feat: Persist the header data

Author: akirak

pkgs/emacs/data/default.nix

@@ -25,6 +25,7 @@ in
     inventories,
     flakeLockFile,
     archiveLockFile,
+    headersJsonFile,
     inputOverrides,
     elispPackagePins,
     defaultMainIsAscii,
@@ -48,6 +49,11 @@ in
       then lib.importJSON archiveLockFile
       else {};
 
+    headerData =
+      if mode == "build" && pathExists headersJsonFile
+      then toLockData (lib.importJSON headersJsonFile)
+      else {};
+
     makeInventory = import ./inventory {
       inherit lib flakeLockData archiveLockData;
     };
@@ -92,8 +98,11 @@ in
           or (throw "Inventory named ${pin} does not exist")
         );
 
+    getPackageData0 =
+      import ./package.nix {inherit lib linkFarm defaultMainIsAscii headerData;};
+
     getPackageData = revDep: ename:
-      lib.makeExtensible (import ./package.nix {inherit lib linkFarm defaultMainIsAscii;}
+      lib.makeExtensible (getPackageData0
         ename
         # It would be nice if it were possible to set the pin from inside
         # overrideInputs, but it causes infinite recursion unfortunately :(

pkgs/emacs/data/package.nix

@@ -26,6 +26,7 @@ in
     lib,
     linkFarm,
     defaultMainIsAscii,
+    headerData,
   }: ename: mkAttrs: self: let
     attrs =
       if isAttrs mkAttrs
@@ -64,17 +65,18 @@ in
     # effectively prevents you from adding elisp packages directly to the flake
     # outputs.
     headers =
-      lib.parseElispHeaders
-      (
-        # Add support for an option to remove IFD.
-        if self.mainIsAscii or defaultMainIsAscii
-        then builtins.readFile (self.src + "/${self.mainFile}")
-        else
-          (lib.readFirstBytes
-            # magit.el has a relatively long header, so other libraries would be shorter.
-            1500
-            (self.src + "/${self.mainFile}"))
-      );
+      headerData.${ename}
+      or (lib.parseElispHeaders
+        (
+          # Add support for an option to remove IFD.
+          if self.mainIsAscii or defaultMainIsAscii
+          then builtins.readFile (self.src + "/${self.mainFile}")
+          else
+            (lib.readFirstBytes
+              # magit.el has a relatively long header, so other libraries would be shorter.
+              1500
+              (self.src + "/${self.mainFile}"))
+        ));
   in
     lib.getAttrs
     (filter (name: hasAttr name attrs) [

pkgs/emacs/default.nix

@@ -70,6 +70,8 @@ in
 
     archiveLockFile = lockDir + "/archive.lock";
 
+    headersJsonFile = lockDir + "/headers.json";
+
     userConfig = lib.pipe self.initFiles [
       (map initReader)
       lib.zipAttrs
@@ -104,6 +106,7 @@ in
         lib
         flakeLockFile
         archiveLockFile
+        headersJsonFile
         builtinLibraries
         inputOverrides
         defaultMainIsAscii
@@ -234,6 +237,7 @@ in
           excludeLocalPackages (enumerateConcretePackageSet "update" explicitPackages);
         flakeNix = true;
         archiveLock = true;
+        headersJson = true;
       })
       .writerScript {inherit postCommandOnGeneratingLockDir;};
 
@@ -248,6 +252,7 @@ in
               excludeLocalPackages (enumerateConcretePackageSet "lock" explicitPackages);
             flakeNix = true;
             archiveLock = true;
+            headersJson = true;
             postCommand = "nix flake lock";
           })
         .asAppWritingToRelativeDir
@@ -260,6 +265,7 @@ in
             packageInputs =
               excludeLocalPackages (enumerateConcretePackageSet "update" explicitPackages);
             archiveLock = true;
+            headersJson = true;
           })
         .asAppWritingToRelativeDir
         lockDirName;

pkgs/emacs/lock/default.nix

@@ -13,6 +13,7 @@
   packageInputs,
   flakeNix ? false,
   archiveLock ? false,
+  headersJson ? false,
   # Command run after writing the directory in asAppWritingToRelativeDir
   postCommand ? null,
 }:
@@ -30,6 +31,8 @@ assert (flakeNix || archiveLock); let
       ]))
   ];
 
+  headerData = mapAttrs (_: {headers, ...}: headers) packageInputs;
+
   data = {
     flakeNix = lib.toNix {
       description = "THIS IS AN AUTO-GENERATED FILE. PLEASE DON'T EDIT IT MANUALLY.";
@@ -40,11 +43,13 @@ assert (flakeNix || archiveLock); let
       outputs = {...}: {};
     };
     archiveLock = toJSON archiveLockData;
+    headersJson = toJSON headerData;
   };
 
   passAsFile =
     lib.optional flakeNix "flakeNix"
-    ++ lib.optional archiveLock "archiveLock";
+    ++ lib.optional archiveLock "archiveLock"
+    ++ lib.optional headersJson "headersJson";
 
   # HACK: Use sed to convert JSON to Nix
   #
@@ -60,6 +65,10 @@ assert (flakeNix || archiveLock); let
     ${jq}/bin/jq . "$archiveLockPath" > "$out/archive.lock"
   '';
 
+  generateHeadersJson = ''
+    ${jq}/bin/jq . "$headersJsonPath" > "$out/headers.json"
+  '';
+
   src =
     runCommandLocal "emacs-twist-lock" ({
         inherit passAsFile;
@@ -70,6 +79,7 @@ assert (flakeNix || archiveLock); let
 
       ${lib.optionalString flakeNix generateFlakeNix}
       ${lib.optionalString archiveLock generateArchiveLock}
+      ${lib.optionalString headersJson generateHeadersJson}
     '';
 in {
   asAppWritingToRelativeDir = outDir: {