ci: fail any build that emits warnings

Using a custom logging.yml we can instruct BitBake's logger to write all
warnings and errors into a separate log file.

Then after the build has finished we can see if the log file is empty and if
not show it and abort the build.

Change-Id: Ida835b5c822941fb513dfb1758b4ec195e0050fc
Signed-off-by: Ross Burton <ross.burton@arm.com>

kas/base.yml

@@ -25,6 +25,9 @@ repos:
     layers:
       meta-oe:
 
+env:
+  BB_LOGCONFIG: ""
+
 local_conf_header:
   base: |
     CONF_VERSION = "1"

kas/check-warnings

@@ -0,0 +1,18 @@
+#! /bin/bash
+
+# Expects the path to a log file as $1, and if this file has any content
+# then display the contents and exit with an error code.
+
+set -e -u
+
+LOGFILE=$1
+
+if test -s $LOGFILE; then
+    echo ==============================
+    echo The build had warnings/errors:
+    echo ==============================
+    cat $LOGFILE
+    exit 1
+fi
+
+exit 0

kas/logging.yml

@@ -0,0 +1,13 @@
+# Python logging configuration to write all warnings to a separate file
+version: 1
+
+handlers:
+  warnings:
+    class: logging.FileHandler
+    level: WARNING
+    filename: warnings.log
+    formatter: BitBake.logfileFormatter
+
+loggers:
+  BitBake:
+    handlers: [warnings]