cmd/compile/internal/types2: systematic detection of missing instantiation
When type-checking expressions, detection of uninstantiated generic
functions and types was somewhat ad-hoc.
Add an extra parameter "allowGenerics" to rawExpr. If not set, the
result operand cannot be generic.
The only place where rawExpr is called with allowGenerics != false
is from exprOrType, which passes an allowGenerics parameter through.
The only place where exprOrType is called with allowGenerics == true
is when handling index expressions and calls. Make sure that we only
accept generic operands where expected, and check the other branches.
As a result, a recently added varType call (CL 345970) can be removed
again.
This also fixes a bug where an error for a conversion to generic
type was reported after the conversion (i.e., with the converted
value, rather than the generic type). Added a test case for that.
For #48048.
Change-Id: I8576326f5fcfb58d78b3ce8572068aa32e66c568
Reviewed-on: https://go-review.googlesource.com/c/go/+/346471
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org> Reviewed-by: Robert Findley <rfindley@google.com>