7 files changed, 209 insertions, 9 deletions

diff --git a/crates/ra_ide_api/src/completion/presentation.rs b/crates/ra_ide_api/src/completion/presentation.rs
index 98060947a..5cf55a496 100644
--- a/crates/ra_ide_api/src/completion/presentation.rs
+++ b/crates/ra_ide_api/src/completion/presentation.rs
@@ -1,5 +1,5 @@
 //! This modules takes care of rendering various defenitions as completion items.
-use hir::{Docs, HasSource, HirDisplay, PerNs, Resolution};
+use hir::{Docs, HasSource, HirDisplay, PerNs, Resolution, Ty};
 use join_to_string::join;
 use ra_syntax::ast::NameOwner;
 use test_utils::tested_by;
@@ -80,10 +80,18 @@ impl Completions {
                 None,
             ),
         };
-        CompletionItem::new(completion_kind, ctx.source_range(), local_name)
-            .kind(kind)
-            .set_documentation(docs)
-            .add_to(self)
+
+        let mut completion_item =
+            CompletionItem::new(completion_kind, ctx.source_range(), local_name);
+        if let Resolution::LocalBinding(pat_id) = def {
+            let ty = ctx
+                .analyzer
+                .type_of_pat_by_id(ctx.db, pat_id.clone())
+                .filter(|t| t != &Ty::Unknown)
+                .map(|t| t.display(ctx.db).to_string());
+            completion_item = completion_item.set_detail(ty);
+        };
+        completion_item.kind(kind).set_documentation(docs).add_to(self)
     }
 
     pub(crate) fn add_function(&mut self, ctx: &CompletionContext, func: hir::Function) {
diff --git a/crates/ra_ide_api/src/completion/snapshots/completion_item__bindings_from_if_let.snap b/crates/ra_ide_api/src/completion/snapshots/completion_item__bindings_from_if_let.snap
index 2a22201ad..f94477b43 100644
--- a/crates/ra_ide_api/src/completion/snapshots/completion_item__bindings_from_if_let.snap
+++ b/crates/ra_ide_api/src/completion/snapshots/completion_item__bindings_from_if_let.snap
@@ -1,5 +1,5 @@
 ---
-created: "2019-05-23T22:23:35.122168608Z"
+created: "2019-07-23T16:11:48.828805910Z"
 creator: [email protected]
 source: crates/ra_ide_api/src/completion/completion_item.rs
 expression: kind_completions
@@ -18,6 +18,7 @@ expression: kind_completions
         delete: [214; 214),
         insert: "b",
         kind: Binding,
+        detail: "i32",
     },
     CompletionItem {
         label: "quux",
diff --git a/crates/ra_ide_api/src/completion/snapshots/completion_item__bindings_from_let.snap b/crates/ra_ide_api/src/completion/snapshots/completion_item__bindings_from_let.snap
index b9a5dc9c8..590e2a820 100644
--- a/crates/ra_ide_api/src/completion/snapshots/completion_item__bindings_from_let.snap
+++ b/crates/ra_ide_api/src/completion/snapshots/completion_item__bindings_from_let.snap
@@ -1,5 +1,5 @@
 ---
-created: "2019-05-23T22:23:35.122797188Z"
+created: "2019-07-23T16:11:48.828811567Z"
 creator: [email protected]
 source: crates/ra_ide_api/src/completion/completion_item.rs
 expression: kind_completions
@@ -19,6 +19,7 @@ expression: kind_completions
         delete: [79; 79),
         insert: "x",
         kind: Binding,
+        detail: "i32",
     },
     CompletionItem {
         label: "y",
@@ -26,5 +27,6 @@ expression: kind_completions
         delete: [79; 79),
         insert: "y",
         kind: Binding,
+        detail: "i32",
     },
 ]
diff --git a/crates/ra_ide_api/src/completion/snapshots/completion_item__dont_show_both_completions_for_shadowing.snap b/crates/ra_ide_api/src/completion/snapshots/completion_item__dont_show_both_completions_for_shadowing.snap
index 57434210d..158a2e5b9 100644
--- a/crates/ra_ide_api/src/completion/snapshots/completion_item__dont_show_both_completions_for_shadowing.snap
+++ b/crates/ra_ide_api/src/completion/snapshots/completion_item__dont_show_both_completions_for_shadowing.snap
@@ -1,5 +1,5 @@
 ---
-created: "2019-05-23T22:23:35.142044205Z"
