Speculative type parsing in expressions does not always suppress parse errors #3062

Bug description

In AssemblyScript, the parser speculatively calls parseType with suppressErrors = true during expression lookahead (such as checking for an arrow function return type after (x) : or type arguments after <), but nested paths inside parseType ignore suppressErrors and emit diagnostics instead of backtracking cleanly.

Inside parseType, tryParseFunctionType does not accept suppressErrors and reports errors when seeing ?, and the union | branch hardcodes suppressErrors = false on recursive parseType calls.

Both functions below are valid TypeScript (tsc parses them cleanly) and should compile without error, just as a ? <i32>c : (a ? b : c) and a < (a >> b) do.

Steps to reproduce

export function test1(a: bool, b: i32, c: i32): i32 {
  return a ? <i32>(c) : (a ? b : c);
}

export function test2(a: i32, b: i32): bool {
  return a < (a | (a >> b));
}

Compiling with asc repro.ts fails with:

ERROR TS1110: Type expected.
 2 │ return a ? <i32>(c) : (a ? b : c);
   │                           ^
ERROR TS1005: ')' expected.
 2 │ return a ? <i32>(c) : (a ? b : c);
   │                          ~
ERROR TS1005: ')' expected.
 6 │ return a < (a | (a >> b));
   │                   ^

Credit: https://ucsbplse.github.io/

AssemblyScript version

v0.28.20

Playground

https://www.assemblyscript.org/editor.html#IyFvcHRpbWl6ZT1zcGVlZCZydW50aW1lPWluY3JlbWVudGFsCmV4cG9ydCBmdW5jdGlvbiB0ZXN0MShhOiBib29sLCBiOiBpMzIsIGM6IGkzMik6IGkzMiB7CiAgcmV0dXJuIGEgPyA8aTMyPihjKSA6IChhID8gYiA6IGMpOwp9CmV4cG9ydCBmdW5jdGlvbiB0ZXN0MihhOiBpMzIsIGI6IGkzMik6IGJvb2wgewogIHJldHVybiBhIDwgKGEgfCAoYSA+PiBiKSk7Cn0KIyFodG1sCg==

Click Run: the module.wat tab shows TS1110: Type expected. and two TS1005: ')' expected. errors for valid code.