Completed the procedural macro for deriving Graphs.

The macro `graph_derive` can automatically write the boiler-plate
codes for wrapper types one of whose sub-fields implements the `Graph`
trait.  The generated implementation will delegate the `Graph`
operations to the sub-field which implements the `Graph` trait.

I plan to add more macros, corresponding to various other
graph-related traits, so that no such boiler-plate codes are needed,
at least for my use-cases.

1 files changed, 654 insertions, 9 deletions

diff --git a/graph_macro/src/lib.rs b/graph_macro/src/lib.rs
index a55efbb..0f56f57 100644
--- a/graph_macro/src/lib.rs
+++ b/graph_macro/src/lib.rs
@@ -1,19 +1,664 @@
-#![allow(unused_imports)]
 //! This file provides a macro to delegate the implementation of a
 //! type that wraps a graph.  More precisely, the macro helps the
 //! wrapper type implement the various Graph-related traits.
+//!
+//! See the macro [`graph_derive`].
 
-use proc_macro::TokenStream;
+use proc_macro::{Delimiter, Group, Ident, Literal, Punct, Spacing, Span, TokenStream, TokenTree};
 
-use core::iter::Peekable;
+use std::{collections::HashMap, iter::Peekable};
 
-#[proc_macro_derive(Testing)]
-pub fn test_derive(input: TokenStream) -> TokenStream {
-    let input = input.into_iter().peekable();
+/// A visibility modifer is either "pub", "pub(restriction)", or
+/// "Private".
+#[derive(Debug, Default)]
+enum VisibilityMod {
+    /// Simple pub visibility.
+    Pub,
+    /// The pub visibility with restrictions.
+    ///
+    /// Since the restrictions can be given in a variety of ways, and
+    /// since it does not matter to us, we just keep them as a
+    /// tokentree.
+    PubRes(TokenTree),
+    #[default]
+    Private,
+}
+
+#[derive(Debug)]
+struct Generic {
+    name: Ident,
+    type_stream: TokenStream,
+}
+
+impl Generic {
+    fn new(name: Ident, type_stream: TokenStream) -> Self {
+        Self { name, type_stream }
+    }
+}
+
+/// The content of the struct
+#[derive(Debug)]
+struct GraphInfo {
+    name: TokenStream,
+    generics: Vec<Generic>,
+    field_name: String,
+    field_type: TokenStream,
+}
+
+impl GraphInfo {
+    fn new(
+        name: TokenStream,
+        generics: Vec<Generic>,
+        field_name: String,
+        field_type: TokenStream,
+    ) -> Self {
+        Self {
+            name,
+            generics,
+            field_name,
+            field_type,
+        }
+    }
+}
+
+/// For custom compiler errors
+#[derive(Debug)]
+struct CompileError {
+    mes: String,
+    span: Span,
+}
+
+impl CompileError {
+    fn new(mes: impl ToString, span: Span) -> Self {
+        Self {
+            mes: mes.to_string(),
+            span,
+        }
+    }
+
+    /// Produce a token stream that will trigger compiler errors.
+    ///
+    /// The point is that the span of the token trees will be set to
+    /// the desired locations, and hence produce the effect we want.
+    fn emit(self) -> TokenStream {
+        // I cannot use the parse method of the type TokenStream, as
+        // that will not set the spans properly.
+
+        let compile_error_ident = TokenTree::Ident(Ident::new("compile_error", self.span.clone()));
+        let mut exclamation_punct = TokenTree::Punct(Punct::new('!', Spacing::Alone));
+
+        exclamation_punct.set_span(self.span.clone());
+
+        let mut arg_mes_literal = TokenTree::Literal(Literal::string(&self.mes));
+
+        arg_mes_literal.set_span(self.span.clone());
+
+        let arg_mes_stream = [arg_mes_literal].into_iter().collect();
+
+        let mut arg_group = TokenTree::Group(Group::new(Delimiter::Parenthesis, arg_mes_stream));
+
+        arg_group.set_span(self.span.clone());
+
+        let mut semi_colon_punct = TokenTree::Punct(Punct::new(';', Spacing::Alone));
+
