Allow relative paths in flakerefs

Also allow "." as an installable to refer to the flake in the current
directory. E.g.

  $ nix build .

will build 'provides.defaultPackage' in the flake in the current
directory.

4 files changed, 15 insertions, 8 deletions

diff --git a/flake.nix b/flake.nix
index b119f0324..695f67fa4 100644
--- a/flake.nix
+++ b/flake.nix
@@ -14,5 +14,6 @@
 
     packages.nix = hydraJobs.build.x86_64-linux;
 
+    defaultPackage = packages.nix;
   };
 }
diff --git a/src/libexpr/primops/flakeref.cc b/src/libexpr/primops/flakeref.cc
index 5f9a29260..1df53bfb8 100644
--- a/src/libexpr/primops/flakeref.cc
+++ b/src/libexpr/primops/flakeref.cc
@@ -32,7 +32,7 @@ const static std::string segmentRegex = "[a-zA-Z0-9._~-]+";
 const static std::string pathRegex = "/?" + segmentRegex + "(?:/" + segmentRegex + ")*";
 const static std::string paramRegex = "[a-z]+=[a-zA-Z0-9._-]*";
 
-FlakeRef::FlakeRef(const std::string & uri)
+FlakeRef::FlakeRef(const std::string & uri, bool allowRelative)
 {
     // FIXME: could combine this into one regex.
 
@@ -106,9 +106,9 @@ FlakeRef::FlakeRef(const std::string & uri)
         data = d;
     }
 
-    else if (hasPrefix(uri, "/")) {
+    else if (hasPrefix(uri, "/") || (allowRelative && (hasPrefix(uri, "./") || uri == "."))) {
         IsPath d;
-        d.path = canonPath(uri);
+        d.path = allowRelative ? absPath(uri) : canonPath(uri);
         data = d;
     }
 
diff --git a/src/libexpr/primops/flakeref.hh b/src/libexpr/primops/flakeref.hh
index 832d7dd03..fa14f7c25 100644
--- a/src/libexpr/primops/flakeref.hh
+++ b/src/libexpr/primops/flakeref.hh
@@ -132,7 +132,7 @@ struct FlakeRef
     std::variant<IsFlakeId, IsGitHub, IsGit, IsPath> data;
 
     // Parse a flake URI.
-    FlakeRef(const std::string & uri);
+    FlakeRef(const std::string & uri, bool allowRelative = false);
 
     // Default constructor
     FlakeRef(const FlakeRef & flakeRef) : data(flakeRef.data) {};
diff --git a/src/nix/installables.cc b/src/nix/installables.cc
index 631a849cd..f3be7b628 100644
--- a/src/nix/installables.cc
+++ b/src/nix/installables.cc
@@ -219,12 +219,18 @@ std::vector<std::shared_ptr<Installable>> SourceExprCommand::parseInstallables(
             else if ((colon = s.rfind(':')) != std::string::npos) {
                 auto flakeRef = std::string(s, 0, colon);
                 auto attrPath = std::string(s, colon + 1);
-                result.push_back(std::make_shared<InstallableFlake>(*this, FlakeRef(flakeRef), attrPath));
+                result.push_back(std::make_shared<InstallableFlake>(*this, FlakeRef(flakeRef, true), attrPath));
             }
 
-            else if (s.find('/') != std::string::npos) {
-                auto path = store->toStorePath(store->followLinksToStore(s));
-                result.push_back(std::make_shared<InstallableStorePath>(path));
+            else if (s.find('/') != std::string::npos || s == ".") {
+                Path storePath;
+                try {
+                    storePath = store->toStorePath(store->followLinksToStore(s));
+                } catch (Error) { }
+                if (storePath != "")
+                    result.push_back(std::make_shared<InstallableStorePath>(storePath));
+                else
+                    result.push_back(std::make_shared<InstallableFlake>(*this, FlakeRef(s, true), "defaultPackage"));
             }
 
             else