results: prevent dangling cstring pointers in result (#63)

stew/results.nim

@@ -304,6 +304,12 @@ template err*[T, E](R: type Result[T, E], x: auto): R =
   ## Example: `Result[int, string].err("uh-oh")`
   R(o: false, e: x)
 
+template err*[T](R: type Result[T, cstring], x: string): R =
+  ## Initialize the result to an error
+  ## Example: `Result[int, string].err("uh-oh")`
+  const s = x
+  R(o: false, e: cstring(s))
+
 template err*[T](R: type Result[T, void]): R =
   R(o: false)
 
@@ -312,6 +318,10 @@ template err*[T, E](self: var Result[T, E], x: auto) =
   ## Example: `result.err("uh-oh")`
   self = err(type self, x)
 
+template err*[T](self: var Result[T, cstring], x: string) =
+  const s = x # Make sure we don't return a dangling pointer
+  self = err(type self, cstring(s))
+
 template err*[T](self: var Result[T, void]) =
   ## Set the result as an error
   ## Example: `result.err()`

tests/test_results.nim

@@ -266,3 +266,12 @@ func voidF2(): VoidRes =
   ok()
 
 doAssert voidF2().isOk
+
+
+type CSRes = Result[void, cstring]
+
+func cstringF(s: string): CSRes =
+  when compiles(err(s)):
+    doAssert false
+
+discard cstringF("test")