Enum variant parsing

examples/airports.rs

@@ -1,36 +1,15 @@
 #[macro_use]
 extern crate enumscribe;
 
-use std::collections::HashMap;
-
-#[derive(EnumStrDeserialize, PartialEq, Eq, Debug)]
-#[case_insensitive]
-enum Airport {
-    #[str_name("LHR")]
-    Heathrow,
-    #[str_name("LGW")]
-    Gatwick,
-    #[str_name("LTN")]
-    Luton,
-    #[str_name("BHX")]
-    BirminghamInternational,
-    #[other]
-    Other(Box<String>),
+#[derive(EnumToString)]
+enum Foo {
+    Baa,
+    #[enumscribe(ignore)]
+    Baz(),
+    #[enumscribe(other)]
+    Lorem { inner: String }
 }
 
 fn main() {
-    let json_str = r#"
-    {
-        "airport_1": "LTN",
-        "airport_2": "bhx",
-        "airport_3": "lHr",
-        "airport_4": "MAN"
-    }"#;
-
-    let json: HashMap<String, Airport> = serde_json::from_str(json_str).unwrap();
-
-    println!("{:?}", json.get("airport_1").unwrap());
-    println!("{:?}", json.get("airport_2").unwrap());
-    println!("{:?}", json.get("airport_3").unwrap());
-    println!("{:?}", json.get("airport_4").unwrap());
+    println!("Hello world!");
 }

src/attribute.rs

@@ -1,4 +1,5 @@
 use std::collections::HashMap;
+use std::fmt;
 
 use proc_macro2::Span;
 use syn::{Attribute, Ident, Lit, Token};
@@ -6,6 +7,8 @@ use syn::parse::{Parse, ParseBuffer, ParseStream};
 use syn::parse::discouraged::Speculative;
 use syn::token::Token;
 
+use crate::error::{MacroError, MacroResult, ValueTypeError, ValueTypeResult};
+
 #[derive(Clone)]
 pub(crate) enum Value {
     None,
@@ -13,9 +16,84 @@ pub(crate) enum Value {
     Ident(Ident),
 }
 
-#[derive(Clone)]
+impl Value {
+    pub(crate) fn type_name(&self) -> &'static str {
+        match self {
+            Value::None => "nothing",
+            Value::Lit(lit) => match lit {
+                Lit::Str(_) => "string",
+                Lit::ByteStr(_) => "byte string",
+                Lit::Byte(_) => "byte",
+                Lit::Char(_) => "character",
+                Lit::Int(_) => "integer",
+                Lit::Float(_) => "float",
+                Lit::Bool(_) => "boolean",
+                Lit::Verbatim(_) => "verbatim literal",
+            },
+            Value::Ident(_) => "identifier",
+        }
+    }
+
+    /// Gets the boolean value associated with this Value. `Value::None` value is considered to
+    /// be true. If this value cannot represent a boolean, a `ValueTypeError` will be returned.
+    pub(crate) fn value_bool(&self) -> ValueTypeResult<bool> {
+        match self {
+            Value::None => Ok(true),
+            Value::Lit(Lit::Bool(lit_bool)) => Ok(lit_bool.value),
+            val => Err(ValueTypeError {
+                message: format!("expected boolean but found {}", val.type_name()).into()
+            })
+        }
+    }
+
+    /// Gets the string value associated with this Value. If this value cannot represent a string,
+    /// a `ValueTypeError` will be returned.
+    pub(crate) fn value_string(&self) -> ValueTypeResult<String> {
+        match self {
+            Value::Lit(Lit::Str(lit_str)) => Ok(lit_str.value()),
+            val => Err(ValueTypeError {
+                message: format!("expected string but found {}", val.type_name()).into()
+            })
+        }
+    }
+}
+
+impl fmt::Debug for Value {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Value::None => write!(f, "ε"),
+            Value::Lit(lit) => match lit {
+                Lit::Str(lit_str) => lit_str.value().fmt(f),
+                Lit::ByteStr(lit_byte_str) => lit_byte_str.value().fmt(f),
+                Lit::Byte(lit_byte) => lit_byte.value().fmt(f),
+                Lit::Char(lit_char) => lit_char.value().fmt(f),
+                Lit::Int(lit_int) => write!(f, "{}", lit_int.base10_digits()),
+                Lit::Float(lit_float) => write!(f, "{}", lit_float.base10_digits()),
+                Lit::Bool(lit_bool) => lit_bool.value.fmt(f),
+                Lit::Verbatim(lit_verbatim) => lit_verbatim.fmt(f),
+            },
+            Value::Ident(ident) => ident.fmt(f),
+        }
+    }
+}
+
+#[derive(Clone, Debug)]
 pub(crate) struct Dict {
-    pub(crate) inner: HashMap<String, (Value, Span)>
+    pub(crate) inner: HashMap<String, (Value, Span)>,
+}
+
+/// Represents the contents of a single `#[tag(...)]`.
+/// The contents are parsed from `key = value` pairs, separated by commas.
+#[derive(Clone, Debug)]
+struct AttributeTag {
+    inner: Vec<(String, Value, Span)>,
+}
+
+#[derive(Clone, Debug)]
+struct KeyValPair {
+    key: String,
+    val: Value,
+    span: Span,
 }
 
