6 files changed, 63 insertions, 1 deletions

diff --git a/crates/hir/src/code_model.rs b/crates/hir/src/code_model.rs
index 3c83231cf..62eccf475 100644
--- a/crates/hir/src/code_model.rs
+++ b/crates/hir/src/code_model.rs
@@ -39,7 +39,7 @@ use hir_ty::{
     TyDefId, TyKind, TypeCtor,
 };
 use rustc_hash::FxHashSet;
-use stdx::impl_from;
+use stdx::{format_to, impl_from};
 use syntax::{
     ast::{self, AttrsOwner, NameOwner},
     AstNode, SmolStr,
@@ -797,6 +797,19 @@ impl Function {
     pub fn has_body(self, db: &dyn HirDatabase) -> bool {
         db.function_data(self.id).has_body
     }
+
+    /// A textual representation of the HIR of this function for debugging purposes.
+    pub fn debug_hir(self, db: &dyn HirDatabase) -> String {
+        let body = db.body(self.id.into());
+
+        let mut result = String::new();
+        format_to!(result, "HIR expressions in the body of `{}`:\n", self.name(db));
+        for (id, expr) in body.exprs.iter() {
+            format_to!(result, "{:?}: {:?}\n", id, expr);
+        }
+
+        result
+    }
 }
 
 // Note: logically, this belongs to `hir_ty`, but we are not using it there yet.
diff --git a/crates/ide/src/lib.rs b/crates/ide/src/lib.rs
index b3331f03f..a450794f3 100644
--- a/crates/ide/src/lib.rs
+++ b/crates/ide/src/lib.rs
@@ -31,6 +31,7 @@ mod folding_ranges;
 mod goto_definition;
 mod goto_implementation;
 mod goto_type_definition;
+mod view_hir;
 mod hover;
 mod inlay_hints;
 mod join_lines;
@@ -271,6 +272,10 @@ impl Analysis {
         self.with_db(|db| syntax_tree::syntax_tree(&db, file_id, text_range))
     }
 
+    pub fn view_hir(&self, position: FilePosition) -> Cancelable<String> {
+        self.with_db(|db| view_hir::view_hir(&db, position))
+    }
+
     pub fn expand_macro(&self, position: FilePosition) -> Cancelable<Option<ExpandedMacro>> {
         self.with_db(|db| expand_macro::expand_macro(db, position))
     }
diff --git a/crates/ide/src/view_hir.rs b/crates/ide/src/view_hir.rs
new file mode 100644
index 000000000..cfcfb7cfb
--- /dev/null
+++ b/crates/ide/src/view_hir.rs
@@ -0,0 +1,25 @@
+use hir::{Function, Semantics};
+use ide_db::base_db::FilePosition;
+use ide_db::RootDatabase;
+use syntax::{algo::find_node_at_offset, ast, AstNode};
+
+// Feature: View Hir
+//
+// |===
+// | Editor  | Action Name
+//
+// | VS Code | **Rust Analyzer: View Hir**
+// |===
+pub(crate) fn view_hir(db: &RootDatabase, position: FilePosition) -> String {
+    body_hir(db, position).unwrap_or("Not inside a function body".to_string())
+}
+
+fn body_hir(db: &RootDatabase, position: FilePosition) -> Option<String> {
+    let sema = Semantics::new(db);
+    let source_file = sema.parse(position.file_id);
+
+    let function = find_node_at_offset::<ast::Fn>(source_file.syntax(), position.offset)?;
+
+    let function: Function = sema.to_def(&function)?;
+    Some(function.debug_hir(db))
+}
diff --git a/crates/rust-analyzer/src/handlers.rs b/crates/rust-analyzer/src/handlers.rs
index 948cfc17c..dd486070b 100644
--- a/crates/rust-analyzer/src/handlers.rs
+++ b/crates/rust-analyzer/src/handlers.rs
@@ -105,6 +105,16 @@ pub(crate) fn handle_syntax_tree(
     Ok(res)
 }
 
+pub(crate) fn handle_view_hir(
+    snap: GlobalStateSnapshot,
+    params: lsp_types::TextDocumentPositionParams,
+) -> Result<String> {
+    let _p = profile::span("handle_view_hir");
+    let position = from_proto::file_position(&snap, params)?;
+    let res = snap.analysis.view_hir(position)?;
+    Ok(res)
+}
+
 pub(crate) fn handle_expand_macro(
     snap: GlobalStateSnapshot,
     params: lsp_ext::ExpandMacroParams,
diff --git a/crates/rust-analyzer/src/lsp_ext.rs b/crates/rust-analyzer/src/lsp_ext.rs
index 93ac45415..a85978737 100644
--- a/crates/rust-analyzer/src/lsp_ext.rs
+++ b/crates/rust-analyzer/src/lsp_ext.rs
@@ -53,6 +53,14 @@ pub struct SyntaxTreeParams {
     pub range: Option<Range>,
 }
 
+pub enum ViewHir {}
+
+impl Request for ViewHir {
+    type Params = lsp_types::TextDocumentPositionParams;
+    type Result = String;
+    const METHOD: &'static str = "rust-analyzer/viewHir";
+}
+
 pub enum ExpandMacro {}
 
 impl Request for ExpandMacro {
diff --git a/crates/rust-analyzer/src/main_loop.rs b/crates/rust-analyzer/src/main_loop.rs
index 5d55dc96e..8eca79f7e 100644
--- a/crates/rust-analyzer/src/main_loop.rs
+++ b/crates/rust-analyzer/src/main_loop.rs
@@ -443,6 +443,7 @@ impl GlobalState {
             .on_sync::<lsp_ext::MemoryUsage>(|s, p| handlers::handle_memory_usage(s, p))?
             .on::<lsp_ext::AnalyzerStatus>(handlers::handle_analyzer_status)
             .on::<lsp_ext::SyntaxTree>(handlers::handle_syntax_tree)
+            .on::<lsp_ext::ViewHir>(handlers::handle_view_hir)
             .on::<lsp_ext::ExpandMacro>(handlers::handle_expand_macro)
             .on::<lsp_ext::ParentModule>(handlers::handle_parent_module)
             .on::<lsp_ext::Runnables>(handlers::handle_runnables)