Merge remote-tracking branch 'other/master'

lib/default.nix

@@ -79,7 +79,8 @@ let
       fromHexString toHexString toBaseDigits inPureEvalMode isBool isInt pathExists
       genericClosure readFile;
     inherit (self.fixedPoints) fix fix' converge extends composeExtensions
-      composeManyExtensions makeExtensible makeExtensibleWithCustomName;
+      composeManyExtensions makeExtensible makeExtensibleWithCustomName
+      toExtension;
     inherit (self.attrsets) attrByPath hasAttrByPath setAttrByPath
       getAttrFromPath attrVals attrNames attrValues getAttrs catAttrs filterAttrs
       filterAttrsRecursive foldlAttrs foldAttrs collect nameValuePair mapAttrs

lib/fetchers.nix

@@ -1,6 +1,17 @@
 # snippets that can be shared by multiple fetchers (pkgs/build-support)
 { lib }:
-{
+let
+  commonH = hashTypes: rec {
+      hashNames = [ "hash" ] ++ hashTypes;
+      hashSet = lib.genAttrs hashNames (lib.const {});
+  };
+
+  fakeH = {
+    hash = lib.fakeHash;
+    sha256 = lib.fakeSha256;
+    sha512 = lib.fakeSha512;
+  };
+in rec {
 
   proxyImpureEnvVars = [
     # We borrow these environment variables from the caller to allow
@@ -14,4 +25,165 @@
     "NIX_SSL_CERT_FILE"
   ];
 
+  /**
+    Converts an attrset containing one of `hash`, `sha256` or `sha512`,
+    into one containing `outputHash{,Algo}` as accepted by `mkDerivation`.
+
+    An appropriate “fake hash” is substituted when the hash value is `""`,
+    as is the [convention for fetchers](#sec-pkgs-fetchers-updating-source-hashes-fakehash-method).
+
+    All other attributes in the set remain as-is.
+
+    # Example
+
+    ```nix
+    normalizeHash { } { hash = ""; foo = "bar"; }
+    =>
+    {
+      outputHash = lib.fakeHash;
+      outputHashAlgo = null;
+      foo = "bar";
+    }
+    ```
+
+    ```nix
+    normalizeHash { } { sha256 = lib.fakeSha256; }
+    =>
+    {
+      outputHash = lib.fakeSha256;
+      outputHashAlgo = "sha256";
+    }
+    ```
+
+    ```nix
+    normalizeHash { } { sha512 = lib.fakeSha512; }
+    =>
+    {
+      outputHash = lib.fakeSha512;
+      outputHashAlgo = "sha512";
+    }
+    ```
+
+    # Type
+    ```
+    normalizeHash :: { hashTypes :: List String, required :: Bool } -> AttrSet -> AttrSet
+    ```
+
+    # Arguments
+
+    hashTypes
+    : the set of attribute names accepted as hash inputs, in addition to `hash`
+
+    required
+    : whether to throw if no hash was present in the input; otherwise returns the original input, unmodified
+  */
+  normalizeHash = {
+    hashTypes ? [ "sha256" ],
+    required ? true,
+  }:
+    let
+      inherit (lib) concatMapStringsSep head tail throwIf;
+      inherit (lib.attrsets) attrsToList intersectAttrs removeAttrs optionalAttrs;
+
+      inherit (commonH hashTypes) hashNames hashSet;
+    in
+      args:
+        if args ? "outputHash" then
+          args
+        else
+          let
+            # The argument hash, as a {name, value} pair
+            h =
+              # All hashes passed in arguments (possibly 0 or >1) as a list of {name, value} pairs
+              let hashesAsNVPairs = attrsToList (intersectAttrs hashSet args); in
+              if hashesAsNVPairs == [] then
+                throwIf required "fetcher called without `hash`" null
+              else if tail hashesAsNVPairs != [] then
+                throw "fetcher called with mutually-incompatible arguments: ${concatMapStringsSep ", " (a: a.name) hashesAsNVPairs}"
+              else
+                head hashesAsNVPairs
+            ;
+          in
+            removeAttrs args hashNames // (optionalAttrs (h != null) {
+              outputHashAlgo = if h.name == "hash" then null else h.name;
+              outputHash =
+                if h.value == "" then
+                  fakeH.${h.name} or (throw "no “fake hash” defined for ${h.name}")
+                else
+                  h.value;
+            })
+  ;
+
+  /**
+    Wraps a function which accepts `outputHash{,Algo}` into one which accepts `hash` or `sha{256,512}`
+
+    # Example
+    ```nix
+    withNormalizedHash { hashTypes = [ "sha256" "sha512" ]; } (
+      { outputHash, outputHashAlgo, ... }:
+      ...
+    )
+    ```
+    is a function which accepts one of `hash`, `sha256`, or `sha512` (or the original's `outputHash` and `outputHashAlgo`).
+
+    Its `functionArgs` metadata only lists `hash` as a parameter, optional iff. `outputHash` was an optional parameter of
+    the original function.  `sha256`, `sha512`, `outputHash`, or `outputHashAlgo` are not mentioned in the `functionArgs`
+    metadata.
+
+    # Type
+    ```
+    withNormalizedHash :: { hashTypes :: List String } -> (AttrSet -> T) -> (AttrSet -> T)
+    ```
+
+    # Arguments
+
+    hashTypes
+    : the set of attribute names accepted as hash inputs, in addition to `hash`
+    : they must correspond to a valid value for `outputHashAlgo`, currently one of: `md5`, `sha1`, `sha256`, or `sha512`.
+
+    f
+    : the function to be wrapped
+
+    ::: {.note}
+    In nixpkgs, `mkDerivation` rejects MD5 `outputHash`es, and SHA-1 is being deprecated.
+
+    As such, there is no reason to add `md5` to `hashTypes`, and
+    `sha1` should only ever be included for backwards compatibility.
+    :::
+
+    # Output
+
+    `withNormalizedHash { inherit hashTypes; } f` is functionally equivalent to
+    ```nix
+    args: f (normalizeHash {
+      inherit hashTypes;
+      required = !(lib.functionArgs f).outputHash;
+    } args)
+    ```
+
+    However, `withNormalizedHash` preserves `functionArgs` metadata insofar as possible,
+    and is implemented somewhat more efficiently.
+  */
+  withNormalizedHash = {
+    hashTypes ? [ "sha256" ]
+  }: fetcher:
+    let
+      inherit (lib.attrsets) genAttrs intersectAttrs removeAttrs;
+      inherit (lib.trivial) const functionArgs setFunctionArgs;
+
+      inherit (commonH hashTypes) hashSet;
+      fArgs = functionArgs fetcher;
+
+      normalize = normalizeHash {
+        inherit hashTypes;
+        required = !fArgs.outputHash;
+      };
+    in
+    # The o.g. fetcher must *only* accept outputHash and outputHashAlgo
+    assert fArgs ? outputHash && fArgs ? outputHashAlgo;
+    assert intersectAttrs fArgs hashSet == {};
+
+    setFunctionArgs
+      (args: fetcher (normalize args))
+      (removeAttrs fArgs [ "outputHash" "outputHashAlgo" ] // { hash = fArgs.outputHash; });
 }

