v: add support for `$if freestanding {`, without using it (part 1) (#9656)

doc/docs.md

@@ -3700,8 +3700,8 @@ Full list of builtin options:
 | ---                           | ---               | ---                   | ---                       |
 | `windows`, `linux`, `macos`   | `gcc`, `tinyc`    | `amd64`, `aarch64`    | `debug`, `prod`, `test`   |
 | `mac`, `darwin`, `ios`,       | `clang`, `mingw`  | `x64`, `x32`          | `js`, `glibc`, `prealloc` |
-| `android`,`mach`, `dragonfly` | `msvc`            | `little_endian`       | `no_bounds_checking`      |
-| `gnu`, `hpux`, `haiku`, `qnx` | `cplusplus`       | `big_endian`          | |
+| `android`,`mach`, `dragonfly` | `msvc`            | `little_endian`       | `no_bounds_checking`, `freestanding`    |
+| `gnu`, `hpux`, `haiku`, `qnx` | `cplusplus`       | `big_endian`          |
 | `solaris`, `linux_or_macos`   | | | |
 
 #### $embed_file

vlib/v/builder/compile.v

@@ -198,15 +198,15 @@ pub fn (v Builder) get_builtin_files() []string {
 	for location in v.pref.lookup_path {
 		if os.exists(os.join_path(location, 'builtin')) {
 			mut builtin_files := []string{}
-			if v.pref.is_bare {
-				builtin_files << v.v_files_from_dir(os.join_path(location, 'builtin',
-					'bare'))
-			} else if v.pref.backend == .js {
+			if v.pref.backend == .js {
 				builtin_files << v.v_files_from_dir(os.join_path(location, 'builtin',
 					'js'))
 			} else {
 				builtin_files << v.v_files_from_dir(os.join_path(location, 'builtin'))
 			}
+			if v.pref.is_bare {
+				builtin_files << v.v_files_from_dir(v.pref.bare_builtin_dir)
+			}
 			if v.pref.backend == .c {
 				// TODO JavaScript backend doesn't handle os for now
 				if v.pref.is_vsh && os.exists(os.join_path(location, 'os')) {

vlib/v/checker/checker.v

@@ -25,8 +25,7 @@ const (
 	valid_comp_if_compilers = ['gcc', 'tinyc', 'clang', 'mingw', 'msvc', 'cplusplus']
 	valid_comp_if_platforms = ['amd64', 'aarch64', 'x64', 'x32', 'little_endian', 'big_endian']
 	valid_comp_if_other     = ['js', 'debug', 'prod', 'test', 'glibc', 'prealloc',
-		'no_bounds_checking',
-	]
+		'no_bounds_checking', 'freestanding']
 	array_builtin_methods   = ['filter', 'clone', 'repeat', 'reverse', 'map', 'slice', 'sort',
 		'contains', 'index', 'wait', 'any', 'all', 'first', 'last', 'pop']
 )
@@ -5582,6 +5581,7 @@ fn (mut c Checker) comp_if_branch(cond ast.Expr, pos token.Position) bool {
 					'glibc' { return false } // TODO
 					'prealloc' { return !c.pref.prealloc }
 					'no_bounds_checking' { return cond.name !in c.pref.compile_defines_all }
+					'freestanding' { return !c.pref.is_bare }
 					else { return false }
 				}
 			} else if cond.name !in c.pref.compile_defines_all {

vlib/v/gen/c/comptime.v

@@ -575,6 +575,9 @@ fn (mut g Gen) comp_if_to_ifdef(name string, is_comptime_optional bool) ?string
 		'no_bounds_checking' {
 			return 'CUSTOM_DEFINE_no_bounds_checking'
 		}
+		'freestanding' {
+			return '_VFREESTANDING'
+		}
 		// architectures:
 		'amd64' {
 			return '__V_amd64'

vlib/v/pref/default.v

@@ -130,6 +130,9 @@ pub fn (mut p Preferences) fill_with_defaults() {
 		// eprintln('-usecache and -shared flags are not compatible')
 		p.use_cache = false
 	}
+	if p.bare_builtin_dir == '' {
+		p.bare_builtin_dir = os.join_path(p.vroot, 'vlib', 'builtin', 'linux_bare')
+	}
 }
 
 fn (mut p Preferences) find_cc_if_cross_compiling() {

vlib/v/pref/pref.v

@@ -130,6 +130,7 @@ pub mut:
 	no_preludes      bool   // Prevents V from generating preludes in resulting .c files
 	custom_prelude   string // Contents of custom V prelude that will be prepended before code in resulting .c files
 	lookup_path      []string
+	bare_builtin_dir string // Path to implementation of malloc, memset, etc. Only used if is_bare is true
 	output_cross_c   bool
 	prealloc         bool
 	vroot            string
@@ -464,6 +465,12 @@ pub fn parse_args(known_external_commands []string, args []string) (&Preferences
 				res.lookup_path = path.replace('|', os.path_delimiter).split(os.path_delimiter)
 				i++
 			}
+			'-bare-builtin-dir' {
+				bare_builtin_dir := cmdline.option(current_args, arg, '')
+				res.build_options << '$arg "$bare_builtin_dir"'
+				res.bare_builtin_dir = bare_builtin_dir
+				i++
+			}
 			'-custom-prelude' {
 				path := cmdline.option(current_args, '-custom-prelude', '')
 				res.build_options << '$arg $path'

vlib/v/pref/should_compile.v

@@ -8,6 +8,9 @@ pub fn (prefs &Preferences) should_compile_filtered_files(dir string, files_ []s
 	files.sort()
 	mut all_v_files := []string{}
 	for file in files {
+		if prefs.is_bare && os.join_path(dir, file).ends_with('/vlib/builtin/builtin_nix.c.v') {
+			continue
+		}
 		if !file.ends_with('.v') && !file.ends_with('.vh') {
 			continue
 		}
@@ -123,6 +126,9 @@ pub fn (prefs &Preferences) should_compile_c(file string) bool {
 	if prefs.os == .all {
 		return true
 	}
+	if !prefs.is_bare && file.ends_with('.freestanding.v') {
+		return false
+	}
 	if (file.ends_with('_windows.c.v') || file.ends_with('_windows.v')) && prefs.os != .windows {
 		return false
 	}