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fix(lance-linalg): check fp16kernels feature before arch-specific code#5747

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wjones127 merged 3 commits intolance-format:mainfrom
open-horizon-labs:fix-ios-fp16kernels-build-v1.0.1
Jan 20, 2026
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fix(lance-linalg): check fp16kernels feature before arch-specific code#5747
wjones127 merged 3 commits intolance-format:mainfrom
open-horizon-labs:fix-ios-fp16kernels-build-v1.0.1

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@durch durch commented Jan 18, 2026

Summary

The build script was checking target architecture BEFORE verifying if the fp16kernels feature was enabled. This caused builds to fail on platforms like iOS/Android when falling through to the error branch, even when the feature was disabled.

The Problem

On line 78-79 of rust/lance-linalg/build.rs:

} else {
    return Err("Unable to build f16 kernels on given target_arch.  Please use x86_64 or aarch64 or remove the fp16kernels feature".to_string());
}

This error is returned for any target_arch not in the supported list (x86_64, aarch64 macos/linux, loongarch64), before the feature check in build_f16_with_flags() is ever called.

Additionally, cfg!(not(feature = "fp16kernels")) inside build_f16_with_flags() checks the build script's features, not the library's features (build scripts are compiled for the host, not the target).

The Fix

Add an early exit using CARGO_FEATURE_FP16KERNELS env var check (which correctly reflects the library's features, not the build script's) before the target_arch branching logic.

Testing

Verified fix enables successful iOS builds with:

  • lancedb v0.23.1
  • Tauri 2.x iOS target
  • fp16kernels feature disabled (default)

Fixes: #5746

@github-actions github-actions Bot added bug Something isn't working python java labels Jan 18, 2026
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github-actions Bot commented Jan 18, 2026

ACTION NEEDED
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@durch
fix(lance-linalg): Check fp16kernels feature before arch-specific code
a7a6397 
The build script was checking target architecture BEFORE verifying if the
fp16kernels feature was enabled. This caused builds to fail on platforms
like iOS/Android when falling through to the error branch, even when the
feature was disabled.

The fix adds an early exit using CARGO_FEATURE_FP16KERNELS env var check
(not cfg!() which checks build script features, not library features).

Fixes: lance-format#5746
@durch durch force-pushed the fix-ios-fp16kernels-build-v1.0.1 branch from 1e02163 to a7a6397 Compare January 18, 2026 20:33
@durch durch changed the title fix(lance-linalg): Check fp16kernels feature before arch-specific code fix(lance-linalg): check fp16kernels feature before arch-specific code Jan 18, 2026
wjones127
wjones127 requested changes Jan 18, 2026
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@durch Thanks for creating a PR.

I think we still want to execute build_dist_table_with_flags if fp16kernels is not enabled, but this short-circuits before that. Could you address that?

@durch
fix: move feature check to else branch per review
8647a7c 
Address review feedback: instead of early exit which skips
build_dist_table_with_flags on x86_64, only error in the else
branch when fp16kernels is explicitly requested on unsupported
platforms.

This preserves dist_table kernel builds on supported platforms
while still allowing iOS/Android builds when fp16kernels is disabled.
@durch
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durch commented Jan 18, 2026 •
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@durch Thanks for creating a PR.

I think we still want to execute build_dist_table_with_flags if fp16kernels is not enabled, but this short-circuits before that. Could you address that?

@wjones127, thanks for the speedy review, this should do it

@durch durch requested a review from wjones127 January 18, 2026 23:08
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Codecov Report

✅ All modified and coverable lines are covered by tests.

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wjones127
wjones127 approved these changes Jan 20, 2026
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This looks good. Thanks!

