scons: Disable protobuf if pkg-config and CheckLib fails

This patch changes the use of pkg-config such that protobuf is still
evaluated with CheckLib even if it fails. This is to allow setups
where libprotobuf is available, but not configured through
protobuf. Moreover, if CheckLib fails to use libprotobuf then all the
tracing is disabled, but scons is allowed to continue with a warning.

diff --git a/SConstruct b/SConstruct
index 26d993e8399fcd3ff50afe9f79d3dccafc9526ec..93adc85de27d2ed4044e07e64c35819b3e902fef 100755 (executable)
--- a/SConstruct
+++ b/SConstruct
@@ -637,21 +637,32 @@ if len(protoc_version) < 2 or protoc_version[0] != 'libprotoc':
         termcap.Normal
     main['PROTOC'] = False
 else:
-    # Determine the appropriate include path and library path using
-    # pkg-config, that means we also need to check for pkg-config
-    if not readCommand(['pkg-config', '--version'], exception=''):
-        print 'Error: pkg-config not found. Please install and retry.'
-        Exit(1)
-
-    main.ParseConfig('pkg-config --cflags --libs-only-L protobuf')
-
     # Based on the availability of the compress stream wrappers,
     # require 2.1.0
     min_protoc_version = '2.1.0'
     if compareVersions(protoc_version[1], min_protoc_version) < 0:
-        print 'Error: protoc version', min_protoc_version, 'or newer required.'
-        print '       Installed version:', protoc_version[1]
-        Exit(1)
+        print termcap.Yellow + termcap.Bold + \
+            'Warning: protoc version', min_protoc_version, \
+            'or newer required.\n' + \
+            '         Installed version:', protoc_version[1], \
+            termcap.Normal
+        main['PROTOC'] = False
+    else:
+        # Attempt to determine the appropriate include path and
+        # library path using pkg-config, that means we also need to
+        # check for pkg-config. Note that it is possible to use
+        # protobuf without the involvement of pkg-config. Later on we
+        # check go a library config check and at that point the test
+        # will fail if libprotobuf cannot be found.
+        if readCommand(['pkg-config', '--version'], exception=''):
+            try:
+                # Attempt to establish what linking flags to add for protobuf
+                # using pkg-config
+                main.ParseConfig('pkg-config --cflags --libs-only-L protobuf')
+            except:
+                print termcap.Yellow + termcap.Bold + \
+                    'Warning: pkg-config could not get protobuf flags.' + \
+                    termcap.Normal
 
 # Check for SWIG
 if not main.has_key('SWIG'):
@@ -846,11 +857,12 @@ main['HAVE_PROTOBUF'] = main['PROTOC'] and \
     conf.CheckLibWithHeader('protobuf', 'google/protobuf/message.h',
                             'C++', 'GOOGLE_PROTOBUF_VERIFY_VERSION;')
 
-# If we have the compiler but not the library, treat it as an error.
+# If we have the compiler but not the library, print another warning.
 if main['PROTOC'] and not main['HAVE_PROTOBUF']:
-    print 'Error: did not find protocol buffer library and/or headers.'
-    print '       Please install libprotobuf-dev and try again.'
-    Exit(1)
+    print termcap.Yellow + termcap.Bold + \
+        'Warning: did not find protocol buffer library and/or headers.\n' + \
+    '       Please install libprotobuf-dev for tracing support.' + \
+    termcap.Normal
 
 # Check for librt.
 have_posix_clock = \