Make EOL after interpolation a proper error (#279)

src/compilation_error.rs

@@ -37,6 +37,7 @@ pub enum CompilationErrorKind<'a> {
   UnknownDependency{recipe: &'a str, unknown: &'a str},
   UnknownFunction{function: &'a str},
   UnknownStartOfToken,
+  UnterminatedInterpolation,
   UnterminatedString,
 }
 
@@ -130,6 +131,9 @@ impl<'a> Display for CompilationError<'a> {
       UnknownStartOfToken => {
         writeln!(f, "Unknown start of token:")?;
       }
+      UnterminatedInterpolation => {
+        writeln!(f, "Unterminated interpolation")?;
+      }
       UnterminatedString => {
         writeln!(f, "Unterminated string")?;
       }

src/lexer.rs

@@ -200,9 +200,7 @@ impl<'a> Lexer<'a> {
         (captures.get(1).unwrap().as_str(), captures.get(2).unwrap().as_str(), Name)
       } else if let Some(captures) = EOL.captures(self.rest) {
         if self.state.last().unwrap() == &State::Interpolation {
-          return Err(self.error(Internal {
-            message: "hit EOL while still in interpolation state".to_string()
-          }));
+          return Err(self.error(UnterminatedInterpolation));
         }
         (captures.get(1).unwrap().as_str(), captures.get(2).unwrap().as_str(), Eol)
       } else if let Some(captures) = BACKTICK.captures(self.rest) {
@@ -602,6 +600,17 @@ c: b
     kind:   UnterminatedString,
   }
 
+  error_test! {
+    name:  unterminated_interpolation,
+    input: "foo:\n echo {{
+",
+    index:  13,
+    line:   1,
+    column: 8,
+    width:  None,
+    kind:   UnterminatedInterpolation,
+  }
+
   error_test! {
     name: mixed_leading_whitespace,
     input: "a:\n\t echo hello",