5 files changed, 107 insertions, 17 deletions

diff --git a/crates/ra_ide/src/lib.rs b/crates/ra_ide/src/lib.rs
index 7b187eba3..837315ca7 100644
--- a/crates/ra_ide/src/lib.rs
+++ b/crates/ra_ide/src/lib.rs
@@ -75,7 +75,7 @@ pub use crate::{
     inlay_hints::{InlayHint, InlayKind},
     line_index::{LineCol, LineIndex},
     line_index_utils::translate_offset_with_edit,
-    references::{Reference, ReferenceKind, ReferenceSearchResult, SearchScope},
+    references::{Reference, ReferenceAccess, ReferenceKind, ReferenceSearchResult, SearchScope},
     runnables::{Runnable, RunnableKind},
     source_change::{FileSystemEdit, SourceChange, SourceFileEdit},
     syntax_highlighting::HighlightedRange,
diff --git a/crates/ra_ide/src/references.rs b/crates/ra_ide/src/references.rs
index 5a3ec4eb9..b9d8a6b1e 100644
--- a/crates/ra_ide/src/references.rs
+++ b/crates/ra_ide/src/references.rs
@@ -19,8 +19,8 @@ use once_cell::unsync::Lazy;
 use ra_db::{SourceDatabase, SourceDatabaseExt};
 use ra_prof::profile;
 use ra_syntax::{
-    algo::find_node_at_offset, ast, AstNode, SourceFile, SyntaxKind, SyntaxNode, TextUnit,
-    TokenAtOffset,
+    algo::find_node_at_offset, ast, match_ast, AstNode, SourceFile, SyntaxKind, SyntaxNode,
+    TextUnit, TokenAtOffset,
 };
 
 use crate::{
@@ -46,6 +46,7 @@ pub struct ReferenceSearchResult {
 pub struct Reference {
     pub file_range: FileRange,
     pub kind: ReferenceKind,
+    pub access: Option<ReferenceAccess>,
 }
 
 #[derive(Debug, Clone, PartialEq)]
@@ -54,6 +55,12 @@ pub enum ReferenceKind {
     Other,
 }
 
+#[derive(Debug, Clone, PartialEq)]
+pub enum ReferenceAccess {
+    Read,
+    Write,
+}
+
 impl ReferenceSearchResult {
     pub fn declaration(&self) -> &NavigationTarget {
         &self.declaration
@@ -72,7 +79,7 @@ impl ReferenceSearchResult {
 }
 
 // allow turning ReferenceSearchResult into an iterator
-// over FileRanges
+// over References
 impl IntoIterator for ReferenceSearchResult {
     type Item = Reference;
     type IntoIter = std::vec::IntoIter<Reference>;
@@ -85,6 +92,7 @@ impl IntoIterator for ReferenceSearchResult {
                 range: self.declaration.range(),
             },
             kind: self.declaration_kind,
+            access: None,
         });
         v.append(&mut self.references);
         v.into_iter()
@@ -201,7 +209,13 @@ fn process_definition(
                         } else {
                             ReferenceKind::Other
                         };
-                        refs.push(Reference { file_range: FileRange { file_id, range }, kind });
+                        let access = access_mode(d.kind, &name_ref);
+
+                        refs.push(Reference {
+                            file_range: FileRange { file_id, range },
+                            kind,
+                            access,
+                        });
                     }
                 }
             }
@@ -210,11 +224,46 @@ fn process_definition(
     refs
 }
 
+fn access_mode(kind: NameKind, name_ref: &ast::NameRef) -> Option<ReferenceAccess> {
+    match kind {
+        NameKind::Local(_) | NameKind::Field(_) => {
+            //LetExpr or BinExpr
+            name_ref.syntax().ancestors().find_map(|node| {
+                match_ast! {
+                    match (node) {
+                        ast::BinExpr(expr) => {
+                            match expr.op_kind() {
+                                Some(kind) if kind.is_assignment() => {
+                                    if let Some(lhs) = expr.lhs() {
+                                        if lhs.syntax().text_range() == name_ref.syntax().text_range() {
+                                            return Some(ReferenceAccess::Write);
+                                        }
+                                    }
+
+                                    if let Some(rhs) = expr.rhs() {
+                                        if rhs.syntax().text_range().is_subrange(&name_ref.syntax().text_range()) {
+                                            return Some(ReferenceAccess::Read);
+                                        }
+                                    }
+                                },
+                                _ => { return Some(ReferenceAccess::Read) },
+                            }
+                            None
+                        },
+                        _ => {None}
+                    }
+                }
+            })
+        }
+        _ => None,
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use crate::{
         mock_analysis::{analysis_and_position, single_file_with_position, MockAnalysis},
-        Reference, ReferenceKind, ReferenceSearchResult, SearchScope,
+        Reference, ReferenceAccess, ReferenceKind, ReferenceSearchResult, SearchScope,
     };
 
