From: Sergei Trofimovich <slyfox@gentoo.org>
Date: Thu, 26 Mar 2020 08:22:50 +0000 (+0000)
Subject: flag-o-matic.eclass: document assumptions and limitations of test-flag-PROG()
X-Git-Url: http://git.tremily.us/?a=commitdiff_plain;h=9c5a9175843ce79427b04a5f23927a415d78d057;p=gentoo.git

flag-o-matic.eclass: document assumptions and limitations of test-flag-PROG()

Bug: https://bugs.gentoo.org/712488
Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>
---

diff --git a/eclass/flag-o-matic.eclass b/eclass/flag-o-matic.eclass
index 9ef9ac3685e0..e76eef293e89 100644
--- a/eclass/flag-o-matic.eclass
+++ b/eclass/flag-o-matic.eclass
@@ -487,6 +487,17 @@ test-flag-PROG() {
 
 	printf "%s\n" "${in_src}" > "${test_in}" || die "Failed to create '${test_in}'"
 
+	# Currently we rely on warning-free output of a compiler
+	# before the flag to see if a flag prduces any warnings.
+	# This has a few drawbacks:
+	# - if compiler already generates warnings we filter out
+	#   every single flag: bug #712488
+	# - if user actually wants to see warnings we just strip
+	#   them regardless of warnings type.
+	#
+	# We can add more selective detection of no-op flags via
+	# '-Werror=ignored-optimization-argument' and similar error options
+	# similar to what we are doing with '-Qunused-arguments'.
 	local cmdline=(
 		"${comp[@]}"
 		# Clang will warn about unknown gcc flags but exit 0.