Merge #1960

1960: Replace AST visitors with macro r=viorina a=viorina

Fixes #1672.

Co-authored-by: Ekaterina Babshukova <[email protected]>

4 files changed, 31 insertions, 132 deletions

diff --git a/crates/ra_syntax/src/algo.rs b/crates/ra_syntax/src/algo.rs
index d55534ede..7cfea70f9 100644
--- a/crates/ra_syntax/src/algo.rs
+++ b/crates/ra_syntax/src/algo.rs
@@ -1,7 +1,5 @@
 //! FIXME: write short doc here
 
-pub mod visit;
-
 use std::ops::RangeInclusive;
 
 use itertools::Itertools;
diff --git a/crates/ra_syntax/src/algo/visit.rs b/crates/ra_syntax/src/algo/visit.rs
deleted file mode 100644
index 4df275ba4..000000000
--- a/crates/ra_syntax/src/algo/visit.rs
+++ /dev/null
@@ -1,112 +0,0 @@
-//! FIXME: write short doc here
-
-use crate::{AstNode, SyntaxNode};
-
-use std::marker::PhantomData;
-
-pub fn visitor<'a, T>() -> impl Visitor<'a, Output = T> {
-    EmptyVisitor { ph: PhantomData }
-}
-
-pub fn visitor_ctx<'a, T, C>(ctx: C) -> impl VisitorCtx<'a, Output = T, Ctx = C> {
-    EmptyVisitorCtx { ph: PhantomData, ctx }
-}
-
-pub trait Visitor<'a>: Sized {
-    type Output;
-    fn accept(self, node: &'a SyntaxNode) -> Option<Self::Output>;
-    fn visit<N, F>(self, f: F) -> Vis<Self, N, F>
-    where
-        N: AstNode + 'a,
-        F: FnOnce(N) -> Self::Output,
-    {
-        Vis { inner: self, f, ph: PhantomData }
-    }
-}
-
-pub trait VisitorCtx<'a>: Sized {
-    type Output;
-    type Ctx;
-    fn accept(self, node: &'a SyntaxNode) -> Result<Self::Output, Self::Ctx>;
-    fn visit<N, F>(self, f: F) -> VisCtx<Self, N, F>
-    where
-        N: AstNode + 'a,
-        F: FnOnce(N, Self::Ctx) -> Self::Output,
-    {
-        VisCtx { inner: self, f, ph: PhantomData }
-    }
-}
-
-#[derive(Debug)]
-struct EmptyVisitor<T> {
-    ph: PhantomData<fn() -> T>,
-}
-
-impl<'a, T> Visitor<'a> for EmptyVisitor<T> {
-    type Output = T;
-
-    fn accept(self, _node: &'a SyntaxNode) -> Option<T> {
-        None
-    }
-}
-
-#[derive(Debug)]
-struct EmptyVisitorCtx<T, C> {
-    ctx: C,
-    ph: PhantomData<fn() -> T>,
-}
-
-impl<'a, T, C> VisitorCtx<'a> for EmptyVisitorCtx<T, C> {
-    type Output = T;
-    type Ctx = C;
-
-    fn accept(self, _node: &'a SyntaxNode) -> Result<T, C> {
-        Err(self.ctx)
-    }
-}
-
-#[derive(Debug)]
-pub struct Vis<V, N, F> {
-    inner: V,
-    f: F,
-    ph: PhantomData<fn(N)>,
-}
-
-impl<'a, V, N, F> Visitor<'a> for Vis<V, N, F>
-where
-    V: Visitor<'a>,
-    N: AstNode + 'a,
-    F: FnOnce(N) -> <V as Visitor<'a>>::Output,
-{
-    type Output = <V as Visitor<'a>>::Output;
-
-    fn accept(self, node: &'a SyntaxNode) -> Option<Self::Output> {
-        let Vis { inner, f, .. } = self;
-        inner.accept(node).or_else(|| N::cast(node.clone()).map(f))
-    }
-}
-
-#[derive(Debug)]
-pub struct VisCtx<V, N, F> {
-    inner: V,
-    f: F,
-    ph: PhantomData<fn(N)>,
-}
-
-impl<'a, V, N, F> VisitorCtx<'a> for VisCtx<V, N, F>
-where
-    V: VisitorCtx<'a>,
-    N: AstNode + 'a,
-    F: FnOnce(N, <V as VisitorCtx<'a>>::Ctx) -> <V as VisitorCtx<'a>>::Output,
-{
-    type Output = <V as VisitorCtx<'a>>::Output;
-    type Ctx = <V as VisitorCtx<'a>>::Ctx;
-
-    fn accept(self, node: &'a SyntaxNode) -> Result<Self::Output, Self::Ctx> {
-        let VisCtx { inner, f, .. } = self;
-        inner.accept(node).or_else(|ctx| match N::cast(node.clone()) {
-            None => Err(ctx),
-            Some(node) => Ok(f(node, ctx)),
-        })
-    }
-}
diff --git a/crates/ra_syntax/src/lib.rs b/crates/ra_syntax/src/lib.rs
index edb6076bb..c315ba552 100644
--- a/crates/ra_syntax/src/lib.rs
+++ b/crates/ra_syntax/src/lib.rs
@@ -160,6 +160,17 @@ impl SourceFile {
     }
 }
 
