[PATCH 3/6] Makefile: refactor out "ln || ln -s || cp" pattern

["Ævar Arnfjörð Bjarmason" <avarab@gmail.com>]

Refactor out the hard-to-read and maintain "ln || ln -s || cp"
pattern.

This was initially added in 3e073dc5611 (Makefile: always provide a
fallback when hardlinks fail, 2008-08-25), but since then it's become
a lot more complex as we've added:

 * 3426e34fedd (Add NO_CROSS_DIRECTORY_HARDLINKS support to the
   Makefile, 2009-05-11)

 * NO_INSTALL_HARDLINKS in 70de5e65e8c (Makefile:
   NO_INSTALL_HARDLINKS, 2012-05-02)

 * INSTALL_SYMLINKS in ad874608d8c (Makefile: optionally symlink
   libexec/git-core binaries to bin/git, 2018-03-13)

 * SKIP_DASHED_BUILT_INS 179227d6e21 (Optionally skip linking/copying
   the built-ins, 2020-09-21)

Each of those commits had to add a new special-case to this code,
resulting in quite an unmaintainable mess for adding any sort of new
option.

Let's use the newly introduced ln-or-cp.sh script instead, note that
we only sometimes pass the --no-cross-directory-hardlinks option, per
the previous behavior. The target of the "ln -s" is also another
special snowflake, but we're careful to carry that forward.

As in an earlier commit this also changes the behavior to emit any
errors to stdout. In that earlier case that was done to simplify the
script so that it can use one "ln -s" instead of the two, likewise
we're now unconditionally emitting to stderr if ln (without -s, to
create the hardlink) fails. We always emitted to stderr if "cp"
failed.

As in that earlier commit let's let that pass for now, yes it might be
very verbose in some scenarios, but we're working our way towards a
simpler end-state here.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
---
 Makefile    | 41 +++++++++++++++++-----------------
 ln-or-cp.sh | 63 ++++++++++++++++++++++++++++++++++++++++++++++++++---
 2 files changed, 81 insertions(+), 23 deletions(-)

