[naga] Support textureSampleBaseClampToEdge() for texture2d

[jamienicol]

Adds a new flag to the IR indicating when image sample coordinates are to be clamped. Adds wgsl-in support for parsing and lowering to IR. Validation ensures this flag is only used when sampling a 2D non-arrayed sampled texture, without offset, gather, or depth comparison. This matches the WGSL requirements, with the exception of supporting texture_external textures, which will follow in a later patch.

SPIRV, HLSL, and Metal backends are supported so far, with GLSL left for a follow up. (In GLSL the texture will simply be sampled without the coordinates being clamped.)

It may seem unfortunate to have to handle this separately for each backend, and indeed it would have been possible to implement this simply in the WGSL frontend. However, future patches will add support for using textureSampleBaseClampToEdge() with external textures, which will actually have to be handled by each backend. This patch is laying the groundwork for that.

Connections
Part of #4386
Fixes #7539
Depends on #7804 (for texturesample CTS tests to pass on Mac)

Testing
Added snapshot test

Makes these CTS tests pass

Squash or Rebase?

Rebase

Checklist

• Run cargo fmt.
• Run taplo format.
• Run cargo clippy --tests. If applicable, add:
  • --target wasm32-unknown-unknown
• Run cargo xtask test to run tests.
• If this contains user-facing changes, add a CHANGELOG.md entry.

[jimblandy]

@jamienicol This is a bit dumb, but does b71a0e2 look okay to you? The MSL backend has no obligations here, since it's a validation error, but I just felt it would be nicer for the MSL backend to die instead of quietly misbehaving.

[jamienicol]

@jimblandy I don't mind it at all. I wouldn't want to go hugely out of the way to repeat validation in the backends, but that is simple enough.

Personally I'd prefer an assertion to returning an error: if we hit that case there's a bug somewhere and I'd rather we know about it via crash reports than users just suffering in silence. But I might be in the minority of preferring crashes to errors.

[jamienicol]

Any reason to limit that to MSL rather than doing it for all backends? or was that just as an example?

[ErichDonGubler]

Looks like @jimblandy is ramping up on review now, so I won't drive a full review myself, but I'll comment on some things I noticed before I left on vacation and now.

[jimblandy]

Any reason to limit that to MSL rather than doing it for all backends? or was that just as an example?

It'd make sense for all backends.

[jimblandy]

Thoughts so far:

[jamienicol]

@jamienicol This is a bit dumb, but does b71a0e2 look okay to you? The MSL backend has no obligations here, since it's a validation error, but I just felt it would be nicer for the MSL backend to die instead of quietly misbehaving.

Did the same thing for HLSL in 2fb382c. Slightly different approach for SPIRV as the implementation is different. In theory it should be able to handle other sample flags, except for the level which must be zero. So I've added a check for that alone - I don't think the backends should be in the business of repeating validation in its entirety - rather they should make a reasonable effort to ensure their own constraints are satisfied.

[jimblandy]

I don't think the backends should be in the business of repeating validation in its entirety - rather they should make a reasonable effort to ensure their own constraints are satisfied.

Yes, 100%. Backends are allowed to panic and misbehave when validation is buggy. My wanting to tighten up these matches was just opportunistic: it seemed like a small change might save someone some debugging time in he future.

[crowlKats]

Deno part LGTM

[jimblandy]

Looks good to me.

[jimblandy]

Oops, this needs #7804. Sorry for pushing my rebase prematurely.