meson: fix cross-compilation issues with gperf header file preprocessing

Pass c_args to the compiler when preprocessing the gperf header file,
they might contain important bits without which compilation/preprocessing
might fail (e.g. with clang on Android). cc.cmd_array() does not include
the c_args and we can't easily look them up from the meson.build file, so
we have to retrieve from the introspection info.

This is basically the Meson equivalent to commit 57103773.

2 files changed, 18 insertions, 3 deletions

diff --git a/src/cutout.py b/src/cutout.py
index 96cafd2..323eec8 100644
--- a/src/cutout.py
+++ b/src/cutout.py
@@ -1,5 +1,6 @@
 import argparse
 import subprocess
+import json
 import os
 import re
 
@@ -7,12 +8,23 @@ if __name__== '__main__':
     parser = argparse.ArgumentParser()
     parser.add_argument('input')
     parser.add_argument('output')
+    parser.add_argument('buildroot')
 
     args = parser.parse_known_args()
-    print (args[0].output)
+
+    # c_args might contain things that are essential for crosscompilation, but
+    # are not included in cc.cmd_array(), so we have to look them up ourselves
+    host_cargs = []
+    buildroot = args[0].buildroot
+    with open(os.path.join(buildroot, 'meson-info', 'intro-buildoptions.json')) as json_file:
+        bopts = json.load(json_file)
+        for opt in bopts:
+            if opt['name'] == 'c_args' and opt['section'] == 'compiler' and opt['machine'] == 'host':
+                host_cargs = opt['value']
+                break
 
     cpp = args[1]
-    ret = subprocess.run(cpp + [args[0].input], stdout=subprocess.PIPE, check=True)
+    ret = subprocess.run(cpp + host_cargs + [args[0].input], stdout=subprocess.PIPE, check=True)
 
     stdout = ret.stdout.decode('utf8')
 
diff --git a/src/meson.build b/src/meson.build
index f2a4861..7f9bf31 100644
--- a/src/meson.build
+++ b/src/meson.build
@@ -44,10 +44,13 @@ endif
 
 cpp += ['-I', join_paths(meson.current_source_dir(), '..')]
 
+# Can use meson.project_build_dir() once we require Meson 0.56
+project_build_dir = meson.current_build_dir() / '..'
+
 fcobjshash_gperf = custom_target('fcobjshash.gperf',
   input: 'fcobjshash.gperf.h',
   output: 'fcobjshash.gperf',
-  command: [python3, files('cutout.py')[0], '@INPUT@', '@OUTPUT@', cpp],
+  command: [python3, files('cutout.py')[0], '@INPUT@', '@OUTPUT@', project_build_dir, cpp],
   build_by_default: true,
 )