+        semi_colon_punct.set_span(self.span);
+
+        [
+            compile_error_ident,
+            exclamation_punct,
+            arg_group,
+            semi_colon_punct,
+        ]
+        .into_iter()
+        .collect()
+    }
+}
+
+macro_rules! unwrap_or_emit {
+    ($value:ident) => {
+        if let Err(err) = $value {
+            return err.emit();
+        }
+
+        let $value = $value.unwrap();
+    };
+}
+
+#[allow(unused)]
+macro_rules! mytodo {
+    () => {
+        Err(CompileError::new("not umplemented yet", Span::mixed_site()))
+    };
+}
+
+macro_rules! myerror {
+    ($mes:tt, $input:ident) => {
+        Err(CompileError::new($mes, $input.peek().unwrap().span()))
+    };
+}
+
+#[proc_macro_derive(Graph, attributes(graph))]
+pub fn graph_derive(input: TokenStream) -> TokenStream {
+    let mut input = input.into_iter().peekable();
+
+    while move_attributes(&mut input).is_ok() {}
+
+    let _ = get_visibility_mod(&mut input);
+
+    let info = get_info(&mut input);
+
+    unwrap_or_emit!(info);
+
+    let name = info.name;
+    let generics = info.generics;
+    let field_name = info.field_name;
+    let field_type = info.field_type;
+
+    let generics_impl_string = {
+        let mut result = String::new();
+
+        if !generics.is_empty() {
+            result.push_str("<");
+        }
+
+        for generic in generics.iter() {
+            result.push_str(&format!("{}:{},", generic.name, generic.type_stream));
+        }
+
+        if !generics.is_empty() {
+            result.push_str(">");
+        }
+
+        result
+    };
+
+    let generic_struct_string = {
+        let mut result = String::new();
+
+        if !generics.is_empty() {
+            result.push_str("<");
+        }
+
+        for generic in generics.iter() {
+            result.push_str(&format!("{},", generic.name));
+        }
+
+        if !generics.is_empty() {
+            result.push_str(">");
+        }
+
+        result
+    };
+
+    let generic_where_string = {
+        let mut result = String::new();
+
+        if !generics.is_empty() {
+            result.push_str("\nwhere\n");
+        }
+
+        for generic in generics.iter() {
+            result.push_str(&format!("{}: 'a,\n", generic.name));
+        }
+
+        result
+    };
+
+    let result =     format!(
+        "
+#[automatically_derived]
+impl{generics_impl_string} graph::Graph for {name}{generic_struct_string} {{
+type Iter<'a> = <{field_type} as graph::Graph>::Iter<'a>{generic_where_string};
+
+#[inline]
+fn is_empty(&self) -> bool {{self.{field_name}.is_empty()}}
+
+#[inline]
+fn nodes_len(&self) -> usize {{ self.{field_name}.nodes_len() }}
+
+#[inline]
+fn children_of(&self, node: usize) -> Result<<Self as graph::Graph>::Iter<'_>, graph::error::Error> {{
+self.{field_name}.children_of(node)
+}}
+
+#[inline]
+fn degree(&self, node: usize) -> Result<usize, graph::error::Error> {{ self.{field_name}.degree(node) }}
+
+#[inline]
+fn is_empty_node(&self, node: usize) -> Result<bool, graph::error::Error> {{ self.{field_name}.is_empty_node(node) }}
+
+#[inline]
+fn has_edge(&self, nodea: usize, nodeb: usize) -> Result<bool, graph::error::Error> {{
+self.{field_name}.has_edge(nodea, nodeb)
+}}
+
+#[inline]
+fn replace_by_builder(&mut self, _builder: impl graph::builder::Builder<Result = Self>) {{
+unimplemented!()
+}}
+}}"
+    );
+
+    result.parse().unwrap()
+}
+
+fn get_visibility_mod(
+    input: &mut Peekable<impl Iterator<Item = TokenTree>>,
+) -> Result<VisibilityMod, CompileError> {
+    if let Some(TokenTree::Ident(id)) = input.peek() {
+        if id.to_string() == "pub" {
+            input.next();
+
+            if let Some(TokenTree::Group(g)) = input.peek() {
+                let delimiter = g.delimiter();
+
+                if delimiter != Delimiter::Parenthesis {
