feat: make ndarray std support conditional

.github/workflows/ci.yml

@@ -57,6 +57,7 @@ jobs:
           - "--features serde"
           - "--features datasets"
           - "--features ndarray-bindings"
+          - "--features std,ndarray-bindings"
           - ""
     steps:
       - uses: actions/checkout@v4
@@ -72,9 +73,39 @@ jobs:
         uses: dtolnay/rust-toolchain@stable
       - name: Stable Build
         run: cargo build --no-default-features ${{ matrix.features }}
+      - name: Assert ndarray feature resolution
+        shell: bash
+        run: |
+          case "${{ matrix.features }}" in
+            "--features ndarray-bindings")
+              ci/check-ndarray-features.sh no-std --no-default-features ${{ matrix.features }}
+              ;;
+            "--features std,ndarray-bindings")
+              ci/check-ndarray-features.sh std --no-default-features ${{ matrix.features }}
+              ;;
+            "")
+              ci/check-ndarray-features.sh absent --no-default-features
+              # Default features and explicit std must not activate ndarray.
+              ci/check-ndarray-features.sh absent
+              ci/check-ndarray-features.sh absent --no-default-features --features std
+              # Default plus bindings keeps ndarray's std feature on.
+              ci/check-ndarray-features.sh std --features default,ndarray-bindings
+              ;;
+            *)
+              ci/check-ndarray-features.sh absent --no-default-features ${{ matrix.features }}
+              ;;
+          esac
       - name: Tests
-        if: matrix.features == '--features ndarray-bindings'
+        if: matrix.features == '--features ndarray-bindings' || matrix.features == '--features std,ndarray-bindings'
         run: cargo test --no-default-features ${{ matrix.features }}
+      - name: Explicit std does not activate ndarray
+        if: matrix.features == ''
+        run: cargo build --no-default-features --features std
+      - name: Default plus ndarray-bindings
+        if: matrix.features == ''
+        run: |
+          cargo build --features default,ndarray-bindings
+          cargo test --features default,ndarray-bindings
 
   msrv:
     # Verify the declared rust-version (MSRV) in Cargo.toml still builds.

CHANGELOG.md

@@ -4,6 +4,11 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [0.7.0]
+### Changed
+- `Cargo.toml`: optional `ndarray` is now `default-features = false`, and the default feature set is `std` (`ndarray?/std`). Ordinary builds still enable ndarray's standard-library support when `ndarray-bindings` is on, while `std` alone does not activate ndarray. The `std` feature only controls ndarray's standard-library support; smartcore itself is not `no_std` (#421).
+  - **Migration:** builds that use `--no-default-features --features ndarray-bindings` (or `default-features = false` with `ndarray-bindings`) no longer get ndarray's `std` feature. Add `std` to the feature list to keep the previous behavior.
+
 ## [0.6.16]
 ### Fixed
 - `predict`, `predict_proba`, `predict_oob`, `predict_matrix` and `decision_function` now return `Err(Failed)` instead of panicking when `fit` has not run (#469, #470). Models return the same unfitted error even after deserialization, when the state fields are `None`. The guarded methods cover the decision trees, the random forests, the extra-trees regressor, the KNN classifier and regressor, `SVC`, `MultiClassSVC`, `SVR`, the linear models, the naive Bayes classifiers and `XGRegressor`.

Cargo.toml

@@ -24,7 +24,7 @@ exclude = [
 [dependencies]
 approx = "0.5.1"
 cfg-if = "1.0.0"
-ndarray = { version = "0.17", optional = true }
+ndarray = { version = "0.17", optional = true, default-features = false }
 num-traits = "0.2.12"
 num = "0.4"
 rand = { version = "0.10.1", default-features = false, features = ["alloc"] }
@@ -35,9 +35,17 @@ ordered-float = "5.1.0"
 typetag = { version = "0.2", optional = true }
 
 [features]
-# No features enabled by default; keeps the build WASM-compatible
-# and avoids pulling in serde/rand unless explicitly requested.
-default = []
+# `std` stays on by default so ordinary builds keep ndarray's standard-library
+# support when `ndarray-bindings` is enabled. Weak forwarding (`ndarray?/std`)
+# does not activate the optional ndarray dependency by itself. `std` only
+# controls ndarray's standard-library support; smartcore itself is not
+# `no_std`. serde and rand stay opt-in, which keeps the default dependency set
+# WASM-compatible.
+default = ["std"]
+
+# Enable ndarray's `std` feature when ndarray is already enabled.
+# The `?` keeps `--features std` from pulling ndarray in on its own.
+std = ["ndarray?/std"]
 
 # Enable serde Serialize/Deserialize for models and related types.
 # Also enables typetag on non-wasm targets for trait object serialization.

ci/check-ndarray-features.sh

@@ -0,0 +1,30 @@
+#!/usr/bin/env bash
+# Assert how ndarray resolves for a set of cargo feature flags.
+# Usage: ci/check-ndarray-features.sh <absent|std|no-std> [cargo feature flags...]
+set -euo pipefail
+
+expect="$1"
+shift
+
+# `-i ndarray --depth 0` prints only the ndarray node, as "ndarray vX.Y.Z|feat1,feat2".
+# Dev-dependency edges are excluded so test-only crates cannot affect the result.
+if ! line="$(cargo tree -q -e normal,build -i ndarray --depth 0 --format '{p}|{f}' "$@" 2>&1)"; then
+  case "$line" in
+    *"did not match any packages"*) line="" ;;
+    *) printf '%s\n' "$line" >&2; exit 1 ;;
+  esac
+fi
+
+if [ -z "$line" ]; then
+  actual="absent"
+elif [[ ",${line#*|}," == *",std,"* ]]; then
+  actual="std"
+else
+  actual="no-std"
+fi
+
+if [ "$actual" != "$expect" ]; then
+  echo "ndarray with [$*]: expected $expect, got $actual (${line:-not in graph})" >&2
+  exit 1
+fi
+echo "ndarray with [$*]: $actual"