4 files changed, 180 insertions, 27 deletions

diff --git a/crates/ra_ide_api/src/display/structure.rs b/crates/ra_ide_api/src/display/structure.rs
index bd2e908da..2ba10b2ef 100644
--- a/crates/ra_ide_api/src/display/structure.rs
+++ b/crates/ra_ide_api/src/display/structure.rs
@@ -1,6 +1,5 @@
 use crate::TextRange;
 
-use ra_syntax::ast::PatKind;
 use ra_syntax::{
     algo::visit::{visitor, Visitor},
     ast::{self, AttrsOwner, NameOwner, TypeAscriptionOwner, TypeParamsOwner},
@@ -156,32 +155,6 @@ fn structure_node(node: &SyntaxNode) -> Option<StructureNode> {
             }
             decl(mc)
         })
-        .visit(|let_statement: ast::LetStmt| {
-            let let_syntax = let_statement.syntax();
-
-            let mut label = String::new();
-            collapse_ws(let_syntax, &mut label);
-
-            if let_statement.ascribed_type().is_some() {
-                return None;
-            }
-
-            let pat_range = match let_statement.pat()?.kind() {
-                PatKind::BindPat(bind_pat) => bind_pat.syntax().range(),
-                PatKind::TuplePat(tuple_pat) => tuple_pat.syntax().range(),
-                _ => return None,
-            };
-
-            Some(StructureNode {
-                parent: None,
-                label,
-                navigation_range: pat_range,
-                node_range: let_syntax.range(),
-                kind: let_syntax.kind(),
-                detail: None,
-                deprecated: false,
-            })
-        })
         .accept(&node)?
 }
 
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..4d1df65d0
--- /dev/null
+++ b/crates/ra_ide_api/src/inlay_hints.rs
@@ -0,0 +1,110 @@
+use ra_syntax::{
+    algo::visit::{visitor, Visitor},
+    ast::{self, PatKind, TypeAscriptionOwner},
+    AstNode, SmolStr, SourceFile, SyntaxNode, TextRange,
+};
+
+#[derive(Debug, PartialEq, Eq)]
+pub enum InlayKind {
+    LetBinding,
+    ClosureParameter,
+}
+
+#[derive(Debug)]
+pub struct InlayHint {
+    pub range: TextRange,
+    pub text: SmolStr,
+    pub inlay_kind: InlayKind,
+}
+
+pub(crate) fn inlay_hints(file: &SourceFile) -> Vec<InlayHint> {
+    file.syntax().descendants().map(|node| get_inlay_hints(&node)).flatten().collect()
+}
+
+fn get_inlay_hints(node: &SyntaxNode) -> Vec<InlayHint> {
+    visitor()
+        .visit(|let_statement: ast::LetStmt| {
+            let let_syntax = let_statement.syntax();
+
+            if let_statement.ascribed_type().is_some() {
+                return Vec::new();
+            }
+
+            let pat_range = match let_statement.pat().map(|pat| pat.kind()) {
+                Some(PatKind::BindPat(bind_pat)) => bind_pat.syntax().text_range(),
+                Some(PatKind::TuplePat(tuple_pat)) => tuple_pat.syntax().text_range(),
+                _ => return Vec::new(),
+            };
+
+            vec![InlayHint {
+                range: pat_range,
+                text: let_syntax.text().to_smol_string(),
+                inlay_kind: InlayKind::LetBinding,
+            }]
+        })
+        .visit(|closure_parameter: ast::LambdaExpr| {
+            if let Some(param_list) = closure_parameter.param_list() {
+                param_list
+                    .params()
+                    .filter(|closure_param| closure_param.ascribed_type().is_none())
+                    .map(|closure_param| {
+                        let closure_param_syntax = closure_param.syntax();
+                        InlayHint {
+                            range: closure_param_syntax.text_range(),
+                            text: closure_param_syntax.text().to_smol_string(),
+                            inlay_kind: InlayKind::ClosureParameter,
+                        }
+                    })
+                    .collect()
+            } else {
+                Vec::new()
+            }
+        })
+        .accept(&node)
+        .unwrap_or_else(Vec::new)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use insta::assert_debug_snapshot_matches;
+
+    #[test]
+    fn test_inlay_hints() {
+        let file = SourceFile::parse(
+            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');
+}
+
+"#,
+        )
+        .ok()
+        .unwrap();
+        let hints = inlay_hints(&file);
+        assert_debug_snapshot_matches!("inlay_hints", hints);
+    }
+}
diff --git a/crates/ra_ide_api/src/lib.rs b/crates/ra_ide_api/src/lib.rs
index c54d574bc..af163088a 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) -> Vec<InlayHint> {
+        inlay_hints::inlay_hints(&self.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);
diff --git a/crates/ra_ide_api/src/snapshots/tests__inlay_hints.snap b/crates/ra_ide_api/src/snapshots/tests__inlay_hints.snap
new file mode 100644
index 000000000..f4d562314
--- /dev/null
+++ b/crates/ra_ide_api/src/snapshots/tests__inlay_hints.snap
@@ -0,0 +1,63 @@
+---
+created: "2019-07-20T20:13:53.385368Z"
+creator: [email protected]
+source: crates/ra_ide_api/src/inlay_hints.rs
+expression: hints
+---
+[
+    InlayHint {
+        range: [71; 75),
+        text: "let test = 54;",
+        inlay_kind: LetBinding,
+    },
+    InlayHint {
+        range: [90; 94),
+        text: "let test = InnerStruct {};",
+        inlay_kind: LetBinding,
+    },
+    InlayHint {
+        range: [121; 125),
+        text: "let test = OuterStruct {};",
+        inlay_kind: LetBinding,
+    },
+    InlayHint {
+        range: [152; 156),
+        text: "let test = vec![222];",
+        inlay_kind: LetBinding,
+    },
+    InlayHint {
+        range: [178; 186),
+        text: "let mut test = Vec::new();",
+        inlay_kind: LetBinding,
+    },
+    InlayHint {
+        range: [229; 233),
+        text: "let test = test.into_iter().map(|i| i * i).collect::<Vec<_>>();",
+        inlay_kind: LetBinding,
+    },
+    InlayHint {
+        range: [258; 259),
+        text: "i",
+        inlay_kind: ClosureParameter,
+    },
+    InlayHint {
+        range: [297; 305),
+        text: "let mut test = 33;",
+        inlay_kind: LetBinding,
+    },
+    InlayHint {
+        range: [417; 426),
+        text: "let i_squared = i * i;",
+        inlay_kind: LetBinding,
+    },
+    InlayHint {
+        range: [500; 506),
+        text: "let (x, c) = (42, \'a\');",
+        inlay_kind: LetBinding,
+    },
+    InlayHint {
+        range: [528; 532),
+        text: "let test = (42, \'a\');",
+        inlay_kind: LetBinding,
+    },
+]