+                    return Err(CompileError::new("invalid bracket", g.span()));
+                }
+
+                let tree = TokenTree::Group(g.clone());
+
+                input.next();
+
+                return Ok(VisibilityMod::PubRes(tree));
+            } else {
+                return Ok(VisibilityMod::Pub);
+            }
+        }
+    }
+
+    Ok(Default::default())
+}
+
+fn get_info(
+    input: &mut Peekable<impl Iterator<Item = TokenTree>>,
+) -> Result<GraphInfo, CompileError> {
+    if let Some(TokenTree::Ident(id)) = input.peek() {
+        if id.to_string() != "struct" {
+            let span = input.next().unwrap().span();
+            return Err(CompileError::new("Only struct is supported", span));
+        }
+
+        input.next();
+
+        let struct_name = get_until(
+            input,
+            |tree| match tree {
+                TokenTree::Group(g)
+                    if g.delimiter() == Delimiter::Brace
+                        || g.delimiter() == Delimiter::Parenthesis =>
+                {
+                    true
+                }
+                TokenTree::Punct(p) if p.as_char() == ';' || p.as_char() == '<' => true,
+                _ => false,
+            },
+            false,
+            false,
+        )?;
+
+        // We are not at the end as guaranteed by `get_until`.
+        let peek = input.peek().unwrap();
+
+        if matches!(peek, TokenTree::Punct(p) if p.as_char()  == ';') {
+            // unit struct
+
+            return myerror!("Cannot derive graph for unit structs", input);
+        }
+
+        let mut generics = Vec::new();
+
+        if matches!(peek, TokenTree::Punct(p) if p.as_char() == '<') {
+            // Extract generics
+
+            input.next();
+
+            generics = get_generics(input)?;
+
+            // println!("generics: {generics:?}");
+        }
+
+        let (graph_field_name, graph_field_type) = get_graph_field_name_type(input)?;
+
+        Ok(GraphInfo::new(
+            struct_name,
+            generics,
+            graph_field_name,
+            graph_field_type,
+        ))
+    } else {
+        myerror!("unexpected token", input)
+    }
+}
+
+fn get_graph_field_name_type(
+    input: &mut Peekable<impl Iterator<Item = TokenTree>>,
+) -> Result<(String, TokenStream), CompileError> {
+    let end_of_input = Err(CompileError::new(
+        "unexpected end of input",
+        Span::mixed_site(),
+    ));
+
+    match input.peek() {
+        Some(TokenTree::Group(g)) => {
+            let delimiter = g.delimiter();
+
+            if delimiter != Delimiter::Parenthesis && delimiter != Delimiter::Brace {
+                return myerror!(
+                    "expected a group enclosed in curly brackets or parentheses",
+                    input
+                );
+            }
+
+            if delimiter == Delimiter::Parenthesis {
+                // a named tuple
+
+                // in this case only a tuple with one field is
+                // supported
+
+                let mut body = g.stream().into_iter().peekable();
+
+                while let Some(tree) = body.peek() {
+                    if matches!(tree, TokenTree::Punct(p) if p.as_char() == ',') {
+                        return myerror!(
+                            "Among named tuples, only those with one field are supported",
+                            input
+                        );
+                    }
+
+                    body.next();
+                }
+
+                let mut body = g.stream().into_iter().peekable();
+
+                let _vis = get_visibility_mod(&mut body)?;
+
+                return Ok(("0".to_string(), body.collect()));
+            }
+
+            let mut body = g.stream().into_iter().peekable();