 impl Dict {
@@ -23,53 +101,71 @@ impl Dict {
         Dict { inner: HashMap::new() }
     }
 
-    pub(crate) fn from_attrs(name: &str, attrs: &[Attribute]) -> syn::Result<Self> {
+    pub(crate) fn from_attrs(name: &str, attrs: &[Attribute]) -> MacroResult<Self> {
         let mut dict = Dict::new();
 
-        let sub_dicts = attrs.iter()
+        let attribute_tags = attrs.iter()
             .filter(|attr| attr.path.is_ident(name))
-            .map(|attr| attr.parse_args::<Dict>());
+            .map(|attr| attr.parse_args::<AttributeTag>());
 
-        for sub_dict in sub_dicts {
-            dict.inner.extend(sub_dict?.inner.into_iter());
+        for tag in attribute_tags {
+            let tag = tag.map_err(MacroError::from)?;
+
+            for (key, val, span) in tag.inner {
+                if dict.inner.contains_key(&key) {
+                    return Err(MacroError::new(format!(
+                        "key appears more than once: {}", key
+                    ), span));
+                }
+
+                dict.inner.insert(key, (val, span));
+            }
         }
 
         Ok(dict)
     }
 
-    pub(crate) fn require_keys(&self, keys: &[&str]) -> Result<(), String> {
-        match keys.iter().find(|&&key| !self.inner.contains_key(key)) {
-            Some(absent_key) => Err(absent_key.to_string()),
-            None => Ok(())
-        }
-    }
-
-    pub(crate) fn allow_keys(&self, keys: &[&str]) -> Result<(), String> {
-        match self.inner.keys().find(|key| !keys.contains(&key.as_str())) {
-            Some(disallowed_key) => Err(disallowed_key.clone()),
-            None => Ok(())
+    pub(crate) fn remove_typed_value<T, F>(&mut self, key: &str, converter: F) -> MacroResult<Option<(T, Span)>>
+        where
+            F: Fn(&Value) -> ValueTypeResult<T>
+    {
+        match self.inner.remove(key) {
+            None => Ok(None),
+            Some((val, span)) => match converter(&val) {
+                Ok(converted) => Ok(Some((converted, span))),
+                Err(ValueTypeError { message }) => Err(MacroError::new(
+                    format!("{} for key: {}", message, key),
+                    span,
+                ))
             }
         }
     }
 
