ci/eval: add rebuildsByPlatform to the comparison result

ci/eval/compare/default.nix

@@ -3,14 +3,66 @@
   jq,
   runCommand,
   writeText,
-  supportedSystems,
   ...
 }:
 { beforeResultDir, afterResultDir }:
 let
+  /*
+    Derivation that computes which packages are affected (added, changed or removed) between two revisions of nixpkgs.
+    Note: "platforms" are "x86_64-linux", "aarch64-darwin", ...
+
+    ---
+    Inputs:
+    - beforeResultDir, afterResultDir: The evaluation result from before and after the change.
+      They can be obtained by running `nix-build -A ci.eval.full` on both revisions.
+
+    ---
+    Outputs:
+      - changed-paths.json: Various information about the changes:
+        {
+          attrdiff: {
+            added: ["package1"],
+            changed: ["package2", "package3"],
+            removed: ["package4"],
+          },
+          labels: [
+            "10.rebuild-darwin: 1-10",
+            "10.rebuild-linux: 1-10"
+          ],
+          rebuildsByKernel: {
+            darwin: ["package1", "package2"],
+            linux: ["package1", "package2", "package3"]
+          },
+          rebuildCountByKernel: {
+            darwin: 2,
+            linux: 3,
+          },
+          rebuildsByPlatform: {
+            aarch64-darwin: ["package1", "package2"],
+            aarch64-linux: ["package1", "package2"],
+            x86_64-linux: ["package1", "package2", "package3"],
+            x86_64-darwin: ["package1"],
+          },
+        }
+      - step-summary.md: A markdown render of the changes
+
+    ---
+    Implementation details:
+
+    Helper functions can be found in ./utils.nix.
+    Two main "types" are important:
+
+    - `packagePlatformPath`: A string of the form "<PACKAGE_PATH>.<PLATFORM>"
+      Example: "python312Packages.numpy.x86_64-linux"
+
+    - `packagePlatformAttr`: An attrs representation of a packagePlatformPath:
+      Example: { name = "python312Packages.numpy"; platform = "x86_64-linux"; }
+  */
   inherit (import ./utils.nix { inherit lib; })
     diff
     groupByKernel
+    convertToPackagePlatformAttrs
+    groupByPlatform
     extractPackageNames
     getLabels
     uniqueStrings
@@ -20,21 +72,30 @@ let
   beforeAttrs = getAttrs beforeResultDir;
   afterAttrs = getAttrs afterResultDir;
 
+  # Attrs
+  # - keys: "added", "changed" and "removed"
+  # - values: lists of `packagePlatformPath`s
   diffAttrs = diff beforeAttrs afterAttrs;
 
   changed-paths =
     let
       rebuilds = uniqueStrings (diffAttrs.added ++ diffAttrs.changed);
+      rebuildsPackagePlatformAttrs = convertToPackagePlatformAttrs rebuilds;
 
-      rebuildsByKernel = groupByKernel rebuilds;
+      rebuildsByPlatform = groupByPlatform rebuildsPackagePlatformAttrs;
+      rebuildsByKernel = groupByKernel rebuildsPackagePlatformAttrs;
       rebuildCountByKernel = lib.mapAttrs (
         kernel: kernelRebuilds: lib.length kernelRebuilds
       ) rebuildsByKernel;
     in
     writeText "changed-paths.json" (
       builtins.toJSON {
-        attrdiff = lib.mapAttrs (_: v: extractPackageNames v) diffAttrs;
+        attrdiff = lib.mapAttrs (_: extractPackageNames) diffAttrs;
-        inherit rebuildsByKernel rebuildCountByKernel;
+        inherit
+          rebuildsByPlatform
+          rebuildsByKernel
+          rebuildCountByKernel
+          ;
         labels = getLabels rebuildCountByKernel;
       }
     );

ci/eval/compare/utils.nix

@@ -3,55 +3,101 @@ rec {
   # Borrowed from https://github.com/NixOS/nixpkgs/pull/355616
   uniqueStrings = list: builtins.attrNames (builtins.groupBy lib.id list);
 
