help: use HTML as the default help format on Windows

When 'git help $cmd' is run without a format option (e.g. -w), the
'man' format is always used. On some platforms, however, manual page
viewers are not often available.

Introduce DEFAULT_HELP_FORMAT make variable in order to allow the
default format configurable at compile time, and set it to HTML when
compiling on Windows (but not Cygwin).
Helped-by: NJeff King <peff@peff.net>
Signed-off-by: NVincent van Ravesteijn <vfr@lyx.org>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Makefile

@@ -296,6 +296,10 @@ all::
 # the diff algorithm.  It gives a nice speedup if your processor has
 # fast unaligned word loads.  Does NOT work on big-endian systems!
 # Enabled by default on x86_64.
+#
+# Define DEFAULT_HELP_FORMAT to "man", "info" or "html"
+# (defaults to "man") if you want to have a different default when
+# "git help" is called without a parameter specifying the format.
 
 GIT-VERSION-FILE: FORCE
 	@$(SHELL_PATH) ./GIT-VERSION-GEN
@@ -1236,6 +1240,7 @@ ifeq ($(uname_S),Windows)
 	BLK_SHA1 = YesPlease
 	NO_POSIX_GOODIES = UnfortunatelyYes
 	NATIVE_CRLF = YesPlease
+	DEFAULT_HELP_FORMAT = html
 
 	CC = compat/vcbuild/scripts/clink.pl
 	AR = compat/vcbuild/scripts/lib.pl
@@ -1915,6 +1920,10 @@ SHELL_PATH_CQ_SQ = $(subst ','\'',$(SHELL_PATH_CQ))
 BASIC_CFLAGS += -DSHELL_PATH='$(SHELL_PATH_CQ_SQ)'
 endif
 
+ifdef DEFAULT_HELP_FORMAT
+BASIC_CFLAGS += -DDEFAULT_HELP_FORMAT='"$(DEFAULT_HELP_FORMAT)"'
+endif
+
 ALL_CFLAGS += $(BASIC_CFLAGS)
 ALL_LDFLAGS += $(BASIC_LDFLAGS)
 

builtin/help.c

@@ -12,6 +12,10 @@
 #include "column.h"
 #include "help.h"
 
+#ifndef DEFAULT_HELP_FORMAT
+#define DEFAULT_HELP_FORMAT "man"
+#endif
+
 static struct man_viewer_list {
 	struct man_viewer_list *next;
 	char name[FLEX_ARRAY];
@@ -445,7 +449,9 @@ int cmd_help(int argc, const char **argv, const char *prefix)
 	setup_git_directory_gently(&nongit);
 	git_config(git_help_config, NULL);
 
-	if (parsed_help_format != HELP_FORMAT_NONE)
+	if (parsed_help_format == HELP_FORMAT_NONE)
+		help_format = parse_help_format(DEFAULT_HELP_FORMAT);
+	else
 		help_format = parsed_help_format;
 
 	alias = alias_lookup(argv[0]);