Merge #7068

7068: Add VSCode command to view the hir of a function body r=theotherphil a=theotherphil

Will fix https://github.com/rust-analyzer/rust-analyzer/issues/7061. Very rough initial version just to work out where I needed to wire everything up.

@matklad would you be happy merging a hir visualiser of some kind? If so, do you have any thoughts on what you'd like it show, and how?

I've spent very little time on this thus far, so I'm fine with throwing away the contents of this PR, but I want to avoid taking the time to make this more polished/interactive/useful only to discover that no-one else has any interest in this functionality.

![image](https://user-images.githubusercontent.com/1974256/103236081-bb58f700-493b-11eb-9d12-55ae1b870f8f.png)


Co-authored-by: Phil Ellison <[email protected]>

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)