+#[macro_export]
+macro_rules! match_ast {
+    (match $node:ident {
+        $( ast::$ast:ident($it:ident) => $res:block, )*
+        _ => $catch_all:expr,
+    }) => {{
+        $( if let Some($it) = ast::$ast::cast($node.clone()) $res else )*
+        { $catch_all }
+    }};
+}
+
 /// This test does not assert anything and instead just shows off the crate's
 /// API.
 #[test]
@@ -294,7 +305,7 @@ fn api_walkthrough() {
     // To recursively process the tree, there are three approaches:
     // 1. explicitly call getter methods on AST nodes.
     // 2. use descendants and `AstNode::cast`.
-    // 3. use descendants and the visitor.
+    // 3. use descendants and `match_ast!`.
     //
     // Here's how the first one looks like:
     let exprs_cast: Vec<String> = file
@@ -304,17 +315,17 @@ fn api_walkthrough() {
         .map(|expr| expr.syntax().text().to_string())
         .collect();
 
-    // An alternative is to use a visitor. The visitor does not do traversal
-    // automatically (so it's more akin to a generic lambda) and is constructed
-    // from closures. This seems more flexible than a single generated visitor
-    // trait.
-    use algo::visit::{visitor, Visitor};
+    // An alternative is to use a macro.
     let mut exprs_visit = Vec::new();
     for node in file.syntax().descendants() {
-        if let Some(result) =
-            visitor().visit::<ast::Expr, _>(|expr| expr.syntax().text().to_string()).accept(&node)
-        {
-            exprs_visit.push(result);
+        match_ast! {
+            match node {
+                ast::Expr(it) => {
+                    let res = it.syntax().text().to_string();
+                    exprs_visit.push(res);
+                },
+                _ => (),
+            }
         }
     }
     assert_eq!(exprs_cast, exprs_visit);
diff --git a/crates/ra_syntax/src/validation.rs b/crates/ra_syntax/src/validation.rs
index 4f8935b2c..ab4f15908 100644
--- a/crates/ra_syntax/src/validation.rs
+++ b/crates/ra_syntax/src/validation.rs
@@ -5,8 +5,7 @@ mod block;
 use rustc_lexer::unescape;
 
 use crate::{
-    algo::visit::{visitor_ctx, VisitorCtx},
-    ast, AstNode, SyntaxError, SyntaxErrorKind,
+    ast, match_ast, AstNode, SyntaxError, SyntaxErrorKind,
     SyntaxKind::{BYTE, BYTE_STRING, CHAR, INT_NUMBER, STRING},
     SyntaxNode, SyntaxToken, TextUnit, T,
 };
@@ -97,12 +96,15 @@ impl From<rustc_lexer::unescape::EscapeError> for SyntaxErrorKind {
 pub(crate) fn validate(root: &SyntaxNode) -> Vec<SyntaxError> {
     let mut errors = Vec::new();
     for node in root.descendants() {
-        let _ = visitor_ctx(&mut errors)
-            .visit::<ast::Literal, _>(validate_literal)
-            .visit::<ast::BlockExpr, _>(block::validate_block_expr)
-            .visit::<ast::FieldExpr, _>(|it, errors| validate_numeric_name(it.name_ref(), errors))
-            .visit::<ast::RecordField, _>(|it, errors| validate_numeric_name(it.name_ref(), errors))
-            .accept(&node);
+        match_ast! {
+            match node {
+                ast::Literal(it) => { validate_literal(it, &mut errors) },
+                ast::BlockExpr(it) => { block::validate_block_expr(it, &mut errors) },
+                ast::FieldExpr(it) => { validate_numeric_name(it.name_ref(), &mut errors) },
+                ast::RecordField(it) => { validate_numeric_name(it.name_ref(), &mut errors) },
+                _ => (),
+            }
+        }
     }
     errors
 }