API: Drop direct blas-src dependency, update docs for blas integration

We can in theory unchain ourselves from the blas-src version and let the
user be responsible for linking in blas in the final product.

Update xtest-blas to test this configuration.

Update instructions in readme for how to use it.

Cargo.toml

@@ -39,7 +39,6 @@ approx = { version = "0.4", optional = true , default-features = false }
 
 # Use via the `blas` crate feature!
 cblas-sys = { version = "0.1.4", optional = true, default-features = false }
-blas-src = { version = "0.7.0", optional = true, default-features = false }
 libc = { version = "0.2.82", optional = true }
 
 matrixmultiply = { version = "0.3.0", default-features = false}
@@ -58,7 +57,7 @@ default = ["std"]
 
 # Enable blas usage
 # See README for more instructions
-blas = ["cblas-sys", "blas-src", "libc"]
+blas = ["cblas-sys", "libc"]
 
 # Old name for the serde feature
 serde-1 = ["serde"]

README.rst

@@ -96,21 +96,34 @@ How to use with cargo
 ::
 
     [dependencies]
-    ndarray = "0.14.0"
+    ndarray = "0.15.0"
 
-How to enable blas integration. Depend on ``blas-src`` directly to pick a blas
-provider. Depend on the same ``blas-src`` version as ``ndarray`` does, for the
-selection to work.  An example configuration using system openblas is shown
-below. Note that only end-user projects (not libraries) should select
-provider::
+How to enable blas integration
+-----------------------------
 
+Blas integration is an optional add-on.
+
+Depend and link to ``blas-src`` directly to pick a blas provider. Ndarray
+presently requires a blas provider that provides the ``cblas-sys`` interface.  If
+further feature selection is needed then you might need to depend directly on
+the backend crate's source too (for example ``openblas-src``, to select
+``cblas``).  The backend version **must** be the one that ``blas-src`` also
+depends on.
+
+An example configuration using system openblas is shown below. Note that only
+end-user projects (not libraries) should select provider::
 
     [dependencies]
-    ndarray = { version = "0.14.0", features = ["blas"] }
+    ndarray = { version = "0.15.0", features = ["blas"] }
     blas-src = { version = "0.7.0", default-features = false, features = ["openblas"] }
     openblas-src = { version = "0.9", default-features = false, features = ["cblas", "system"] }
 
-For official releases of ``ndarray``, the versions are:
+When this is done, your program must also link to ``blas_src`` by using it or
+explicitly including it in your code::
+
+    extern crate blas_src;
+
+For official releases of ``ndarray``, versions that have been verified to work are:
 
 =========== ============ ================
 ``ndarray`` ``blas-src`` ``openblas-src``

src/lib.rs

@@ -124,8 +124,6 @@ extern crate std;
 #[cfg(not(feature = "std"))]
 extern crate core as std;
 
-#[cfg(feature = "blas")]
-extern crate blas_src;
 #[cfg(feature = "blas")]
 extern crate cblas_sys;
 

xtest-blas/src/lib.rs

@@ -1 +0,0 @@
-

xtest-blas/tests/oper.rs

@@ -2,6 +2,7 @@ extern crate approx;
 extern crate defmac;
 extern crate ndarray;
 extern crate num_traits;
+extern crate blas_src;
 
 use ndarray::linalg::general_mat_mul;
 use ndarray::linalg::general_mat_vec_mul;