build: add back the Bash EXIT trap to handle cases that ERR doesn't

ERR unfortunately doesn't trigger for e.g. 'exit 1'. Unfortunately
the backtrace we generate in the EXIT trap won't be able to get the
correct line number for the first frame.

See http://gnu-bash.2382.n7.nabble.com/trap-echo-quot-trap-exit-on-LINENO-quot-EXIT-gt-wrong-linenumber-td3666.html

Therefore the metadata-relative backtrace will just not have the
first frame. Example:

| WARNING: /home/laplante/repos/oe-core/build/tmp-glibc/work/core2-64-oe-linux/libsolv/0.7.14-r0/temp/run.do_compile.85057:1 exit 1 from 'exit 1'
| WARNING: Backtrace (BB generated script):
| 	#1: myclass_do_something, /home/laplante/repos/oe-core/build/tmp-glibc/work/core2-64-oe-linux/libsolv/0.7.14-r0/temp/run.do_compile.85057, line ?
| 	#2: do_something, /home/laplante/repos/oe-core/build/tmp-glibc/work/core2-64-oe-linux/libsolv/0.7.14-r0/temp/run.do_compile.85057, line 156
| 	#3: actually_fail, /home/laplante/repos/oe-core/build/tmp-glibc/work/core2-64-oe-linux/libsolv/0.7.14-r0/temp/run.do_compile.85057, line 144
| 	#4: my_compile_extra, /home/laplante/repos/oe-core/build/tmp-glibc/work/core2-64-oe-linux/libsolv/0.7.14-r0/temp/run.do_compile.85057, line 146
| 	#5: do_compile, /home/laplante/repos/oe-core/build/tmp-glibc/work/core2-64-oe-linux/libsolv/0.7.14-r0/temp/run.do_compile.85057, line 137
| 	#6: main, /home/laplante/repos/oe-core/build/tmp-glibc/work/core2-64-oe-linux/libsolv/0.7.14-r0/temp/run.do_compile.85057, line 180
|
| Backtrace (metadata-relative locations):
| 	#2: do_something, autogenerated, line 2
| 	#3: actually_fail, /home/laplante/repos/oe-core/meta/recipes-extended/libsolv/libsolv_0.7.14.bb, line 36
| 	#4: my_compile_extra, /home/laplante/repos/oe-core/meta/recipes-extended/libsolv/libsolv_0.7.14.bb, line 38
| 	#5: do_compile, autogenerated, line 3

Signed-off-by: Chris Laplante <chris.laplante@agilent.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

lib/bb/build.py

@@ -314,6 +314,26 @@ def shell_trap_code():
     exit $ret
 }
 
+bb_bash_exit_handler() {
+    ret=$?
+    if [ "$ret" != 0 ]; then
+        echo "WARNING: ${BASH_SOURCE[0]}:${BASH_LINENO[0]} exit $ret from '$BASH_COMMAND'"
+
+        echo "WARNING: Backtrace (BB generated script): "
+        for ((i=1; i<${#FUNCNAME[@]}; i++)); do
+            if [ $i -eq 1 ]; then
+                # TODO: maybe manually track LINENO with a DEBUG trap?
+                # LINENO / BASH_LINENO for the first frame in an EXIT trap is wrong :/
+                # http://gnu-bash.2382.n7.nabble.com/trap-echo-quot-trap-exit-on-LINENO-quot-EXIT-gt-wrong-linenumber-td3666.html
+                echo "\t#$((i)): ${FUNCNAME[$i]}, ${BASH_SOURCE[$((i-1))]}, line ?"
+            else
+                echo "\t#$((i)): ${FUNCNAME[$i]}, ${BASH_SOURCE[$((i-1))]}, line ${BASH_LINENO[$((i-1))]}"
+            fi
+        done
+    fi
+    exit $ret
+}
+
 bb_bash_err_handler() {
     ret=$?
     echo "WARNING: ${BASH_SOURCE[0]}:${BASH_LINENO[0]} exit $ret from '$BASH_COMMAND'"
@@ -323,6 +343,7 @@ def shell_trap_code():
         echo "\t#$((i-1)): ${FUNCNAME[$i]}, ${BASH_SOURCE[$((i-1))]}, line ${BASH_LINENO[$((i-1))]}"
     done
 
+    trap "" EXIT
     exit $ret
 }
 
@@ -331,6 +352,7 @@ def shell_trap_code():
     set -e
     ;;
 *)  trap 'bb_bash_err_handler' ERR
+    trap 'bb_bash_exit_handler' 0
     set -eE
 esac
 '''