Merge pull request #34 from guzba/master

docs + fail if not arc

.github/workflows/build.yml

@@ -12,5 +12,5 @@ jobs:
     steps:
     - uses: actions/checkout@v2
     - uses: jiro4989/setup-nim-action@v1
-    - run: nimble test -y
+    - run: nimble test --gc:arc -y
     - run: nimble test --gc:orc -y

README.md

@@ -10,6 +10,8 @@ So you made a cool Nim library but you want it to be available to other language
 
 https://nimdocs.com/treeform/genny
 
+See [Pixie's nimble file](https://github.com/treeform/pixie/blob/master/pixie.nimble#L16) for an example of how to compile bindings with `genny`.
+
 ## Installation:
 
 `nimble install genny`

src/genny/internal.nim

@@ -242,8 +242,14 @@ proc generateSeqs(sym: NimNode) =
 proc exportSeqInternal*(sym: NimNode) =
   generateSeqs(sym)
 
+const header = """
+when not defined(gcArc) and not defined(gcOrc):
+  {.error: "Please use --gc:arc or --gc:orc when using Genny.".}
+
+"""
+
 proc writeInternal*(dir, lib: string) =
   writeFile(
     &"{dir}/internal.nim",
-    internal.replace("$Lib", lib).replace("$lib", toSnakeCase(lib))
+    header & internal.replace("$Lib", lib).replace("$lib", toSnakeCase(lib))
   )