builder,pref: add support for `-no-builtin` (useful for writing Linux kernel modules)

vlib/v/builder/compile.v

@@ -211,6 +211,10 @@ fn (mut v Builder) set_module_lookup_paths() {
 }
 
 pub fn (v Builder) get_builtin_files() []string {
+	if v.pref.no_builtin {
+		v.log('v.pref.no_builtin is true, get_builtin_files == []')
+		return []
+	}
 	v.log('v.pref.lookup_path: $v.pref.lookup_path')
 	// Lookup for built-in folder in lookup path.
 	// Assumption: `builtin/` folder implies usable implementation of builtin

vlib/v/checker/checker.v

@@ -290,6 +290,11 @@ pub fn (mut c Checker) check_files(ast_files []&ast.File) {
 		// shared libs do not need to have a main
 		return
 	}
+	if c.pref.no_builtin {
+		// `v -no-builtin module/` do not necessarily need to have a `main` function
+		// This is useful for compiling linux kernel modules for example.
+		return
+	}
 	if !has_main_mod_file {
 		c.error('project must include a `main` module or be a shared library (compile with `v -shared`)',
 			token.Position{})

vlib/v/gen/c/cgen.v

@@ -591,11 +591,13 @@ pub fn (mut g Gen) init() {
 	g.write_multi_return_types()
 	g.definitions.writeln('// end of definitions #endif')
 	//
+	if !g.pref.no_builtin {
 		g.stringliterals.writeln('')
 		g.stringliterals.writeln('// >> string literal consts')
 		if g.pref.build_mode != .build_module {
 			g.stringliterals.writeln('void vinit_string_literals(){')
 		}
+	}
 	if g.pref.compile_defines_all.len > 0 {
 		g.comptime_defines.writeln('// V compile time defines by -d or -define flags:')
 		g.comptime_defines.writeln('//     All custom defines      : ' +
@@ -665,11 +667,13 @@ pub fn (mut g Gen) init() {
 }
 
 pub fn (mut g Gen) finish() {
+	if !g.pref.no_builtin {
 		if g.pref.build_mode != .build_module {
 			g.stringliterals.writeln('}')
 		}
 		g.stringliterals.writeln('// << string literal consts')
 		g.stringliterals.writeln('')
+	}
 	if g.pref.is_prof && g.pref.build_mode != .build_module {
 		g.gen_vprint_profile_stats()
 	}
@@ -736,6 +740,9 @@ pub fn (mut g Gen) write_typeof_functions() {
 			}
 			g.writeln('}')
 		} else if typ.kind == .interface_ {
+			if typ.info !is ast.Interface {
+				continue
+			}
 			inter_info := typ.info as ast.Interface
 			if inter_info.is_generic {
 				continue
@@ -1153,6 +1160,9 @@ pub fn (mut g Gen) write_interface_typedef(sym ast.TypeSymbol) {
 }
 
 pub fn (mut g Gen) write_interface_typesymbol_declaration(sym ast.TypeSymbol) {
+	if sym.info !is ast.Interface {
+		return
+	}
 	info := sym.info as ast.Interface
 	if info.is_generic {
 		return
@@ -6094,6 +6104,9 @@ fn (g &Gen) checker_bug(s string, pos token.Position) {
 }
 
 fn (mut g Gen) write_init_function() {
+	if g.pref.no_builtin {
+		return
+	}
 	util.timing_start(@METHOD)
 	defer {
 		util.timing_measure(@METHOD)
@@ -6179,6 +6192,9 @@ const (
 )
 
 fn (mut g Gen) write_builtin_types() {
+	if g.pref.no_builtin {
+		return
+	}
 	mut builtin_types := []ast.TypeSymbol{} // builtin types
 	// builtin types need to be on top
 	// everything except builtin will get sorted
@@ -6313,7 +6329,7 @@ fn (mut g Gen) write_types(types []ast.TypeSymbol) {
 						g.type_definitions.writeln('} $name;')
 					}
 				} else {
-					if !g.pref.is_bare {
+					if !g.pref.is_bare && !g.pref.no_builtin {
 						g.type_definitions.writeln('typedef pthread_t $name;')
 					}
 				}
@@ -7038,6 +7054,9 @@ fn (mut g Gen) interface_table() string {
 		if ityp.kind != .interface_ {
 			continue
 		}
+		if ityp.info !is ast.Interface {
+			continue
+		}
 		inter_info := ityp.info as ast.Interface
 		if inter_info.is_generic {
 			continue

vlib/v/gen/c/fn.v

@@ -305,6 +305,9 @@ fn (mut g Gen) gen_fn_decl(node &ast.FnDecl, skip bool) {
 		g.writeln(');')
 		return
 	}
+	if node.params.len == 0 {
+		g.definitions.write_string('void')
+	}
 	g.definitions.writeln(');')
 	g.writeln(') {')
 	for i, is_promoted in heap_promoted {

vlib/v/pref/pref.v

@@ -144,19 +144,16 @@ pub mut:
 	autofree           bool // `v -manualfree` => false, `v -autofree` => true; false by default for now.
 	// Disabling `free()` insertion results in better performance in some applications (e.g. compilers)
 	compress bool // when set, use `upx` to compress the generated executable
-	// skip_builtin     bool   // Skips re-compilation of the builtin module
-	// to increase compilation time.
-	// This is on by default, since a vast majority of users do not
-	// work on the builtin module itself.
 	// generating_vh    bool
+	no_builtin       bool // Skip adding the `builtin` module implicitly. The generated C code may not compile.
 	enable_globals   bool // allow __global for low level code
 	is_fmt           bool
 	is_vet           bool
-	is_bare          bool
+	is_bare          bool   // set by -freestanding
+	bare_builtin_dir string // Set by -bare-builtin-dir xyz/ . The xyz/ module should contain implementations of malloc, memset, etc, that are used by the rest of V's `builtin` module. That option is only useful with -freestanding (i.e. when is_bare is true).
 	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 // true, when the user passed `-os cross`
 	prealloc         bool
 	vroot            string
@@ -405,6 +402,10 @@ pub fn parse_args(known_external_commands []string, args []string) (&Preferences
 			'-no-retry-compilation' {
 				res.retry_compilation = false
 			}
+			'-no-builtin' {
+				res.no_builtin = true
+				res.build_options << arg
+			}
 			'-no-preludes' {
 				res.no_preludes = true
 				res.build_options << arg