go-modules: Augment builds w/ vendor src

This is done in response to complaints that the module format is not
human readable. The vendor source blob is flat files and should be
extremely readable.

(cherry picked from commit 9761128)

pkgs/development/go-modules/generic/default.nix

@@ -13,12 +13,15 @@
 # path to go.mod and go.sum directory
 , modRoot ? "./"
 
-# modSha256 is the sha256 of the vendored dependencies
+# vendorSha256 is the sha256 of the vendored dependencies
 #
-# CAUTION: if `null` is used as a value, the derivation won't be a
-# fixed-output derivation but disable the build sandbox instead. Don't use
-# this in nixpkgs as Hydra won't build those packages.
-, modSha256
+# if vendorSha256 is null, then we won't fetch any dependencies and
+# rely on the vendor folder within the source.
+, vendorSha256 ? null
+# Whether to delete the vendor folder supplied with the source.
+, deleteVendor ? false
+
+, modSha256 ? null
 
 # We want parallel builds by default
 , enableParallelBuilding ? true
@@ -37,21 +40,26 @@
 with builtins;
 
 let
-  args = removeAttrs args' [ "overrideModAttrs" "modSha256" "disabled" ];
+  args = removeAttrs args' [ "overrideModAttrs" "vendorSha256" "disabled" ];
 
   removeReferences = [ ] ++ lib.optional (!allowGoReference) go;
 
   removeExpr = refs: ''remove-references-to ${lib.concatMapStrings (ref: " -t ${ref}") refs}'';
 
-  go-modules = go.stdenv.mkDerivation (let modArgs = {
+  deleteFlag = if deleteVendor then "true" else "false";
+
+  go-modules = if vendorSha256 != null then go.stdenv.mkDerivation (let modArgs = {
+
     name = "${name}-go-modules";
 
-    nativeBuildInputs = [ go git cacert ];
+    nativeBuildInputs = (args.nativeBuildInputs or []) ++ [ go git cacert ];
 
     inherit (args) src;
     inherit (go) GOOS GOARCH;
 
     patches = args.patches or [];
+    preBuild = args.preBuild or "";
+    sourceRoot = args.sourceRoot or "";
 
     GO111MODULE = "on";
 
@@ -64,15 +72,23 @@ let
 
       export GOCACHE=$TMPDIR/go-cache
       export GOPATH="$TMPDIR/go"
-      mkdir -p "''${GOPATH}/pkg/mod/cache/download"
       cd "${modRoot}"
       runHook postConfigure
     '';
 
     buildPhase = args.modBuildPhase or ''
       runHook preBuild
 
-      go mod download
+      if [ ${deleteFlag} == "true" ]; then
+        rm -rf vendor
+      fi
+
+      if [ -e vendor ]; then
+        echo "vendor folder exists, please set 'vendorSha256=null;' or 'deleteVendor=true;' in your expression"
+        exit 10
+      fi
+      go mod vendor
+      mkdir -p vendor
 
       runHook postBuild
     '';
@@ -81,40 +97,40 @@ let
       runHook preInstall
 
       # remove cached lookup results and tiles
-      rm -rf "''${GOPATH}/pkg/mod/cache/download/sumdb"
-      cp -r "''${GOPATH}/pkg/mod/cache/download" $out
+      cp -r --reflink=auto vendor $out
 
       runHook postInstall
     '';
 
     dontFixup = true;
   }; in modArgs // (
-    if modSha256 == null then
-      { __noChroot = true; }
-    else
       {
         outputHashMode = "recursive";
         outputHashAlgo = "sha256";
-        outputHash = modSha256;
+        outputHash = vendorSha256;
       }
-  ) // overrideModAttrs modArgs);
+  ) // overrideModAttrs modArgs) else "";
 
   package = go.stdenv.mkDerivation (args // {
     nativeBuildInputs = [ removeReferencesTo go ] ++ nativeBuildInputs;
 
     inherit (go) GOOS GOARCH;
 
     GO111MODULE = "on";
+    GOFLAGS = "-mod=vendor";
 
     configurePhase = args.configurePhase or ''
       runHook preConfigure
 
       export GOCACHE=$TMPDIR/go-cache
       export GOPATH="$TMPDIR/go"
       export GOSUMDB=off
-      export GOPROXY=file://${go-modules}
-
+      export GOPROXY=off
       cd "$modRoot"
+      if [ -n "${go-modules}" ]; then 
+          rm -rf vendor
+          ln -s ${go-modules} vendor
+      fi
 
       runHook postConfigure
     '';
@@ -210,7 +226,7 @@ let
 
     disallowedReferences = lib.optional (!allowGoReference) go;
 
-    passthru = passthru // { inherit go go-modules modSha256; };
+    passthru = passthru // { inherit go go-modules vendorSha256 ; };
 
     meta = {
       # Add default meta information
@@ -223,5 +239,7 @@ let
   });
 in if disabled then
   throw "${package.name} not supported for go ${go.meta.branch}"
+else if modSha256 != null then
+  throw "${package.name} should use vendorSha256 not modSha256"
 else
   package