Add error message when using cfg(docsrs) with RUSTFLAGS

.github/docsrs-error-1.60.txt

@@ -0,0 +1,2 @@
+`--cfg docsrs` must only be used via `RUSTDOCFLAGS`, not `RUSTFLAGS`
+aborting due to previous error

.github/docsrs-error-nightly.txt

@@ -0,0 +1 @@
+`--cfg docsrs` must only be used via `RUSTDOCFLAGS`, not `RUSTFLAGS`

.github/docsrs-error-stable.txt

@@ -0,0 +1 @@
+`--cfg docsrs` must only be used via `RUSTDOCFLAGS`, not `RUSTFLAGS`

.github/workflows/build.yaml

@@ -204,3 +204,57 @@ jobs:
           cargo update -p syn --precise 2.0.67
       - name: Build
         run: cargo build ${{ matrix.features.features }} --target ${{ matrix.target.target }}
+
+  docsrs-error:
+    name: |
+      `cfg(docsrs)` error message ${{ matrix.target.description }} ${{ matrix.rust.description }} ${{ matrix.features.description }}
+
+    runs-on: ubuntu-latest
+
+    strategy:
+      fail-fast: false
+      matrix:
+        target:
+          - { target: x86_64-unknown-linux-gnu, description: Native }
+          - { target: wasm32-unknown-unknown, description: Web }
+          - { target: wasm32v1-none, description: Wasm v1 }
+        rust:
+          - { version: "1.60", description: MSRV }
+          - { version: stable }
+          - { version: nightly }
+        # We don't check `serde` because it fails on the dependency itself already.
+        features:
+          - { features: "", no_std: false }
+          - { features: --no-default-features, no_std: true, description: (`no_std`) }
+        exclude:
+          - target: { target: x86_64-unknown-linux-gnu, description: Native }
+            rust: { version: nightly }
+          - target: { target: wasm32-unknown-unknown, description: Web }
+            rust: { version: nightly }
+          - target: { target: wasm32v1-none, description: Wasm v1 }
+            rust: { version: "1.60" }
+          - target: { target: wasm32v1-none, description: Wasm v1 }
+            rust: { version: stable }
+          - target: { target: wasm32v1-none, description: Wasm v1 }
+            features: { no_std: false }
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+      - name: Install Rust
+        run: |
+          rustup toolchain install ${{ matrix.rust.version }} --profile minimal --target ${{ matrix.target.target }}
+          rustup default ${{ matrix.rust.version }}
+      - name: Fix MSRV dependencies
+        if: matrix.rust.version == '1.60'
+        run: |
+          cargo update -p bumpalo --precise 3.14.0
+          cargo update -p serde --precise 1.0.210
+          cargo update -p syn --precise 2.0.67
+      - name: Build
+        env:
+          RUSTFLAGS: --cfg docsrs
+        run:
+          diff <(cargo build --target ${{ matrix.target.target }} ${{ matrix.features.features }}
+          --message-format json | jq -r "select(.reason == \"compiler-message\") |
+          .message.message") .github/docsrs-error-${{ matrix.rust.version }}.txt

src/lib.rs

@@ -153,7 +153,7 @@
 
 #![cfg_attr(all(target_family = "wasm", not(feature = "std")), no_std)]
 #![cfg_attr(all(test, target_family = "wasm"), no_main)]
-#![cfg_attr(docsrs, feature(doc_cfg))]
+#![cfg_attr(all(doc, docsrs), feature(doc_cfg))]
 #![cfg_attr(wasm_bindgen_unstable_test_coverage, feature(coverage_attribute))]
 #![cfg_attr(
 	all(
@@ -173,9 +173,9 @@ mod time;
 		any(target_os = "unknown", target_os = "none"),
 		feature = "std"
 	),
-	docsrs
+	all(doc, docsrs)
 ))]
-#[cfg_attr(docsrs, doc(cfg(all(Web, feature = "std"))))]
+#[cfg_attr(all(doc, docsrs), doc(cfg(all(Web, feature = "std"))))]
 pub mod web;
 
 #[cfg(not(all(target_family = "wasm", any(target_os = "unknown", target_os = "none"))))]
@@ -187,6 +187,9 @@ use tests_web as _;
 #[cfg(all(target_family = "wasm", any(target_os = "unknown", target_os = "none")))]
 pub use self::time::*;
 
+#[cfg(all(not(doc), docsrs))]
+compile_error!("`--cfg docsrs` must only be used via `RUSTDOCFLAGS`, not `RUSTFLAGS`");
+
 #[cfg(all(test, target_family = "wasm"))]
 wasm_bindgen_test::wasm_bindgen_test_configure!(run_in_browser);
 

src/time/system_time.rs

@@ -6,7 +6,7 @@
 	doc = "[`std::time::SystemTime`]: https://doc.rust-lang.org/std/time/struct.SystemTime.html"
 )]
 
-#[cfg(all(doc, not(feature = "std")))]
+#[cfg(all(all(doc, docsrs), not(feature = "std")))]
 use core::error::Error;
 use core::fmt::{self, Display, Formatter};
 use core::ops::{Add, AddAssign, Sub, SubAssign};
@@ -162,6 +162,6 @@ impl Display for SystemTimeError {
 	}
 }
 
-#[cfg(any(feature = "std", docsrs))]
-#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
+#[cfg(any(feature = "std", all(doc, docsrs)))]
+#[cfg_attr(all(doc, docsrs), doc(cfg(feature = "std")))]
 impl Error for SystemTimeError {}