diff --git a/Makefile b/Makefile
index cfc87d7734d..a4784f28f5b 100644
--- a/Makefile
+++ b/Makefile
@@ -3007,40 +3007,41 @@ endif
 	{ test "$$bindir/" = "$$execdir/" || \
 	  for p in git$X $(filter $(install_bindir_programs),$(ALL_PROGRAMS)); do \
 		$(RM) "$$execdir/$$p" && \
-		test -n "$(INSTALL_SYMLINKS)" && \
-		ln -s "$$destdir_from_execdir_SQ/$(bindir_relative_SQ)/$$p" "$$execdir/$$p" || \
-		{ test -z "$(NO_INSTALL_HARDLINKS)$(NO_CROSS_DIRECTORY_HARDLINKS)" && \
-		  ln "$$bindir/$$p" "$$execdir/$$p" 2>/dev/null || \
-		  cp "$$bindir/$$p" "$$execdir/$$p" || exit; } \
+		./ln-or-cp.sh \
+			--install-symlinks "$(INSTALL_SYMLINKS)" \
+			--no-install-hardlinks "$(NO_INSTALL_HARDLINKS)" \
+			--no-cross-directory-hardlinks "$(NO_CROSS_DIRECTORY_HARDLINKS)" \
+			--symlink-target "$$destdir_from_execdir_SQ/$(bindir_relative_SQ)/$$p" \
+			"$$bindir/$$p" "$$execdir/$$p"; \
 	  done; \
 	} && \
 	for p in $(filter $(install_bindir_programs),$(BUILT_INS)); do \
 		$(RM) "$$bindir/$$p" && \
-		test -n "$(INSTALL_SYMLINKS)" -o "$(NO_INSTALL_HARDLINKS)" && \
-		ln -s "git$X" "$$bindir/$$p" || \
-		{ test -z "$(NO_INSTALL_HARDLINKS)" && \
-		  ln "$$bindir/git$X" "$$bindir/$$p" 2>/dev/null || \
-		  cp "$$bindir/git$X" "$$bindir/$$p" || exit; }; \
+		./ln-or-cp.sh \
+			--install-symlinks "$(INSTALL_SYMLINKS)" \
+			--no-install-hardlinks "$(NO_INSTALL_HARDLINKS)" \
+			--symlink-target "git$X" \
+			"$$bindir/git$X" "$$bindir/$$p"; \
 	done && \
 	for p in $(BUILT_INS); do \
 		$(RM) "$$execdir/$$p" && \
 		if test -z "$(SKIP_DASHED_BUILT_INS)"; \
 		then \
-			test -n "$(INSTALL_SYMLINKS)" -o "$(NO_INSTALL_HARDLINKS)" && \
-			ln -s "$$destdir_from_execdir_SQ/$(bindir_relative_SQ)/git$X" "$$execdir/$$p" || \
-			{ test -z "$(NO_INSTALL_HARDLINKS)" && \
-			  ln "$$execdir/git$X" "$$execdir/$$p" 2>/dev/null || \
-			  cp "$$execdir/git$X" "$$execdir/$$p" || exit; }; \
+			./ln-or-cp.sh \
+				--install-symlinks "$(INSTALL_SYMLINKS)" \
+				--no-install-hardlinks "$(NO_INSTALL_HARDLINKS)" \
+				--symlink-target "$$destdir_from_execdir_SQ/$(bindir_relative_SQ)/git$X" \
+				"$$execdir/git$X" "$$execdir/$$p"; \
 		fi \
 	done && \
 	remote_curl_aliases="$(REMOTE_CURL_ALIASES)" && \
 	for p in $$remote_curl_aliases; do \
 		$(RM) "$$execdir/$$p" && \
-		test -n "$(INSTALL_SYMLINKS)" -o "$(NO_INSTALL_HARDLINKS)" && \
-		ln -s "git-remote-http$X" "$$execdir/$$p" || \
-		{ test -z "$(NO_INSTALL_HARDLINKS)" && \
-		  ln "$$execdir/git-remote-http$X" "$$execdir/$$p" 2>/dev/null || \
-		  cp "$$execdir/git-remote-http$X" "$$execdir/$$p" || exit; } \
+		./ln-or-cp.sh \
+			--install-symlinks "$(INSTALL_SYMLINKS)" \
+			--no-install-hardlinks "$(NO_INSTALL_HARDLINKS)" \
+			--symlink-target "git-remote-http$X" \
+			"$$execdir/git-remote-http$X" "$$execdir/$$p"; \
 	done && \
 	./check_bindir "z$$bindir" "z$$execdir" "$$bindir/git-add$X"
 
diff --git a/ln-or-cp.sh b/ln-or-cp.sh
index de79cd85a81..663ffd0489d 100755
--- a/ln-or-cp.sh
+++ b/ln-or-cp.sh
@@ -1,8 +1,65 @@
 #!/bin/sh
 
+install_symlinks=
+no_install_hardlinks=
+no_cross_directory_hardlinks=
+symlink_target=
+while test $# != 0
+do
+	case "$1" in
+	--install-symlinks)
+		install_symlinks="$2"
+		shift
+		;;
+	--no-install-hardlinks)
+		no_install_hardlinks="$2"
+		shift
+		;;
+	--no-cross-directory-hardlinks)
+		no_cross_directory_hardlinks="$2"
+		shift
+		;;
+	--symlink-target)
+		symlink_target="$2"
+		shift
+		;;
+	*)
+		break
+		;;
+	esac
+	shift
+done
+
 target="$1"
+if test -z "$symlink_target"
+then
+	symlink_target="$target"
+fi
 link="$2"
 
-ln "$target" "$link" 2>/dev/null ||
-ln -s "$target" "$link" 2>/dev/null ||
-cp "$target" "$link"
+hardlink_or_cp () {
+	if test -z "$no_install_hardlinks" -a -z "$no_cross_directory_hardlinks"
+	then
+		if ! ln "$target" "$link"
+		then
+			cp "$target" "$link"
+		fi
+
+	else
+		cp "$target" "$link"
+	fi
+}
+
+main_with_fallbacks () {
+	if test -n "$install_symlinks" -o -n "$no_install_hardlinks"
+	then
+		if ! ln -s "$symlink_target" "$link"
+		then
+			hardlink_or_cp
+		fi
+	else
+		hardlink_or_cp
+	fi
+}
+
+main_with_fallbacks
-- 
2.31.1.461.gd47399f6574