1 files changed, 149 insertions, 0 deletions
diff --git a/components/config_plugins/parse.rs b/components/config_plugins/parse.rs
new file mode 100644
index 00000000000..715b60f50e9
--- /dev/null
+++ b/components/config_plugins/parse.rs
@@ -0,0 +1,149 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+use proc_macro2::Span;
+use syn::parse::{Parse, ParseStream, Result};
+use syn::{braced, punctuated::Punctuated, token, Attribute, Ident, Path, Token, Type};
+
+#[allow(non_camel_case_types)]
+mod kw {
+    syn::custom_keyword!(accessor_type);
+    syn::custom_keyword!(gen_accessors);
+    syn::custom_keyword!(gen_types);
+}
+
+pub struct MacroInput {
+    pub type_def: RootTypeDef,
+    pub gen_accessors: Ident,
+    pub accessor_type: Path,
+}
+
+enum MacroArg {
+    GenAccessors(ArgInner<kw::gen_accessors, Ident>),
+    AccessorType(ArgInner<kw::accessor_type, Path>),
+    Types(ArgInner<kw::gen_types, RootTypeDef>),
+}
+
+struct ArgInner<K, V> {
+    _field_kw: K,
+    _equals: Token![=],
+    value: V,
+}
+
+pub struct Field {
+    pub attributes: Vec<Attribute>,
+    pub name: Ident,
+    _colon: Token![:],
+    pub field_type: FieldType,
+}
+
+pub enum FieldType {
+    Existing(Type),
+    NewTypeDef(NewTypeDef),
+}
+
+pub struct NewTypeDef {
+    _braces: token::Brace,
+    pub fields: Punctuated<Field, Token![, ]>,
+}
+
+pub struct RootTypeDef {
+    pub type_name: Ident,
+    pub type_def: NewTypeDef,
+}
+
+impl Parse for MacroInput {
+    fn parse(input: ParseStream) -> Result<Self> {
+        let fields: Punctuated<MacroArg, Token![, ]> = input.parse_terminated(MacroArg::parse)?;
+        let mut gen_accessors = None;
+        let mut type_def = None;
+        let mut accessor_type = None;
+        for arg in fields.into_iter() {
+            match arg {
+                MacroArg::GenAccessors(ArgInner { value, .. }) => gen_accessors = Some(value),
+                MacroArg::AccessorType(ArgInner { value, .. }) => accessor_type = Some(value),
+                MacroArg::Types(ArgInner { value, .. }) => type_def = Some(value),
+            }
+        }
+
+        fn missing_attr(att_name: &str) -> syn::Error {
+            syn::Error::new(
+                Span::call_site(),
+                format!("Expected `{}` attribute", att_name),
+            )
+        }
+
+        Ok(MacroInput {
+            type_def: type_def.ok_or_else(|| missing_attr("gen_types"))?,
+            gen_accessors: gen_accessors.ok_or_else(|| missing_attr("gen_accessors"))?,
+            accessor_type: accessor_type.ok_or_else(|| missing_attr("accessor_type"))?,
+        })
+    }
+}
+
+impl Parse for MacroArg {
+    fn parse(input: ParseStream) -> Result<Self> {
+        let lookahead = input.lookahead1();
+        if lookahead.peek(kw::gen_types) {
+            Ok(MacroArg::Types(input.parse()?))
+        } else if lookahead.peek(kw::gen_accessors) {
+            Ok(MacroArg::GenAccessors(input.parse()?))
+        } else if lookahead.peek(kw::accessor_type) {
+            Ok(MacroArg::AccessorType(input.parse()?))
+        } else {
+            Err(lookahead.error())
+        }
+    }
+}
+
+impl<K: Parse, V: Parse> Parse for ArgInner<K, V> {
+    fn parse(input: ParseStream) -> Result<Self> {
+        Ok(ArgInner {
+            _field_kw: input.parse()?,
+            _equals: input.parse()?,
+            value: input.parse()?,
+        })
+    }
+}
+
+impl Parse for Field {
+    fn parse(input: ParseStream) -> Result<Self> {
+        Ok(Field {
+            attributes: input.call(Attribute::parse_outer)?,
+            name: input.parse()?,
+            _colon: input.parse()?,
+            field_type: input.parse()?,
+        })
+    }
+}
+
+impl Parse for RootTypeDef {
+    fn parse(input: ParseStream) -> Result<Self> {
+        Ok(RootTypeDef {
+            type_name: input.parse()?,
+            type_def: input.parse()?,
+        })
+    }
+}
+
+impl Parse for NewTypeDef {
+    fn parse(input: ParseStream) -> Result<Self> {
+        let content;
+        #[allow(clippy::eval_order_dependence)]
+        Ok(NewTypeDef {
+            _braces: braced!(content in input),
+            fields: content.parse_terminated(Field::parse)?,
+        })
+    }
+}
+
+impl Parse for FieldType {
+    fn parse(input: ParseStream) -> Result<Self> {
+        if input.peek(token::Brace) {
+            Ok(FieldType::NewTypeDef(input.parse()?))
+        } else {
+            Ok(FieldType::Existing(input.parse()?))
+        }
+    }
+}