acorn-typescript

A type assertion without parentheses in the head of a loop fails with at , while the same head without gets as far as the assignment target check (#148): Expected: the first two parse, with the assertion as the loop's left side. TypeScript 5.9.3 reports no parse or checker diagnostic for them (apart from the undeclared names), and typescript-estree 8.56.1 and @babel/parser 7.29.3 parse them. The third is #148. Cause. acorn's reads the head of a loop with , which is right for JavaScript's . acorn-typescript reads and only in , which doesn't reach, so the head ends before , no follows, and acorn fails at (L341). TypeScript's parser reads the head of every loop as an expression ( with disallowed), and works here because acorn-typescript reads as a subscript. Fix direction. In a head, read an or after the expression, as does (a or around it), before checking for . With #148 fixed, the assertion is kept as the assignment target. #110 doesn't change this. Found through TSRX, which uses this parser.

A decorated after fails to parse, with or without , though the same class parses at the start of a statement: Expected, as TypeScript 5.9 and typescript-estree parse them: an of a with (and ) and the decorators, whose name is optional (). After , TypeScript reads as the start of a declaration (), and and after the decorators as its modifiers, in either order. It reports nothing for them. Without the decorators, is a syntax error in TypeScript too (TS1005), since is then the exported value. Cause. reads and , and leaves the rest to acorn, which reads the decorators as the start of a class expression (#124), and after them as the exported expression. Fix direction. After decorators, read , and before or after it on the same line, as the modifiers of an ambient class with an optional name, as is read at the start of a statement. This goes with #124. #110 doesn't change this. Found through TSRX, which uses this parser.

A modifier that only a class member takes, or a repeated or misplaced modifier, before a declaration fails to parse, where TypeScript's parser reads the declaration and its checker reports the modifier. One of them parses without an error: Expected, as TypeScript 5.9 reads them: its takes , , , , , , and before a declaration on the same line, on any line, and , and reads them all, repeated or not, as modifiers of the declaration. Its checker () then reports the first one the declaration can't take, which typescript-estree reports for most of these too: Inside a block (a function's body), any of them but on a class or on a function is TS1184 at the first one. A second is TypeScript's parser error TS1146 (), as reads only one . Cause. acorn reads these words at the start of a statement as names (, and the other strict-mode reserved words as reserved ones), and this parser reads only and as modifiers there (, , ), each once and only before a class or an interface (#143). After , takes none of the other words for the start of a declaration, and reads after without checking it. Fix direction. Where TypeScript's reads modifiers before a declaration, read them all, parse the declaration with the ones the tree keeps (, , on a class, on a function), and raise the error TypeScript's checker reports, as typescript-estree does. This goes with #143, which covers before a declaration other than a class. #110 doesn't change this. Found through TSRX, which uses this parser.