Show error reason when template could not be read

rinja_derive/src/config.rs

@@ -302,21 +302,24 @@ pub(crate) fn get_template_source(
     tpl_path: &Path,
     import_from: Option<(&Rc<Path>, &str, &str)>,
 ) -> Result<String, CompileError> {
-    if let Ok(mut source) = fs::read_to_string(tpl_path) {
+    match fs::read_to_string(tpl_path) {
+        Ok(mut source) => {
             if source.ends_with('\n') {
                 let _ = source.pop();
             }
             Ok(source)
-    } else {
+        }
+        Err(err) => {
             let msg = format!(
-            "unable to open template file '{}'",
+                "unable to open template file '{}': {err}",
-            tpl_path.to_str().unwrap()
+                tpl_path.to_str().unwrap(),
             );
             let file_info = import_from.map(|(node_file, file_source, node_source)| {
                 FileInfo::new(node_file, Some(file_source), Some(node_source))
             });
             Err(CompileError::new(msg, file_info))
         }
+    }
 }
 
 static CONFIG_FILE_NAME: &str = "rinja.toml";

testing/templates/a_file_that_is_actually_a_folder.html/.gitignore

@@ -0,0 +1,2 @@
+*
+!.gitignore

testing/tests/ui/include-a-folder.rs

@@ -0,0 +1,8 @@
+use rinja::Template;
+
+#[derive(Template)]
+#[template(ext = "txt", source = r#"{% include "a_file_that_is_actually_a_folder.html" %}"#)]
+struct YouCannotIncludeFolders;
+
+fn main() {
+}

testing/tests/ui/include-a-folder.stderr

@@ -0,0 +1,9 @@
+error: unable to open template file '$WORKSPACE/target/tests/trybuild/rinja_testing/templates/a_file_that_is_actually_a_folder.html': Is a directory (os error 21)
+ --> YouCannotIncludeFolders.txt:1:2
+       " include \"a_file_that_is_actually_a_fold"...
+ --> tests/ui/include-a-folder.rs:3:10
+  |
+3 | #[derive(Template)]
+  |          ^^^^^^^^
+  |
+  = note: this error originates in the derive macro `Template` (in Nightly builds, run with -Z macro-backtrace for more info)