Add Config::META to access the configuration definition at runtime

src/lib.rs

@@ -5,6 +5,7 @@ pub mod internal;
 
 mod error;
 mod file;
+pub mod meta;
 
 
 pub use serde;
@@ -40,6 +41,12 @@ pub trait Config: Sized {
     /// values defined.
     type Partial: Partial;
 
+    /// A description of this configuration.
+    ///
+    /// This is a runtime representation from the struct definition of your
+    /// configuration type.
+    const META: meta::Meta;
+
     /// Tries to create `Self` from a potentially partial object.
     ///
     /// If any required values are not defined in `partial`, an [`Error`] is

src/meta.rs

@@ -0,0 +1,64 @@
+//! Types for [`Config::META`][super::Config::META]. Represent information about
+//! a configuration type.
+
+// TODO: having all these fields public make me uncomfortable. For now it's
+// fine, but before reaching 1.0 I need to figure out how to allow future
+// additions without breaking stuff.
+
+#[derive(Clone, Copy, Debug)]
+pub struct Meta {
+    /// The type (struct) name.
+    pub name: &'static str,
+
+    /// Doc comments.
+    pub doc: &'static [&'static str],
+
+    pub fields: &'static [Field],
+}
+
+#[derive(Clone, Copy, Debug)]
+pub struct Field {
+    pub name: &'static str,
+    pub kind: FieldKind,
+    pub doc: &'static [&'static str],
+}
+
+#[derive(Clone, Copy, Debug)]
+pub enum FieldKind {
+    Leaf {
+        default: Option<Expr>,
+    },
+    Child {
+        meta: &'static Meta,
+    },
+}
+
+#[derive(Debug, Clone, Copy)]
+pub enum Expr {
+    Str(&'static str),
+    Float(Float),
+    Integer(Integer),
+    Bool(bool),
+}
+
+#[derive(Debug, Clone, Copy, PartialEq)]
+pub enum Float {
+    F32(f32),
+    F64(f64),
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum Integer {
+    U8(u8),
+    U16(u16),
+    U32(u32),
+    U64(u64),
+    U128(u128),
+    Usize(usize),
+    I8(i8),
+    I16(i16),
+    I32(i32),
+    I64(i64),
+    I128(i128),
+    Isize(isize),
+}