Stop the arctic backend from dragging std in, and 0.1.5

.github/workflows/ci.yml

@@ -13,6 +13,7 @@ jobs:
       - uses: dtolnay/rust-toolchain@stable
         with:
           components: rustfmt, clippy
+          targets: x86_64-unknown-none
       - uses: Swatinem/rust-cache@v2
       - run: cargo fmt --all -- --check
       - run: cargo clippy --all-targets --no-default-features -- -D warnings
@@ -21,6 +22,19 @@ jobs:
       - run: cargo test --all-targets --features arctic
       - run: cargo clippy --all-targets --all-features -- -D warnings
       - run: cargo test --all-targets --all-features
+      # A crate that says `#![no_std]` and is only ever built on a host with one
+      # proves nothing. This target has no `std` to find.
+      - run: cargo build --target x86_64-unknown-none --no-default-features
+      - run: cargo build --target x86_64-unknown-none --no-default-features --features hydrate
+      # The arctic backend needs an OS for its thread-local storage, so it
+      # cannot be built for a bare target - but it must still not pull `std` in.
+      - name: The arctic backend does not enable std
+        run: |
+          graph=$(cargo tree --no-default-features --features arctic -f '{p} [{f}]')
+          echo "$graph" | grep -E 'arctic-wt|ps-reclaim'
+          if echo "$graph" | grep -E '(arctic-wt|ps-reclaim) v[^[]*\[[^]]*std'; then
+            echo "std leaked into the arctic backend"; exit 1
+          fi
 
   package:
     name: Release dry run

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "worktable-vec"
-version = "0.1.4"
+version = "0.1.5"
 edition = "2024"
 rust-version = "1.85"
 license = "MIT OR Apache-2.0"
@@ -12,12 +12,16 @@ categories = ["data-structures"]
 
 [features]
 default = []
+# On by default for nobody: this crate is `#![no_std]` and the core never needed
+# `std`. The feature exists so a backend that does need one can say so, and so a
+# bare-metal caller can prove it is not getting one.
+std = ["arctic?/std"]
 # Load and unload rows as pages. Optional because it is the only thing here
 # that needs a serializer.
 hydrate = ["dep:rkyv", "dep:embedded-io"]
 arctic = ["dep:arctic"]
-congee = ["dep:congee"]
-wti = ["dep:wti"]
+congee = ["dep:congee", "std"]
+wti = ["dep:wti", "std"]
 
 [dependencies]
 rkyv = { version = "0.8.17", default-features = false, features = ["alloc", "bytecheck"], optional = true }
@@ -26,7 +30,10 @@ rkyv = { version = "0.8.17", default-features = false, features = ["alloc", "byt
 # a caller with an OS gets real files and a caller without one plugs in whatever
 # it has. Nothing here needs `std` either way.
 embedded-io = { version = "0.7", default-features = false, features = ["alloc"], optional = true }
-arctic = { package = "arctic-wt", version = "^0.1, >=0.1.9", optional = true }
+# `default-features = false` and an explicit SMR backend, so enabling `arctic`
+# does not silently enable `std`. 0.1.11 is the first release where that is
+# possible: before it, `smr-ps-reclaim` forced `std` on.
+arctic = { package = "arctic-wt", version = "^0.1, >=0.1.11", optional = true, default-features = false, features = ["smr-ps-reclaim"] }
 congee = { package = "congee-wt", version = "^0.4, >=0.4.4", optional = true }
 wti = { package = "WorkTablesIndex", version = "^0.0, >=0.0.11", optional = true, default-features = false, features = ["concurrent"] }