-impl Parse for Dict {
+    pub(crate) fn assert_empty(&self) -> MacroResult<()> {
+        if self.inner.is_empty() {
+            Ok(())
+        } else {
+            let (unexpected_key, (_, unexpected_span)) = self.inner.iter().next().unwrap();
+            Err(MacroError::new(
+                format!("unexpected key: {}", unexpected_key),
+                *unexpected_span,
+            ))
+        }
+    }
+}
+
+impl Parse for AttributeTag {
     fn parse(input: ParseStream) -> syn::Result<Self> {
-        Ok(Dict {
+        Ok(AttributeTag {
             inner: input
                 .parse_terminated::<KeyValPair, Token![,]>(KeyValPair::parse)?
                 .into_iter()
-                .map(|pair| (pair.key, (pair.val, pair.span)))
-                .collect::<HashMap<_, _>>()
+                .map(|pair| (pair.key, pair.val, pair.span))
+                .collect::<Vec<_>>()
         })
     }
 }
 
-struct KeyValPair {
-    key: String,
-    val: Value,
-    span: Span,
-}
-
 impl Parse for KeyValPair {
     fn parse(input: ParseStream) -> syn::Result<Self> {
         let key = input
@@ -77,15 +173,15 @@ impl Parse for KeyValPair {
 
         let val = if input.peek(Token![=]) {
             input.parse::<Token![=]>()?;
+
             if let Ok(lit) = speculative_parse::<Lit>(input) {
                 Value::Lit(lit)
             } else if let Ok(ident) = speculative_parse::<Ident>(input) {
                 Value::Ident(ident)
             } else {
-                let err_msg = format!(
-                    "expected either a literal or identifier as the value corresponding to the \
-                     key \"{}\", but found neither", key);
-                return Err(input.error(err_msg));
+                return Err(input.error(format!(
+                    "could not parse value corresponding to key: {}", key
+                )));
             }
         } else {
             Value::None

src/error.rs

@@ -1,18 +1,24 @@
 use std::borrow::Cow;
+use std::fmt;
+use std::error;
+use std::result;
 
 use proc_macro2::Span;
 use quote::quote_spanned;
+use syn::Error;
 
 #[derive(Clone, Debug)]
 pub(crate) struct MacroError {
-    message: Cow<'static, str>,
-    span: Span,
+    pub(crate) message: Cow<'static, str>,
+    pub(crate) span: Span,
 }
 
+pub(crate) type MacroResult<T> = result::Result<T, MacroError>;
+
 impl MacroError {
-    pub(crate) fn new(message: Cow<'static, str>, span: Span) -> Self {
+    pub(crate) fn new<T>(message: T, span: Span) -> Self where T : Into<Cow<'static, str>> {
         MacroError {
-            message,
+            message: message.into(),
             span,
         }
     }
@@ -29,4 +35,31 @@ impl MacroError {
     }
 }
 
-pub(crate) type Result<T> = std::result::Result<T, MacroError>;
+impl From<syn::Error> for MacroError {
+    fn from(err: Error) -> Self {
+        MacroError::new(err.to_string(), err.span())
+    }
+}
+
+impl fmt::Display for MacroError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{}", self.message)
+    }
+}
+
+impl error::Error for MacroError {}
+
+#[derive(Clone, Debug)]
+pub(crate) struct ValueTypeError {
+    pub(crate) message: Cow<'static, str>
+}
+
+pub(crate) type ValueTypeResult<T> = result::Result<T, ValueTypeError>;
+
+impl fmt::Display for ValueTypeError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{}", self.message)
+    }
+}
+
+impl error::Error for ValueTypeError {}

src/lib.rs

@@ -1,88 +1,169 @@
 use proc_macro::TokenStream;
+use std::collections::HashSet;
 
-use quote::quote;
-use syn::{Attribute, Data, DeriveInput, LitStr};
+use proc_macro2::Span;
+use quote::{quote, quote_spanned};
+use syn::{Attribute, Data, DataEnum, DeriveInput, Fields, LitStr};
+use syn::parse::{ParseBuffer, ParseStream};
+use syn::spanned::Spanned;
 