+created: "2019-07-23T16:11:48.860949870Z"
 creator: [email protected]
 source: crates/ra_ide_api/src/completion/completion_item.rs
 expression: kind_completions
@@ -11,6 +11,7 @@ expression: kind_completions
         delete: [126; 126),
         insert: "bar",
         kind: Binding,
+        detail: "i32",
     },
     CompletionItem {
         label: "foo",
diff --git a/crates/ra_ide_api/src/completion/snapshots/completion_item__self_in_methods.snap b/crates/ra_ide_api/src/completion/snapshots/completion_item__self_in_methods.snap
index e1af94870..b7bcbe864 100644
--- a/crates/ra_ide_api/src/completion/snapshots/completion_item__self_in_methods.snap
+++ b/crates/ra_ide_api/src/completion/snapshots/completion_item__self_in_methods.snap
@@ -1,5 +1,5 @@
 ---
-created: "2019-05-23T22:23:35.141900902Z"
+created: "2019-07-23T16:11:48.859812318Z"
 creator: [email protected]
 source: crates/ra_ide_api/src/completion/completion_item.rs
 expression: kind_completions
@@ -18,5 +18,6 @@ expression: kind_completions
         delete: [25; 25),
         insert: "self",
         kind: Binding,
+        detail: "&{unknown}",
     },
 ]
diff --git a/crates/ra_ide_api/src/inlay_hints.rs b/crates/ra_ide_api/src/inlay_hints.rs
new file mode 100644
index 000000000..174662beb
--- /dev/null
+++ b/crates/ra_ide_api/src/inlay_hints.rs
@@ -0,0 +1,180 @@
+use crate::{db::RootDatabase, FileId};
+use hir::{HirDisplay, Ty};
+use ra_syntax::ast::Pat;
+use ra_syntax::{
+    algo::visit::{visitor, Visitor},
+    ast::{self, PatKind, TypeAscriptionOwner},
+    AstNode, SmolStr, SourceFile, SyntaxNode, TextRange,
+};
+
+#[derive(Debug, PartialEq, Eq)]
+pub enum InlayKind {
+    LetBindingType,
+    ClosureParameterType,
+}
+
+#[derive(Debug)]
+pub struct InlayHint {
+    pub range: TextRange,
+    pub kind: InlayKind,
+    pub label: SmolStr,
+}
+
+pub(crate) fn inlay_hints(db: &RootDatabase, file_id: FileId, file: &SourceFile) -> Vec<InlayHint> {
+    file.syntax()
+        .descendants()
+        .map(|node| get_inlay_hints(db, file_id, &node).unwrap_or_default())
+        .flatten()
+        .collect()
+}
+
+fn get_inlay_hints(
+    db: &RootDatabase,
+    file_id: FileId,
+    node: &SyntaxNode,
+) -> Option<Vec<InlayHint>> {
+    visitor()
+        .visit(|let_statement: ast::LetStmt| {
+            let let_syntax = let_statement.syntax();
+
+            if let_statement.ascribed_type().is_some() {
+                return None;
+            }
+
+            let let_pat = let_statement.pat()?;
+            let inlay_type_string = get_node_displayable_type(db, file_id, let_syntax, &let_pat)?
+                .display(db)
+                .to_string()
+                .into();
+
+            let pat_range = match let_pat.kind() {
+                PatKind::BindPat(bind_pat) => bind_pat.syntax().text_range(),
+                PatKind::TuplePat(tuple_pat) => tuple_pat.syntax().text_range(),
+                _ => return None,
+            };
+
+            Some(vec![InlayHint {
+                range: pat_range,
+                kind: InlayKind::LetBindingType,
+                label: inlay_type_string,
+            }])
+        })
+        .visit(|closure_parameter: ast::LambdaExpr| match closure_parameter.param_list() {
+            Some(param_list) => Some(
+                param_list
+                    .params()
+                    .filter(|closure_param| closure_param.ascribed_type().is_none())
+                    .filter_map(|closure_param| {
+                        let closure_param_syntax = closure_param.syntax();
+                        let inlay_type_string = get_node_displayable_type(
+                            db,
+                            file_id,
+                            closure_param_syntax,
+                            &closure_param.pat()?,
+                        )?
