JSON reading

2 files changed, 44 insertions, 0 deletions

diff --git a/src/library/mod.rs b/src/library/mod.rs
index 566a4f26..d806f298 100644
--- a/src/library/mod.rs
+++ b/src/library/mod.rs
@@ -97,6 +97,7 @@ pub fn new() -> Scope {
     std.def_fn("symbol", utility::symbol);
     std.def_fn("lorem", utility::lorem);
     std.def_fn("csv", utility::csv);
+    std.def_fn("json", utility::json);
 
     // Predefined colors.
     std.define("black", Color::BLACK);
diff --git a/src/library/utility/data.rs b/src/library/utility/data.rs
index 1ae8949a..e3efe6e7 100644
--- a/src/library/utility/data.rs
+++ b/src/library/utility/data.rs
@@ -41,3 +41,46 @@ fn format_csv_error(error: csv::Error) -> String {
         _ => "failed to parse csv file".into(),
     }
 }
+
+/// Read structured data from a JSON file.
+pub fn json(vm: &mut Vm, args: &mut Args) -> SourceResult<Value> {
+    let Spanned { v: path, span } =
+        args.expect::<Spanned<EcoString>>("path to json file")?;
+
+    let path = vm.locate(&path).at(span)?;
+    let data = vm.world.file(&path).at(span)?;
+    let value: serde_json::Value =
+        serde_json::from_slice(&data).map_err(format_json_error).at(span)?;
+
+    Ok(convert_json(value))
+}
+
+/// Convert a JSON value to a Typst value.
+fn convert_json(value: serde_json::Value) -> Value {
+    match value {
+        serde_json::Value::Null => Value::None,
+        serde_json::Value::Bool(v) => Value::Bool(v),
+        serde_json::Value::Number(v) => match v.as_i64() {
+            Some(int) => Value::Int(int),
+            None => Value::Float(v.as_f64().unwrap_or(f64::NAN)),
+        },
+        serde_json::Value::String(v) => Value::Str(v.into()),
+        serde_json::Value::Array(v) => {
+            Value::Array(v.into_iter().map(convert_json).collect())
+        }
+        serde_json::Value::Object(v) => Value::Dict(
+            v.into_iter()
+                .map(|(key, value)| (key.into(), convert_json(value)))
+                .collect(),
+        ),
+    }
+}
+
+/// Format the user-facing JSON error message.
+fn format_json_error(error: serde_json::Error) -> String {
+    assert!(error.is_syntax() || error.is_eof());
+    format!(
+        "failed to parse json file: syntax error in line {}",
+        error.line()
+    )
+}