-/// Derives `serde::Deserialize` for an enum with variants associated with strings.
-/// The `#[str_name("...")]` attribute is used to specify the string associated with each variant.
-///
-/// An "other" variant can be specified with `#[other]`. This variant should have a parameter
-/// which implements `From<String>` to store the string that could not be deserialized to any
-/// of the other variants.
-///
-/// If no "other" variant is specified, strings which are not associated with any of the variants
-/// will produce a deserialization error.
-///
-/// The enum may have the attribute `#[case_insensitive]`, in which case string comparisons will
-/// be done case-insensitively.
-#[proc_macro_derive(EnumStrDeserialize, attributes(case_insensitive, str_name, other))]
-pub fn derive_enum_str_de(ast: TokenStream) -> TokenStream {
-    const ATTR_CASE_INSENSITIVE: &'static str = "case_insensitive";
-    const ATTR_STR_NAME: &'static str = "str_name";
-    const ATTR_OTHER: &'static str = "other";
+use attribute::*;
+use error::{MacroError, MacroResult};
 
-    let ast: DeriveInput = syn::parse(ast).unwrap();
+mod error;
+mod attribute;
 
-    let enum_name = &ast.ident;
-    let enum_names = std::iter::repeat(enum_name);
+const CRATE_ATTR: &'static str = "enumscribe";
 
-    let case_insensitive = find_attribute(ATTR_CASE_INSENSITIVE, &ast.attrs).is_some();
+#[derive(Clone, Debug)]
+struct Enum {
+    variants: Vec<Variant>,
+}
 
-    let enum_data = match ast.data {
-        Data::Enum(e) => e,
-        _ => panic!("cannot derive EnumStrDeserialize for anything other than an enum"),
+#[derive(Clone, Debug)]
+struct Variant {
+    ident: String,
+    v_type: VariantType,
+    span: Span,
+}
+
+#[derive(Clone, Debug)]
+enum VariantType {
+    Ignore,
+    Named { name: String, constructor: VariantConstructor },
+    Other { field_name: Option<String> }, //use {} for constructor if Some, use () if None
+}
+
+#[derive(Clone, Copy, Debug)]
+enum VariantConstructor {
+    None,
+    Paren,
+    Brace,
+}
+
+fn parse_enum(data: DataEnum) -> MacroResult<Enum> {
+    const NAME: &'static str = "str";
+    const OTHER: &'static str = "other";
+    const IGNORE: &'static str = "ignore";
+
+    let mut variants = Vec::with_capacity(data.variants.len());
+    let mut taken_names = HashSet::new();
+
+    for variant in data.variants {
+        let variant_ident = variant.ident.to_string();
+        let variant_span = variant.span();
+
+        let mut dict = Dict::from_attrs(CRATE_ATTR, &variant.attrs)?;
+
+        let name_opt = dict.remove_typed_value(NAME, Value::value_string)?;
+
+        let other = match dict.remove_typed_value(OTHER, Value::value_bool)? {
+            Some((other, _)) => other,
+            None => false
         };
 
-    let (variant_names, variant_strings): (Vec<_>, Vec<_>) = enum_data.variants.iter()
-        .map(|variant| (&variant.ident, find_attribute(ATTR_STR_NAME, &variant.attrs)))
-        .filter(|(_, attribute)| attribute.is_some())
-        .map(|(variant_ident, attribute)| (variant_ident, attribute
-            .unwrap()
-            .parse_args::<LitStr>()
-            .unwrap()
-            .value()))
-        .map(|(variant_ident, attribute)| (variant_ident, if case_insensitive {
-            attribute.to_lowercase()
-        } else {
-            attribute
-        }))
-        .unzip();
-
-    let other_variant = enum_data.variants.iter()
-        .find(|variant| find_attribute(ATTR_OTHER, &variant.attrs).is_some());
-
-    let matching_string = if case_insensitive {
-        quote! { deserialized_string.to_lowercase() }
-    } else {
-        quote! { deserialized_string }
+        let ignore = match dict.remove_typed_value(IGNORE, Value::value_bool)? {
+            Some((ignore, _)) => ignore,
+            None => false
         };
 
