[llvm-dev] MemoryBuffer: Migrating to Expected/llvm::Error from ErrorOr/std::error_code

[David Blaikie via llvm-dev]

Hey folks - I'm/we're considering a somewhat laborious/disruptive
refactoring for MemoryBuffer's APIs to improve error handling safety.
Details here:  https://reviews.llvm.org/D109345

Duncan's pointed out that a reasonable migration strategy would be to:

   1. Add MemoryBufferErrorAPI (wrapping APIs with errorOrToExpected) and
   MemoryBufferErrorCodeAPI (alias for MemoryBuffer) in the same commit.
   2. Migrate in-tree callers to MemoryBufferErrorCodeAPI (via mass
   rename). (Could even move some to MemoryBufferErrorAPI?)
   3. Update MemoryBuffer to use Error/Expected APIs, change
   MemoryBufferErrorAPI to an alias of it, and leave behind
   MemoryBufferErrorCodeAPI (wrapping APIs with expectedToErrorOr).
   4. One or more commits:
      1. Migrate in-tree callers to MemoryBuffer.
      2. Delete MemoryBufferErrorAPI alias.
   5. Delete MemoryBufferErrorCodeAPI wrappers.

(this isn't the only option (some variations discussed on the code review)
- but something along these lines that separates the semantic changes from
the renaming and makes it easier for folks with stable release branches to
still cherry pick pieces of this without other pieces (eg: they can pick
any amount of 1-4 without 5, specifically they could take 1-2, do a
mass-rename on their branch of "MemoryBuffer:: ->
MemoryBufferErrorCodeAPI::" and then be pretty stable/relatively easy to
cherry pick things after that)

What do folks think of this? Any major objections (including "the churn
doesn't seem worth the benefit" - happy to discuss that further), nuanced
situations/tweaks/particular scenarios that we should make an effort to
account for?

If there aren't huge objections - I'll probably start this in the next
O(weeks).
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