lib/fixed-points.nix

@@ -438,4 +438,76 @@ rec {
         ${extenderName} = f: makeExtensibleWithCustomName extenderName (extends f rattrs);
       }
     );
+
+  /**
+    Convert to an extending function (overlay).
+
+    `toExtension` is the `toFunction` for extending functions (a.k.a. extensions or overlays).
+    It converts a non-function or a single-argument function to an extending function,
+    while returning a two-argument function as-is.
+
+    That is, it takes a value of the shape `x`, `prev: x`, or `final: prev: x`,
+    and returns `final: prev: x`, assuming `x` is not a function.
+
+    This function takes care of the input to `stdenv.mkDerivation`'s
+    `overrideAttrs` function.
+    It bridges the gap between `<pkg>.overrideAttrs`
+    before and after the overlay-style support.
+
+    # Inputs
+
+    `f`
+    : The function or value to convert to an extending function.
+
+    # Type
+
+    ```
+    toExtension ::
+      b' -> Any -> Any -> b'
+    or
+    toExtension ::
+      (a -> b') -> Any -> a -> b'
+    or
+    toExtension ::
+      (a -> a -> b) -> a -> a -> b
+    where b' = ! Callable
+
+    Set a = b = b' = AttrSet & ! Callable to make toExtension return an extending function.
+    ```
+
+    # Examples
+    :::{.example}
+    ## `lib.fixedPoints.toExtension` usage example
+
+    ```nix
+    fix (final: { a = 0; c = final.a; })
+    => { a = 0; c = 0; };
+
+    fix (extends (toExtension { a = 1; b = 2; }) (final: { a = 0; c = final.a; }))
+    => { a = 1; b = 2; c = 1; };
+
+    fix (extends (toExtension (prev: { a = 1; b = prev.a; })) (final: { a = 0; c = final.a; }))
+    => { a = 1; b = 0; c = 1; };
+
+    fix (extends (toExtension (final: prev: { a = 1; b = prev.a; c = final.a + 1 })) (final: { a = 0; c = final.a; }))
+    => { a = 1; b = 0; c = 2; };
+    ```
+    :::
+  */
+  toExtension =
+    f:
+    if lib.isFunction f then
+      final: prev:
+      let
+        fPrev = f prev;
+      in
+      if lib.isFunction fPrev then
+        # f is (final: prev: { ... })
+        f final prev
+      else
+        # f is (prev: { ... })
+        fPrev
+    else
+      # f is not a function; probably { ... }
+      final: prev: f;
 }