command macros that will hopefully work

regex_command_attr/src/attributes.rs

@@ -0,0 +1,293 @@
+use proc_macro2::Span;
+use syn::parse::{Error, Result};
+use syn::spanned::Spanned;
+use syn::{Attribute, Ident, Lit, LitStr, Meta, NestedMeta, Path};
+
+use crate::structures::PermissionLevel;
+use crate::util::{AsOption, LitExt};
+
+use std::fmt::{self, Write};
+
+#[derive(Debug, Clone, Copy, PartialEq)]
+pub enum ValueKind {
+    // #[<name>]
+    Name,
+
+    // #[<name> = <value>]
+    Equals,
+
+    // #[<name>([<value>, <value>, <value>, ...])]
+    List,
+
+    // #[<name>(<value>)]
+    SingleList,
+}
+
+impl fmt::Display for ValueKind {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            ValueKind::Name => f.pad("`#[<name>]`"),
+            ValueKind::Equals => f.pad("`#[<name> = <value>]`"),
+            ValueKind::List => f.pad("`#[<name>([<value>, <value>, <value>, ...])]`"),
+            ValueKind::SingleList => f.pad("`#[<name>(<value>)]`"),
+        }
+    }
+}
+
+fn to_ident(p: Path) -> Result<Ident> {
+    if p.segments.is_empty() {
+        return Err(Error::new(
+            p.span(),
+            "cannot convert an empty path to an identifier",
+        ));
+    }
+
+    if p.segments.len() > 1 {
+        return Err(Error::new(
+            p.span(),
+            "the path must not have more than one segment",
+        ));
+    }
+
+    if !p.segments[0].arguments.is_empty() {
+        return Err(Error::new(
+            p.span(),
+            "the singular path segment must not have any arguments",
+        ));
+    }
+
+    Ok(p.segments[0].ident.clone())
+}
+
+#[derive(Debug)]
+pub struct Values {
+    pub name: Ident,
+    pub literals: Vec<Lit>,
+    pub kind: ValueKind,
+    pub span: Span,
+}
+
+impl Values {
+    #[inline]
+    pub fn new(name: Ident, kind: ValueKind, literals: Vec<Lit>, span: Span) -> Self {
+        Values {
+            name,
+            literals,
+            kind,
+            span,
+        }
+    }
+}
+
+pub fn parse_values(attr: &Attribute) -> Result<Values> {
+    let meta = attr.parse_meta()?;
+
+    match meta {
+        Meta::Path(path) => {
+            let name = to_ident(path)?;
+
+            Ok(Values::new(name, ValueKind::Name, Vec::new(), attr.span()))
+        }
+        Meta::List(meta) => {
+            let name = to_ident(meta.path)?;
+            let nested = meta.nested;
+
+            if nested.is_empty() {
+                return Err(Error::new(attr.span(), "list cannot be empty"));
+            }
+
+            let mut lits = Vec::with_capacity(nested.len());
+
+            for meta in nested {
+                match meta {
+                    NestedMeta::Lit(l) => lits.push(l),
+                    NestedMeta::Meta(m) => match m {
+                        Meta::Path(path) => {
+                            let i = to_ident(path)?;
+                            lits.push(Lit::Str(LitStr::new(&i.to_string(), i.span())))
+                        }
+                        Meta::List(_) | Meta::NameValue(_) => {
+                            return Err(Error::new(attr.span(), "cannot nest a list; only accept literals and identifiers at this level"))
+                        }
+                    },
+                }
+            }
+
+            let kind = if lits.len() == 1 {
+                ValueKind::SingleList
+            } else {
+                ValueKind::List
+            };
+
+            Ok(Values::new(name, kind, lits, attr.span()))
+        }
+        Meta::NameValue(meta) => {
+            let name = to_ident(meta.path)?;
+            let lit = meta.lit;
+
+            Ok(Values::new(name, ValueKind::Equals, vec![lit], attr.span()))
+        }
+    }
+}
+
+#[derive(Debug, Clone)]
+struct DisplaySlice<'a, T>(&'a [T]);
+
+impl<'a, T: fmt::Display> fmt::Display for DisplaySlice<'a, T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let mut iter = self.0.iter().enumerate();
+
+        match iter.next() {
+            None => f.write_str("nothing")?,
+            Some((idx, elem)) => {
+                write!(f, "{}: {}", idx, elem)?;
+
+                for (idx, elem) in iter {
+                    f.write_char('\n')?;
+                    write!(f, "{}: {}", idx, elem)?;
+                }
+            }
+        }
+
+        Ok(())
+    }
+}
+
+#[inline]
+fn is_form_acceptable(expect: &[ValueKind], kind: ValueKind) -> bool {
+    if expect.contains(&ValueKind::List) && kind == ValueKind::SingleList {
+        true
+    } else {
+        expect.contains(&kind)
+    }
+}
+
+#[inline]
+fn validate(values: &Values, forms: &[ValueKind]) -> Result<()> {
+    if !is_form_acceptable(forms, values.kind) {
+        return Err(Error::new(
+            values.span,
+            // Using the `_args` version here to avoid an allocation.
