ast, parser: support $d() in fixed size array struct fields (#21731)

vlib/v/ast/ast.v

@@ -1967,6 +1967,19 @@ pub fn (mut cc ComptimeCall) resolve_compile_value(compile_values map[string]str
 	cc.is_d_resolved = true
 }
 
+// expr_str returns the string representation of `ComptimeCall` for use with
+// `ast.Expr`'s `str()' method (used by e.g. vfmt).
+pub fn (cc ComptimeCall) expr_str() string {
+	mut str := 'ast.ComptimeCall'
+	if cc.is_compile_value {
+		arg := cc.args[0] or { return str }
+		if arg.expr.is_pure_literal() {
+			str = "\$${cc.method_name}('${cc.args_var}', ${arg})"
+		}
+	}
+	return str
+}
+
 pub struct None {
 pub:
 	pos token.Pos

vlib/v/ast/str.v

@@ -662,7 +662,7 @@ pub fn (x Expr) str() string {
 			return 'ast.ChanInit'
 		}
 		ComptimeCall {
-			return 'ast.ComptimeCall'
+			return x.expr_str()
 		}
 		EmptyExpr {
 			return 'ast.EmptyExpr'

vlib/v/checker/tests/comptime_value_d_only_d_in_fixed_size_array.out

@@ -0,0 +1,5 @@
+vlib/v/checker/tests/comptime_value_d_only_d_in_fixed_size_array.vv:2:7: error: only $d() is supported as fixed array size quantifier at compile time
+    1 | struct St {
+    2 |     fsa [$env('size')]int
+      |          ~~~~~~~~~~~~
+    3 | }

vlib/v/checker/tests/comptime_value_d_only_d_in_fixed_size_array.vv

@@ -0,0 +1,3 @@
+struct St {
+	fsa [$env('size')]int
+}

vlib/v/checker/tests/run/using_comptime_d_value.run.out

@@ -2,3 +2,4 @@
 false
 done
 [0, 0, 0, 0]
+[0, 0, 0, 0, 0, 0, 0, 0, 0, 0]

vlib/v/checker/tests/run/using_comptime_d_value.vv

@@ -3,6 +3,10 @@
 
 const my_f64 = $d('my_f64', 42.0)
 
+struct StructFSAWithDSize {
+	fsa [$d('field_fsa_size', 10)]int
+}
+
 fn main() {
 	println(my_f64)
 	cv_bool := $d('my_bool', false)
@@ -10,4 +14,6 @@ fn main() {
 	println('done')
 	fsa := [$d('fixed_size', 4)]int{}
 	println(fsa)
+	s := StructFSAWithDSize{}
+	println(s.fsa)
 }

vlib/v/gen/c/testdata/use_flag_comptime_values.vv

@@ -1,11 +1,15 @@
 // This file should pass if compiled/run with:
-// vtest vflags: -d my_f64=2.0 -d my_i64=3 -d my_string="a four" -d my_bool -d my_char=g -d my_size=8
+// vtest vflags: -d my_f64=2.0 -d my_i64=3 -d my_string="a four" -d my_bool -d my_char=g -d my_size=8 -d field_fsa_size=16
 const my_f64 = $d('my_f64', 1.0)
 const my_i64 = $d('my_i64', 2)
 const my_string = $d('my_string', 'three')
 const my_bool = $d('my_bool', false)
 const my_char = $d('my_char', `f`)
 
+struct StructFSAWithDSize {
+	fsa [$d('field_fsa_size', 10)]int
+}
+
 fn main() {
 	assert my_f64 == 2.0
 	assert my_i64 == 3
@@ -14,6 +18,8 @@ fn main() {
 	assert my_char == `g`
 	my_fixed_size_array := [$d('my_size', 4)]int{}
 	assert my_fixed_size_array.len == 8
+	s := StructFSAWithDSize{}
+	assert s.fsa.len == 16
 	println(my_f64)
 	println(my_i64)
 	println(my_string)

vlib/v/parser/parse_type.v

@@ -13,7 +13,7 @@ const maximum_inline_sum_type_variants = 3
 fn (mut p Parser) parse_array_type(expecting token.Kind, is_option bool) ast.Type {
 	p.check(expecting)
 	// fixed array
-	if p.tok.kind in [.number, .name] {
+	if p.tok.kind in [.number, .name, .dollar] {
 		mut fixed_size := 0
 		mut size_expr := p.expr(0)
 		mut size_unresolved := true
@@ -36,6 +36,9 @@ fn (mut p Parser) parse_array_type(expecting token.Kind, is_option bool) ast.Typ
 						}
 						fixed_size = size_expr.compile_value.int()
 						size_unresolved = false
+					} else {
+						p.error_with_pos('only \$d() is supported as fixed array size quantifier at compile time',
+							size_expr.pos)
 					}
 				}
 				ast.Ident {