cmd/compile/internal/syntax: handle parentheses around constraints consistently
Generally, the parser strips (i.e., does not record in the syntax tree)
unnecessary parentheses. Specifically, given a type parameter list of
the form
[P (C),]
it records it as
[P C]
and then no comma is required when printing. However it did only strip
one level of parentheses, and
[P ((C)),]
made it through, causing a panic when printing. Somewhat related,
the printer stripped parentheses around constraints as well.
This CL implements a more consistent behavior:
1) The parser strips all parentheses around constraints. For testing
purposes, a local flag (keep_parens) can be set to retain the
parentheses.
2) The printer code now correctly intruces a comma if parentheses
are present (e.g., when testing with keep_parens). This case does
not occur in normal operation.
3) The printer does not strip parentheses around constraints since
the parser does it already.
For #69206.
Change-Id: I974a800265625e8daf9477faa9ee4dd74dbd17ce
Reviewed-on: https://go-review.googlesource.com/c/go/+/610758
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Robert Findley <rfindley@google.com>
Auto-Submit: Robert Griesemer <gri@google.com> Reviewed-by: Robert Griesemer <gri@google.com>