compiler: fix error in case of void function used as a value

vlib/compiler/aparser.v

@@ -1597,11 +1597,13 @@ fn ($v.name mut $v.typ) ${p.cur_fn.name}(...) {
 		}
 		else {
 			p.gen(' ' + p.tok.str() + ' ')
-		}}
+		}
+	}
 	p.fspace()
 	p.next()
 	p.fspace()
 	pos := p.cgen.cur_line.len
+	expr_tok := p.cur_tok_index()
 	p.is_var_decl = true
 	expr_type := p.bool_expression()
 	p.is_var_decl = false
@@ -1609,8 +1611,8 @@ fn ($v.name mut $v.typ) ${p.cur_fn.name}(...) {
 	// p.warn('expecting array got $expr_type')
 	// }
 	if expr_type == 'void' {
-		_,fn_name := p.is_expr_fn_call(p.token_idx - 3)
-		p.error_with_token_index('${fn_name}() $err_used_as_value', p.token_idx - 2)
+		_,fn_name := p.is_expr_fn_call(expr_tok+1)
+		p.error_with_token_index('${fn_name}() $err_used_as_value', expr_tok)
 	}
 	// Allow `num = 4` where `num` is an `?int`
 	if p.assigned_type.starts_with('Option_') && expr_type == parse_pointer(p.assigned_type['Option_'.len..]) {
@@ -1714,6 +1716,7 @@ fn (p mut Parser) var_decl() {
 	else {
 		p.error('expected `=` or `:=`')
 	}
+	expr_tok := p.cur_tok_index()
 	// all vars on left of `:=` already defined (or `_`)
 	if is_decl_assign && var_names.len == 1 && var_names[0] == '_' {
 		p.error_with_token_index('use `=` instead of `:=`', var_token_idxs.last())
@@ -1721,8 +1724,8 @@ fn (p mut Parser) var_decl() {
 	p.var_decl_name = if var_names.len > 1 { '_V_mret_${p.token_idx}_' + var_names.join('_') } else { var_names[0] }
 	t := p.gen_var_decl(p.var_decl_name, is_static)
 	if t == 'void' {
-		_,fn_name := p.is_expr_fn_call(p.token_idx - 3)
-		p.error_with_token_index('${fn_name}() $err_used_as_value', p.token_idx - 2)
+		_,fn_name := p.is_expr_fn_call(expr_tok+1)
+		p.error_with_token_index('${fn_name}() $err_used_as_value', expr_tok)
 	}
 	mut var_types := [t]
 	// multiple returns types

vlib/compiler/compile_errors.v

@@ -197,6 +197,33 @@ fn (p mut Parser) print_error_context() {
 	// p.scanner.debug_tokens()
 }
 
+fn ienv_default(ename string, idefault int) int {
+	es := os.getenv(ename)
+	if es.len == 0 { return idefault }
+	return es.int()
+}
+
+// print_current_tokens/1 pretty prints the current token context, like this:
+// // Your label: tokens[  32] = Token{ .line:   8, .pos:   93, .tok:  85 } = mut
+// // Your label: tokens[> 33] = Token{ .line:   8, .pos:   95, .tok:   1 } = b
+// // Your label: tokens[  34] = Token{ .line:   8, .pos:   98, .tok:  31 } = :=
+// It is useful while debugging the v compiler itself. > marks p.token_idx
+fn (p &Parser) print_current_tokens(label string){
+	btokens := ienv_default('V_BTOKENS', 5)
+	atokens := ienv_default('V_ATOKENS', 5)
+	ctoken_idx := p.token_idx
+	stoken_idx := imax(0, ctoken_idx - btokens)
+	etoken_idx := imin( ctoken_idx + atokens + 1, p.tokens.len)
+	for i := stoken_idx; i < etoken_idx; i++ {
+		idx := if i == ctoken_idx {
+			'>${i:3d}'
+		} else {
+			' ${i:3d}'
+		}
+		eprintln('$label: tokens[$idx] = ' + p.tokens[ i ].detailed_str())
+	}
+}
+
 fn normalized_error(s string) string {
 	mut res := s
 	if !res.contains('__') {

vlib/compiler/gen_c.v

@@ -65,10 +65,11 @@ fn (p mut Parser) gen_blank_identifier_assign() {
 	is_indexer := p.peek() == .lsbr
 	is_fn_call,next_expr := p.is_expr_fn_call(p.token_idx)
 	pos := p.cgen.add_placeholder()
+	expr_tok := p.cur_tok_index()
 	p.is_var_decl = true
 	typ := p.bool_expression()
 	if typ == 'void' {
-		p.error_with_token_index('${next_expr}() $err_used_as_value', p.token_idx - 2)
+		p.error_with_token_index('${next_expr}() $err_used_as_value', expr_tok)
 	}
 	p.is_var_decl = false
 	if !is_indexer && !is_fn_call {

vlib/compiler/token.v

@@ -292,9 +292,16 @@ pub fn (t Token) str() string {
 	if t.tok == .str {
 		return "'$t.lit'"
 	}
+	if t.tok == .eof {
+		return '.EOF'
+	}
 	if t.tok < .plus {
 		return t.lit // string, number etc
 	}
 	return t.tok.str()
 }
 
+pub fn (t Token) detailed_str() string {
+	return 'Token{ .line:${t.line_nr:4d}, .pos:${t.pos:5d}, .tok: ${t.tok:3d} } = $t '
+}
+