1 files changed, 179 insertions, 0 deletions

diff --git a/crates/ra_assists/src/ast_transform.rs b/crates/ra_assists/src/ast_transform.rs
new file mode 100644
index 000000000..cbddc50ac
--- /dev/null
+++ b/crates/ra_assists/src/ast_transform.rs
@@ -0,0 +1,179 @@
+//! `AstTransformer`s are functions that replace nodes in an AST and can be easily combined.
+use rustc_hash::FxHashMap;
+
+use hir::{db::HirDatabase, InFile, PathResolution};
+use ra_syntax::ast::{self, make, AstNode};
+
+pub trait AstTransform<'a> {
+    fn get_substitution(
+        &self,
+        node: InFile<&ra_syntax::SyntaxNode>,
+    ) -> Option<ra_syntax::SyntaxNode>;
+
+    fn chain_before(self, other: Box<dyn AstTransform<'a> + 'a>) -> Box<dyn AstTransform<'a> + 'a>;
+    fn or<T: AstTransform<'a> + 'a>(self, other: T) -> Box<dyn AstTransform<'a> + 'a>
+    where
+        Self: Sized + 'a,
+    {
+        self.chain_before(Box::new(other))
+    }
+}
+
+struct NullTransformer;
+
+impl<'a> AstTransform<'a> for NullTransformer {
+    fn get_substitution(
+        &self,
+        _node: InFile<&ra_syntax::SyntaxNode>,
+    ) -> Option<ra_syntax::SyntaxNode> {
+        None
+    }
+    fn chain_before(self, other: Box<dyn AstTransform<'a> + 'a>) -> Box<dyn AstTransform<'a> + 'a> {
+        other
+    }
+}
+
+pub struct SubstituteTypeParams<'a, DB: HirDatabase> {
+    db: &'a DB,
+    substs: FxHashMap<hir::TypeParam, ast::TypeRef>,
+    previous: Box<dyn AstTransform<'a> + 'a>,
+}
+
+impl<'a, DB: HirDatabase> SubstituteTypeParams<'a, DB> {
+    pub fn for_trait_impl(
+        db: &'a DB,
+        trait_: hir::Trait,
+        impl_block: ast::ImplBlock,
+    ) -> SubstituteTypeParams<'a, DB> {
+        let substs = get_syntactic_substs(impl_block).unwrap_or_default();
+        let generic_def: hir::GenericDef = trait_.into();
+        let substs_by_param: FxHashMap<_, _> = generic_def
+            .params(db)
+            .into_iter()
+            // this is a trait impl, so we need to skip the first type parameter -- this is a bit hacky
+            .skip(1)
+            .zip(substs.into_iter())
+            .collect();
+        return SubstituteTypeParams {
+            db,
+            substs: substs_by_param,
+            previous: Box::new(NullTransformer),
+        };
+
+        // FIXME: It would probably be nicer if we could get this via HIR (i.e. get the
+        // trait ref, and then go from the types in the substs back to the syntax)
+        fn get_syntactic_substs(impl_block: ast::ImplBlock) -> Option<Vec<ast::TypeRef>> {
+            let target_trait = impl_block.target_trait()?;
+            let path_type = match target_trait {
+                ast::TypeRef::PathType(path) => path,
+                _ => return None,
+            };
+            let type_arg_list = path_type.path()?.segment()?.type_arg_list()?;
+            let mut result = Vec::new();
+            for type_arg in type_arg_list.type_args() {
+                let type_arg: ast::TypeArg = type_arg;
+                result.push(type_arg.type_ref()?);
+            }
+            Some(result)
+        }
+    }
+    fn get_substitution_inner(
+        &self,
+        node: InFile<&ra_syntax::SyntaxNode>,
+    ) -> Option<ra_syntax::SyntaxNode> {
+        let type_ref = ast::TypeRef::cast(node.value.clone())?;
+        let path = match &type_ref {
+            ast::TypeRef::PathType(path_type) => path_type.path()?,
+            _ => return None,
+        };
+        let analyzer = hir::SourceAnalyzer::new(self.db, node, None);
