cgen,markused: skip struct map { and related type declarations, when no V maps are used (#24826)

vlib/v/gen/c/cgen.v

@@ -993,6 +993,9 @@ pub fn (mut g Gen) init() {
 			g.cheaders.writeln('#define VNOFLOAT 1')
 		}
 		g.cheaders.writeln(c_builtin_types)
+		if !g.pref.skip_unused || g.table.used_features.used_maps > 0 {
+			g.cheaders.writeln(c_mapfn_callback_types)
+		}
 		if g.pref.is_bare {
 			g.cheaders.writeln(c_bare_headers)
 		} else {
@@ -1752,6 +1755,9 @@ static inline void __${sym.cname}_pushval(${sym.cname} ch, ${push_arg} val) {
 				}
 			}
 			.map {
+				if g.pref.skip_unused && g.table.used_features.used_maps == 0 {
+					continue
+				}
 				g.type_definitions.writeln('typedef map ${sym.cname};')
 			}
 			else {
@@ -1885,7 +1891,6 @@ pub fn (mut g Gen) write_fn_typesymbol_declaration(sym ast.TypeSymbol) {
 	if !info.has_decl && (not_anon || is_fn_sig) && !func.return_type.has_flag(.generic)
 		&& !has_generic_arg {
 		fn_name := sym.cname
-
 		mut call_conv := ''
 		mut msvc_call_conv := ''
 		for attr in func.attrs {
@@ -6642,6 +6647,11 @@ fn (mut g Gen) write_types(symbols []&ast.TypeSymbol) {
 			g.typedefs.writeln('typedef struct none none;')
 		}
 		mut name := sym.scoped_cname()
+		if g.pref.skip_unused && g.table.used_features.used_maps == 0 {
+			if name in ['map', 'mapnode', 'SortedMap', 'MapMode', 'DenseArray'] {
+				continue
+			}
+		}
 		match sym.info {
 			ast.Struct {
 				if !struct_names[name] {

vlib/v/gen/c/cheaders.v

@@ -780,7 +780,9 @@ typedef struct sync__Channel* chan;
 		#endif
 	#endif
 #endif
+'
 
+const c_mapfn_callback_types = '
 typedef u64 (*MapHashFn)(voidptr);
 typedef bool (*MapEqFn)(voidptr, voidptr);
 typedef void (*MapCloneFn)(voidptr, voidptr);

vlib/v/markused/markused.v

@@ -505,7 +505,8 @@ pub fn mark_used(mut table ast.Table, mut pref_ pref.Preferences, ast_files []&a
 			}
 		}
 	} else {
-		for map_fn_name in ['new_map', 'new_map_init', 'map_hash_string', 'new_dense_array'] {
+		for map_fn_name in ['new_map', 'new_map_init', 'map_hash_string', 'new_dense_array',
+			'new_dense_array_noscan'] {
 			walker.used_fns.delete(map_fn_name)
 		}
 		for k, mut mfn in all_fns {

vlib/v/markused/walker.v

@@ -16,6 +16,7 @@ pub mut:
 	used_globals map[string]bool
 	used_structs map[string]bool
 	used_fields  map[string]bool
+	used_ifaces  map[string]bool
 	used_none    int
 	n_asserts    int
 	pref         &pref.Preferences = unsafe { nil }
@@ -358,6 +359,9 @@ fn (mut w Walker) expr(node_ ast.Expr) {
 			if node.is_vweb {
 				w.stmts(node.veb_tmpl.stmts)
 			}
+			if node.is_embed {
+				w.features.used_maps++
+			}
 		}
 		ast.DumpExpr {
 			w.expr(node.expr)
@@ -515,6 +519,10 @@ fn (mut w Walker) expr(node_ ast.Expr) {
 		ast.SelectorExpr {
 			w.expr(node.expr)
 			if node.expr_type != 0 {
+				esym := w.table.sym(node.expr_type)
+				if esym.kind == .interface {
+					w.mark_interface_by_symbol(esym)
+				}
 				if method := w.table.find_method(w.table.sym(node.expr_type), node.field_name) {
 					w.fn_by_name(method.fkey())
 				}
@@ -683,6 +691,7 @@ pub fn (mut w Walker) call_expr(mut node ast.CallExpr) {
 				}
 			}
 		} else if left_sym.info is ast.Interface {
+			w.mark_interface_by_symbol(left_sym)
 			for typ in left_sym.info.types {
 				sym := w.table.sym(typ)
 				_, embed_types := w.table.find_method_from_embeds(sym, node.name) or {
@@ -777,3 +786,18 @@ pub fn (mut w Walker) or_block(node ast.OrExpr) {
 		w.stmts(node.stmts)
 	}
 }
+
+pub fn (mut w Walker) mark_interface_by_symbol(isym ast.TypeSymbol) {
+	if isym.name in w.used_ifaces {
+		return
+	}
+	w.used_ifaces[isym.name] = true
+	if isym.info is ast.Interface {
+		for typ in isym.info.types {
+			if typ == ast.map_type {
+				w.features.used_maps++
+			}
+			// sym := w.table.sym(typ); eprintln('>>>>>>>>> typ: ${typ.str():-30} | sym.name: ${sym.name}')
+		}
+	}
+}