Add support for TOML files (#633)

TOML maps well to Lua, is easier to read and write than JSON, and is
commonly used by Roblox tools.

Use cases:
* Put game, plugin, or library config in a toml file
* Sync in toml files generated by tools
* Sync in config files for tools so that the game can double-check that
the config file has been followed. (e.g. check that packages match
versions specified in wally.toml)

src/snapshot_middleware/toml.rs

@@ -0,0 +1,123 @@
+use std::path::Path;
+
+use anyhow::Context;
+use maplit::hashmap;
+use memofs::{IoResultExt, Vfs};
+
+use crate::{
+    lua_ast::{Expression, Statement},
+    snapshot::{InstanceContext, InstanceMetadata, InstanceSnapshot},
+};
+
+use super::{meta_file::AdjacentMetadata, util::PathExt};
+
+pub fn snapshot_toml(
+    context: &InstanceContext,
+    vfs: &Vfs,
+    path: &Path,
+) -> anyhow::Result<Option<InstanceSnapshot>> {
+    let name = path.file_name_trim_end(".toml")?;
+    let contents = vfs.read(path)?;
+
+    let value: toml::Value = toml::from_slice(&contents)
+        .with_context(|| format!("File contains malformed TOML: {}", path.display()))?;
+
+    let as_lua = toml_to_lua(value).to_string();
+
+    let properties = hashmap! {
+        "Source".to_owned() => as_lua.into(),
+    };
+
+    let meta_path = path.with_file_name(format!("{}.meta.json", name));
+
+    let mut snapshot = InstanceSnapshot::new()
+        .name(name)
+        .class_name("ModuleScript")
+        .properties(properties)
+        .metadata(
+            InstanceMetadata::new()
+                .instigating_source(path)
+                .relevant_paths(vec![path.to_path_buf(), meta_path.clone()])
+                .context(context),
+        );
+
+    if let Some(meta_contents) = vfs.read(&meta_path).with_not_found()? {
+        let mut metadata = AdjacentMetadata::from_slice(&meta_contents, meta_path)?;
+        metadata.apply_all(&mut snapshot)?;
+    }
+
+    Ok(Some(snapshot))
+}
+
+fn toml_to_lua(value: toml::Value) -> Statement {
+    Statement::Return(toml_to_lua_value(value))
+}
+
+fn toml_to_lua_value(value: toml::Value) -> Expression {
+    use toml::Value;
+
+    match value {
+        Value::Datetime(value) => Expression::String(value.to_string()),
+        Value::Boolean(value) => Expression::Bool(value),
+        Value::Float(value) => Expression::Number(value),
+        Value::Integer(value) => Expression::Number(value as f64),
+        Value::String(value) => Expression::String(value),
+        Value::Array(values) => {
+            Expression::Array(values.into_iter().map(toml_to_lua_value).collect())
+        }
+        Value::Table(values) => Expression::table(
+            values
+                .into_iter()
+                .map(|(key, value)| (key.into(), toml_to_lua_value(value)))
+                .collect(),
+        ),
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    use memofs::{InMemoryFs, VfsSnapshot};
+
+    #[test]
+    fn instance_from_vfs() {
+        let mut imfs = InMemoryFs::new();
+        imfs.load_snapshot(
+            "/foo.toml",
+            VfsSnapshot::file(
+                r#"
+                  array = [1, 2, 3]
+                  true = true
+                  false = false
+                  int = 1234
+                  float = 1234.5452
+                  "1invalidident" = "nice"
+
+                  [object]
+                  hello = "world"
+
+                  [dates]
+                  offset1 = 1979-05-27T00:32:00.999999-07:00
+                  offset2 = 1979-05-27 07:32:00Z
+                  localdatetime = 1979-05-27T07:32:00
+                  localdate = 1979-05-27
+                  localtime = 00:32:00.999999
+                "#,
+            ),
+        )
+        .unwrap();
+
+        let mut vfs = Vfs::new(imfs.clone());
+
+        let instance_snapshot = snapshot_toml(
+            &InstanceContext::default(),
+            &mut vfs,
+            Path::new("/foo.toml"),
+        )
+        .unwrap()
+        .unwrap();
+
+        insta::assert_yaml_snapshot!(instance_snapshot);
+    }
+}