2 files changed, 158 insertions, 0 deletions

diff --git a/crates/ra_hir_def/src/body.rs b/crates/ra_hir_def/src/body.rs
index bff17fd62..c3e9d0c23 100644
--- a/crates/ra_hir_def/src/body.rs
+++ b/crates/ra_hir_def/src/body.rs
@@ -1,5 +1,6 @@
 //! FIXME: write short doc here
 mod lower;
+pub mod scope;
 
 use std::{ops::Index, sync::Arc};
 
diff --git a/crates/ra_hir_def/src/body/scope.rs b/crates/ra_hir_def/src/body/scope.rs
new file mode 100644
index 000000000..dd8d06d11
--- /dev/null
+++ b/crates/ra_hir_def/src/body/scope.rs
@@ -0,0 +1,157 @@
+//! FIXME: write short doc here
+
+use hir_expand::name::Name;
+use ra_arena::{impl_arena_id, Arena, RawId};
+use rustc_hash::FxHashMap;
+
+use crate::{
+    body::Body,
+    expr::{Expr, ExprId, Pat, PatId, Statement},
+};
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub struct ScopeId(RawId);
+impl_arena_id!(ScopeId);
+
+#[derive(Debug, PartialEq, Eq)]
+pub struct ExprScopes {
+    scopes: Arena<ScopeId, ScopeData>,
+    scope_by_expr: FxHashMap<ExprId, ScopeId>,
+}
+
+#[derive(Debug, PartialEq, Eq)]
+pub struct ScopeEntry {
+    name: Name,
+    pat: PatId,
+}
+
+impl ScopeEntry {
+    pub fn name(&self) -> &Name {
+        &self.name
+    }
+
+    pub fn pat(&self) -> PatId {
+        self.pat
+    }
+}
+
+#[derive(Debug, PartialEq, Eq)]
+pub struct ScopeData {
+    parent: Option<ScopeId>,
+    entries: Vec<ScopeEntry>,
+}
+
+impl ExprScopes {
+    pub fn new(body: &Body) -> ExprScopes {
+        let mut scopes =
+            ExprScopes { scopes: Arena::default(), scope_by_expr: FxHashMap::default() };
+        let root = scopes.root_scope();
+        scopes.add_params_bindings(body, root, body.params());
+        compute_expr_scopes(body.body_expr(), body, &mut scopes, root);
+        scopes
+    }
+
+    pub fn entries(&self, scope: ScopeId) -> &[ScopeEntry] {
+        &self.scopes[scope].entries
+    }
+
+    pub fn scope_chain(&self, scope: Option<ScopeId>) -> impl Iterator<Item = ScopeId> + '_ {
+        std::iter::successors(scope, move |&scope| self.scopes[scope].parent)
+    }
+
+    pub fn scope_for(&self, expr: ExprId) -> Option<ScopeId> {
+        self.scope_by_expr.get(&expr).copied()
+    }
+
+    pub fn scope_by_expr(&self) -> &FxHashMap<ExprId, ScopeId> {
+        &self.scope_by_expr
+    }
+
+    fn root_scope(&mut self) -> ScopeId {
+        self.scopes.alloc(ScopeData { parent: None, entries: vec![] })
+    }
+
+    fn new_scope(&mut self, parent: ScopeId) -> ScopeId {
+        self.scopes.alloc(ScopeData { parent: Some(parent), entries: vec![] })
+    }
+
+    fn add_bindings(&mut self, body: &Body, scope: ScopeId, pat: PatId) {
+        match &body[pat] {
+            Pat::Bind { name, .. } => {
+                // bind can have a sub pattern, but it's actually not allowed
+                // to bind to things in there
+                let entry = ScopeEntry { name: name.clone(), pat };
+                self.scopes[scope].entries.push(entry)
+            }
+            p => p.walk_child_pats(|pat| self.add_bindings(body, scope, pat)),
+        }
+    }
+
+    fn add_params_bindings(&mut self, body: &Body, scope: ScopeId, params: &[PatId]) {
+        params.iter().for_each(|pat| self.add_bindings(body, scope, *pat));
+    }
+
+    fn set_scope(&mut self, node: ExprId, scope: ScopeId) {
+        self.scope_by_expr.insert(node, scope);
+    }
+}
+
+fn compute_block_scopes(
+    statements: &[Statement],
+    tail: Option<ExprId>,
+    body: &Body,
+    scopes: &mut ExprScopes,
+    mut scope: ScopeId,
+) {
+    for stmt in statements {
+        match stmt {
+            Statement::Let { pat, initializer, .. } => {
+                if let Some(expr) = initializer {
+                    scopes.set_scope(*expr, scope);
+                    compute_expr_scopes(*expr, body, scopes, scope);
+                }
+                scope = scopes.new_scope(scope);
+                scopes.add_bindings(body, scope, *pat);
+            }
+            Statement::Expr(expr) => {
+                scopes.set_scope(*expr, scope);
+                compute_expr_scopes(*expr, body, scopes, scope);
+            }
+        }
+    }
+    if let Some(expr) = tail {
+        compute_expr_scopes(expr, body, scopes, scope);
+    }
+}
+
+fn compute_expr_scopes(expr: ExprId, body: &Body, scopes: &mut ExprScopes, scope: ScopeId) {
+    scopes.set_scope(expr, scope);
+    match &body[expr] {
+        Expr::Block { statements, tail } => {
+            compute_block_scopes(&statements, *tail, body, scopes, scope);
+        }
+        Expr::For { iterable, pat, body: body_expr } => {
+            compute_expr_scopes(*iterable, body, scopes, scope);
+            let scope = scopes.new_scope(scope);
+            scopes.add_bindings(body, scope, *pat);
+            compute_expr_scopes(*body_expr, body, scopes, scope);
+        }
+        Expr::Lambda { args, body: body_expr, .. } => {
+            let scope = scopes.new_scope(scope);
+            scopes.add_params_bindings(body, scope, &args);
+            compute_expr_scopes(*body_expr, body, scopes, scope);
+        }
+        Expr::Match { expr, arms } => {
+            compute_expr_scopes(*expr, body, scopes, scope);
+            for arm in arms {
+                let scope = scopes.new_scope(scope);
+                for pat in &arm.pats {
+                    scopes.add_bindings(body, scope, *pat);
+                }
+                scopes.set_scope(arm.expr, scope);
+                compute_expr_scopes(arm.expr, body, scopes, scope);
+            }
+        }
+        e => e.walk_child_exprs(|e| compute_expr_scopes(e, body, scopes, scope)),
+    };
+}