+                        .display(db)
+                        .to_string()
+                        .into();
+
+                        Some(InlayHint {
+                            range: closure_param_syntax.text_range(),
+                            kind: InlayKind::ClosureParameterType,
+                            label: inlay_type_string,
+                        })
+                    })
+                    .collect(),
+            ),
+            None => None,
+        })
+        .accept(&node)?
+}
+
+fn get_node_displayable_type(
+    db: &RootDatabase,
+    file_id: FileId,
+    node_syntax: &SyntaxNode,
+    node_pat: &Pat,
+) -> Option<Ty> {
+    let analyzer = hir::SourceAnalyzer::new(db, file_id, node_syntax, None);
+    analyzer.type_of_pat(db, node_pat).and_then(|resolved_type| {
+        if let Ty::Apply(_) = resolved_type {
+            Some(resolved_type)
+        } else {
+            None
+        }
+    })
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::mock_analysis::single_file;
+    use insta::assert_debug_snapshot_matches;
+
+    #[test]
+    fn test_inlay_hints() {
+        let (analysis, file_id) = single_file(
+            r#"
+struct OuterStruct {}
+
+fn main() {
+    struct InnerStruct {}
+
+    let test = 54;
+    let test = InnerStruct {};
+    let test = OuterStruct {};
+    let test = vec![222];
+    let mut test = Vec::new();
+    test.push(333);
+    let test = test.into_iter().map(|i| i * i).collect::<Vec<_>>();
+    let mut test = 33;
+    let _ = 22;
+    let test: Vec<_> = (0..3).collect();
+
+    let _ = (0..23).map(|i: u32| {
+        let i_squared = i * i;
+        i_squared
+    });
+
+    let test: i32 = 33;
+
+    let (x, c) = (42, 'a');
+    let test = (42, 'a');
+}
+"#,
+        );
+
+        assert_debug_snapshot_matches!(analysis.inlay_hints(file_id).unwrap(), @r#"[
+    InlayHint {
+        range: [71; 75),
+        kind: LetBindingType,
+        label: "i32",
+    },
+    InlayHint {
+        range: [121; 125),
+        kind: LetBindingType,
+        label: "OuterStruct",
+    },
+    InlayHint {
+        range: [297; 305),
+        kind: LetBindingType,
+        label: "i32",
+    },
+    InlayHint {
+        range: [417; 426),
+        kind: LetBindingType,
+        label: "u32",
+    },
+    InlayHint {
+        range: [496; 502),
+        kind: LetBindingType,
+        label: "(i32, char)",
+    },
+    InlayHint {
+        range: [524; 528),
+        kind: LetBindingType,
+        label: "(i32, char)",
+    },
+]"#
+        );
+    }
+}
diff --git a/crates/ra_ide_api/src/lib.rs b/crates/ra_ide_api/src/lib.rs
index c54d574bc..16ffb03ce 100644
--- a/crates/ra_ide_api/src/lib.rs
+++ b/crates/ra_ide_api/src/lib.rs
@@ -38,6 +38,7 @@ mod join_lines;
 mod typing;
 mod matching_brace;
 mod display;
+mod inlay_hints;
 
 #[cfg(test)]
 mod marks;
@@ -64,6 +65,7 @@ pub use crate::{
     display::{file_structure, FunctionSignature, NavigationTarget, StructureNode},
     folding_ranges::{Fold, FoldKind},
     hover::HoverResult,
+    inlay_hints::{InlayHint, InlayKind},
     line_index::{LineCol, LineIndex},
     line_index_utils::translate_offset_with_edit,
     references::ReferenceSearchResult,
@@ -396,6 +398,11 @@ impl Analysis {
         file_structure(&parse.tree())
     }
 
+    /// Returns a list of the places in the file where type hints can be displayed.
+    pub fn inlay_hints(&self, file_id: FileId) -> Cancelable<Vec<InlayHint>> {
+        self.with_db(|db| inlay_hints::inlay_hints(db, file_id, &db.parse(file_id).tree()))
+    }
+
     /// Returns the set of folding ranges.
     pub fn folding_ranges(&self, file_id: FileId) -> Vec<Fold> {
         let parse = self.db.parse(file_id);