+            format_args!(
+                "the attribute must be in of these forms:\n{}",
+                DisplaySlice(forms)
+            ),
+        ));
+    }
+
+    Ok(())
+}
+
+#[inline]
+pub fn parse<T: AttributeOption>(values: Values) -> Result<T> {
+    T::parse(values)
+}
+
+pub trait AttributeOption: Sized {
+    fn parse(values: Values) -> Result<Self>;
+}
+
+impl AttributeOption for Vec<String> {
+    fn parse(values: Values) -> Result<Self> {
+        validate(&values, &[ValueKind::List])?;
+
+        Ok(values
+            .literals
+            .into_iter()
+            .map(|lit| lit.to_str())
+            .collect())
+    }
+}
+
+impl AttributeOption for String {
+    #[inline]
+    fn parse(values: Values) -> Result<Self> {
+        validate(&values, &[ValueKind::Equals, ValueKind::SingleList])?;
+
+        Ok(values.literals[0].to_str())
+    }
+}
+
+impl AttributeOption for bool {
+    #[inline]
+    fn parse(values: Values) -> Result<Self> {
+        validate(&values, &[ValueKind::Name, ValueKind::SingleList])?;
+
+        Ok(values.literals.get(0).map_or(true, |l| l.to_bool()))
+    }
+}
+
+impl AttributeOption for Ident {
+    #[inline]
+    fn parse(values: Values) -> Result<Self> {
+        validate(&values, &[ValueKind::SingleList])?;
+
+        Ok(values.literals[0].to_ident())
+    }
+}
+
+impl AttributeOption for Vec<Ident> {
+    #[inline]
+    fn parse(values: Values) -> Result<Self> {
+        validate(&values, &[ValueKind::List])?;
+
+        Ok(values.literals.into_iter().map(|l| l.to_ident()).collect())
+    }
+}
+
+impl AttributeOption for Option<String> {
+    fn parse(values: Values) -> Result<Self> {
+        validate(&values, &[ValueKind::Name, ValueKind::Equals, ValueKind::SingleList])?;
+
+        Ok(values.literals.get(0).map(|l| l.to_str()))
+    }
+}
+
+impl AttributeOption for PermissionLevel {
+    fn parse(values: Values) -> Result<Self> {
+        validate(&values, &[ValueKind::SingleList])?;
+
+        Ok(values.literals.get(0).map(|l| PermissionLevel::from_str(&*l.to_str()).unwrap()).unwrap())
+    }
+}
+
+impl<T: AttributeOption> AttributeOption for AsOption<T> {
+    #[inline]
+    fn parse(values: Values) -> Result<Self> {
+        Ok(AsOption(Some(T::parse(values)?)))
+    }
+}
+
+macro_rules! attr_option_num {
+    ($($n:ty),*) => {
+        $(
+            impl AttributeOption for $n {
+                fn parse(values: Values) -> Result<Self> {
+                    validate(&values, &[ValueKind::SingleList])?;
+
+                    Ok(match &values.literals[0] {
+                        Lit::Int(l) => l.base10_parse::<$n>()?,
+                        l => {
+                            let s = l.to_str();
+                            // Use `as_str` to guide the compiler to use `&str`'s parse method.
+                            // We don't want to use our `parse` method here (`impl AttributeOption for String`).
+                            match s.as_str().parse::<$n>() {
+                                Ok(n) => n,
+                                Err(_) => return Err(Error::new(l.span(), "invalid integer")),
+                            }
+                        }
+                    })
+                }
+            }
+
+            impl AttributeOption for Option<$n> {
+                #[inline]
+                fn parse(values: Values) -> Result<Self> {
+                    <$n as AttributeOption>::parse(values).map(Some)
+                }
+            }
+        )*
+    }
+}
+
+attr_option_num!(u16, u32, usize);