+
+            if body.peek().is_none() {
+                return end_of_input;
+            }
+
+            get_visibility_mod(&mut body)?;
+
+            let mut cloned_body = body.clone();
+
+            let mut result_name = get_first_ident(&mut cloned_body, g.span())?.to_string();
+
+            move_punct(&mut cloned_body, ':')?;
+
+            if cloned_body.peek().is_none() {
+                return end_of_input;
+            }
+
+            let mut result_type = get_until(
+                &mut cloned_body,
+                |tree| matches!(tree, TokenTree::Punct(p) if p.as_char() == ','),
+                true,
+                true,
+            )?;
+
+            let mut result = (result_name, result_type);
+
+            'search: while let Some(tree) = body.next() {
+                match tree {
+                    TokenTree::Punct(p) if p.as_char() == '#' => match body.peek() {
+                        Some(TokenTree::Group(g)) if g.delimiter() == Delimiter::Bracket => {
+                            let mut attr_stream = g.stream().into_iter().peekable();
+
+                            let mut found_attribute = false;
+
+                            while let Some(TokenTree::Ident(id)) = attr_stream.next() {
+                                if id.to_string() == "graph" {
+                                    found_attribute = true;
+
+                                    break;
+                                }
+
+                                let _ = move_punct(&mut attr_stream, ',');
+                            }
+
+                            body.next();
+
+                            if found_attribute {
+                                get_visibility_mod(&mut body)?;
+
+                                result_name = get_ident(&mut body)?.to_string();
+
+                                move_punct(&mut body, ':')?;
+
+                                result_type = get_until(
+                                    &mut body,
+                                    |tree| matches!(tree, TokenTree::Punct(p) if p.as_char() == ','),
+                                    true,
+                                    true,
+                                )?;
+
+                                result = (result_name, result_type);
+
+                                break 'search;
+                            }
+                        }
+                        Some(_) => {
+                            return myerror!("expected a group enclosed in square brackets", body);
+                        }
+                        None => {
+                            return end_of_input;
+                        }
+                    },
+                    _ => {}
+                }
+            }
+
+            Ok(result)
+        }
+        Some(_) => myerror!("expected a group or a semicolon", input),
+
+        _ => end_of_input,
+    }
+}
+
+fn get_generics(
+    input: &mut Peekable<impl Iterator<Item = TokenTree>>,
+) -> Result<Vec<Generic>, CompileError> {
+    // Assume the starting '<' punct has already been consumed.
+
+    let mut generic_map: HashMap<String, TokenStream> = Default::default();
+
+    let mut result: Vec<Generic> = Vec::new();
+
+    while !matches!(input.peek(), Some(TokenTree::Punct(p)) if p.as_char() == '>') {
+        let ident = get_ident(input)?.to_string();
+
+        let mut stream = TokenStream::new();
+
+        if matches!(input.peek(), Some(TokenTree::Punct(p)) if p.as_char() == ':') {
+            input.next();
+            stream = get_until(
+                input,
+                |tree| matches!(tree, TokenTree::Punct(p) if p.as_char() == ',' || p.as_char() == '>'),
+                false,
+                false,
+            )?;
+        }
+
+        generic_map.insert(ident, stream);
 
