refactor: factor out transform module

1 files changed, 158 insertions, 0 deletions

diff --git a/src/transform.rs b/src/transform.rs
new file mode 100644
index 0000000..4fc22f5
--- /dev/null
+++ b/src/transform.rs
@@ -0,0 +1,158 @@
+use std::collections::HashMap;
+
+use proc_macro2::Span;
+use syn::{
+    spanned::Spanned, GenericParam, Generics, Ident, PathArguments, Type, TypeParamBound, TypePath,
+};
+
+use crate::{
+    parse_trait_sig::{MethodParseError, TypeTransform},
+    syn_utils::{find_in_path, find_in_type},
+    As, AssocTypeMatcher,
+};
+
+#[derive(Default)]
+pub struct AssocTypeConversions<'a>(pub HashMap<&'a Ident, &'a Type>);
+
+pub enum TransformError {
+    UnconvertibleAssocType(Span),
+    AssocTypeInUnsupportedType(Span),
+}
+
+impl AssocTypeConversions<'_> {
+    pub fn parse_type_path(&self, type_: &mut Type) -> Result<TypeTransform, TransformError> {
+        let assoc_span = match find_in_type(type_, &AssocTypeMatcher) {
+            Some(path) => path.span(),
+            None => return Ok(TypeTransform::NoOp),
+        };
+
+        if let Type::Path(TypePath { path, qself: None }) = type_ {
+            let ident = &path.segments.first().unwrap().ident;
+
+            // TODO: support &mut dyn Iterator<Item = Self::A>
+            // conversion to  Box<dyn Iterator<Item = Whatever>> via .map(Into::into)
+
+            if ident == "Self" && path.segments.len() == 2 {
+                let ident = &path.segments.last().unwrap().ident;
+                *type_ = (*self
+                    .0
+                    .get(&ident)
+                    .ok_or_else(|| TransformError::UnconvertibleAssocType(ident.span()))?)
+                .clone();
+                return Ok(TypeTransform::Into);
+            } else if ident == "Option" && path.segments.len() == 1 {
+                let first_seg = path.segments.first_mut().unwrap();
+
+                if let Some(args) = first_seg.arguments.get_as_mut() {
+                    if args.args.len() == 1 {
+                        if let Some(generic_type) = args.args.first_mut().unwrap().get_as_mut() {
+                            if find_in_type(generic_type, &AssocTypeMatcher).is_some() {
+                                return Ok(TypeTransform::Map(
+                                    self.parse_type_path(generic_type)?.into(),
+                                ));
+                            }
+                        }
+                    }
+                }
+            } else if ident == "Result" && path.segments.len() == 1 {
+                let first_seg = path.segments.first_mut().unwrap();
+                if let Some(args) = first_seg.arguments.get_as_mut() {
+                    if args.args.len() == 2 {
+                        let mut args_iter = args.args.iter_mut();
+                        if let (Some(ok_type), Some(err_type)) = (
+                            args_iter.next().unwrap().get_as_mut(),
+                            args_iter.next().unwrap().get_as_mut(),
+                        ) {
+                            if find_in_type(ok_type, &AssocTypeMatcher).is_some()
+                                || find_in_type(err_type, &AssocTypeMatcher).is_some()
+                            {
+                                return Ok(TypeTransform::Result(
+                                    self.parse_type_path(ok_type)?.into(),
+                                    self.parse_type_path(err_type)?.into(),
+                                ));
+                            }
+                        }
+                    }
+                }
+            } else {
+                let last_seg = &path.segments.last().unwrap();
+                if last_seg.ident == "Result" {
+                    let last_seg = path.segments.last_mut().unwrap();
+                    if let Some(args) = last_seg.arguments.get_as_mut() {
+                        if args.args.len() == 1 {
+                            if let Some(generic_type) = args.args.first_mut().unwrap().get_as_mut()
+                            {
+                                if find_in_type(generic_type, &AssocTypeMatcher).is_some() {
+                                    return Ok(TypeTransform::Map(
+                                        self.parse_type_path(generic_type)?.into(),
+                                    ));
+                                }
+                            }
+                        }
+                    }
+                }
+            }
+        }
+
+        // the type contains an associated type but we
+        // don't know how to deal with it so we abort
+        Err(TransformError::AssocTypeInUnsupportedType(assoc_span))
+    }
+}
+
+pub fn dynamize_function_bounds<'a>(
+    generics: &'a mut Generics,
+    assoc_type_conversions: &AssocTypeConversions<'a>,
+) -> Result<HashMap<&'a Ident, Vec<TypeTransform>>, (Span, MethodParseError)> {
+    let mut type_param_transforms = HashMap::new();
+
+    for generic_param in &mut generics.params {
+        if let GenericParam::Type(type_param) = generic_param {
+            for bound in &mut type_param.bounds {
+                if let TypeParamBound::Trait(bound) = bound {
+                    if bound.path.segments.len() == 1 {
+                        let segment = bound.path.segments.first_mut().unwrap();
+
+                        if let PathArguments::Parenthesized(args) = &mut segment.arguments {
+                            if segment.ident == "Fn"
+                                || segment.ident == "FnOnce"
+                                || segment.ident == "FnMut"
+                            {
+                                let mut transforms = Vec::new();
+                                for input_type in &mut args.inputs {
+                                    match assoc_type_conversions.parse_type_path(input_type) {
+                                        Ok(ret_type) => {
+                                            transforms.push(ret_type);
+                                        }
+                                        Err(TransformError::UnconvertibleAssocType(span)) => {
+                                            return Err((
+                                                span,
+                                                MethodParseError::UnconvertibleAssocType,
+                                            ));
+                                        }
+                                        Err(TransformError::AssocTypeInUnsupportedType(span)) => {
+                                            return Err((
+                                                span,
+                                                MethodParseError::UnconvertibleAssocTypeInFnInput,
+                                            ));
+                                        }
+                                    }
+                                }
+                                if transforms.iter().any(|t| !matches!(t, TypeTransform::NoOp)) {
+                                    type_param_transforms.insert(&type_param.ident, transforms);
+                                }
+                            }
+                        }
+                    }
+                    if let Some(path) = find_in_path(&bound.path, &AssocTypeMatcher) {
+                        return Err((
+                            path.span(),
+                            MethodParseError::UnconvertibleAssocTypeInTraitBound,
+                        ));
+                    }
+                }
+            }
+        }
+    }
+    Ok(type_param_transforms)
+}