\dotenv-rs#61 Address review comments

Author: jharrilim

.gitignore

@@ -1,4 +1,2 @@
 target/
 Cargo.lock
-.idea
-wip

dotenv_codegen/tests/ui/dotenv_no_args.rs

@@ -3,4 +3,4 @@ extern crate dotenv_codegen;
 
 pub fn main() {
     dotenv!();
-}
+}

dotenv_codegen/tests/ui/dotenv_or_default_no_args.rs

@@ -3,4 +3,4 @@ extern crate dotenv_codegen;
 
 pub fn main() {
     dotenv_or_default!();
-}
+}

dotenv_codegen/tests/ui/dotenv_or_default_three_args.rs

@@ -3,4 +3,4 @@ extern crate dotenv_codegen;
 
 pub fn main() {
     dotenv_or_default!("a", "b", "c");
-}
+}

dotenv_codegen/tests/ui/dotenv_three_args.rs

@@ -3,4 +3,4 @@ extern crate dotenv_codegen;
 
 pub fn main() {
     dotenv!("a", "b", "c");
-}
+}

dotenv_codegen_implementation/src/lib.rs

@@ -37,14 +37,19 @@ pub fn dotenv_or_default(input: TokenStream) -> TokenStream {
 
     // Either everything was fine, or we didn't find an .env file (which we ignore)
     let (var_name, second_value) = expand_env(input);
-    let default_val = match second_value {
-        Some(default) => default,
-        None => panic!("Missing default value for: {}", var_name),
-    };
 
-    match env::var(var_name) {
-        Ok(val) => quote!(#val).into(),
-        Err(VarError::NotPresent) | Err(VarError::NotUnicode(_)) => quote!(#default_val).into(),
+    match second_value {
+        Some(default) => match env::var(var_name) {
+            Ok(val) => quote!(#val).into(),
+            Err(VarError::NotPresent) | Err(VarError::NotUnicode(_)) => quote!(#default).into(),
+        },
+        None => {
+            let err_msg = format!("Missing default value for: {}", var_name);
+            (quote! {
+                compile_error!(#err_msg)
+            })
+            .into()
+        }
     }
 }