From 7d9af348db3f118f6c5136630fe89481fac8325f Mon Sep 17 00:00:00 2001
From: Matt Van Horn <455140+mvanhorn@users.noreply.github.com>
Date: Fri, 2 Oct 2026 02:19:39 -0700
Subject: [PATCH 1/3] feat: make ndarray std support conditional

ndarray is now optional with default-features = false. A new std feature
is part of default and forwards ndarray?/std, so a normal build that
also enables ndarray-bindings still compiles ndarray with std, while std
alone does not activate ndarray. CI checks the resolved graph: no std
token for --no-default-features --features ndarray-bindings, std present
for std,ndarray-bindings and default,ndarray-bindings, and ndarray
absent for std alone and for the other feature rows. Tests cover both
ndarray-bindings configurations, and the changelog notes that disabling
std only controls ndarray's standard-library support and does not yet
make the rest of smartcore usable without std.

Fixes #421
---
 .github/workflows/ci.yml | 94 +++++++++++++++++++++++++++++++++++++++-
 CHANGELOG.md             |  1 +
 Cargo.toml               | 16 +++++--
 3 files changed, 106 insertions(+), 5 deletions(-)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 7715aed7..db4a0270 100644
--- a/.github/workflows/ci.yml
+++ b/.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 +73,100 @@ 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: |
+          set -euo pipefail
+
+          # `cargo tree --edges normal,build` omits dev-dependency edges.
+          # `{p} {f}` is "name version feat1,feat2". Match the ndarray package
+          # name exactly and compare the comma-separated feature tokens to
+          # "std" so a substring on another package cannot pass.
+          assert_ndarray() {
+            local expect="$1"
+            shift
+            local tree line features has_std token found
+            # Assign separately so `local` cannot mask a failing `cargo tree`.
+            tree="$(cargo tree --edges normal,build --prefix none --format '{p} {f}' "$@")"
+            found=0
+            while IFS= read -r line; do
+              [ -z "$line" ] && continue
+              # Cargo appends " (*)" on repeated packages; it is not a feature.
+              line="${line% (*)}"
+              case "$line" in
+                ndarray[[:space:]]*) ;;
+                *) continue ;;
+              esac
+              found=1
+              # Drop the package name and version; the rest is `{f}`.
+              features="$(printf '%s\n' "$line" | awk '{ $1=""; $2=""; sub(/^[[:space:]]+/, ""); print }')"
+              has_std=0
+              if [ -n "$features" ]; then
+                IFS=',' read -ra tokens <<< "$features"
+                for token in "${tokens[@]}"; do
+                  token="${token#"${token%%[![:space:]]*}"}"
+                  token="${token%"${token##*[![:space:]]}"}"
+                  if [ "$token" = "std" ]; then
+                    has_std=1
+                  fi
+                done
+              fi
+              if [ "$expect" = "absent" ]; then
+                echo "ndarray unexpectedly present in the normal/build graph: $line" >&2
+                exit 1
+              fi
+              if [ "$expect" = "std" ] && [ "$has_std" -ne 1 ]; then
+                echo "ndarray is missing the std feature token: $line" >&2
+                exit 1
+              fi
+              if [ "$expect" = "no-std" ] && [ "$has_std" -ne 0 ]; then
+                echo "ndarray unexpectedly enables std: $line" >&2
+                exit 1
+              fi
+              echo "ndarray feature check passed ($expect): $line"
+            done <<< "$tree"
+            if [ "$found" -eq 0 ]; then
+              if [ "$expect" = "absent" ]; then
+                echo "ndarray is absent from the normal/build graph"
+                return 0
+              fi
+              echo "expected ndarray package line is missing" >&2
+              printf '%s\n' "$tree" >&2
+              exit 1
+            fi
+          }
+
+          case "${{ matrix.features }}" in
+            "--features ndarray-bindings")
+              assert_ndarray no-std --no-default-features ${{ matrix.features }}
+              ;;
+            "--features std,ndarray-bindings")
+              assert_ndarray std --no-default-features ${{ matrix.features }}
+              ;;
+            "")
+              assert_ndarray absent --no-default-features
+              # Default features and explicit std must not activate ndarray.
+              # This catches strong `ndarray/std` forwarding.
+              assert_ndarray absent
+              assert_ndarray absent --no-default-features --features std
+              # Default plus bindings keeps ndarray's std feature on.
+              assert_ndarray std --features default,ndarray-bindings
+              ;;
+            *)
+              assert_ndarray 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.
diff --git a/CHANGELOG.md b/CHANGELOG.md
index c250a5db..7e330a35 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - `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`.
 
