Move deserialization to node_types module; propagate errors to caller

generator/src/main.rs

@@ -8,19 +8,6 @@ use std::fs::File;
 use std::io::LineWriter;
 use std::path::PathBuf;
 
-fn read_node_types(language: &Language) -> Option<Vec<NodeInfo>> {
-    let json_data = match std::fs::read_to_string(&language.node_types_path) {
-        Ok(s) => s,
-        Err(_) => return None,
-    };
-    let nodes: Vec<NodeInfo> = match serde_json::from_str(&json_data) {
-        Ok(n) => n,
-        Err(_) => return None,
-    };
-
-    Some(nodes)
-}
-
 /// Given a tree-sitter node type's (kind, named) pair, returns a single string
 /// representing the (unescaped) name we'll use to refer to corresponding QL
 /// type.
@@ -301,12 +288,19 @@ fn main() {
         node_types_path: PathBuf::from("tree-sitter-ruby/src/node-types.json"),
         dbscheme_path: PathBuf::from("ruby.dbscheme"),
     };
-    match read_node_types(&ruby) {
-        None => {
-            println!("Failed to read node types");
+    match node_types::read(&ruby.node_types_path) {
+        Err(e) => {
+            println!(
+                "Failed to read '{}': {}",
+                match ruby.node_types_path.to_str() {
+                    None => "<undisplayable>",
+                    Some(p) => p,
+                },
+                e
+            );
             std::process::exit(1);
         }
-        Some(nodes) => {
+        Ok(nodes) => {
             let mut dbscheme_entries = convert_nodes(&nodes);
             dbscheme_entries.push(create_location_entry());
             dbscheme_entries.push(create_source_location_prefix_entry());

generator/src/node_types.rs

@@ -1,5 +1,7 @@
 use serde::Deserialize;
 use std::collections::BTreeMap;
+use std::fmt;
+use std::path::Path;
 
 #[derive(Deserialize)]
 pub struct NodeInfo {
@@ -37,3 +39,36 @@ impl Default for FieldInfo {
         }
     }
 }
+
+pub enum Error {
+    IOError(std::io::Error),
+    JsonError(serde_json::error::Error),
+}
+
+impl From<std::io::Error> for Error {
+    fn from(error: std::io::Error) -> Self {
+        Error::IOError(error)
+    }
+}
+
+impl From<serde_json::Error> for Error {
+    fn from(error: serde_json::Error) -> Self {
+        Error::JsonError(error)
+    }
+}
+
+impl fmt::Display for Error {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Error::IOError(e) => write!(f, "{}", e),
+            Error::JsonError(e) => write!(f, "{}", e),
+        }
+    }
+}
+
+/// Deserializes the node types from the JSON at the given `path`.
+pub fn read(path: &Path) -> Result<Vec<NodeInfo>, Error> {
+    let json_data = std::fs::read_to_string(path)?;
+    let node_types: Vec<NodeInfo> = serde_json::from_str(&json_data)?;
+    Ok(node_types)
+}