Improve parse errors on parenthized "special" expressions

[john-h-kastner-aws]

Category

Error message improvements

Describe the feature you'd like to request

When we expect for example a string literal in cst-to-ast conversion, we require the expression is immediately a string literal without any surrounding parentheses. This is mostly fine, but leads to some confusing errors where we might claim that "attr" is not a valid attribute. We should update the error to specify that ("attr") isn't valid (but "attr" would be).

[jkastner@dev-dsk-jkastner-1a-3309db3b cedar]$ cargo -q run check-parse <<<'permit(principal, action, resource) when { principal has ("attr") };'
  × failed to parse policy set
  ╰─▶ invalid attribute name: "attr"
   ╭────
 1 │ permit(principal, action, resource) when { principal has ("attr") };
   ·                                                           ──────
   ╰────
  help: attribute names can either be identifiers or string literals

[jkastner@dev-dsk-jkastner-1a-3309db3b cedar]$ cargo -q run check-parse <<<'permit(principal, action, resource) when { principal like ("*") };'
  × failed to parse policy set
  ╰─▶ right hand side of a `like` expression must be a pattern literal, but got `"*"`
   ╭────
 1 │ permit(principal, action, resource) when { principal like ("*") };
   ·                                                            ───
   ╰────

[jkastner@dev-dsk-jkastner-1a-3309db3b cedar]$ cargo -q run check-parse <<<'permit(principal, action, resource) when { {("attr"): 1} };'
  × failed to parse policy set
  ╰─▶ invalid attribute name: "attr"
   ╭────
 1 │ permit(principal, action, resource) when { {("attr"): 1} };
   ·                                              ──────
   ╰────
  help: attribute names can either be identifiers or string literals

[jkastner@dev-dsk-jkastner-1a-3309db3b cedar]$ cargo -q run check-parse <<<'permit(principal, action, resource) when { {(principal): 1} };'
  × failed to parse policy set
  ╰─▶ invalid attribute name: principal
   ╭────
 1 │ permit(principal, action, resource) when { {(principal): 1} };
   ·                                              ─────────
   ╰────
  help: attribute names can either be identifiers or string literals

[jkastner@dev-dsk-jkastner-1a-3309db3b cedar]$ cargo -q run check-parse <<<'permit(principal, action, resource) when { principal is (User) };'
  × failed to parse policy set
  ╰─▶ invalid variable: User
   ╭────
 1 │ permit(principal, action, resource) when { principal is (User) };
   ·                                                          ────
   ╰────
  help: the valid Cedar variables are `principal`, `action`, `resource`, and `context`; did you mean to enclose `User` in quotes to make a string?

Describe alternatives you've considered

.

Additional context

No response

Is this something that you'd be interested in working on?

• 👋 I may be able to implement this feature request
• ⚠️ This feature might incur a breaking change