 ### 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. Disabling `std` controls ndarray's std support at this stage; it does not yet make all of smartcore usable on a bare-metal target (#421).
 - The error text for an unfitted `MultiClassSVC::predict` changed from "MultiClassSVC is not fitted" to the common "'fit' should be called before calling 'predict'". Code that matched the old string must be updated.
 
 ## [0.6.15]
diff --git a/Cargo.toml b/Cargo.toml
index 4ec3a4b5..ffa01965 100644
--- a/Cargo.toml
+++ b/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. Disabling `std`
+# controls ndarray's std support at this stage; it does not yet make all of
+# smartcore usable on a bare-metal target. 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.

From 6848000815ba7ca3364e71f4aac89a448a132762 Mon Sep 17 00:00:00 2001
From: Matt Van Horn <455140+mvanhorn@users.noreply.github.com>
Date: Fri, 2 Oct 2026 17:26:59 -0700
Subject: [PATCH 2/3] ci: check ndarray features with a script and note the
 migration

Move the ndarray feature assertion out of ci.yml into
ci/check-ndarray-features.sh, which reads the resolved feature list from
`cargo tree -i ndarray --depth 0` instead of parsing the whole tree.

Add a CHANGELOG migration note for `--no-default-features --features
ndarray-bindings` builds, and drop the bare-metal wording: the `std`
feature only controls ndarray's std support.
---
 .github/workflows/ci.yml     | 75 ++++--------------------------------
 CHANGELOG.md                 |  3 +-
 Cargo.toml                   |  8 ++--
 ci/check-ndarray-features.sh | 30 +++++++++++++++
 4 files changed, 43 insertions(+), 73 deletions(-)
 create mode 100755 ci/check-ndarray-features.sh

