasonboard.com>

5 files changed, 152 insertions, 31 deletions

diff --git a/Documentation/Doxyfile.in b/Documentation/Doxyfile-common.in
index 203f8e67..a70aee43 100644
--- a/Documentation/Doxyfile.in
+++ b/Documentation/Doxyfile-common.in
@@ -17,21 +17,11 @@ EXTENSION_MAPPING      = h=C++
 
 TOC_INCLUDE_HEADINGS   = 0
 
-ENABLED_SECTIONS       = internal
-INTERNAL_DOCS          = YES
 CASE_SENSE_NAMES       = YES
 
 QUIET                  = YES
 WARN_AS_ERROR          = @WARN_AS_ERROR@
 
-INPUT                  = "@TOP_SRCDIR@/Documentation" \
-                         "@TOP_SRCDIR@/include/libcamera" \
-                         "@TOP_SRCDIR@/src/ipa/ipu3" \
-                         "@TOP_SRCDIR@/src/ipa/libipa" \
-                         "@TOP_SRCDIR@/src/libcamera" \
-                         "@TOP_BUILDDIR@/include/libcamera" \
-                         "@TOP_BUILDDIR@/src/libcamera"
-
 FILE_PATTERNS          = *.c \
                          *.cpp \
                          *.dox \
@@ -39,19 +29,6 @@ FILE_PATTERNS          = *.c \
 
 RECURSIVE              = YES
 
-EXCLUDE                = @TOP_SRCDIR@/include/libcamera/base/span.h \
-                         @TOP_SRCDIR@/include/libcamera/internal/device_enumerator_sysfs.h \
-                         @TOP_SRCDIR@/include/libcamera/internal/device_enumerator_udev.h \
-                         @TOP_SRCDIR@/include/libcamera/internal/ipc_pipe_unixsocket.h \
-                         @TOP_SRCDIR@/src/libcamera/device_enumerator_sysfs.cpp \
-                         @TOP_SRCDIR@/src/libcamera/device_enumerator_udev.cpp \
-                         @TOP_SRCDIR@/src/libcamera/ipc_pipe_unixsocket.cpp \
-                         @TOP_SRCDIR@/src/libcamera/pipeline/ \
-                         @TOP_SRCDIR@/src/libcamera/tracepoints.cpp \
-                         @TOP_BUILDDIR@/include/libcamera/internal/tracepoints.h \
-                         @TOP_BUILDDIR@/include/libcamera/ipa/soft_ipa_interface.h \
-                         @TOP_BUILDDIR@/src/libcamera/proxy/
-
 EXCLUDE_PATTERNS       = @TOP_BUILDDIR@/include/libcamera/ipa/*_serializer.h \
                          @TOP_BUILDDIR@/include/libcamera/ipa/*_proxy.h \
                          @TOP_BUILDDIR@/include/libcamera/ipa/ipu3_*.h \
@@ -74,8 +51,6 @@ EXCLUDE_SYMBOLS        = libcamera::BoundMethodArgs \
 