+        let resolution = analyzer.resolve_path(self.db, &path)?;
+        match resolution {
+            hir::PathResolution::TypeParam(tp) => Some(self.substs.get(&tp)?.syntax().clone()),
+            _ => None,
+        }
+    }
+}
+
+impl<'a, DB: HirDatabase> AstTransform<'a> for SubstituteTypeParams<'a, DB> {
+    fn get_substitution(
+        &self,
+        node: InFile<&ra_syntax::SyntaxNode>,
+    ) -> Option<ra_syntax::SyntaxNode> {
+        self.get_substitution_inner(node).or_else(|| self.previous.get_substitution(node))
+    }
+    fn chain_before(self, other: Box<dyn AstTransform<'a> + 'a>) -> Box<dyn AstTransform<'a> + 'a> {
+        Box::new(SubstituteTypeParams { previous: other, ..self })
+    }
+}
+
+pub struct QualifyPaths<'a, DB: HirDatabase> {
+    db: &'a DB,
+    from: Option<hir::Module>,
+    previous: Box<dyn AstTransform<'a> + 'a>,
+}
+
+impl<'a, DB: HirDatabase> QualifyPaths<'a, DB> {
+    pub fn new(db: &'a DB, from: Option<hir::Module>) -> Self {
+        Self { db, from, previous: Box::new(NullTransformer) }
+    }
+
+    fn get_substitution_inner(
+        &self,
+        node: InFile<&ra_syntax::SyntaxNode>,
+    ) -> Option<ra_syntax::SyntaxNode> {
+        // FIXME handle value ns?
+        let from = self.from?;
+        let p = ast::Path::cast(node.value.clone())?;
+        if p.segment().and_then(|s| s.param_list()).is_some() {
+            // don't try to qualify `Fn(Foo) -> Bar` paths, they are in prelude anyway
+            return None;
+        }
+        let analyzer = hir::SourceAnalyzer::new(self.db, node, None);
+        let resolution = analyzer.resolve_path(self.db, &p)?;
+        match resolution {
+            PathResolution::Def(def) => {
+                let found_path = from.find_use_path(self.db, def)?;
+                let args = p
+                    .segment()
+                    .and_then(|s| s.type_arg_list())
+                    .map(|arg_list| apply(self, node.with_value(arg_list)));
+                Some(make::path_with_type_arg_list(path_to_ast(found_path), args).syntax().clone())
+            }
+            PathResolution::Local(_)
+            | PathResolution::TypeParam(_)
+            | PathResolution::SelfType(_) => None,
+            PathResolution::Macro(_) => None,
+            PathResolution::AssocItem(_) => None,
+        }
+    }
+}
+
+pub fn apply<'a, N: AstNode>(transformer: &dyn AstTransform<'a>, node: InFile<N>) -> N {
+    let syntax = node.value.syntax();
+    let result = ra_syntax::algo::replace_descendants(syntax, &|element| match element {
+        ra_syntax::SyntaxElement::Node(n) => {
+            let replacement = transformer.get_substitution(node.with_value(&n))?;
+            Some(replacement.into())
+        }
+        _ => None,
+    });
+    N::cast(result).unwrap()
+}
+
+impl<'a, DB: HirDatabase> AstTransform<'a> for QualifyPaths<'a, DB> {
+    fn get_substitution(
+        &self,
+        node: InFile<&ra_syntax::SyntaxNode>,
+    ) -> Option<ra_syntax::SyntaxNode> {
+        self.get_substitution_inner(node).or_else(|| self.previous.get_substitution(node))
+    }
+    fn chain_before(self, other: Box<dyn AstTransform<'a> + 'a>) -> Box<dyn AstTransform<'a> + 'a> {
+        Box::new(QualifyPaths { previous: other, ..self })
+    }
+}
+
+fn path_to_ast(path: hir::ModPath) -> ast::Path {
+    let parse = ast::SourceFile::parse(&path.to_string());
+    parse.tree().syntax().descendants().find_map(ast::Path::cast).unwrap()
+}