@wjones127 wjones127 merged commit 918324b into lance-format:main Jan 20, 2026
23 of 28 checks passed
jackye1995 pushed a commit to jackye1995/lance that referenced this pull request Jan 21, 2026
@durch @jackye1995
fix(lance-linalg): check fp16kernels feature before arch-specific code (
12892af 
lance-format#5747)

## Summary

The build script was checking target architecture BEFORE verifying if
the `fp16kernels` feature was enabled. This caused builds to fail on
platforms like iOS/Android when falling through to the error branch,
even when the feature was disabled.

## The Problem

On line 78-79 of `rust/lance-linalg/build.rs`:
```rust
} else {
    return Err("Unable to build f16 kernels on given target_arch.  Please use x86_64 or aarch64 or remove the fp16kernels feature".to_string());
}
```

This error is returned for any target_arch not in the supported list
(x86_64, aarch64 macos/linux, loongarch64), **before** the feature check
in `build_f16_with_flags()` is ever called.

Additionally, `cfg!(not(feature = "fp16kernels"))` inside
`build_f16_with_flags()` checks the **build script's** features, not the
library's features (build scripts are compiled for the host, not the
target).

## The Fix

Add an early exit using `CARGO_FEATURE_FP16KERNELS` env var check (which
correctly reflects the library's features, not the build script's)
**before** the target_arch branching logic.

## Testing

Verified fix enables successful iOS builds with:
- lancedb v0.23.1
- Tauri 2.x iOS target
- `fp16kernels` feature disabled (default)

Fixes: lance-format#5746
vivek-bharathan pushed a commit to vivek-bharathan/lance that referenced this pull request Feb 2, 2026
@durch @vivek-bharathan
fix(lance-linalg): check fp16kernels feature before arch-specific code (
4e97d38 
lance-format#5747)

## Summary

The build script was checking target architecture BEFORE verifying if
the `fp16kernels` feature was enabled. This caused builds to fail on
platforms like iOS/Android when falling through to the error branch,
even when the feature was disabled.

## The Problem

On line 78-79 of `rust/lance-linalg/build.rs`:
```rust
} else {
    return Err("Unable to build f16 kernels on given target_arch.  Please use x86_64 or aarch64 or remove the fp16kernels feature".to_string());
}
```

This error is returned for any target_arch not in the supported list
(x86_64, aarch64 macos/linux, loongarch64), **before** the feature check
in `build_f16_with_flags()` is ever called.

Additionally, `cfg!(not(feature = "fp16kernels"))` inside
`build_f16_with_flags()` checks the **build script's** features, not the
library's features (build scripts are compiled for the host, not the
target).

## The Fix

Add an early exit using `CARGO_FEATURE_FP16KERNELS` env var check (which
correctly reflects the library's features, not the build script's)
**before** the target_arch branching logic.

## Testing

Verified fix enables successful iOS builds with:
- lancedb v0.23.1
- Tauri 2.x iOS target
- `fp16kernels` feature disabled (default)

Fixes: lance-format#5746
@wjones127 wjones127 mentioned this pull request Feb 6, 2026
Closed
This was referenced Feb 9, 2026
Closed
Merged
wjones127 pushed a commit that referenced this pull request Feb 10, 2026
@chyyran
perf: build fp16kernels with NEON support on iOS (#5917)
df04df4 
This PR also adds support for `mtune=apple-a13` when building
lance-linalg for iOS, which is the earliest supported iOS architecture
at time of writing.

This is pulled out of #5866
after the initial bug was fixed in
#5747 and lancedb updated to
Lance 2.x
w4nderlust added a commit to atelico/lance that referenced this pull request Feb 25, 2026
@w4nderlust
fix(lance-linalg): add iOS support and check fp16kernels feature early
c9a056e 
Backport of lance-format#5747 to v2.0.0:
- Check fp16kernels feature before arch-specific code so builds without
  the feature succeed on any platform
- Add explicit iOS (aarch64-apple-ios) NEON support with A13 baseline
@andrea-reale andrea-reale mentioned this pull request Mar 30, 2026
Closed
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iOS build fails: fp16kernels feature check in build.rs doesn't work for unsupported targets

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@durch @wjones127