1 files changed, 176 insertions, 0 deletions

diff --git a/crates/ra_analysis/src/hover.rs b/crates/ra_analysis/src/hover.rs
new file mode 100644
index 000000000..766fa0547
--- /dev/null
+++ b/crates/ra_analysis/src/hover.rs
@@ -0,0 +1,176 @@
+use ra_db::{Cancelable, SyntaxDatabase};
+use ra_syntax::{
+    AstNode, SyntaxNode,
+    ast::{self, NameOwner},
+    algo::{find_covering_node, visit::{visitor, Visitor}},
+};
+
+use crate::{db::RootDatabase, RangeInfo, FilePosition, FileRange, NavigationTarget};
+
+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(doc_text_for(db, 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(type_of(db, frange)?);
+        expr.syntax().range()
+    };
+    if res.is_empty() {
+        return Ok(None);
+    }
+    let res = RangeInfo::new(range, res.join("\n\n---\n"));
+    Ok(Some(res))
+}
+
+pub(crate) fn type_of(db: &RootDatabase, frange: FileRange) -> Cancelable<Option<String>> {
+    let file = db.source_file(frange.file_id);
+    let syntax = file.syntax();
+    let node = find_covering_node(syntax, frange.range);
+    let parent_fn = ctry!(node.ancestors().find_map(ast::FnDef::cast));
+    let function = ctry!(hir::source_binder::function_from_source(
+        db,
+        frange.file_id,
+        parent_fn
+    )?);
+    let infer = function.infer(db)?;
+    Ok(infer.type_of_node(node).map(|t| t.to_string()))
+}
+
+// FIXME: this should not really use navigation target. Rather, approximatelly
+// resovled symbol should return a `DefId`.
+fn doc_text_for(db: &RootDatabase, nav: NavigationTarget) -> Cancelable<Option<String>> {
+    let result = match (nav.description(db), nav.docs(db)) {
+        (Some(desc), Some(docs)) => Some("```rust\n".to_string() + &*desc + "\n```\n\n" + &*docs),
+        (Some(desc), None) => Some("```rust\n".to_string() + &*desc + "\n```"),
+        (None, Some(docs)) => Some(docs),
+        _ => None,
+    };
+
+    Ok(result)
+}
+
+impl NavigationTarget {
+    fn node(&self, db: &RootDatabase) -> Option<SyntaxNode> {
+        let source_file = db.source_file(self.file_id);
+        let source_file = source_file.syntax();
+        let node = source_file
+            .descendants()
+            .find(|node| node.kind() == self.kind && node.range() == self.range)?
+            .owned();
+        Some(node)
+    }
+
+    fn docs(&self, db: &RootDatabase) -> Option<String> {
+        let node = self.node(db)?;
+        let node = node.borrowed();
+        fn doc_comments<'a, N: ast::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)?
+    }
+
+    /// Get a description of this node.
+    ///
+    /// e.g. `struct Name`, `enum Name`, `fn Name`
+    fn description(&self, db: &RootDatabase) -> Option<String> {
+        // TODO: After type inference is done, add type information to improve the output
+        let node = self.node(db)?;
+        let node = node.borrowed();
+        // TODO: Refactor to be have less repetition
+        visitor()
+            .visit(|node: ast::FnDef| {
+                let mut string = "fn ".to_string();
+                node.name()?.syntax().text().push_to(&mut string);
+                Some(string)
+            })
+            .visit(|node: ast::StructDef| {
+                let mut string = "struct ".to_string();
+                node.name()?.syntax().text().push_to(&mut string);
+                Some(string)
+            })
+            .visit(|node: ast::EnumDef| {
+                let mut string = "enum ".to_string();
+                node.name()?.syntax().text().push_to(&mut string);
+                Some(string)
+            })
+            .visit(|node: ast::TraitDef| {
+                let mut string = "trait ".to_string();
+                node.name()?.syntax().text().push_to(&mut string);
+                Some(string)
+            })
+            .visit(|node: ast::Module| {
+                let mut string = "mod ".to_string();
+                node.name()?.syntax().text().push_to(&mut string);
+                Some(string)
+            })
+            .visit(|node: ast::TypeDef| {
+                let mut string = "type ".to_string();
+                node.name()?.syntax().text().push_to(&mut string);
+                Some(string)
+            })
+            .visit(|node: ast::ConstDef| {
+                let mut string = "const ".to_string();
+                node.name()?.syntax().text().push_to(&mut string);
+                Some(string)
+            })
+            .visit(|node: ast::StaticDef| {
+                let mut string = "static ".to_string();
+                node.name()?.syntax().text().push_to(&mut string);
+                Some(string)
+            })
+            .accept(node)?
+    }
+}
+
+#[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");
+    }
+}