+
+# AT_SYNCLINES_COMPILE(FILE)
+# --------------------------
+# Compile FILE expecting an error, and save in the file stdout the
+# normalized output. Ignore the exit status, since some compilers
+# (e.g. c89 on IRIX 6.5) trigger warnings on `#error', instead of
+# errors.
+m4_define([AT_SYNCLINES_COMPILE],
+[AT_CHECK([$CC $CFLAGS $CPPFLAGS -c $1], [ignore], [], [stderr])
+
+# Transform stderr into something like this:
+#
+# input.y:4: #error "4"
+#
+# In case GCC displays column information, strip it down.
+#
+# input.y:4:2: #error "4" or
+# input.y:4.2: #error "4" or
+# input.y:4:2: error: #error "4"
+# =>
+# input.y:4: #error "4"
+#
+# It may also issue more context information:
+#
+# input.y: In function 'yyparse':
+# input.y:8: #error "8"
+# =>
+# input.y:4: #error "8"
+#
+# The message may include a caret-error (indented by GCC 4.8,
+# not by clang 3.2):
+#
+# input.y:1:2: error: #error "1"
+# #error "1"
+# ^
+#
+# Possibly distcc adds its bits.
+#
+# distcc[33187] ERROR: compile (null) on localhost failed
+# syncline.c:1:2: error: #error "1"
+# distcc[33185] ERROR: compile syncline.c on localhost failed
+#
+# or even
+#
+# distcc[35882] (dcc_connect_by_name) ERROR: failed to look up host "chrisimac": Unknown host
+# distcc[35882] Warning: failed to distribute input.c to chrisimac/4, running locally instead
+#
+# The compiler might end by the number of messages issued (Clang 3.2):
+#
+# syncline.c:1:2: error: "1"
+# #error "1"
+# ^
+# 1 error generated.
+#
+# When c++ is used to compiler C, we might have more messages (Clang 3.2):
+#
+# clang: warning: treating 'c' input as 'c++' when in C++ mode, this behavior is deprecated
+
+AT_CHECK([[$PERL -p -0777 - stderr <<\EOF
+ # 1. Remove useless lines.
+
+ # distcc clutter.
+ s/^distcc\[\d+\] .*\n//gm;
+ # c vs. c++.
+ s/^clang: warning: treating 'c' input as 'c\+\+'.*\n//gm;
+ # Function context.
+ s/^[^:]*: In function '[^']+':\n//gm;
+ # Caret error.
+ s/^ *#error.*\n *\^\n//gm;
+ # Number of errors.
+ s/^1 error generated\.\n//gm;
+
+ # 2. Normalize the lines we kept.
+
+ # Remove column.
+ s/^([^:]+:\d+)[.:][^:]+:(.+)$/$][1:$][2/gm;
+ # Map all combinations of "error: " and "#error: " to "#error ".
+ s/^([^:]+:\d+):( |#error|error|:)+/$][1: #error /gm;
+EOF
+]],
+ 0, [stdout])
+])
+
+# AT_TEST(TITLE, INPUT, ERROR-MSG)
+# --------------------------------