-    let (base_case_pattern, base_case_value) = if let Some(other_variant) = other_variant {
-        let other_variant_name = &other_variant.ident;
-        (quote! { _ }, quote! { ::core::result::Result::Ok(#enum_name::#other_variant_name(deserialized_string.into())) })
+        dict.assert_empty()?;
+
+        let scribe_variant = if ignore {
+            Variant {
+                ident: variant_ident,
+                v_type: VariantType::Ignore,
+                span: variant_span,
+            }
+        } else if other {
+            if let Some((_, name_span)) = name_opt {
+                return Err(MacroError::new(
+                    format!(
+                        "cannot use {} for variant {} because it is marked as {}",
+                        NAME, variant_ident, OTHER
+                    ),
+                    name_span,
+                ));
+            }
+
+            if variant.fields.len() != 1 {
+                return Err(MacroError::new(
+                    format!(
+                        "the variant {} must have exactly one field because it is marked as {}",
+                        variant_ident, OTHER
+                    ),
+                    variant_span,
+                ));
+            }
+
+            let field_name = variant.fields.iter().next()
+                .and_then(|field| field.ident.as_ref().map(|ident| ident.to_string()));
+
+            Variant {
+                ident: variant_ident,
+                v_type: VariantType::Other { field_name },
+                span: variant_span,
+            }
         } else {
-        (quote! { s }, quote! { ::core::result::Result::Err(::serde::de::Error::unknown_variant(s, &[#(#variant_strings),*])) })
+            let (name, name_span) = match name_opt {
+                Some((name, name_span)) => (name, name_span),
+                None => (variant.ident.to_string(), variant.ident.span())
             };
 
-    (quote! {
-        impl<'de> ::serde::Deserialize<'de> for #enum_name {
-            fn deserialize<D>(deserializer: D) -> ::core::result::Result<Self, D::Error>
-                where
-                    D: ::serde::Deserializer<'de>,
-            {
-                let deserialized_string = ::std::string::String::deserialize(deserializer)?;
-                match #matching_string.as_str() {
-                    #(#variant_strings => ::core::result::Result::Ok(#enum_names::#variant_names),)*
-                    #base_case_pattern => #base_case_value,
-                }
-            }
-        }
-    }).into()
+            if taken_names.contains(&name) {
+                return Err(MacroError::new(
+                    format!("duplicate name \"{}\"", name),
+                    name_span,
+                ));
             }
 
-fn find_attribute<'a>(name: &str, attributes: &'a [Attribute]) -> Option<&'a Attribute> {
-    attributes
-        .iter()
-        .find(|attribute| attribute.path.is_ident(name))
+            if variant.fields.len() != 0 {
+                return Err(MacroError::new(
+                    format!(
+                        "the variant {} must not have any fields",
+                        variant_ident
+                    ),
+                    variant_span,
+                ));
             }
 
+            let constructor = match variant.fields {
+                Fields::Named(_) => VariantConstructor::Brace,
+                Fields::Unnamed(_) => VariantConstructor::Paren,
+                Fields::Unit => VariantConstructor::None,
+            };
+
+            taken_names.insert(name.clone());
+
+            Variant {
+                ident: variant_ident,
+                v_type: VariantType::Named { name, constructor },
+                span: variant_span,
+            }
+        };
+
+        variants.push(scribe_variant);
+    }
+
+    Ok(Enum { variants })
+}
+
+#[proc_macro_derive(EnumToString, attributes(enumscribe))]
+pub fn derive_enum_to_string(input: TokenStream) -> TokenStream {
+    let input: DeriveInput = syn::parse(input).unwrap();
+
+    let enum_data = match input.data {
+        Data::Enum(data) => data,
+        Data::Struct(_) => return MacroError::new("cannot use enumscribe for structs", input.ident.span()).to_token_stream(),
+        Data::Union(_) => return MacroError::new("cannot use enumscribe for unions", input.ident.span()).to_token_stream()
+    };
+
+    let variants = match parse_enum(enum_data) {
+        Ok(variants) => variants,
+        Err(err) => return err.to_token_stream()
+    };
+
+    println!("{:?}", variants);
+
+    TokenStream::new()
+}