parser: warn on unused imported functions used via import math { sin, cos }

vlib/v/checker/tests/import_symbol_fn_err.out

@@ -1,3 +1,8 @@
+vlib/v/checker/tests/import_symbol_fn_err.vv:1:8: warning: module 'crypto' is imported but never used
+    1 | import crypto { userper }
+      |        ~~~~~~
+    2 | fn main() {
+    3 |   usurper()
 vlib/v/checker/tests/import_symbol_fn_err.vv:1:17: error: module `crypto` has no constant or function `userper`
     1 | import crypto { userper }
       |                 ~~~~~~~

vlib/v/checker/tests/selective_const_import.out

@@ -1,3 +1,6 @@
+vlib/v/checker/tests/selective_const_import.vv:1:8: warning: module 'time' is imported but never used
+    1 | import time { second }
+      |        ~~~~
 vlib/v/checker/tests/selective_const_import.vv:1:15: error: cannot selectively import constant `second` from `time`, import `time` and use `time.second` instead
     1 | import time { second }
       |               ~~~~~~

vlib/v/parser/fn.v

@@ -73,6 +73,7 @@ fn (mut p Parser) call_expr(language ast.Language, mod string) ast.CallExpr {
 	}
 	if fn_name in p.imported_symbols {
 		fn_name = p.imported_symbols[fn_name]
+		p.register_used_import_for_symbol_name(fn_name)
 	}
 	comments := p.eat_comments(same_line: true)
 	pos.update_last_line(p.prev_tok.line_nr)

vlib/v/parser/module.v

@@ -31,6 +31,11 @@ fn (mut p Parser) register_used_import(alias string) {
 	}
 }
 
+fn (mut p Parser) register_used_import_for_symbol_name(sym_name string) {
+	short_import_name := sym_name.all_before_last('.').all_after_last('.')
+	p.register_used_import(short_import_name)
+}
+
 fn (mut p Parser) register_auto_import(alias string) {
 	if alias !in p.imports {
 		p.imports[alias] = alias

vlib/v/parser/parse_type.v

@@ -577,6 +577,7 @@ fn (mut p Parser) parse_any_type(language ast.Language, is_ptr bool, check_dot b
 		name = p.expr_mod + '.' + name
 	} else if name in p.imported_symbols {
 		name = p.imported_symbols[name]
+		p.register_used_import_for_symbol_name(name)
 	} else if !p.builtin_mod && name.len > 1 && name !in p.table.type_idxs {
 		// `Foo` in module `mod` means `mod.Foo`
 		name = p.mod + '.' + name

vlib/v/parser/parser.v

@@ -3699,7 +3699,6 @@ fn (mut p Parser) import_stmt() ast.Import {
 			syms_pos: initial_syms_pos
 			pos: import_node.pos.extend(initial_syms_pos)
 		}
-		p.register_used_import(mod_alias) // no `unused import` msg for parent
 	}
 	pos_t := p.tok.pos()
 	if import_pos.line_nr == pos_t.line_nr {

vlib/v/parser/tests/import_sym_fn_unused_warning_err.out

@@ -0,0 +1,5 @@
+vlib/v/parser/tests/import_sym_fn_unused_warning_err.vv:1:8: warning: module 'math' is imported but never used
+    1 | import math { sin, cos }
+      |        ~~~~
+    2 | 
+    3 | fn main() {}

vlib/v/parser/tests/import_sym_fn_unused_warning_err.vv

@@ -0,0 +1,3 @@
+import math { sin, cos }
+
+fn main() {}