Add helper `selectLatestNightlyWith`

README.md

@@ -137,6 +137,13 @@ Running `nix develop` will create a shell with the default nightly Rust toolchai
     # Same as `fromRustupToolchain` but read from a `rust-toolchain` file (legacy one-line string or in TOML).
     fromRustupToolchainFile = rust-toolchain-file-path: «derivation»;
 
+    # Select the latest nightly toolchain which have specific components or profile available.
+    # This helps nightly users in case of latest nightly may not contains all components they want.
+    #
+    # `selectLatestNightlyWith (toolchain: toolchain.default)` selects the latest nightly toolchain
+    # with all `default` components (rustc, cargo, rustfmt, ...) available.
+    selectLatestNightlyWith = selector: «derivation»;
+
     # [Experimental]
     # Custom toolchain from a specific rustc git revision.
     # This does almost the same thing as `rustup-toolchain-install-master`. (https://crates.io/crates/rustup-toolchain-install-master)
@@ -179,6 +186,9 @@ Running `nix develop` will create a shell with the default nightly Rust toolchai
 
     nightly = {
       # The latest nightly toolchain.
+      # It is preferred to use `selectLatestNightlyWith` instead of this since
+      # nightly toolchain may have components (like `rustfmt` or `rls`) missing,
+      # making `default` profile unusable.
       latest = { /* toolchain */ };
       "2020-12-31" = { /* toolchain */ };
       "2020-12-30" = { /* toolchain */ };
@@ -224,6 +234,14 @@ Some examples (assume `nixpkgs` had the overlay applied):
   }
   ```
 
+- Select the latest nightly toolchain with default components and `llvm-tools-preview` all available.
+  It may select toolchain earlier than `rust-bin.nightly.latest` due to lack of components.
+  ```nix
+  rust-bin.selectLatestNightlyWith (toolchain: toolchain.default.override {
+    extensions = [ "llvm-tools-preview" ];
+  })
+  ```
+
 - If you already have a [`rust-toolchain` file for rustup][rust-toolchain],
   you can simply use `fromRustupToolchainFile` to get the customized toolchain derivation.
 

flake.nix

@@ -164,7 +164,9 @@
           });
       };
 
-      checkDrvs = {};
+      checkDrvs = lib.optionalAttrs (lib.elem system [ "aarch64-linux" "x86_64-linux" ]) {
+        latest-nightly-default = rust-bin.selectLatestNightlyWith (toolchain: toolchain.default);
+      };
 
       failedAssertions =
         lib.filter (msg: msg != null) (

rust-overlay.nix

@@ -535,6 +535,28 @@ let
       components = builtins.attrValues components';
     };
 
+  # Select latest nightly toolchain which makes selected profile builds.
+  # Some components are missing in some nightly releases.
+  # Usage:
+  # `selectLatestNightlyWith (toolchain: toolchain.default.override { extensions = "llvm-tools-preview"; })`
+  selectLatestNightlyWith = selector:
+    let
+      inherit (builtins) attrNames removeAttrs elemAt length trace tryEval;
+      nightlyDates = attrNames (removeAttrs self.rust-bin.nightly [ "latest" ]);
+      dateLength = length nightlyDates;
+      go = idx:
+        let ret = selector (self.rust-bin.nightly.${elemAt nightlyDates idx}); in
+        if idx == 0 then
+          ret
+        else if dateLength - idx >= 256 then
+          trace "Failed to select nightly version after 100 tries" ret
+        else if ret != null && (tryEval ret.drvPath).success then
+          ret
+        else
+          go (idx - 1);
+    in
+      go (length nightlyDates - 1);
+
 in {
   # For each channel:
   #   rust-bin.stable.latest.cargo
@@ -558,6 +580,7 @@ in {
     mapAttrs (channel: mapAttrs (version: toolchainFromManifest)) super.rust-bin.manifests //
     {
       inherit fromRustupToolchain fromRustupToolchainFile;
+      inherit selectLatestNightlyWith;
       # Experimental feature.
       inherit fromRustcRev;
     };