simplify git shortcut + add versionField

src/fetchers/default.nix

@@ -35,6 +35,19 @@ rec {
   fetchViaShortcut = shortcut:
     let
 
+      checkArgs = fetcherName: args:
+        let
+          fetcher = fetchers."${fetcherName}";
+          unknownArgNames = lib.filter (argName: ! lib.elem argName fetcher.inputs) (lib.attrNames args);
+          missingArgNames = lib.filter (inputName: ! args ? "${inputName}") fetcher.inputs;
+        in
+          if lib.length unknownArgNames > 0 then
+            throw "Received unknown arguments for fetcher '${fetcherName}': ${b.toString unknownArgNames}"
+          else if lib.length missingArgNames > 0 then
+            throw "Missing arguments for fetcher '${fetcherName}': ${b.toString missingArgNames}"
+          else
+            args;
+
       fetchViaHttpUrl = 
         let
           fetcher = fetchers.fetchurl;
@@ -60,7 +73,7 @@ rec {
           ));
           fetcher = fetchers.git;
           args = params // { inherit url; };
-          fetcherOutputs = fetcher.outputs args;
+          fetcherOutputs = fetcher.outputs (checkArgs "git" args);
         in
           rec {
             hash = fetcherOutputs.calcHash "sha256";

src/fetchers/git/default.nix

@@ -17,16 +17,28 @@ in
     "rev"
   ];
 
-  outputs = { url, ref ? null, rev ? null, ... }@inp: 
-    if ref == null && rev == null then
-      throw "At least 'rev' or 'ref' must be specified for fetcher 'git'"
-    else if rev != null && ! (builtins.match "[a-f0-9]*" rev) then
-      throw "Argument 'rev' for fetcher git must be a sha1 hash. Try using 'ref' instead"
-    else if ref != null && b.match "refs/(heads|tags)/.*" ref == null then
-      throw ''ref must be of format "refs/heads/branch-name" or "refs/tags/tag-name"''
+  versionField = "rev";
+
+  outputs = { url, rev }@inp:
+    if b.match "refs/(heads|tags)/.*" rev == null && builtins.match "[a-f0-9]*" rev == null then
+      throw ''rev must either be a sha1 hash or "refs/heads/branch-name" or "refs/tags/tag-name"''
     else
     let
+
       b = builtins;
+
+      ref =
+        if b.match "refs/(heads|tags)/.*" inp.rev != null then
+          inp.rev
+        else
+          null;
+
+      rev =
+        if b.match "refs/(heads|tags)/.*" inp.rev != null then
+          null
+        else
+          inp.rev;
+  
       refAndRev =
         (lib.optionalAttrs (ref != null) {
           inherit ref;
@@ -35,6 +47,7 @@ in
         (lib.optionalAttrs (rev != null) {
           inherit rev;
         });
+
     in
     {
 

src/fetchers/github/default.nix

@@ -17,6 +17,8 @@
     "rev"
   ];
 
+  versionField = "rev";
+
   outputs = { owner, repo, rev, ... }@inp: 
     let
       b = builtins;

src/fetchers/gitlab/default.nix

@@ -14,6 +14,8 @@
     "rev"
   ];
 
+  versionField = "rev";
+
   outputs = { owner, repo, rev, ... }@inp: 
     let
       b = builtins;

src/fetchers/pypi-sdist/default.nix

@@ -0,0 +1,33 @@
+{
+  python3,
+
+  utils,
+  # config
+  allowBuiltinFetchers,
+  ...
+}:
+{
+
+  inputs = [
+    "pname"
+    "version"
+  ];
+
+  versionField = "version";
+
+  outputs = { pname, version, extension ? "tar.gz", ... }@inp:
+    let
+      b = builtins;
+    in
+    {
+
+      calcHash = algo: utils.hashPath algo (b.fetchurl {
+        url = "https://files.pythonhosted.org/packages/${builtins.substring 0 1 pname}/${pname}/${pname}-${version}.${extension}";
+      });
+
+      fetched = hash:
+        python3.pkgs.fetchPypi {
+          inherit pname version extension hash;
+        };
+    };
+}