parser: fix panic when single letter receiver parsed (#8381)

vlib/v/checker/checker.v

@@ -5296,7 +5296,7 @@ fn (mut c Checker) fn_decl(mut node ast.FnDecl) {
 			sym := c.table.get_type_symbol(arg.typ)
 			if sym.kind == .placeholder
 				|| (sym.kind in [table.Kind.int_literal, .float_literal] && !c.is_builtin_mod) {
-				c.error('unknown type `$sym.name`', node.pos)
+				c.error('unknown type `$sym.name`', node.receiver_pos)
 			}
 		}
 	}

vlib/v/checker/tests/receiver_unknown_type_single_letter.out

@@ -0,0 +1,3 @@
+vlib/v/checker/tests/receiver_unknown_type_single_letter.vv:1:5: error: unknown type `A`
+    1 | fn (p A) foo() {}
+      |     ~~~

vlib/v/checker/tests/receiver_unknown_type_single_letter.vv

@@ -0,0 +1 @@
+fn (p A) foo() {}

vlib/v/parser/fn.v

@@ -190,6 +190,7 @@ fn (mut p Parser) fn_decl() ast.FnDecl {
 	mut rec_mut := false
 	mut params := []table.Param{}
 	if p.tok.kind == .lpar {
+		p.is_parsing_receiver = true
 		lpar_pos := p.tok.position()
 		p.next() // (
 		is_method = true
@@ -246,6 +247,7 @@ fn (mut p Parser) fn_decl() ast.FnDecl {
 			typ: rec_type
 		}
 		p.check(.rpar)
+		p.is_parsing_receiver = false
 	}
 	mut name := ''
 	if p.tok.kind == .name {

vlib/v/parser/parse_type.v

@@ -373,7 +373,7 @@ pub fn (mut p Parser) parse_any_type(language table.Language, is_ptr bool, check
 					return table.int_literal_type
 				}
 				else {
-					if name.len == 1 && name[0].is_capital() {
+					if name.len == 1 && name[0].is_capital() && !p.is_parsing_receiver {
 						return p.parse_generic_template_type(name)
 					}
 					if p.peek_tok.kind == .lt {

vlib/v/parser/parser.v

@@ -29,48 +29,49 @@ mut:
 	scanner           &scanner.Scanner
 	comments_mode     scanner.CommentsMode = .skip_comments
 	// see comment in parse_file
-	tok               token.Token
+	tok                 token.Token
-	prev_tok          token.Token
+	prev_tok            token.Token
-	peek_tok          token.Token
+	peek_tok            token.Token
-	peek_tok2         token.Token
+	peek_tok2           token.Token
-	peek_tok3         token.Token
+	peek_tok3           token.Token
-	table             &table.Table
+	table               &table.Table
-	language          table.Language
+	language            table.Language
-	inside_if         bool
+	inside_if           bool
-	inside_if_expr    bool
+	inside_if_expr      bool
-	inside_ct_if_expr bool
+	inside_ct_if_expr   bool
-	inside_or_expr    bool
+	inside_or_expr      bool
-	inside_for        bool
+	inside_for          bool
-	inside_fn         bool // true even with implicit main
+	inside_fn           bool // true even with implicit main
-	inside_str_interp bool
+	inside_str_interp   bool
-	or_is_handled     bool         // ignore `or` in this expression
+	or_is_handled       bool         // ignore `or` in this expression
-	builtin_mod       bool         // are we in the `builtin` module?
+	builtin_mod         bool         // are we in the `builtin` module?
-	mod               string       // current module name
+	mod                 string       // current module name
-	is_manualfree     bool         // true when `[manualfree] module abc`, makes *all* fns in the current .v file, opt out of autofree
+	is_manualfree       bool         // true when `[manualfree] module abc`, makes *all* fns in the current .v file, opt out of autofree
-	attrs             []table.Attr // attributes before next decl stmt
+	attrs               []table.Attr // attributes before next decl stmt
-	expr_mod          string       // for constructing full type names in parse_type()
+	expr_mod            string       // for constructing full type names in parse_type()
-	scope             &ast.Scope
+	scope               &ast.Scope
-	global_scope      &ast.Scope
+	global_scope        &ast.Scope
-	imports           map[string]string // alias => mod_name
+	imports             map[string]string // alias => mod_name
-	ast_imports       []ast.Import      // mod_names
+	ast_imports         []ast.Import      // mod_names
-	used_imports      []string // alias
+	used_imports        []string // alias
-	auto_imports      []string // imports, the user does not need to specify
+	auto_imports        []string // imports, the user does not need to specify
-	imported_symbols  map[string]string
+	imported_symbols    map[string]string
-	is_amp            bool // for generating the right code for `&Foo{}`
+	is_amp              bool // for generating the right code for `&Foo{}`
-	returns           bool
+	returns             bool
-	inside_match      bool // to separate `match A { }` from `Struct{}`
+	inside_match        bool // to separate `match A { }` from `Struct{}`
-	inside_select     bool // to allow `ch <- Struct{} {` inside `select`
+	inside_select       bool // to allow `ch <- Struct{} {` inside `select`
-	inside_match_case bool // to separate `match_expr { }` from `Struct{}`
+	inside_match_case   bool // to separate `match_expr { }` from `Struct{}`
-	inside_match_body bool // to fix eval not used TODO
+	inside_match_body   bool // to fix eval not used TODO
-	inside_unsafe     bool
+	inside_unsafe       bool
-	is_stmt_ident     bool // true while the beginning of a statement is an ident/selector
+	is_stmt_ident       bool // true while the beginning of a statement is an ident/selector
-	expecting_type    bool // `is Type`, expecting type
+	expecting_type      bool // `is Type`, expecting type
-	errors            []errors.Error
+	errors              []errors.Error
-	warnings          []errors.Warning
+	warnings            []errors.Warning
-	vet_errors        []vet.Error
+	vet_errors          []vet.Error
-	cur_fn_name       string
+	cur_fn_name         string
-	in_generic_params bool // indicates if parsing between `<` and `>` of a method/function
+	in_generic_params   bool // indicates if parsing between `<` and `>` of a method/function
-	name_error        bool // indicates if the token is not a name or the name is on another line
+	name_error          bool // indicates if the token is not a name or the name is on another line
+	is_parsing_receiver bool // indicates if parser is parsing receiver fn (x Xxx)
 }
 
 // for tests