Introducing CArrayToPtrAssignment gadget and implementing fixits for some cases
of array being assigned to pointer.
Key observations:
- const size array can be assigned to std::span and bounds are propagated
- const size array can't be on LHS of assignment
This means array to pointer assignment has no strategy implications.
Fixits are implemented for cases where one of the variables in the assignment is
safe. For assignment of a safe array to unsafe pointer we know that the RHS will
never be transformed since it's safe and can immediately emit the optimal fixit.
Similarly for assignment of unsafe array to safe pointer.
(Obviously this is not and can't be future-proof in regards to what
variables we consider unsafe and that is fine.)
Fixits for assignment from unsafe array to unsafe pointer (from Array to Span
strategy) are not implemented in this patch as that needs to be properly designed
first - we might possibly implement optimal fixits for partially transformed
cases, put both variables in a single fixit group or do something else.
Array subscript on a const size array is not bounds-checked. The idiomatic
replacement is std::array which is bounds-safe in hardened mode of libc++.
This commit extends the fixit-producing machine to consider std::array as a
transformation target type and teaches it to handle the array subscript on const
size arrays with a trivial (empty) fixit.
Debug notes for unclaimed DeclRefExpr should report any DRE of an unsafe
variable that is not covered by a Fixable (i. e. fixit for the
particular AST pattern isn't implemented for whatever reason). Currently
not all unclaimed DeclRefExpr-s are reported which is a bug. The debug
notes report only those DREs where the referred VarDecl has at least one
other DeclRefExpr which is claimed (covered by a fixit). If there is an
unsafe VarDecl that has exactly one DRE and the DRE isn't claimed then
the debug note about missing fixit won't be emitted. That is because the
debug note is emitted from within a loop over set of successfully
matched FixableGadgets which by-definition is missing those DRE that are
not matched at all.
The new code simply iterates over all unsafe VarDecls and all of their
unclaimed DREs.
