v.pref: add a simple options_test.v to check for -cflags regressions

vlib/v/builder/msvc.v

@@ -287,16 +287,16 @@ pub fn (mut v Builder) cc_msvc() {
 	a << ['-w', '/we4013', '/volatile:ms', '/Fo"$out_name_obj"']
 	if v.pref.is_prod {
 		a << '/O2'
-		a << '/MD'
-		a << '/DNDEBUG'
-	} else {
-		a << '/MDd'
-		a << '/D_DEBUG'
 	}
 	if v.pref.is_debug {
+		a << '/MDd'
+		a << '/D_DEBUG'
 		// /Zi generates a .pdb
 		// /Fd sets the pdb file name (so its not just vc140 all the time)
 		a << ['/Zi', '/Fd"$out_name_pdb"']
+	} else {
+		a << '/MD'
+		a << '/DNDEBUG'
 	}
 	if v.pref.is_shared {
 		if !v.pref.out_name.ends_with('.dll') {

vlib/v/gen/c/coutput_test.v

@@ -33,7 +33,7 @@ fn test_out_files() ? {
 		print(term.colorize(term.magenta, 'v run $relpath') + ' == ' +
 			term.colorize(term.magenta, out_relpath) + ' ')
 		pexe := os.join_path(output_path, '${basename}.exe')
-		compilation := os.execute('$vexe -o $pexe $path')
+		compilation := os.execute('"$vexe" -o "$pexe" "$path"')
 		ensure_compilation_succeeded(compilation)
 		res := os.execute(pexe)
 		if res.exit_code < 0 {

vlib/v/pref/options_test.v

@@ -0,0 +1,52 @@
+// vtest retry: 3
+import os
+import time
+
+const vexe = @VEXE
+
+const vroot = os.real_path(@VMODROOT)
+
+fn testsuite_begin() {
+	os.chdir(vroot) or {}
+}
+
+fn test_cflags() ? {
+	println('> test whether -cflags is passed to the backend C compiler')
+	compilation := os.execute('"$vexe" -cflags NONSENSE_OPTION examples/hello_world.v')
+	assert compilation.exit_code != 0
+	println('> NONSENSE_OPTION failed the C build, OK')
+	//
+	mut debug_arg := '-g3 -O0'
+	mut optimised_arg := '-O1'
+	$if msvc {
+		debug_arg = '/MDd /D_DEBUG'
+		optimised_arg = '/O1'
+	}
+	tmpdir := os.temp_dir()
+	//
+	dbgexe := os.join_path(os.temp_dir(), 'debug_hw.exe')
+	debug_sw := time.new_stopwatch()
+	debug_compilation := os.execute('"$vexe" -cflags "$debug_arg" -o "$dbgexe" examples/hello_world.v')
+	debug_delta := debug_sw.elapsed().microseconds()
+	assert debug_compilation.exit_code == 0
+	debug_file_size := os.file_size(dbgexe)
+	assert debug_file_size > 0
+	println('> debug build took: $debug_delta ms with "$debug_arg", file size: $debug_file_size')
+	//
+	optexe := os.join_path(os.temp_dir(), 'optimised_hw.exe')
+	optimised_sw := time.new_stopwatch()
+	optimised_compilation := os.execute('"$vexe" -cflags "$optimised_arg" -o "$optexe" examples/hello_world.v')
+	optimised_delta := optimised_sw.elapsed().microseconds()
+	assert optimised_compilation.exit_code == 0
+	optimised_file_size := os.file_size(optexe)
+	assert optimised_file_size > 0
+	println('> optimised build took: $optimised_delta ms with "$optimised_arg", file size: $optimised_file_size')
+	//
+	$if !tinyc {
+		// tcc does almost no optimisations, so the differences are very insignificant
+		assert optimised_file_size <= debug_file_size
+		assert optimised_delta >= debug_delta
+	}
+	os.rm(optexe) or {}
+	os.rm(dbgexe) or {}
+}