make: support $+ and $^ as POSIX 202X features

Austin Group defect reports 514 and 1520 have both been accepted.
Together these introduce the internal macros $+ and $^:

- $+ lists all prerequisites, with duplicates retained;

- $^ lists all prerequisites, with duplicates removed.

$^ had already been implemented as a non-POSIX extension, it now
becomes a POSIX 202X extension.  $+ has been added as a POSIX
202X extension.

Neither of the above defect reports mentions how $? should handle
duplicate prerequisites.  In POSIX mode duplicates are retained.
Removal of duplicates is implemented as a non-POSIX extension to
match existing practice in other versions of make.

1 files changed, 12 insertions, 0 deletions

diff --git a/testsuite/make.tests b/testsuite/make.tests
index 3d0d14dd0..67617f8a2 100755
--- a/testsuite/make.tests
+++ b/testsuite/make.tests
@@ -255,6 +255,18 @@ mk:
 -include mk
 '
 
+# $^ skips duplicate prerequisites, $+ doesn't
+mkdir make.tempdir && cd make.tempdir || exit 1
+touch file1 file2 file3
+testing "make skip duplicate entries in \$^ but not \$+" \
+        "make -f -" \
+        "file1 file2 file3\nfile1 file2 file2 file3 file3\n" "" '
+target: file1 file2 file2 file3 file3
+        @echo $^
+        @echo $+
+'
+cd .. || exit 1; rm -rf make.tempdir 2>/dev/null
+
 # Nested macro expansion is allowed.  This should be compatible
 # with other implementations.
 testing "make nested macro expansion" \