scons: Simplify the check for protoc.

Collapse nesting, and constrain the try/except to only the line in that
section which might actually be expected to throw an exception when
things are working normally.

This makes the code easier to read, and won't absorb and discard
exceptions which are thrown for unexpected reasons.

Change-Id: Id3ac417ab5545bef35ed8a87d05211c8ef2f5a50
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/40867
Tested-by: kokoro <noreply+kokoro@google.com>
Maintainer: Gabe Black <gabe.black@gmail.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>

diff --git a/SConstruct b/SConstruct
index 27816bfb5852dcb0f94dac7b0c4d8f8cd8f0bcb2..d0fd852a0222462b5100aec521567b4091847ebe 100755 (executable)
--- a/SConstruct
+++ b/SConstruct
@@ -455,39 +455,37 @@ if sys.platform == 'cygwin':
     main.Append(CCFLAGS=["-Wno-uninitialized"])
 
 
-have_pkg_config = readCommand(['pkg-config', '--version'], exception='')
+have_pkg_config = main.Detect('pkg-config')
 
 # Check for the protobuf compiler
+main['HAVE_PROTOC'] = False
+protoc_version = []
 try:
-    main['HAVE_PROTOC'] = True
     protoc_version = readCommand([main['PROTOC'], '--version']).split()
-
-    # First two words should be "libprotoc x.y.z"
-    if len(protoc_version) < 2 or protoc_version[0] != 'libprotoc':
-        warning('Protocol buffer compiler (protoc) not found.\n'
-                'Please install protobuf-compiler for tracing support.')
-        main['HAVE_PROTOC'] = False
-    else:
-        # 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:
-            warning('protoc version', min_protoc_version,
-                    'or newer required.\n'
-                    'Installed version:', protoc_version[1])
-            main['HAVE_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 have_pkg_config:
-                conf.CheckPkgConfig('protobuf', '--cflags', '--libs-only-L')
 except Exception as e:
     warning('While checking protoc version:', str(e))
-    main['HAVE_PROTOC'] = False
+
+# Based on the availability of the compress stream wrappers, require 2.1.0.
+min_protoc_version = '2.1.0'
+
+# First two words should be "libprotoc x.y.z"
+if len(protoc_version) < 2 or protoc_version[0] != 'libprotoc':
+    warning('Protocol buffer compiler (protoc) not found.\n'
+            'Please install protobuf-compiler for tracing support.')
+elif compareVersions(protoc_version[1], min_protoc_version) < 0:
+    warning('protoc version', min_protoc_version, 'or newer required.\n'
+            'Installed version:', protoc_version[1])
+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 have_pkg_config:
+        conf.CheckPkgConfig('protobuf', '--cflags', '--libs-only-L')
+    main['HAVE_PROTOC'] = True
+
 
 
 # Cache build files in the supplied directory.