     #[test]
@@ -515,6 +564,20 @@ mod tests {
         );
     }
 
+    #[test]
+    fn test_basic_highlight_read() {
+        let code = r#"
+        fn foo() {
+            let i<|> = 0;
+            i = i + 1;
+        }"#;
+
+        let refs = get_all_refs(code);
+        assert_eq!(refs.len(), 3);
+        assert_eq!(refs.references[0].access, Some(ReferenceAccess::Write));
+        assert_eq!(refs.references[1].access, Some(ReferenceAccess::Read));
+    }
+
     fn get_all_refs(text: &str) -> ReferenceSearchResult {
         let (analysis, position) = single_file_with_position(text);
         analysis.find_all_refs(position, None).unwrap().unwrap()
diff --git a/crates/ra_lsp_server/src/conv.rs b/crates/ra_lsp_server/src/conv.rs
index c260b51c4..1b93195d7 100644
--- a/crates/ra_lsp_server/src/conv.rs
+++ b/crates/ra_lsp_server/src/conv.rs
@@ -9,7 +9,7 @@ use lsp_types::{
 use ra_ide::{
     translate_offset_with_edit, CompletionItem, CompletionItemKind, FileId, FilePosition,
     FileRange, FileSystemEdit, Fold, FoldKind, InsertTextFormat, LineCol, LineIndex,
-    NavigationTarget, RangeInfo, Severity, SourceChange, SourceFileEdit,
+    NavigationTarget, RangeInfo, ReferenceAccess, Severity, SourceChange, SourceFileEdit,
 };
 use ra_syntax::{SyntaxKind, TextRange, TextUnit};
 use ra_text_edit::{AtomTextEdit, TextEdit};
@@ -53,6 +53,18 @@ impl Conv for SyntaxKind {
     }
 }
 
+impl Conv for ReferenceAccess {
+    type Output = ::lsp_types::DocumentHighlightKind;
+
+    fn conv(self) -> Self::Output {
+        use lsp_types::DocumentHighlightKind::*;
+        match self {
+            ReferenceAccess::Read => Read,
+            ReferenceAccess::Write => Write,
+        }
+    }
+}
+
 impl Conv for CompletionItemKind {
     type Output = ::lsp_types::CompletionItemKind;
 
diff --git a/crates/ra_lsp_server/src/main_loop/handlers.rs b/crates/ra_lsp_server/src/main_loop/handlers.rs
index a5b6f48af..a592f0a12 100644
--- a/crates/ra_lsp_server/src/main_loop/handlers.rs
+++ b/crates/ra_lsp_server/src/main_loop/handlers.rs
@@ -536,18 +536,32 @@ pub fn handle_references(
 
     let locations = if params.context.include_declaration {
         refs.into_iter()
-            .filter_map(|r| {
-                let line_index = world.analysis().file_line_index(r.file_range.file_id).ok()?;
-                to_location(r.file_range.file_id, r.file_range.range, &world, &line_index).ok()
+            .filter_map(|reference| {
+                let line_index =
+                    world.analysis().file_line_index(reference.file_range.file_id).ok()?;
+                to_location(
+                    reference.file_range.file_id,
+                    reference.file_range.range,
+                    &world,
+                    &line_index,
+                )
+                .ok()
             })
             .collect()
     } else {
         // Only iterate over the references if include_declaration was false
         refs.references()
             .iter()
-            .filter_map(|r| {
-                let line_index = world.analysis().file_line_index(r.file_range.file_id).ok()?;
-                to_location(r.file_range.file_id, r.file_range.range, &world, &line_index).ok()
+            .filter_map(|reference| {
+                let line_index =
+                    world.analysis().file_line_index(reference.file_range.file_id).ok()?;
+                to_location(
+                    reference.file_range.file_id,
+                    reference.file_range.range,
+                    &world,
+                    &line_index,
+                )
+                .ok()
             })
             .collect()
     };
@@ -836,10 +850,10 @@ pub fn handle_document_highlight(
 
     Ok(Some(
         refs.into_iter()
-            .filter(|r| r.file_range.file_id == file_id)
-            .map(|r| DocumentHighlight {
-                range: r.file_range.range.conv_with(&line_index),
-                kind: None,
+            .filter(|reference| reference.file_range.file_id == file_id)
+            .map(|reference| DocumentHighlight {
+                range: reference.file_range.range.conv_with(&line_index),
+                kind: reference.access.map(|it| it.conv()),
             })
             .collect(),
     ))
diff --git a/crates/ra_syntax/src/ast/expr_extensions.rs b/crates/ra_syntax/src/ast/expr_extensions.rs
index 23b6aa901..3dfecfe76 100644
--- a/crates/ra_syntax/src/ast/expr_extensions.rs
+++ b/crates/ra_syntax/src/ast/expr_extensions.rs
@@ -144,6 +144,7 @@ impl BinOp {
         }
     }
 }
+
 impl ast::BinExpr {
     pub fn op_details(&self) -> Option<(SyntaxToken, BinOp)> {
         self.syntax().children_with_tokens().filter_map(|it| it.into_token()).find_map(|c| {