-  _processSystemPath =
+  /*
-    packageSystemPath:
+    Converts a `packagePlatformPath` into a `packagePlatformAttr`
-    let
-      # python312Packages.torch.aarch64-linux -> ["python312Packages" "torch" "aarch64-linux"]
-      # splittedPath = lib.splitString "." attrName;
-      splittedPath = lib.splitString "." packageSystemPath;
 
-      # ["python312Packages" "torch" "aarch64-linux"] -> ["python312Packages" "torch"]
+    Turns
-      packagePath = lib.sublist 0 (lib.length splittedPath - 1) splittedPath;
+      "hello.aarch64-linux"
-    in
+    into
       {
-      # "python312Packages.torch"
+        name = "hello";
+        platform = "aarch64-linux";
+      }
+  */
+  convertToPackagePlatformAttr =
+    packagePlatformPath:
+    let
+      # python312Packages.numpy.aarch64-linux -> ["python312Packages" "numpy" "aarch64-linux"]
+      splittedPath = lib.splitString "." packagePlatformPath;
+
+      # ["python312Packages" "numpy" "aarch64-linux"] -> ["python312Packages" "numpy"]
+      packagePath = lib.sublist 0 (lib.length splittedPath - 1) splittedPath;
+
+      # "python312Packages.numpy"
       name = lib.concatStringsSep "." packagePath;
+    in
+    if name == "" then
+      null
+    else
+      {
+        # python312Packages.numpy
+        inherit name;
 
         # "aarch64-linux"
-      system = lib.last splittedPath;
+        platform = lib.last splittedPath;
       };
 
-  # Turns
+  /*
-  # [
+    Converts a list of `packagePlatformPath`s into a list of `packagePlatformAttr`s
-  #   "hello.aarch64-linux"
-  #   "hello.x86_64-linux"
-  #   "hello.aarch64-darwin"
-  #   "hello.x86_64-darwin"
-  #   "bye.x86_64-darwin"
-  #   "bye.aarch64-darwin"
-  # ]
-  #
-  # into
-  #
-  # [
-  #   "hello"
-  #   "bye"
-  # ]
-  extractPackageNames =
-    packageSystemPaths:
-    builtins.attrNames (
-      builtins.removeAttrs (builtins.groupBy (
-        packageSystemPath: (_processSystemPath packageSystemPath).name
-      ) packageSystemPaths) [ "" ]
-    );
 
-  # Computes a diff between two attrs
+    Turns
-  # {
+      [
-  #   added: [ <keys only in the second object> ],
+        "hello.aarch64-linux"
-  #   removed: [ <keys only in the first object> ],
+        "hello.x86_64-linux"
-  #   changed: [ <keys with different values between the two objects> ],
+        "hello.aarch64-darwin"
-  # }
+        "hello.x86_64-darwin"
-  #
+        "bye.x86_64-darwin"
+        "bye.aarch64-darwin"
+        "release-checks"  <- Will be dropped
+      ]
+    into
+      [
+        { name = "hello"; platform = "aarch64-linux"; }
+        { name = "hello"; platform = "x86_64-linux"; }
+        { name = "hello"; platform = "aarch64-darwin"; }
+        { name = "hello"; platform = "x86_64-darwin"; }
+        { name = "bye"; platform = "aarch64-darwin"; }
+        { name = "bye"; platform = "x86_64-darwin"; }
+      ]
+  */
+  convertToPackagePlatformAttrs =
+    packagePlatformPaths:
+    builtins.filter (x: x != null) (builtins.map convertToPackagePlatformAttr packagePlatformPaths);
+
+  /*
+    Converts a list of `packagePlatformPath`s directly to a list of (unique) package names
+
+    Turns
+      [
+        "hello.aarch64-linux"
+        "hello.x86_64-linux"
+        "hello.aarch64-darwin"
+        "hello.x86_64-darwin"
+        "bye.x86_64-darwin"
+        "bye.aarch64-darwin"
+      ]
+    into
+      [
+        "hello"
+        "bye"
+      ]
+  */
+  extractPackageNames =
+    packagePlatformPaths:
+    let
+      packagePlatformAttrs = convertToPackagePlatformAttrs (uniqueStrings packagePlatformPaths);
+    in
+    uniqueStrings (builtins.map (p: p.name) packagePlatformAttrs);
+
+  /*
+    Computes the key difference between two attrs
+
+    {
+      added: [ <keys only in the second object> ],
+      removed: [ <keys only in the first object> ],
+      changed: [ <keys with different values between the two objects> ],
+    }
+  */
   diff =
     let
       filterKeys = cond: attrs: lib.attrNames (lib.filterAttrs cond attrs);
@@ -69,43 +115,78 @@ rec {
       ) old;
     };
 
