From 2a14c2d53b96c17ff6acf571da5824c26468b4aa Mon Sep 17 00:00:00 2001
From: Ivan Petkov <ivanppetkov@gmail.com>
Date: Thu, 30 Dec 2021 15:08:45 -0800
Subject: [PATCH] Update crateNameFromCargoToml with better fallback error
 messages

* If a derivation is created without a name *and* we cannot infer a name
  from a Cargo.toml file, we'll throw a descriptive error message which
  hints towards the remediation
* Otherwise nix can throw a pretty obtuse "derivation has no name" error
  with no error trace
---
 lib/crateNameFromCargoToml.nix | 30 +++++++++++++++++++++---------
 1 file changed, 21 insertions(+), 9 deletions(-)

diff --git a/lib/crateNameFromCargoToml.nix b/lib/crateNameFromCargoToml.nix
index 86844ea..f2b5e58 100644
--- a/lib/crateNameFromCargoToml.nix
+++ b/lib/crateNameFromCargoToml.nix
@@ -2,15 +2,27 @@
 
 { src ? null
 , cargoToml ? src + /Cargo.toml
-, cargoTomlContents ? builtins.readFile cargoToml
+, cargoTomlContents ? null
 , ...
 }:
 
-let
-  toml = fromTOML cargoTomlContents;
-  p = toml.package;
-in
-{
-  inherit (p) version;
-  pname = p.name;
-}
+if cargoTomlContents == null && (src == null || !builtins.pathExists cargoToml)
+then
+  throw ''
+    unable to infer crate name and version. Please make sure the src directory
+    contains a valid Cargo.toml file, or consider setting a derivation name explicitly
+  ''
+else
+  let
+    cargoTomlRealContents =
+      if cargoTomlContents != null
+      then cargoTomlContents
+      else builtins.readFile cargoToml;
+
+    toml = fromTOML cargoTomlRealContents;
+    p = toml.package;
+  in
+  {
+    inherit (p) version;
+    pname = p.name;
+  }