pager: move pager-specific setup into the build pager-env-v2

Allowing PAGER_ENV to be set at build-time allows us to move
pager-specific knowledge out of our build.  Currently, this
allows us to set a better default for FreeBSD where more(1)
is the same binary as less(1).

This also prepares us for introducing a run-time config knob to
override the build-time environment in the next commit.

Originally-from:
 https://public-inbox.org/git/xmqq61piw4yf.fsf@gitster.dls.corp.google.com/

Signed-off-by: Eric Wong <e@80x24.org>

4 files changed, 50 insertions, 8 deletions

diff --git a/Makefile b/Makefile
index 6a13386c27..0b36b5e02e 100644
--- a/Makefile
+++ b/Makefile
@@ -370,6 +370,14 @@ all::
 # Define HAVE_BSD_SYSCTL if your platform has a BSD-compatible sysctl function.
 #
 # Define HAVE_GETDELIM if your system has the getdelim() function.
+#
+# Define PAGER_ENV to a SP separated VAR=VAL pairs to define
+# default environment variables to be passed when a pager is spawned, e.g.
+#
+#    PAGER_ENV = LESS=FRX LV=-c
+#
+# to say "export LESS=FRX (and LV=-c) if the environment variable
+# LESS (and LV) is not set, respectively".
 
 GIT-VERSION-FILE: FORCE
         @$(SHELL_PATH) ./GIT-VERSION-GEN
@@ -1500,6 +1508,10 @@ ifeq ($(PYTHON_PATH),)
 NO_PYTHON = NoThanks
 endif
 
+ifndef PAGER_ENV
+PAGER_ENV = LESS=FRX LV=-c
+endif
+
 QUIET_SUBDIR0  = +$(MAKE) -C # space to separate -C and subdir
 QUIET_SUBDIR1  =
 
@@ -1629,6 +1641,10 @@ ifdef DEFAULT_HELP_FORMAT
 BASIC_CFLAGS += -DDEFAULT_HELP_FORMAT='"$(DEFAULT_HELP_FORMAT)"'
 endif
 
+PAGER_ENV_CQ = "$(subst ",\",$(subst \,\\,$(PAGER_ENV)))"
+PAGER_ENV_CQ_SQ = $(subst ','\'',$(PAGER_ENV_CQ))
+BASIC_CFLAGS += -DPAGER_ENV='$(PAGER_ENV_CQ_SQ)'
+
 ALL_CFLAGS += $(BASIC_CFLAGS)
 ALL_LDFLAGS += $(BASIC_LDFLAGS)
 
@@ -1753,7 +1769,7 @@ common-cmds.h: $(wildcard Documentation/git-*.txt)
 
 SCRIPT_DEFINES = $(SHELL_PATH_SQ):$(DIFF_SQ):$(GIT_VERSION):\
         $(localedir_SQ):$(NO_CURL):$(USE_GETTEXT_SCHEME):$(SANE_TOOL_PATH_SQ):\
-        $(gitwebdir_SQ):$(PERL_PATH_SQ):$(SANE_TEXT_GREP)
+        $(gitwebdir_SQ):$(PERL_PATH_SQ):$(SANE_TEXT_GREP):$(PAGER_ENV)
 define cmd_munge_script
 $(RM) $@ $@+ && \
 sed -e '1s|#!.*/sh|#!$(SHELL_PATH_SQ)|' \
@@ -1766,6 +1782,7 @@ sed -e '1s|#!.*/sh|#!$(SHELL_PATH_SQ)|' \
     -e 's|@@GITWEBDIR@@|$(gitwebdir_SQ)|g' \
     -e 's|@@PERL@@|$(PERL_PATH_SQ)|g' \
     -e 's|@@SANE_TEXT_GREP@@|$(SANE_TEXT_GREP)|g' \
+    -e 's|@@PAGER_ENV@@|$(PAGER_ENV_SQ)|g' \
     $@.sh >$@+
 endef
 
@@ -2173,6 +2190,7 @@ GIT-BUILD-OPTIONS: FORCE
         @echo NO_PERL=\''$(subst ','\'',$(subst ','\'',$(NO_PERL)))'\' >>$@+
         @echo NO_PYTHON=\''$(subst ','\'',$(subst ','\'',$(NO_PYTHON)))'\' >>$@+
         @echo NO_UNIX_SOCKETS=\''$(subst ','\'',$(subst ','\'',$(NO_UNIX_SOCKETS)))'\' >>$@+
+        @echo PAGER_ENV=\''$(subst ','\'',$(subst ','\'',$(PAGER_ENV)))'\' >>$@+
 ifdef TEST_OUTPUT_DIRECTORY
         @echo TEST_OUTPUT_DIRECTORY=\''$(subst ','\'',$(subst ','\'',$(TEST_OUTPUT_DIRECTORY)))'\' >>$@+
 endif
diff --git a/config.mak.uname b/config.mak.uname
index 17fed2f43a..2484dfbf68 100644
--- a/config.mak.uname
+++ b/config.mak.uname
@@ -209,6 +209,7 @@ ifeq ($(uname_S),FreeBSD)
         HAVE_PATHS_H = YesPlease
         GMTIME_UNRELIABLE_ERRORS = UnfortunatelyYes
         HAVE_BSD_SYSCTL = YesPlease
+        PAGER_ENV = LESS=FRX LV=-c MORE=-R
 endif
 ifeq ($(uname_S),OpenBSD)
         NO_STRCASESTR = YesPlease
diff --git a/git-sh-setup.sh b/git-sh-setup.sh
index 0c34aa62f6..0f5a56f946 100644
--- a/git-sh-setup.sh
+++ b/git-sh-setup.sh
@@ -163,9 +163,11 @@ git_pager() {
         else
                 GIT_PAGER=cat
         fi
-        : "${LESS=-FRX}"
-        : "${LV=-c}"
-        export LESS LV
+        for vardef in @@PAGER_ENV@@
+        do
+                var=${vardef%%=*}
+                eval ": \${$vardef} && export $var"
+        done
 
         eval "$GIT_PAGER" '"$@"'
 }
diff --git a/pager.c b/pager.c
index 4bc048148e..cd1ac54a15 100644
--- a/pager.c
+++ b/pager.c
@@ -63,14 +63,35 @@ const char *git_pager(int stdout_is_tty)
         return pager;
 }
 
+static void setup_pager_env(struct argv_array *env)
+{
+        const char *pager_env = PAGER_ENV;
+
+        while (*pager_env) {
+                struct strbuf buf = STRBUF_INIT;
+                const char *cp = strchrnul(pager_env, '=');
+
+                if (!*cp)
+                        die("malformed build-time PAGER_ENV");
+                strbuf_add(&buf, pager_env, cp - pager_env);
+                cp = strchrnul(pager_env, ' ');
+                if (!getenv(buf.buf)) {
+                        strbuf_reset(&buf);
+                        strbuf_add(&buf, pager_env, cp - pager_env);
+                        argv_array_push(env, strbuf_detach(&buf, NULL));
+                }
+                strbuf_reset(&buf);
+                while (*cp && *cp == ' ')
+                        cp++;
+                pager_env = cp;
+        }
+}
+
 void prepare_pager_args(struct child_process *pager_process, const char *pager)
 {
         argv_array_push(&pager_process->args, pager);
         pager_process->use_shell = 1;
-        if (!getenv("LESS"))
-                argv_array_push(&pager_process->env_array, "LESS=FRX");
-        if (!getenv("LV"))
-                argv_array_push(&pager_process->env_array, "LV=-c");
+        setup_pager_env(&pager_process->env_array);
 }
 
 void setup_pager(void)