 EXCLUDE_SYMLINKS       = YES
 
-HTML_OUTPUT            = api-html
-
 GENERATE_LATEX         = NO
 
 MACRO_EXPANSION        = YES
diff --git a/Documentation/Doxyfile-internal.in b/Documentation/Doxyfile-internal.in
new file mode 100644
index 00000000..cf982553
--- /dev/null
+++ b/Documentation/Doxyfile-internal.in
@@ -0,0 +1,31 @@
+# SPDX-License-Identifier: CC-BY-SA-4.0
+
+@INCLUDE_PATH          = @TOP_BUILDDIR@/Documentation
+@INCLUDE               = Doxyfile-common
+
+HIDE_UNDOC_CLASSES     = NO
+HIDE_UNDOC_MEMBERS     = NO
+HTML_OUTPUT            = internal-api-html
+INTERNAL_DOCS          = YES
+ENABLED_SECTIONS       = internal
+
+INPUT                  = "@TOP_SRCDIR@/Documentation" \
+                         "@TOP_SRCDIR@/include/libcamera" \
+                         "@TOP_SRCDIR@/src/ipa/ipu3" \
+                         "@TOP_SRCDIR@/src/ipa/libipa" \
+                         "@TOP_SRCDIR@/src/libcamera" \
+                         "@TOP_BUILDDIR@/include/libcamera" \
+                         "@TOP_BUILDDIR@/src/libcamera"
+
+EXCLUDE                = @TOP_SRCDIR@/include/libcamera/base/span.h \
+                         @TOP_SRCDIR@/include/libcamera/internal/device_enumerator_sysfs.h \
+                         @TOP_SRCDIR@/include/libcamera/internal/device_enumerator_udev.h \
+                         @TOP_SRCDIR@/include/libcamera/internal/ipc_pipe_unixsocket.h \
+                         @TOP_SRCDIR@/src/libcamera/device_enumerator_sysfs.cpp \
+                         @TOP_SRCDIR@/src/libcamera/device_enumerator_udev.cpp \
+                         @TOP_SRCDIR@/src/libcamera/ipc_pipe_unixsocket.cpp \
+                         @TOP_SRCDIR@/src/libcamera/pipeline/ \
+                         @TOP_SRCDIR@/src/libcamera/tracepoints.cpp \
+                         @TOP_BUILDDIR@/include/libcamera/internal/tracepoints.h \
+                         @TOP_BUILDDIR@/include/libcamera/ipa/soft_ipa_interface.h \
+                         @TOP_BUILDDIR@/src/libcamera/proxy/
diff --git a/Documentation/Doxyfile-public.in b/Documentation/Doxyfile-public.in
new file mode 100644
index 00000000..36bb5758
--- /dev/null
+++ b/Documentation/Doxyfile-public.in
@@ -0,0 +1,20 @@
+# SPDX-License-Identifier: CC-BY-SA-4.0
+
+@INCLUDE_PATH          = @TOP_BUILDDIR@/Documentation
+@INCLUDE               = Doxyfile-common
+
+HIDE_UNDOC_CLASSES     = YES
+HIDE_UNDOC_MEMBERS     = YES
+HTML_OUTPUT            = api-html
+INTERNAL_DOCS          = NO
+
+INPUT                  = "@TOP_SRCDIR@/Documentation" \
+                         ${inputs}
+
+EXCLUDE                = @TOP_SRCDIR@/include/libcamera/base/class.h \
+                         @TOP_SRCDIR@/include/libcamera/base/object.h \
+                         @TOP_SRCDIR@/include/libcamera/base/span.h \
+                         @TOP_SRCDIR@/src/libcamera/base/class.cpp \
+                         @TOP_SRCDIR@/src/libcamera/base/object.cpp
+
+PREDEFINED            += __DOXYGEN_PUBLIC__
diff --git a/Documentation/gen-doxyfile.py b/Documentation/gen-doxyfile.py
new file mode 100755
index 00000000..c265bc2f
--- /dev/null
+++ b/Documentation/gen-doxyfile.py
@@ -0,0 +1,46 @@
+#!/usr/bin/env python3
+# SPDX-License-Identifier: GPL-2.0-or-later
+# Copyright (C) 2024, Google Inc.
+#
+# Author: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
+#
+# Generate Doxyfile from a template
+
+import argparse
+import os
+import string
+import sys
+
+
+def fill_template(template, data):
+
+    template = open(template, 'rb').read()
+    template = template.decode('utf-8')
+    template = string.Template(template)
+
+    return template.substitute(data)
+
+
+def main(argv):
+
+    parser = argparse.ArgumentParser()
+    parser.add_argument('-o', dest='output', metavar='file',
+                        type=argparse.FileType('w', encoding='utf-8'),
+                        default=sys.stdout,
+                        help='Output file name (default: standard output)')
+    parser.add_argument('template', metavar='doxyfile.tmpl', type=str,
+                        help='Doxyfile template')
+    parser.add_argument('inputs', type=str, nargs='*',
+                        help='Input files')
+
+    args = parser.parse_args(argv[1:])
+
+    inputs = [f'"{os.path.realpath(input)}"' for input in args.inputs]
+    data = fill_template(args.template, {'inputs': (' \\\n' + ' ' * 25).join(inputs)})
+    args.output.write(data)
+
+    return 0
+
+
+if __name__ == '__main__':
+    sys.exit(main(sys.argv))
diff --git a/Documentation/meson.build b/Documentation/meson.build
index 1d84ed81..1ba40fdf 100644
--- a/Documentation/meson.build
+++ b/Documentation/meson.build
@@ -24,9 +24,9 @@ if doxygen.found() and dot.found()
 
     cdata.set('PREDEFINED', ' \\\n\t\t\t '.join(doxygen_predefined))
 
-    doxyfile = configure_file(input : 'Doxyfile.in',
-                              output : 'Doxyfile',
-                              configuration : cdata)
+    doxyfile_common = configure_file(input : 'Doxyfile-common.in',
+                                     output : 'Doxyfile-common',
+                                     configuration : cdata)
 
     doxygen_public_input = [
         libcamera_base_public_headers,
@@ -50,17 +50,66 @@ if doxygen.found() and dot.found()
         doxygen_internal_input += [ipu3_ipa_sources]
     endif
 
-    custom_target('doxygen',
+    # We run doxygen twice - the first run excludes internal API objects as it
+    # is intended to document the public API only. A second run covers all of
+    # the library's objects for libcamera developers. Common configuration is
+    # set in an initially generated Doxyfile, which is then included by the two
+    # final Doxyfiles.
+
+    # This is the "public" run of doxygen generating an abridged version of the
+    # API's documentation.
+
+    doxyfile_tmpl = configure_file(input : 'Doxyfile-public.in',
+                                   output : 'Doxyfile-public.tmpl',
+                                   configuration : cdata)
+
+    # The set of public input files stored in the doxygen_public_input array
+    # needs to be set in Doxyfile public. We can't pass them through cdata
+    # cdata, as some of the array members are custom_tgt instances, which
+    # configuration_data.set() doesn't support. Using a separate script invoked
+    # through custom_target(), which supports custom_tgt instances as inputs.
+
+    doxyfile = custom_target('doxyfile-public',
+                             input : [
+                                 doxygen_public_input,
+                             ],
+                             output : 'Doxyfile-public',
+                             command : [
+                                 'gen-doxyfile.py',
+                                 '-o', '@OUTPUT@',
+                                 doxyfile_tmpl,
+                                 '@INPUT@',
+                             ])
+
+    custom_target('doxygen-public',
                   input : [
                       doxyfile,
-                      doxygen_public_input,
-                      doxygen_internal_input,
+                      doxyfile_common,
                   ],
                   output : 'api-html',
                   command : [doxygen, doxyfile],
                   install : true,
                   install_dir : doc_install_dir,
                   install_tag : 'doc')
+
+    # This is the internal documentation, which hard-codes a list of directories
+    # to parse in its doxyfile.
+
+    doxyfile = configure_file(input : 'Doxyfile-internal.in',
+                              output : 'Doxyfile-internal',
+                              configuration : cdata)
+
+    custom_target('doxygen-internal',
+                  input : [
+                      doxyfile,
+                      doxyfile_common,
+                      doxygen_internal_input,
+                  ],
+                  output : 'internal-api-html',
+                  command : [doxygen, doxyfile],
+                  install : true,
+                  install_dir : doc_install_dir,
+                  install_tag : 'doc-internal')
 endif
 
 #