Re-add From<f16> for f64

[beetrees]

This impl was originally added in #122470 before being removed in #123830 due to #123831. However, the issue only affects f32 (which currently only has one From<{float}> impl, From<f32>) as f64 already has two From<{float}> impls (From<f32> and From<f64>) and is also the float literal fallback type anyway. Therefore it is safe to re-add From<f16> for f64.

This PR also updates the FIXME link to point to the open issue #123831 rather than the closed issue #123824.

Tracking issue: #116909

@rustbot label +F-f16_and_f128 +T-libs-api

[rustbot]

r? @joboet

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[joboet]

r? libs-api

[BurntSushi]

I agree with the reasoning here, but I'd like to be cautious and do a crater run. Since this is an unstable API, r=me if the crater run doesn't reveal anything.

@bors try

[bors]

⌛ Trying commit 5cc4ee3 with merge 98ebbae...

[bors]

☀️ Try build successful - checks-actions
Build commit: 98ebbae (98ebbae35138252af77610c20ea5a5e8bf68d639)

[BurntSushi]

@craterbot check

[craterbot]

👌 Experiment pr-124728 created and queued.
🤖 Automatically detected try build 98ebbae
🔍 You can check out the queue and this experiment's details.

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

[tgross35]

Just FYI I removed this intentionally since it seemed inconsistent to have Into one of the existing float types but not the other. I have no significant qualms about adding it back though.

[beetrees]

I just thought it seemed inconsistent not to have it since From<f16> for f128 still exists. IMO the distinction between existing and new floating point types is ideally one that should disappear over time as the new floating point types will hopefully be eventually supported just as well as the existing ones.

[craterbot]

🚧 Experiment pr-124728 is now running

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

[craterbot]

🎉 Experiment pr-124728 is completed!
📊 1 regressed and 2 fixed (446250 total)
📰 Open the full report.

⚠️ If you notice any spurious failure please add them to the blacklist!
ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

[beetrees]

Only regression is spurious:

[INFO] [stderr]     Updating crates.io index
[INFO] [stderr] error: failed to download `assert_matches v1.5.0`
[INFO] [stderr] 
[INFO] [stderr] Caused by:
[INFO] [stderr]   unable to get packages from source
[INFO] [stderr] 
[INFO] [stderr] Caused by:
[INFO] [stderr]   attempting to make an HTTP request, but --frozen was specified

[BurntSushi]

Okey dokey. Good enough for me. @bors r+

[bors]

📌 Commit 5cc4ee3 has been approved by BurntSushi

It is now in the queue for this repository.

[bors]

⌛ Testing commit 5cc4ee3 with merge 2d89cee...

[bors]

☀️ Test successful - checks-actions
Approved by: BurntSushi
Pushing 2d89cee to master...

[rust-timer]

Finished benchmarking commit (2d89cee): 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)	-	-	0
Regressions ❌ (secondary)	2.0%	[2.0%, 2.0%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (primary 2.8%, secondary -4.3%)

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)	-4.3%	[-4.3%, -4.3%]	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: 677.731s -> 682.198s (0.66%)
Artifact size: 316.21 MiB -> 316.23 MiB (0.01%)