v: fix `[if debug] fn abc(){} ... abc()`

vlib/v/ast/ast.v

@@ -319,6 +319,7 @@ pub:
 	is_manualfree   bool // true, when [manualfree] is used on a fn
 	is_main         bool // true for `fn main()`
 	is_test         bool // true for `fn test_abcde`
+	is_conditional  bool // true for `[if abc] fn abc(){}`
 	receiver        Field
 	receiver_pos    token.Position // `(u User)` in `fn (u User) name()` position
 	is_method       bool

vlib/v/parser/fn.v

@@ -171,6 +171,7 @@ fn (mut p Parser) fn_decl() ast.FnDecl {
 	is_manualfree := p.is_manualfree || p.attrs.contains('manualfree')
 	is_deprecated := p.attrs.contains('deprecated')
 	is_direct_arr := p.attrs.contains('direct_array_access')
+	is_conditional, conditional_ctdefine := p.attrs.has_comptime_define()
 	mut is_unsafe := p.attrs.contains('unsafe')
 	is_pub := p.tok.kind == .key_pub
 	if is_pub {
@@ -331,6 +332,8 @@ fn (mut p Parser) fn_decl() ast.FnDecl {
 			is_unsafe: is_unsafe
 			is_main: is_main
 			is_test: is_test
+			is_conditional: is_conditional
+			ctdefine: conditional_ctdefine
 			no_body: no_body
 			mod: p.mod
 			attrs: p.attrs
@@ -358,6 +361,8 @@ fn (mut p Parser) fn_decl() ast.FnDecl {
 			is_unsafe: is_unsafe
 			is_main: is_main
 			is_test: is_test
+			is_conditional: is_conditional
+			ctdefine: conditional_ctdefine
 			no_body: no_body
 			mod: p.mod
 			attrs: p.attrs
@@ -397,6 +402,7 @@ fn (mut p Parser) fn_decl() ast.FnDecl {
 		is_variadic: is_variadic
 		is_main: is_main
 		is_test: is_test
+		is_conditional: is_conditional
 		receiver: ast.Field{
 			name: rec.name
 			typ: rec.typ

vlib/v/pref/pref.v

@@ -451,6 +451,9 @@ pub fn parse_args(known_external_commands []string, args []string) (&Preferences
 			}
 		}
 	}
+	if res.is_debug {
+		parse_define(mut res, 'debug')
+	}
 	// res.use_cache = true
 	if command != 'doc' && res.out_name.ends_with('.v') {
 		eprintln('Cannot save output binary in a .v file.')

vlib/v/table/attr.v

@@ -47,3 +47,12 @@ pub fn (attrs []Attr) contains(str string) bool {
 	}
 	return false
 }
+
+pub fn (attrs []Attr) has_comptime_define() (bool, string) {
+	for a in attrs {
+		if a.is_comptime_define {
+			return true, a.name
+		}
+	}
+	return false, ''
+}

vlib/v/table/table.v

@@ -32,12 +32,13 @@ pub:
 	language       Language
 	generic_names  []string
 	is_pub         bool
-	is_deprecated  bool
-	is_unsafe      bool
+	is_deprecated  bool // `[deprecated] fn abc(){}`
+	is_unsafe      bool // `[unsafe] fn abc(){}`
 	is_placeholder bool
-	is_main        bool
-	is_test        bool
-	no_body        bool
+	is_main        bool // `fn main(){}`
+	is_test        bool // `fn test_abc(){}`
+	is_conditional bool // `[if abc]fn(){}`
+	no_body        bool // a pure declaration like `fn abc(x int)`; used in .vh files, C./JS. fns.
 	mod            string
 	ctdefine       string // compile time define. "myflag", when [if myflag] tag
 	attrs          []Attr