+  /*
+    Group a list of `packagePlatformAttr`s by platforms
+
+    Turns
+      [
+        { name = "hello"; platform = "aarch64-linux"; }
+        { name = "hello"; platform = "x86_64-linux"; }
+        { name = "hello"; platform = "aarch64-darwin"; }
+        { name = "hello"; platform = "x86_64-darwin"; }
+        { name = "bye"; platform = "aarch64-darwin"; }
+        { name = "bye"; platform = "x86_64-darwin"; }
+      ]
+    into
+      {
+        aarch64-linux = [ "hello" ];
+        x86_64-linux = [ "hello" ];
+        aarch64-darwin = [ "hello" "bye" ];
+        x86_64-darwin = [ "hello" "bye" ];
+      }
+  */
+  groupByPlatform =
+    packagePlatformAttrs:
+    let
+      packagePlatformAttrsByPlatform = builtins.groupBy (p: p.platform) packagePlatformAttrs;
+      extractPackageNames = map (p: p.name);
+    in
+    lib.mapAttrs (_: extractPackageNames) packagePlatformAttrsByPlatform;
+
   # Turns
   # [
-  #   "hello.aarch64-linux"
+  #   { name = "hello"; platform = "aarch64-linux"; }
-  #   "hello.x86_64-linux"
+  #   { name = "hello"; platform = "x86_64-linux"; }
-  #   "hello.aarch64-darwin"
+  #   { name = "hello"; platform = "aarch64-darwin"; }
-  #   "hello.x86_64-darwin"
+  #   { name = "hello"; platform = "x86_64-darwin"; }
-  #   "bye.x86_64-darwin"
+  #   { name = "bye"; platform = "aarch64-darwin"; }
-  #   "bye.aarch64-darwin"
+  #   { name = "bye"; platform = "x86_64-darwin"; }
   # ]
   #
   # into
   #
   # {
-  #   linux = [
+  #   linux = [ "hello" ];
-  #     "hello"
+  #   darwin = [ "hello" "bye" ];
-  #   ];
-  #   darwin = [
-  #     "hello"
-  #     "bye"
-  #   ];
   # }
   groupByKernel =
-    systemPaths:
+    packagePlatformAttrs:
     let
-      systemPaths' = builtins.map _processSystemPath systemPaths;
-
       filterKernel =
         kernel:
         builtins.attrNames (
-          builtins.groupBy (systemPath: systemPath.name) (
+          builtins.groupBy (p: p.name) (
-            builtins.filter (systemPath: lib.hasSuffix kernel systemPath.system) systemPaths'
+            builtins.filter (p: lib.hasSuffix kernel p.platform) packagePlatformAttrs
           )
         );
     in
     lib.genAttrs [ "linux" "darwin" ] filterKernel;
 
-  getLabels = lib.mapAttrs (
+  /*
+    Maps an attrs of `kernel - rebuild counts` mappings to a list of labels
+
+    Turns
+      {
+        linux = 56;
+        darwin = 8;
+      }
+    into
+      [
+        "10.rebuild-darwin: 1-10"
+        "10.rebuild-linux: 11-100"
+      ]
+  */
+  getLabels = lib.mapAttrsToList (
     kernel: rebuildCount:
     let
       number =