Zig: revise apps build support

This requires nuttx/pull/11548 to work.

- Zig apps can use normal entrance "main()" now as we
- added RENAMEMAIN for none BUILD_MODULE case.
- enabled Zig program building in BUILD_MODULE case.

Note the Zig main source need to have "fn main(" pattern as
renaming is implemented via `sed`.

Signed-off-by: Yanfeng Liu <yfliu2008@qq.com>

Application.mk

@@ -94,7 +94,7 @@ ifneq ($(BUILD_MODULE),y)
 endif
 
 ifneq ($(strip $(PROGNAME)),)
-  PROGOBJ := $(MAINCOBJ) $(MAINCXXOBJ) $(MAINRUSTOBJ)
+  PROGOBJ := $(MAINCOBJ) $(MAINCXXOBJ) $(MAINRUSTOBJ) $(MAINZIGOBJ)
   PROGLIST := $(addprefix $(BINDIR)$(DELIM),$(PROGNAME))
   REGLIST := $(addprefix $(BUILTIN_REGISTRY)$(DELIM),$(addsuffix .bdat,$(PROGNAME)))
 
@@ -168,9 +168,9 @@ define ELFCOMPILERUST
 	$(ECHO_END)
 endef
 
+# Remove target suffix here since zig compiler add .o automatically
 define ELFCOMPILEZIG
 	$(ECHO_BEGIN)"ZIG: $1 "
-	# Remove target suffix here since zig compiler add .o automatically
 	$(Q) $(ZIG) build-obj $(ZIGELFFLAGS) $($(strip $1)_ZIGELFFLAGS) --name $(basename $2) $1
 	$(ECHO_END)
 endef
@@ -181,6 +181,13 @@ define ELFLD
 	$(ECHO_END)
 endef
 
+# rename "main()" in $1 to "xxx_main()" and save to $2
+define RENAMEMAIN
+	$(ECHO_BEGIN)"Rename main() in $1 and save to $2"
+	$(Q) ${shell cat $1 | sed -e "s/fn[ ]\+main/fn $(addsuffix _main,$(PROGNAME_$@))/" > $2}
+	$(ECHO_END)
+endef
+
 $(RAOBJS): %.s$(SUFFIX)$(OBJEXT): %.s
 	$(if $(and $(CONFIG_BUILD_LOADABLE),$(AELFFLAGS)), \
 		$(call ELFASSEMBLE, $<, $@), $(call ASSEMBLE, $<, $@))
@@ -235,9 +242,13 @@ $(MAINCOBJ): %.c$(SUFFIX)$(OBJEXT): %.c
 	$(if $(and $(CONFIG_BUILD_LOADABLE),$(CELFFLAGS)), \
 		$(call ELFCOMPILE, $<, $@), $(call COMPILE, $<, $@))
 
-$(PROGLIST): $(MAINCOBJ) $(MAINCXXOBJ) $(MAINRUSTOBJ)
+$(MAINZIGOBJ): %$(ZIGEXT)$(SUFFIX)$(OBJEXT): %$(ZIGEXT)
+	$(if $(and $(CONFIG_BUILD_LOADABLE),$(CELFFLAGS)), \
+		$(call ELFCOMPILEZIG, $<, $@), $(call COMPILEZIG, $<, $@))
+
+$(PROGLIST): $(MAINCOBJ) $(MAINCXXOBJ) $(MAINRUSTOBJ) $(MAINZIGOBJ)
 	$(Q) mkdir -p $(BINDIR)
-	$(call ELFLD,$(PROGOBJ_$@),$(call CONVERT_PATH,$@))
+	$(call ELFLD, $(PROGOBJ_$@), $(call CONVERT_PATH,$@))
 	$(Q) chmod +x $@
 ifneq ($(CONFIG_DEBUG_SYMBOLS),y)
 	$(Q) $(STRIP) $@
@@ -265,8 +276,10 @@ $(MAINRUSTOBJ): %$(RUSTEXT)$(SUFFIX)$(OBJEXT): %$(RUSTEXT)
 		$(call ELFCOMPILERUST, $<, $@), $(call COMPILERUST, $<, $@))
 
 $(MAINZIGOBJ): %$(ZIGEXT)$(SUFFIX)$(OBJEXT): %$(ZIGEXT)
+	$(Q) $(call RENAMEMAIN, $<, $(basename $<)_tmp.zig)
 	$(if $(and $(CONFIG_BUILD_LOADABLE),$(CELFFLAGS)), \
-		$(call ELFCOMPILEZIG, $<, $@), $(call COMPILEZIG, $<, $@))
+			$(call ELFCOMPILEZIG, $(basename $<)_tmp.zig, $@), $(call COMPILEZIG, $(basename $<)_tmp.zig, $@))
+	$(Q) rm -f $(basename $<)_tmp.zig
 
 install::
 	@:

examples/hello_zig/Makefile

@@ -22,7 +22,7 @@ include $(APPDIR)/Make.defs
 
 # Hello, Zig! Example
 
-MAINSRC = hello_zig_main.zig
+MAINSRC = hello_zig.zig
 
 # Hello, Zig! built-in application info
 

examples/hello_zig/hello_zig.zig

@@ -0,0 +1,40 @@
+//***************************************************************************
+// examples/hello_zig/hello_zig.zig
+//
+// Licensed to the Apache Software Foundation (ASF) under one or more
+// contributor license agreements.  See the NOTICE file distributed with
+// this work for additional information regarding copyright ownership.  The
+// ASF licenses this file to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance with the
+// License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
+// License for the specific language governing permissions and limitations
+// under the License.
+//
+//***************************************************************************
+
+//***************************************************************************
+// Included Files
+//***************************************************************************
+const std = @import("std");
+
+//****************************************************************************
+//* Externs
+//****************************************************************************
+
+pub extern fn printf(_format: [*:0]const u8) c_int;
+
+//****************************************************************************
+//* hello_zig_main
+//****************************************************************************
+pub export fn main(_argc: c_int, _argv: [*]const [*]const u8) u8 {
+    _ = _argc;
+    _ = _argv;
+    _ = printf("Hello, Zig!\n");
+    return 0;
+}