build: ipa: Fix bug in building multiple IPA interfaces with the same mojom file

In the existing meson scripts, an IPA mojom interface file may not be
built if:

- There are duplicate entries for the mojom file shared by different
  pipeline handlers in pipeline_ipa_mojom_mapping, and
- The IPA is not listed first in pipeline_ipa_mojom_mapping, and
- The first listed IPA for the given mojom file is not selected in the
  build.

Fix this by using a separate list of already built mojom files
(mojoms_built) instead of overloading use of the existing
ipa_mojom_files list.  Now, ipa_mojom_files gets filled in outside of
the IPA list enumeration loop, this also guarantees the IPA
documentation gets built even if the pipeline is not selected.

Fixes: 312e9910ba ("meson: ipa: Add mapping for pipeline handler to mojom interface file")
Signed-off-by: Naushir Patuck <naush@raspberrypi.com>
Reviewed-by: David Plowman <david.plowman@raspberrypi.com>
Reviewed-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

include/libcamera/ipa/meson.build

@@ -68,29 +68,28 @@ pipeline_ipa_mojom_mapping = {
     'vimc': 'vimc.mojom',
 }
 
-ipa_mojom_files = []
-ipa_mojoms = []
-
 #
 # Generate headers from templates.
 #
 
 # TODO Define per-pipeline ControlInfoMap with yaml?
 
+ipa_mojoms = []
+mojoms_built = []
 foreach pipeline, file : pipeline_ipa_mojom_mapping
     name = file.split('.')[0]
 
-    # Ensure we do not build duplicate mojom modules
-    if file in ipa_mojom_files
+    # Avoid building duplicate mojom interfaces with the same interface file
+    if name in mojoms_built
         continue
     endif
 
-    ipa_mojom_files += file
-
     if pipeline not in pipelines
         continue
     endif
 
+    mojoms_built += name
+
     # {interface}.mojom-module
     mojom = custom_target(name + '_mojom_module',
                           input : file,
@@ -155,6 +154,12 @@ foreach pipeline, file : pipeline_ipa_mojom_mapping
     libcamera_generated_ipa_headers += [header, serializer, proxy_header]
 endforeach
 
+ipa_mojom_files = []
+foreach pipeline, file : pipeline_ipa_mojom_mapping
+    if file not in ipa_mojom_files
+        ipa_mojom_files += file
+    endif
+endforeach
 ipa_mojom_files = files(ipa_mojom_files)
 
 # Pass this to the documentation generator in src/libcamera/ipa