buildRustCrate: remove one of the odd library filename cases

It used to be the case (ref missing) that cargo did treat
`src/$libName.rs` as an alternative to `src/lib.rs` when the latter
wasn't present. Recently I failed to reproduce that with vanilla cargo
and it started to cause pain with some crates of the form:

some_crate/
 `- src
   `- main.rs
   `- some_crate.rs

We would build `src/some_crate.rs` and thing it is a library while that
might not be the actual case. This crate is a valid `bin` crate not a
`lib` crate as far as I can tell from the samples I took.

I removed support for the previously required heuristic and commented
out the test cases in case we will need them again. We could crawl in
the Git history but chances are that the next person looking into this
doesn't know about the history.

2 files changed, 11 insertions, 10 deletions

diff --git a/pkgs/build-support/rust/build-rust-crate/build-crate.nix b/pkgs/build-support/rust/build-rust-crate/build-crate.nix
index 4e2e2af1aa7..dec49d24f52 100644
--- a/pkgs/build-support/rust/build-rust-crate/build-crate.nix
+++ b/pkgs/build-support/rust/build-rust-crate/build-crate.nix
@@ -55,9 +55,6 @@
     elif [[ -e src/lib.rs ]]; then
        build_lib src/lib.rs
        ${lib.optionalString buildTests "build_lib_test src/lib.rs"}
-    elif [[ -e "src/$LIB_NAME.rs" ]]; then
-       build_lib src/$LIB_NAME.rs
-       ${lib.optionalString buildTests ''build_lib_test "src/$LIB_NAME.rs"''}
     fi
 
 
diff --git a/pkgs/build-support/rust/build-rust-crate/test/default.nix b/pkgs/build-support/rust/build-rust-crate/test/default.nix
index f0f1ed4d1eb..aa20bd03b18 100644
--- a/pkgs/build-support/rust/build-rust-crate/test/default.nix
+++ b/pkgs/build-support/rust/build-rust-crate/test/default.nix
@@ -92,7 +92,17 @@ let
     cases = {
       libPath =  { libPath = "src/my_lib.rs"; src = mkLib "src/my_lib.rs"; };
       srcLib =  { src = mkLib "src/lib.rs"; };
-      customLibName =  { libName = "test_lib"; src = mkLib "src/test_lib.rs"; };
+
+      # This used to be supported by cargo but as of 1.40.0 I can't make it work like that with just cargo anymore.
+      # This might be a regression or deprecated thing they finally removed…
+      # customLibName =  { libName = "test_lib"; src = mkLib "src/test_lib.rs"; };
+      # rustLibTestsCustomLibName = {
+      #   libName = "test_lib";
+      #   src = mkTestFile "src/test_lib.rs" "foo";
+      #   buildTests = true;
+      #   expectedTestOutputs = [ "test foo ... ok" ];
+      # };
+
       customLibNameAndLibPath =  { libName = "test_lib"; libPath = "src/best-lib.rs"; src = mkLib "src/best-lib.rs"; };
       crateBinWithPath =  { crateBin = [{ name = "test_binary1"; path = "src/foobar.rs"; }]; src = mkBin "src/foobar.rs"; };
       crateBinNoPath1 =  { crateBin = [{ name = "my-binary2"; }]; src = mkBin "src/my_binary2.rs"; };
@@ -122,12 +132,6 @@ let
         buildTests = true;
         expectedTestOutputs = [ "test baz ... ok" ];
       };
-      rustLibTestsCustomLibName = {
-        libName = "test_lib";
-        src = mkTestFile "src/test_lib.rs" "foo";
-        buildTests = true;
-        expectedTestOutputs = [ "test foo ... ok" ];
-      };
       rustLibTestsCustomLibPath = {
         libPath = "src/test_path.rs";
         src = mkTestFile "src/test_path.rs" "bar";