cleanup casts

crates/ra_hir/src/either.rs

@@ -25,6 +25,12 @@ impl<A, B> Either<A, B> {
             Either::B(b) => Either::B(f2(b)),
         }
     }
+    pub fn map_a<U, F>(self, f: F) -> Either<U, B>
+    where
+        F: FnOnce(A) -> U,
+    {
+        self.map(f, |it| it)
+    }
     pub fn a(self) -> Option<A> {
         match self {
             Either::A(it) => Some(it),

crates/ra_hir/src/source_binder.rs

@@ -309,15 +309,11 @@ impl SourceAnalyzer {
             crate::Resolution::LocalBinding(it) => {
                 // We get a `PatId` from resolver, but it actually can only
                 // point at `BindPat`, and not at the arbitrary pattern.
-                let pat_ptr = self.body_source_map.as_ref()?.pat_syntax(it)?;
-                let pat_ptr = match pat_ptr {
-                    Either::A(pat) => {
-                        let pat: AstPtr<ast::BindPat> =
-                            pat.cast_checking_kind(|kind| kind == BIND_PAT).unwrap();
-                        Either::A(pat)
-                    }
-                    Either::B(self_param) => Either::B(self_param),
-                };
+                let pat_ptr = self
+                    .body_source_map
+                    .as_ref()?
+                    .pat_syntax(it)?
+                    .map_a(|ptr| ptr.cast::<ast::BindPat>().unwrap());
                 PathResolution::LocalBinding(pat_ptr)
             }
             crate::Resolution::GenericParam(it) => PathResolution::GenericParam(it),

crates/ra_syntax/src/ast.rs

@@ -10,7 +10,7 @@ use std::marker::PhantomData;
 
 use crate::{
     syntax_node::{SyntaxNode, SyntaxNodeChildren, SyntaxToken},
-    SmolStr,
+    SmolStr, SyntaxKind,
 };
 
 pub use self::{
@@ -26,6 +26,8 @@ pub use self::{
 /// the same representation: a pointer to the tree root and a pointer to the
 /// node itself.
 pub trait AstNode: Clone {
+    fn can_cast(kind: SyntaxKind) -> bool;
+
     fn cast(syntax: SyntaxNode) -> Option<Self>
     where
         Self: Sized;

crates/ra_syntax/src/ast/generated.rs.tera

@@ -12,18 +12,34 @@ the below applies to the result of this template
 #![cfg_attr(rustfmt, rustfmt_skip)]
 
 use crate::{
-    SyntaxNode, SyntaxKind::*,
+    SyntaxNode, SyntaxKind::{self, *},
     ast::{self, AstNode},
 };
 {% for node, methods in ast %}
 // {{ node }}
-
-{%- if methods.enum %}
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
 pub struct {{ node }} {
     pub(crate) syntax: SyntaxNode,
 }
 
+impl AstNode for {{ node }} {
+    fn can_cast(kind: SyntaxKind) -> bool {
+        match kind {
+            {%- if methods.enum %}
+            {% for kind in methods.enum %} | {{ kind | SCREAM }} {%- endfor -%}
+            {% else %}
+            {{ node | SCREAM }}
+            {%- endif %} => true,
+            _ => false,
+        }
+    }
+    fn cast(syntax: SyntaxNode) -> Option<Self> {
+        if Self::can_cast(syntax.kind()) { Some({{ node }} { syntax }) } else { None }
+    }
+    fn syntax(&self) -> &SyntaxNode { &self.syntax }
+}
+
+{% if methods.enum %}
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub enum {{ node }}Kind {
 {%- for kind in methods.enum %}
@@ -33,25 +49,9 @@ pub enum {{ node }}Kind {
 
 {%- for kind in methods.enum %}
 impl From<{{ kind }}> for {{ node }} {
-    fn from(n: {{ kind }}) -> {{ node }} {
-        {{ node }}::cast(n.syntax).unwrap()
-    }
+    fn from(n: {{ kind }}) -> {{ node }} { {{ node }} { syntax: n.syntax } }
 }
 {%- endfor %}
-
-
-impl AstNode for {{ node }} {
-    fn cast(syntax: SyntaxNode) -> Option<Self> {
-        match syntax.kind() {
-            {%- for kind in methods.enum %}
-            | {{ kind | SCREAM }}
-            {%- endfor %} => Some({{ node }} { syntax }),
-            _ => None,
-        }
-    }
-    fn syntax(&self) -> &SyntaxNode { &self.syntax }
-}
-
 impl {{ node }} {
     pub fn kind(&self) -> {{ node }}Kind {
         match self.syntax.kind() {
@@ -62,22 +62,6 @@ impl {{ node }} {
         }
     }
 }
-{% else %}
-#[derive(Debug, Clone, PartialEq, Eq, Hash)]
-pub struct {{ node }} {
-    pub(crate) syntax: SyntaxNode,
-}
-
-impl AstNode for {{ node }} {
-    fn cast(syntax: SyntaxNode) -> Option<Self> {
-        match syntax.kind() {
-            {{ node | SCREAM }} => Some({{ node }} { syntax }),
-            _ => None,
-        }
-    }
-    fn syntax(&self) -> &SyntaxNode { &self.syntax }
-}
-
 {% endif %}
 {% if methods.traits -%}
 

crates/ra_syntax/src/ptr.rs

@@ -61,12 +61,8 @@ impl<N: AstNode> AstPtr<N> {
         self.raw
     }
 
-    // FIXME: extend AstNode to do this safely
-    pub fn cast_checking_kind<U: AstNode>(
-        self,
-        cond: impl FnOnce(SyntaxKind) -> bool,
-    ) -> Option<AstPtr<U>> {
-        if !cond(self.raw.kind()) {
+    pub fn cast<U: AstNode>(self) -> Option<AstPtr<U>> {
+        if !U::can_cast(self.raw.kind()) {
             return None;
         }
         Some(AstPtr { raw: self.raw, _ty: PhantomData })