[RFC PATCH 3/3] kbuild: In quiet mode, print the full command line if it fails

[Ben Hutchings <ben@decadent.org.uk>]

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In the $(run-cmd) macro, add a trap on EXIT that prints the
full command line.  Remove the trap after running the command(s)
successfully.

(A more straightforward approach would be to use "if" or "||" to test
for failure, but that doesn't work.  Some command lines given to
$(run-cmd) have multiple commands separated by semi-colons, and the
caller must run "set -e" to enable exit-on-error.  Testing the result
of such a command line, even if it is probably grouped and run in a
sub-shell, inhibits exit-on-error and would cause some errors to be
ignored.)

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
 scripts/Kbuild.include | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
index 8778ae4a3476..c2525aaa36ac 100644
--- a/scripts/Kbuild.include
+++ b/scripts/Kbuild.include
@@ -224,7 +224,10 @@ flags = $(foreach o,$($(1)),$(if $(filter -I%,$(o)),$(call addtree,$(o)),$(o)))
 echo-cmd = $(if $($(quiet)cmd_$(1)),\
 	echo '  $(call escsq,$($(quiet)cmd_$(1)))$(echo-why)';)
 
-run-cmd = $(echo-cmd) $(cmd_$(1))
+trap-cmd-failed = trap 'test $$? = 0 || echo Failed command: '\''$(call escsq,$(call escsq,$(cmd_$(1))))'\' EXIT
+untrap-cmd-failed = trap - EXIT
+
+run-cmd = $(echo-cmd) $(if $(cmd_$(1)), $(if $(quiet), $(trap-cmd-failed); $(cmd_$(1)); $(untrap-cmd-failed), $(cmd_$(1))))
 
 # printing commands
 cmd = @$(run-cmd)

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