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index db4a0270..71bbc182 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -76,84 +76,23 @@ jobs:
       - name: Assert ndarray feature resolution
         shell: bash
         run: |
-          set -euo pipefail
-
-          # `cargo tree --edges normal,build` omits dev-dependency edges.
-          # `{p} {f}` is "name version feat1,feat2". Match the ndarray package
-          # name exactly and compare the comma-separated feature tokens to
-          # "std" so a substring on another package cannot pass.
-          assert_ndarray() {
-            local expect="$1"
-            shift
-            local tree line features has_std token found
-            # Assign separately so `local` cannot mask a failing `cargo tree`.
-            tree="$(cargo tree --edges normal,build --prefix none --format '{p} {f}' "$@")"
-            found=0
-            while IFS= read -r line; do
-              [ -z "$line" ] && continue
-              # Cargo appends " (*)" on repeated packages; it is not a feature.
-              line="${line% (*)}"
-              case "$line" in
-                ndarray[[:space:]]*) ;;
-                *) continue ;;
-              esac
-              found=1
-              # Drop the package name and version; the rest is `{f}`.
-              features="$(printf '%s\n' "$line" | awk '{ $1=""; $2=""; sub(/^[[:space:]]+/, ""); print }')"
-              has_std=0
-              if [ -n "$features" ]; then
-                IFS=',' read -ra tokens <<< "$features"
-                for token in "${tokens[@]}"; do
-                  token="${token#"${token%%[![:space:]]*}"}"
-                  token="${token%"${token##*[![:space:]]}"}"
-                  if [ "$token" = "std" ]; then
-                    has_std=1
-                  fi
-                done
-              fi
-              if [ "$expect" = "absent" ]; then
-                echo "ndarray unexpectedly present in the normal/build graph: $line" >&2
-                exit 1
-              fi
-              if [ "$expect" = "std" ] && [ "$has_std" -ne 1 ]; then
-                echo "ndarray is missing the std feature token: $line" >&2
-                exit 1
-              fi
-              if [ "$expect" = "no-std" ] && [ "$has_std" -ne 0 ]; then
-                echo "ndarray unexpectedly enables std: $line" >&2
-                exit 1
-              fi
-              echo "ndarray feature check passed ($expect): $line"
-            done <<< "$tree"
-            if [ "$found" -eq 0 ]; then
-              if [ "$expect" = "absent" ]; then
-                echo "ndarray is absent from the normal/build graph"
-                return 0
-              fi
-              echo "expected ndarray package line is missing" >&2
-              printf '%s\n' "$tree" >&2
-              exit 1
-            fi
-          }
-
           case "${{ matrix.features }}" in
             "--features ndarray-bindings")
-              assert_ndarray no-std --no-default-features ${{ matrix.features }}
+              ci/check-ndarray-features.sh no-std --no-default-features ${{ matrix.features }}
               ;;
             "--features std,ndarray-bindings")
-              assert_ndarray std --no-default-features ${{ matrix.features }}
+              ci/check-ndarray-features.sh std --no-default-features ${{ matrix.features }}
               ;;
             "")
-              assert_ndarray absent --no-default-features
+              ci/check-ndarray-features.sh absent --no-default-features
               # Default features and explicit std must not activate ndarray.
-              # This catches strong `ndarray/std` forwarding.
-              assert_ndarray absent
-              assert_ndarray absent --no-default-features --features std
+              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.
-              assert_ndarray std --features default,ndarray-bindings
+              ci/check-ndarray-features.sh std --features default,ndarray-bindings
               ;;
             *)
-              assert_ndarray absent --no-default-features ${{ matrix.features }}
+              ci/check-ndarray-features.sh absent --no-default-features ${{ matrix.features }}
               ;;
           esac
       - name: Tests
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7e330a35..4334b8ff 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,7 +9,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - `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`.
 
 ### 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. Disabling `std` controls ndarray's std support at this stage; it does not yet make all of smartcore usable on a bare-metal target (#421).
+- `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.
 - The error text for an unfitted `MultiClassSVC::predict` changed from "MultiClassSVC is not fitted" to the common "'fit' should be called before calling 'predict'". Code that matched the old string must be updated.
 
 ## [0.6.15]
diff --git a/Cargo.toml b/Cargo.toml
index ffa01965..b94a1a0e 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -37,10 +37,10 @@ typetag = { version = "0.2", optional = true }
 [features]
 # `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. Disabling `std`
-# controls ndarray's std support at this stage; it does not yet make all of
-# smartcore usable on a bare-metal target. serde and rand stay opt-in, which
-# keeps the default dependency set WASM-compatible.
+# 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.
diff --git a/ci/check-ndarray-features.sh b/ci/check-ndarray-features.sh
new file mode 100755
index 00000000..0737f671
--- /dev/null
+++ b/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"

From f3a41960133b5ecd977ec7eabfa795bc60dd565f Mon Sep 17 00:00:00 2001
From: Matt Van Horn <455140+mvanhorn@users.noreply.github.com>
Date: Sat, 3 Oct 2026 16:02:00 -0700
Subject: [PATCH 3/3] docs: list the ndarray std change under 0.7.0

The change is breaking for builds that use default-features = false
with ndarray-bindings, so it belongs with the next minor release rather
than the 0.6.16 entries.
---
 CHANGELOG.md | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 4334b8ff..7d0dfa47 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,13 +4,16 @@ 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`.
 
 ### 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.
 - The error text for an unfitted `MultiClassSVC::predict` changed from "MultiClassSVC is not fitted" to the common "'fit' should be called before calling 'predict'". Code that matched the old string must be updated.
 
 ## [0.6.15]