lib.customisation: add getFinalPassthruWith for unified missing finalAttrs.passthru.<attr> handling

lib/customisation.nix

@@ -3,6 +3,7 @@
 let
   inherit (builtins)
     intersectAttrs
+    unsafeGetAttrPos
     ;
   inherit (lib)
     functionArgs
@@ -33,6 +34,7 @@ let
     extends
     toFunction
     id
+    defaultTo
     ;
   inherit (lib.strings) levenshtein levenshteinAtMost;
 
@@ -303,7 +305,7 @@ rec {
       errorForArg =
         arg:
         let
-          loc = builtins.unsafeGetAttrPos arg fargs;
+          loc = unsafeGetAttrPos arg fargs;
         in
         "Function called without required argument \"${arg}\" at "
         + "${loc.file}:${toString loc.line}${prettySuggestions (getSuggestions arg)}";
@@ -863,4 +865,94 @@ rec {
         transformDrv
         ;
     };
+
+  /**
+    Get informative message string about attribute missing under `finalAttrs.passthru`
+    due to accidental overriting `passthru` when calling `<pkg>.overrideAttrs`.
+
+    # Inputs
+
+    `getFinalPassthruMissingMessage`-specific configurations
+    : `attrName`: the missing attribute name.
+    : `finalAttrs`: the final state of the [fixed-point arguments](#chap-build-helpers-finalAttrs), to get possible possition of incorrect overriding.
+    : `prefix`: Additional prefix to the message for the name of the package and/or the build helper.
+
+    # Type
+
+    ```
+    getFinalPassthruMissingMessage ::
+    {
+      attrName :: String,
+      finalAttrs :: null or { passthru :: AttrSet, ... },
+      prefix :: String,
+    }
+    -> String
+    ```
+  */
+  getFinalPassthruMissingMessage =
+    {
+      attrName,
+      finalAttrs ? null,
+      prefix ? "",
+    }:
+    let
+      pos = unsafeGetAttrPos "passthru" finalAttrs;
+    in
+    "${prefix}passthru.${attrName} missing after overrideAttrs overriding."
+    + optionalString (
+      finalAttrs != null && pos != null
+    ) " Last overridden at ${pos.file}:${toString pos.line}";
+
+  /**
+    Get attribute from finalAttrs.passthru, falling back to a custom default and an optional message.
+
+    `getFinalPassthruWith` roughly resembles
+
+    ```nix
+    finalAttrs.passthru.${attrName} or (handler "message" default)
+    ```
+
+    Where [`getFinalPassthruMissingMessage`](#function-library-lib.customisation.getFinalPassthruMissingMessage) provides the message.
+
+    # Inputs
+
+    `getFinalPassthruWith`-specific configurations
+    : `handler`: Function to take the message and the default value in case the attribute is missing. Typical values include `throw`, `lib.warn` and `null`, where `null` means silently using the default value.
+    : `prefix`: Additional prefix to the message for the name of the package and/or the build helper.
+
+    `finalAttrs`
+    : The final state of the [fixed-point arguments](#chap-build-helpers-finalAttrs).
+
+    `attrName`
+    : The attribute name to get from `finalAttrs.passthru`.
+
+    # Type
+
+    ```
+    getFinalPassthruWith ::
+    {
+      handler :: String -> a -> a,
+      prefix :: String,
+    }
+    -> { passthru :: AttrSet, ... }
+    -> String
+    -> a
+    ```
+  */
+  getFinalPassthruWith =
+    {
+      handler ? throw,
+      prefix ? "",
+    }:
+    finalAttrs: attrName:
+    if finalAttrs.passthru ? ${attrName} then
+      default: finalAttrs.passthru.${attrName}
+    else
+      (defaultTo (m: d: d) handler) (getFinalPassthruMissingMessage {
+        inherit
+          prefix
+          finalAttrs
+          attrName
+          ;
+      });
 }

lib/default.nix

@@ -401,6 +401,8 @@ let
         makeScopeWithSplicing
         makeScopeWithSplicing'
         extendMkDerivation
+        getFinalPassthruMissingMessage
+        getFinalPassthruWith
         ;
       inherit (self.derivations) lazyDerivation optionalDrvAttr warnOnInstantiate;
       inherit (self.generators) mkLuaInline;

lib/tests/misc.nix

@@ -61,6 +61,7 @@ let
     genList
     getExe
     getExe'
+    getFinalPassthruWith
     getLicenseFromSpdxIdOr
     groupBy
     groupBy'
@@ -118,6 +119,7 @@ let
     uniqueStrings
     updateManyAttrsByPath
     versions
+    warn
     xor
     ;
 
@@ -239,6 +241,49 @@ runTests {
       expected = functionArgs f;
     };
 
+  testGetFinalPassthruFallback =
+    let
+      finalAttrs = {
+        passthru = { };
+      };
+    in
+    {
+      expr = {
+        nullWithDefault = getFinalPassthruWith { handler = null; } finalAttrs "foo" "myDefaultValue";
+        throwWithDefault =
+          (builtins.tryEval (getFinalPassthruWith { handler = throw; } finalAttrs "foo" "myDefaultValue"))
+          .success;
+        throwWithoutDefault =
+          (builtins.tryEval (getFinalPassthruWith { handler = throw; } finalAttrs "foo")).success;
+      };
+      expected = {
+        nullWithDefault = "myDefaultValue";
+        throwWithDefault = false;
+        throwWithoutDefault = false;
+      };
+    };
+
+  testGetFinalPassthruSuccess =
+    let
+      finalAttrs = {
+        passthru = {
+          foo = "bar";
+        };
+      };
+    in
+    {
+      expr = {
+        nullWithDefault = getFinalPassthruWith { handler = null; } finalAttrs "foo" "myDefaultValue";
+        warnWithDefault = getFinalPassthruWith { handler = warn; } finalAttrs "foo" "myDefaultValue";
+        throwWithDefault = getFinalPassthruWith { handler = throw; } finalAttrs "foo" "myDefaultValue";
+      };
+      expected = {
+        nullWithDefault = "bar";
+        warnWithDefault = "bar";
+        throwWithDefault = "bar";
+      };
+    };
+
   # TRIVIAL
 
   testId = {

pkgs/build-support/go/module.nix

@@ -69,6 +69,12 @@ lib.extendMkDerivation {
 
       ...
     }@args:
+    let
+      getFinalPassthruOr = lib.getFinalPassthruWith {
+        prefix = "buildGoModule: ${finalAttrs.name or finalAttrs.pname}: ";
+        handler = lib.warn;
+      } finalAttrs;
+    in
     {
       inherit
         modRoot
@@ -205,15 +211,7 @@ lib.extendMkDerivation {
             outputHashAlgo = if finalAttrs.vendorHash == "" then "sha256" else null;
             # in case an overlay clears passthru by accident, don't fail evaluation
           }).overrideAttrs
-            (
-              let
-                pos = builtins.unsafeGetAttrPos "passthru" finalAttrs;
-                posString =
-                  if pos == null then "unknown" else "${pos.file}:${toString pos.line}:${toString pos.column}";
-              in
-              finalAttrs.passthru.overrideModAttrs
-                or (lib.warn "buildGoModule: ${finalAttrs.name or finalAttrs.pname}: passthru.overrideModAttrs missing after overrideAttrs. Last overridden at ${posString}." overrideModAttrs)
-            );
+            (getFinalPassthruOr "overrideModAttrs" overrideModAttrs);
 
       nativeBuildInputs = [ go ] ++ nativeBuildInputs;