6 files changed, 71 insertions, 4 deletions

diff --git a/crates/ra_analysis/src/imp.rs b/crates/ra_analysis/src/imp.rs
index 819827b95..166f1484f 100644
--- a/crates/ra_analysis/src/imp.rs
+++ b/crates/ra_analysis/src/imp.rs
@@ -364,6 +364,16 @@ impl AnalysisImpl {
         ret
     }
 
+    pub fn doc_comment_for(
+        &self,
+        file_id: FileId,
+        symbol: FileSymbol,
+    ) -> Cancelable<Option<String>> {
+        let file = self.db.file_syntax(file_id);
+
+        Ok(symbol.docs(&file))
+    }
+
     pub fn diagnostics(&self, file_id: FileId) -> Cancelable<Vec<Diagnostic>> {
         let module_tree = self.module_tree(file_id)?;
         let syntax = self.db.file_syntax(file_id);
diff --git a/crates/ra_analysis/src/lib.rs b/crates/ra_analysis/src/lib.rs
index 0ea9ebee7..db4e1ba86 100644
--- a/crates/ra_analysis/src/lib.rs
+++ b/crates/ra_analysis/src/lib.rs
@@ -258,6 +258,13 @@ impl Analysis {
     pub fn find_all_refs(&self, position: FilePosition) -> Cancelable<Vec<(FileId, TextRange)>> {
         Ok(self.imp.find_all_refs(position))
     }
+    pub fn doc_comment_for(
+        &self,
+        file_id: FileId,
+        symbol: FileSymbol
+    ) -> Cancelable<Option<String>> {
+        self.imp.doc_comment_for(file_id, symbol)
+    }
     pub fn parent_module(&self, position: FilePosition) -> Cancelable<Vec<(FileId, FileSymbol)>> {
         self.imp.parent_module(position)
     }
diff --git a/crates/ra_editor/src/symbols.rs b/crates/ra_editor/src/symbols.rs
index 4e602d0e3..bf3ac6ff2 100644
--- a/crates/ra_editor/src/symbols.rs
+++ b/crates/ra_editor/src/symbols.rs
@@ -2,7 +2,7 @@ use crate::TextRange;
 
 use ra_syntax::{
     algo::visit::{visitor, Visitor},
-    ast::{self, NameOwner},
+    ast::{self, DocCommentsOwner, NameOwner},
     AstNode, File, SmolStr, SyntaxKind, SyntaxNodeRef, WalkEvent,
 };
 
@@ -22,6 +22,30 @@ pub struct FileSymbol {
     pub kind: SyntaxKind,
 }
 
+impl FileSymbol {
+    pub fn docs(&self, file: &File) -> Option<String> {
+        file.syntax().descendants()
+            .filter(|node| node.kind() == self.kind && node.range() == self.node_range)
+            .filter_map(|node: SyntaxNodeRef| {
+                fn doc_comments<'a, N: DocCommentsOwner<'a>>(node: N) -> Option<String> {
+                    let comments = node.doc_comment_text();
+                    if comments.is_empty() { None } else { Some(comments) }
+                }
+
+                visitor()
+                    .visit(doc_comments::<ast::FnDef>)
+                    .visit(doc_comments::<ast::StructDef>)
+                    .visit(doc_comments::<ast::EnumDef>)
+                    .visit(doc_comments::<ast::TraitDef>)
+                    .visit(doc_comments::<ast::Module>)
+                    .visit(doc_comments::<ast::TypeDef>)
+                    .visit(doc_comments::<ast::ConstDef>)
+                    .visit(doc_comments::<ast::StaticDef>)
+                    .accept(node)?
+            }).nth(0)
+    }
+}
+
 pub fn file_symbols(file: &File) -> Vec<FileSymbol> {
     file.syntax().descendants().filter_map(to_symbol).collect()
 }
diff --git a/crates/ra_lsp_server/src/caps.rs b/crates/ra_lsp_server/src/caps.rs
index 0d02c8073..bcf857fce 100644
--- a/crates/ra_lsp_server/src/caps.rs
+++ b/crates/ra_lsp_server/src/caps.rs
@@ -16,7 +16,7 @@ pub fn server_capabilities() -> ServerCapabilities {
                 save: None,
             },
         )),
-        hover_provider: None,
+        hover_provider: Some(true),
         completion_provider: Some(CompletionOptions {
             resolve_provider: None,
             trigger_characters: None,
diff --git a/crates/ra_lsp_server/src/main_loop/handlers.rs b/crates/ra_lsp_server/src/main_loop/handlers.rs
index 5314a333e..97ab53f91 100644
--- a/crates/ra_lsp_server/src/main_loop/handlers.rs
+++ b/crates/ra_lsp_server/src/main_loop/handlers.rs
@@ -4,9 +4,9 @@ use gen_lsp_server::ErrorCode;
 use languageserver_types::{
     CodeActionResponse, Command, CompletionItem, CompletionItemKind, Diagnostic,
     DiagnosticSeverity, DocumentSymbol, Documentation, FoldingRange, FoldingRangeKind,
-    FoldingRangeParams, InsertTextFormat, Location, MarkupContent, MarkupKind, Position,
+    FoldingRangeParams, InsertTextFormat, Location, MarkupContent, MarkupKind, MarkedString, Position,
     PrepareRenameResponse, RenameParams, SymbolInformation, TextDocumentIdentifier, TextEdit,
-    WorkspaceEdit, ParameterInformation, SignatureInformation,
+    WorkspaceEdit, ParameterInformation, SignatureInformation, Hover, HoverContents,
 };
 use ra_analysis::{FileId, FoldKind, Query, RunnableKind, FilePosition};
 use ra_syntax::text_utils::contains_offset_nonstrict;
@@ -478,6 +478,31 @@ pub fn handle_signature_help(
     }
 }
 
+pub fn handle_hover(
+    world: ServerWorld,
+    params: req::TextDocumentPositionParams,
+) -> Result<Option<Hover>> {
+    let position = params.try_conv_with(&world)?;
+    let line_index = world.analysis().file_line_index(position.file_id);
+
+    for (file_id, symbol) in world.analysis().approximately_resolve_symbol(position)? {
+        let range = symbol.node_range.conv_with(&line_index);
+        let name = symbol.name.to_string();
+        let comment = world.analysis.doc_comment_for(file_id, symbol)?;
+
+        if comment.is_some() {
+            let contents = HoverContents::Scalar(MarkedString::String(comment.unwrap()));
+
+            return Ok(Some(Hover {
+                contents,
+                range: Some(range)
+            }))
+        }
+    }
+
+    Ok(None)
+}
+
 pub fn handle_prepare_rename(
     world: ServerWorld,
     params: req::TextDocumentPositionParams,
diff --git a/crates/ra_lsp_server/src/main_loop/mod.rs b/crates/ra_lsp_server/src/main_loop/mod.rs
index 229d1b0f7..db878e0aa 100644
--- a/crates/ra_lsp_server/src/main_loop/mod.rs
+++ b/crates/ra_lsp_server/src/main_loop/mod.rs
@@ -259,6 +259,7 @@ fn on_request(
         .on::<req::CodeActionRequest>(handlers::handle_code_action)?
         .on::<req::FoldingRangeRequest>(handlers::handle_folding_range)?
         .on::<req::SignatureHelpRequest>(handlers::handle_signature_help)?
+        .on::<req::HoverRequest>(handlers::handle_hover)?
         .on::<req::PrepareRenameRequest>(handlers::handle_prepare_rename)?
         .on::<req::Rename>(handlers::handle_rename)?
         .on::<req::References>(handlers::handle_references)?