-    for tree in input {
-        println!("tree = {tree:?}");
+        let _ = move_punct(input, ',');
     }
 
-    TokenStream::new()
+    assert!(matches!(input.next(), Some(TokenTree::Punct(p)) if p.as_char() == '>'));
+
+    if matches!(input.peek(), Some(TokenTree::Ident(id)) if id.to_string() == "where") {
+        // where clauses
+
+        input.next();
+
+        while !matches!(input.peek(), Some(TokenTree::Group(g)) if g.delimiter() == Delimiter::Brace)
+        {
+            let ident = get_ident(input)?.to_string();
+
+            move_punct(input, ':')?;
+
+            let stream = get_until(
+                input,
+                |tree| match tree {
+                    TokenTree::Punct(p) if p.as_char() == ',' => true,
+                    TokenTree::Group(g) if g.delimiter() == Delimiter::Brace => true,
+                    _ => false,
+                },
+                false,
+                false,
+            )?;
+
+            generic_map.insert(ident, stream);
+
+            let _ = move_punct(input, ',');
+        }
+    }
+
+    if generic_map.is_empty() {
+        // this is not valid syntax anyways
+        return myerror!("empty generics section?", input);
+    }
+
+    for (k, v) in generic_map {
+        result.push(Generic::new(Ident::new(k.as_str(), Span::mixed_site()), v));
+    }
+
+    Ok(result)
+}
+
+fn get_ident(input: &mut Peekable<impl Iterator<Item = TokenTree>>) -> Result<Ident, CompileError> {
+    match input.peek() {
+        Some(TokenTree::Ident(id)) => {
+            let id = id.clone();
+
+            input.next();
+
+            Ok(id)
+        }
+        Some(next_tree) => {
+            let span = next_tree.span();
+
+            Err(CompileError::new("expected an identifier", span))
+        }
+        _ => Err(CompileError::new(
+            "unexpected end of input",
+            Span::mixed_site(),
+        )),
+    }
+}
+
+fn get_first_ident(
+    input: &mut Peekable<impl Iterator<Item = TokenTree>>,
+    span: Span,
+) -> Result<Ident, CompileError> {
+    while let Some(tree) = input.next() {
+        match tree {
+            TokenTree::Ident(id) => {
+                return Ok(id);
+            }
+            _ => {}
+        }
+    }
+
+    Err(CompileError::new("expect at least one identifier", span))
+}
+
+fn get_until(
+    input: &mut Peekable<impl Iterator<Item = TokenTree>>,
+    predicate: impl Fn(&TokenTree) -> bool,
+    accept_end: bool,
+    consume_boundary: bool,
+) -> Result<TokenStream, CompileError> {
+    let mut trees: Vec<TokenTree> = Vec::new();
+
+    let mut found_predicate = false;
+
+    if consume_boundary {
+        while let Some(tree) = input.next() {
+            if predicate(&tree) {
+                found_predicate = true;
+                break;
+            }
+
+            trees.push(tree);
+        }
+    } else {
+        while let Some(tree) = input.peek() {
+            if predicate(tree) {
+                found_predicate = true;
+                break;
+            }
+
+            let tree = input.next().unwrap();
+
+            trees.push(tree);
+        }
+    }
+
+    if found_predicate || accept_end {
+        Ok(trees.into_iter().collect())
+    } else {
+        Err(CompileError::new(
+            "unexpected end of input",
+            Span::mixed_site(),
+        ))
+    }
+}
+
+fn move_punct(
+    input: &mut Peekable<impl Iterator<Item = TokenTree>>,
+    punct: char,
+) -> Result<(), CompileError> {
+    let error_mes = format!("expect punctuation {punct}");
+
+    match input.peek() {
+        Some(TokenTree::Punct(p)) if p.as_char() == punct => {
+            input.next();
+
+            Ok(())
+        }
+        Some(_) => myerror!(error_mes, input),
+        _ => Err(CompileError::new(
+            "unexpected end of input",
+            Span::mixed_site(),
+        )),
+    }
+}
+
+fn move_attributes(
+    input: &mut Peekable<impl Iterator<Item = TokenTree>>,
+) -> Result<(), CompileError> {
+    let error_mes = "expect attributes";
+    let end_of_input = Err(CompileError::new(
+        "unexpected end of input",
+        Span::mixed_site(),
+    ));
+
+    match input.peek() {
+        Some(TokenTree::Punct(p)) if p.as_char() == '#' => {
+            input.next();
+
+            match input.peek() {
+                Some(TokenTree::Group(g)) if g.delimiter() == Delimiter::Bracket => {
+                    input.next();
+                }
+                Some(_) => {
+                    return myerror!("expected a group in square brackets", input);
+                }
+                _ => {
+                    return end_of_input;
+                }
+            }
+
+            Ok(())
+        }
+        Some(_) => myerror!(error_mes, input),
+        _ => end_of_input,
+    }
 }