builder: Use new format for building

builder/default.nix

@@ -1,10 +1,13 @@
 { stdenv
+, stdenvNoCC
 , runCommand
 , buildEnv
 , lib
 , fetchgit
 , removeReferencesTo
 , go
+, jq
+, cacert
 }:
 let
 
@@ -12,6 +15,23 @@ let
 
   removeExpr = refs: ''remove-references-to ${lib.concatMapStrings (ref: " -t ${ref}") refs}'';
 
+  fetchGoModule =
+    { hash
+    , goPackagePath
+    , version
+    }:
+    stdenvNoCC.mkDerivation {
+      name = "${baseNameOf goPackagePath}_${version}";
+      builder = ./fetch.sh;
+      inherit goPackagePath version;
+      nativeBuildInputs = [ go jq ];
+      outputHashMode = "recursive";
+      outputHashAlgo = null;
+      outputHash = hash;
+      SSL_CERT_FILE = "${cacert}/etc/ssl/certs/ca-bundle.crt";
+      impureEnvVars = lib.fetchers.proxyImpureEnvVars;
+    };
+
   buildGoApplication =
     { modules
     , src
@@ -47,17 +67,14 @@ let
           nativeBuildInputs = [ go ];
           json = builtins.toJSON modulesStruct;
 
-          sources = builtins.toJSON (lib.mapAttrs
-            (goPackagePath: meta:
-              let
-                src = fetchgit {
-                  inherit (meta.fetch) url sha256 rev;
-                  fetchSubmodules = true;
-                };
-                srcPath = "${src}/${meta.relPath or ""}";
-              in
-              srcPath)
-            modulesStruct);
+          sources = builtins.toJSON (
+            lib.mapAttrs
+              (goPackagePath: meta: fetchGoModule {
+                goPackagePath = meta.replaced or goPackagePath;
+                inherit (meta) version hash;
+              })
+              modulesStruct.mod
+          );
 
           passAsFile = [ "json" "sources" ];
         }

builder/fetch.sh

@@ -0,0 +1,10 @@
+source $stdenv/setup
+
+export HOME=$(mktemp -d)
+
+# Call once first outside of subshell for better error reporting
+go mod download -x "$goPackagePath@$version"
+
+dir=$(go mod download --json "$goPackagePath@$version" | jq -r .Dir)
+
+cp -r $dir $out

builder/symlink.go

@@ -9,23 +9,21 @@ import (
 	"sort"
 )
 
-type fetchInfo struct {
-	Type   string `toml:"type"`
-	URL    string `toml:"url"`
-	Rev    string `toml:"rev"`
-	Sha256 string `toml:"sha256"`
+type Package struct {
+	GoPackagePath string `json:"-"`
+	Version       string `json:"version"`
+	Hash          string `json:"hash"`
+	ReplacedPath  string `json:"replaced,omitempty"`
 }
 
-type packageT struct {
-	SumVersion string     `toml:"sumVersion"`
-	RelPath    string     `toml:"relPath,omitempty"`
-	VendorPath string     `toml:"vendorPath,omitempty"`
-	Fetch      *fetchInfo `toml:"fetch"`
+type Output struct {
+	SchemaVersion int                 `json:"schema"`
+	Mod           map[string]*Package `json:"mod"`
 }
 
 func main() {
 
-	pkgs := make(map[string]*packageT)
+	var output Output
 	sources := make(map[string]string)
 
 	b, err := ioutil.ReadFile(os.Getenv("sourcesPath"))
@@ -43,11 +41,13 @@ func main() {
 		panic(err)
 	}
 
-	err = json.Unmarshal(b, &pkgs)
+	err = json.Unmarshal(b, &output)
 	if err != nil {
 		panic(err)
 	}
 
+	pkgs := output.Mod
+
 	keys := make([]string, 0, len(pkgs))
 	for key := range pkgs {
 		keys = append(keys, key)
@@ -58,12 +58,8 @@ func main() {
 	for i := len(keys) - 1; i >= 0; i-- {
 		key := keys[i]
 		src := sources[key]
-		pkg := pkgs[key]
 
 		paths := []string{key}
-		if pkg.VendorPath != "" {
-			paths = append(paths, pkg.VendorPath)
-		}
 
 		for _, path := range paths {