3 files changed, 74 insertions, 26 deletions

diff --git a/crates/ra_analysis/src/hover.rs b/crates/ra_analysis/src/hover.rs
new file mode 100644
index 000000000..c3825f6ea
--- /dev/null
+++ b/crates/ra_analysis/src/hover.rs
@@ -0,0 +1,57 @@
+use ra_db::{Cancelable, SyntaxDatabase};
+use ra_syntax::{ast, AstNode};
+
+use crate::{db::RootDatabase, RangeInfo, FilePosition, FileRange};
+
+pub(crate) fn hover(
+    db: &RootDatabase,
+    position: FilePosition,
+) -> Cancelable<Option<RangeInfo<String>>> {
+    let mut res = Vec::new();
+    let range = if let Some(rr) = db.approximately_resolve_symbol(position)? {
+        for nav in rr.resolves_to {
+            res.extend(db.doc_text_for(nav)?)
+        }
+        rr.reference_range
+    } else {
+        let file = db.source_file(position.file_id);
+        let expr: ast::Expr = ctry!(ra_editor::find_node_at_offset(
+            file.syntax(),
+            position.offset
+        ));
+        let frange = FileRange {
+            file_id: position.file_id,
+            range: expr.syntax().range(),
+        };
+        res.extend(db.type_of(frange)?);
+        expr.syntax().range()
+    };
+    if res.is_empty() {
+        return Ok(None);
+    }
+    let res = RangeInfo::new(range, res.join("\n\n---\n"));
+    Ok(Some(res))
+}
+
+#[cfg(test)]
+mod tests {
+    use ra_syntax::TextRange;
+
+    use crate::mock_analysis::single_file_with_position;
+
+    #[test]
+    fn hover_shows_type_of_an_expression() {
+        let (analysis, position) = single_file_with_position(
+            "
+            pub fn foo() -> u32 { 1 }
+
+            fn main() {
+                let foo_test = foo()<|>;
+            }
+        ",
+        );
+        let hover = analysis.hover(position).unwrap().unwrap();
+        assert_eq!(hover.range, TextRange::from_to(95.into(), 100.into()));
+        assert_eq!(hover.info, "u32");
+    }
+}
diff --git a/crates/ra_analysis/src/imp.rs b/crates/ra_analysis/src/imp.rs
index 10248013c..eae73c2c4 100644
--- a/crates/ra_analysis/src/imp.rs
+++ b/crates/ra_analysis/src/imp.rs
@@ -269,32 +269,6 @@ impl db::RootDatabase {
         Ok(result)
     }
 
-    pub(crate) fn hover(&self, position: FilePosition) -> Cancelable<Option<(TextRange, String)>> {
-        let mut res = Vec::new();
-        let range = if let Some(rr) = self.approximately_resolve_symbol(position)? {
-            for nav in rr.resolves_to {
-                res.extend(self.doc_text_for(nav)?)
-            }
-            rr.reference_range
-        } else {
-            let file = self.source_file(position.file_id);
-            let expr: ast::Expr = ctry!(ra_editor::find_node_at_offset(
-                file.syntax(),
-                position.offset
-            ));
-            let frange = FileRange {
-                file_id: position.file_id,
-                range: expr.syntax().range(),
-            };
-            res.extend(self.type_of(frange)?);
-            expr.syntax().range()
-        };
-        if res.is_empty() {
-            return Ok(None);
-        }
-        Ok(Some((range, res.join("\n\n---\n"))))
-    }
-
     pub(crate) fn diagnostics(&self, file_id: FileId) -> Cancelable<Vec<Diagnostic>> {
         let syntax = self.source_file(file_id);
 
diff --git a/crates/ra_analysis/src/lib.rs b/crates/ra_analysis/src/lib.rs
index 1e26a2889..1904ff884 100644
--- a/crates/ra_analysis/src/lib.rs
+++ b/crates/ra_analysis/src/lib.rs
@@ -21,6 +21,7 @@ mod runnables;
 
 mod extend_selection;
 mod syntax_highlighting;
+mod hover;
 
 use std::{fmt, sync::Arc};
 
@@ -260,6 +261,18 @@ impl NavigationTarget {
     }
 }
 
+#[derive(Debug)]
+pub struct RangeInfo<T> {
+    pub range: TextRange,
+    pub info: T,
+}
+
+impl<T> RangeInfo<T> {
+    fn new(range: TextRange, info: T) -> RangeInfo<T> {
+        RangeInfo { range, info }
+    }
+}
+
 /// Result of "goto def" query.
 #[derive(Debug)]
 pub struct ReferenceResolution {
@@ -394,6 +407,10 @@ impl Analysis {
     pub fn doc_text_for(&self, nav: NavigationTarget) -> Cancelable<Option<String>> {
         self.db.doc_text_for(nav)
     }
+    /// Returns a short text descrbing element at position.
+    pub fn hover(&self, position: FilePosition) -> Cancelable<Option<RangeInfo<String>>> {
+        hover::hover(&*self.db, position)
+    }
     /// Returns a `mod name;` declaration which created the current module.
     pub fn parent_module(&self, position: FilePosition) -> Cancelable<Vec<NavigationTarget>> {
         self.db.parent_module(position)