Avoid specialization in the metadata serialization code

[bjorn3]

With the exception of a perf-only specialization for byte slices and byte vectors.

This uses the same trick of introducing a new trait and having the Encodable and Decodable derives add a bound to it as used for TyEncoder/TyDecoder. The new code is clearer about which encoder/decoder uses which impl and it reduces the dependency of rustc on specialization, making it easier to remove support for specialization entirely or turn it into a construct that is only allowed for perf optimizations if we decide to do this.

[rustbot]

r? @wesleywiser

(rustbot has picked a reviewer for you, use r? to override)

[rustbot]

These commits modify the Cargo.lock file. Unintentional changes to Cargo.lock can be introduced when switching branches and rebasing PRs.

If this was unintentional then you should revert the changes before this PR is merged.
Otherwise, you can ignore this comment.

[bjorn3]

@bors try @rust-timer queue

[bors]

⌛ Trying commit 47936b4 with merge 2230d93...

[bjorn3]

@rust-timer check 2230d93

[bjorn3]

@rust-timer build 2230d93

[Noratrieb]

very cool. I'm wondering whether it makes sense to have the extra Span{En,De}coder traits or whether it may make more sense to just merge rustc_serialize and rustc_span and unify it into a single {En,De}coder trait...

[rust-timer]

Finished benchmarking commit (2230d93): comparison URL.

Overall result: no relevant changes - no action needed

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. While you can manually mark this PR as fit for rollup, we strongly recommend not doing so since this PR may lead to changes in compiler perf.

@bors rollup=never
@rustbot label: -S-waiting-on-perf -perf-regression

Instruction count

This benchmark run did not return any relevant results for this metric.

Max RSS (memory usage)

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	2.8%	[2.8%, 2.8%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-4.1%	[-4.1%, -4.1%]	1
All ❌✅ (primary)	2.8%	[2.8%, 2.8%]	1

Cycles

This benchmark run did not return any relevant results for this metric.

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 666.95s -> 666.518s (-0.06%)
Artifact size: 311.74 MiB -> 311.74 MiB (-0.00%)

[bjorn3]

@Nilstrieb I've considered that, but assumed it would be more controversial.

[Noratrieb]

Let's keep it like this for now, we can always change it later.

[wesleywiser]

@bors r+

[bors]

📌 Commit 8fb8e6e has been approved by wesleywiser

It is now in the queue for this repository.

[bors]

🌲 The tree is currently closed for pull requests below priority 100. This pull request will be tested once the tree is reopened.

[bors]

⌛ Testing commit 8fb8e6e with merge e21f4cd...

[bors]

☀️ Test successful - checks-actions
Approved by: wesleywiser
Pushing e21f4cd to master...

[rust-timer]

Finished benchmarking commit (e21f4cd): comparison URL.

Overall result: ❌ regressions - no action needed

@rustbot label: -perf-regression

Instruction count

This is a highly reliable metric that was used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	3.8%	[3.8%, 3.8%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	3.8%	[3.8%, 3.8%]	1

Max RSS (memory usage)

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	3.8%	[3.7%, 3.9%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-6.5%	[-10.0%, -3.1%]	2
All ❌✅ (primary)	-	-	0

Cycles

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	3.5%	[3.5%, 3.5%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	3.5%	[3.5%, 3.5%]	1

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 665.332s -> 666.487s (0.17%)
Artifact size: 308.58 MiB -> 308.53 MiB (-0.02%)