compiler: implement -W and -reuse-tmpc

cmd/v/help/build-c.txt

@@ -58,3 +58,6 @@ These build flags are enabled on `build` and `run` as long as the backend is set
    -custom-prelude <path>
       Useful for similar use-case as above option, except it replaces V-generated prelude with
       your custom one loaded from specified <path>.
+
+   -reuse-tmpc
+      Do not remove the temporary .tmp.c and .tmp.c.rsp files. Also do not use a random prefix for them, so they would be fixed and predictable.

cmd/v/help/build.txt

@@ -118,6 +118,9 @@ The build flags are shared by the build and run commands:
          C GEN: 103ms
          C tcc: 95ms
 
+   -W
+      Treat all warnings as errors, even in development builds.
+
 For C-specific build flags, use `v help build-c`.
 
 See also:

vlib/v/builder/c.v

@@ -75,9 +75,9 @@ pub fn (mut b Builder) compile_c() {
 		println('all .v files:')
 		println(files)
 	}
-	mut out_name_c := get_vtmp_filename(b.pref.out_name, '.tmp.c')
+	mut out_name_c := b.get_vtmp_filename(b.pref.out_name, '.tmp.c')
 	if b.pref.is_shared {
-		out_name_c = get_vtmp_filename(b.pref.out_name, '.tmp.so.c')
+		out_name_c = b.get_vtmp_filename(b.pref.out_name, '.tmp.so.c')
 	}
 	b.build_c(files, out_name_c)
 	if b.pref.os == .ios {

vlib/v/builder/cc.v

@@ -78,6 +78,9 @@ fn (mut v Builder) find_win_cc() ? {
 
 fn (mut v Builder) post_process_c_compiler_output(res os.Result) {
 	if res.exit_code == 0 {
+		if v.pref.reuse_tmpc {
+			return
+		}
 		for tmpfile in v.pref.cleanup_files {
 			if os.is_file(tmpfile) {
 				if v.pref.is_verbose {

vlib/v/builder/compile.v

@@ -22,10 +22,13 @@ fn get_vtmp_folder() string {
 	return vtmp
 }
 
-fn get_vtmp_filename(base_file_name string, postfix string) string {
+fn (mut b Builder) get_vtmp_filename(base_file_name string, postfix string) string {
 	vtmp := get_vtmp_folder()
-	uniq := rand.u64()
+	mut uniq := ''
-	return os.real_path(os.join_path(vtmp, os.file_name(os.real_path(base_file_name)) + '.$uniq$postfix'))
+	if !b.pref.reuse_tmpc {
+		uniq = '.${rand.u64()}'
+	}
+	return os.real_path(os.join_path(vtmp, os.file_name(os.real_path(base_file_name)) + '$uniq$postfix'))
 }
 
 pub fn compile(command string, pref &pref.Preferences) {

vlib/v/checker/checker.v

@@ -90,11 +90,7 @@ pub fn (mut c Checker) check_scope_vars(sc &ast.Scope) {
 			ast.Var {
 				if !c.pref.is_repl {
 					if !obj.is_used && obj.name[0] != `_` {
-						if c.pref.is_prod {
+						c.warn('unused variable: `$obj.name`', obj.pos)
-							c.error('unused variable: `$obj.name`', obj.pos)
-						} else {
-							c.warn('unused variable: `$obj.name`', obj.pos)
-						}
 					}
 				}
 				if obj.is_mut && !obj.is_changed && !c.is_builtin_mod && obj.name != 'it' {
@@ -3854,7 +3850,7 @@ pub fn (mut c Checker) add_error_detail(s string) {
 }
 
 pub fn (mut c Checker) warn(s string, pos token.Position) {
-	allow_warnings := !c.pref.is_prod // allow warnings only in dev builds
+	allow_warnings := !(c.pref.is_prod || c.pref.warns_are_errors)// allow warnings only in dev builds
 	c.warn_or_error(s, pos, allow_warnings) // allow warnings only in dev builds
 }
 

vlib/v/parser/parser.v

@@ -816,6 +816,10 @@ pub fn (mut p Parser) error_with_pos(s string, pos token.Position) {
 }
 
 pub fn (mut p Parser) warn_with_pos(s string, pos token.Position) {
+	if p.pref.warns_are_errors {
+		p.error_with_pos(s, pos)
+		return
+	}
 	if p.pref.skip_warnings {
 		return
 	}

vlib/v/pref/pref.v

@@ -117,6 +117,8 @@ pub mut:
 	print_v_files       bool // when true, just print the list of all parsed .v files then stop.
 	skip_running        bool // when true, do no try to run the produced file (set by b.cc(), when -o x.c or -o x.js)
 	skip_warnings       bool // like C's "-w"
+	warns_are_errors    bool // -W, like C's "-Werror", treat *every* warning is an error
+	reuse_tmpc          bool // do not use random names for .tmp.c and .tmp.c.rsp files, and do not remove them
 	use_color           ColorOutput // whether the warnings/errors should use ANSI color escapes.
 	is_parallel         bool
 	error_limit         int
@@ -248,6 +250,12 @@ pub fn parse_args(args []string) (&Preferences, string) {
 			'-x64' {
 				res.backend = .x64
 			}
+			'-W' {
+				res.warns_are_errors = true
+			}
+			'-reuse-tmpc' {
+				res.reuse_tmpc = true
+			}
 			'-w' {
 				res.skip_warnings = true
 			}