2 files changed, 179 insertions, 2 deletions

diff --git a/crates/ra_assists/src/handlers/add_explicit_type.rs b/crates/ra_assists/src/handlers/add_explicit_type.rs
index a63ef48b1..d86d804b2 100644
--- a/crates/ra_assists/src/handlers/add_explicit_type.rs
+++ b/crates/ra_assists/src/handlers/add_explicit_type.rs
@@ -130,8 +130,8 @@ mod tests {
     fn add_explicit_type_works_for_macro_call() {
         check_assist(
             add_explicit_type,
-            "macro_rules! v { () => {0u64} } fn f() { let a<|> = v!(); }",
-            "macro_rules! v { () => {0u64} } fn f() { let a<|>: u64 = v!(); }",
+            r"macro_rules! v { () => {0u64} } fn f() { let a<|> = v!(); }",
+            r"macro_rules! v { () => {0u64} } fn f() { let a<|>: u64 = v!(); }",
         );
     }
 
diff --git a/crates/ra_assists/src/handlers/replace_unwrap_with_match.rs b/crates/ra_assists/src/handlers/replace_unwrap_with_match.rs
new file mode 100644
index 000000000..62cb7a763
--- /dev/null
+++ b/crates/ra_assists/src/handlers/replace_unwrap_with_match.rs
@@ -0,0 +1,177 @@
+use std::iter;
+
+use ra_syntax::{
+    ast::{self, make},
+    AstNode,
+};
+
+use crate::{Assist, AssistCtx, AssistId};
+use ast::edit::IndentLevel;
+
+// Assist: replace_unwrap_with_match
+//
+// Replaces `unwrap` a `match` expression. Works for Result and Option.
+//
+// ```
+// enum Result<T, E> { Ok(T), Err(E) }
+// fn main() {
+//     let x: Result<i32, i32> = Result::Ok(92);
+//     let y = x.<|>unwrap();
+// }
+// ```
+// ->
+// ```
+// enum Result<T, E> { Ok(T), Err(E) }
+// fn main() {
+//     let x: Result<i32, i32> = Result::Ok(92);
+//     let y = match x {
+//         Ok(a) => a,
+//         _ => unreachable!(),
+//     };
+// }
+// ```
+pub(crate) fn replace_unwrap_with_match(ctx: AssistCtx) -> Option<Assist> {
+    let method_call: ast::MethodCallExpr = ctx.find_node_at_offset()?;
+    let name = method_call.name_ref()?;
+    if name.text() != "unwrap" {
+        return None;
+    }
+    let caller = method_call.expr()?;
+    let ty = ctx.sema.type_of_expr(&caller)?;
+
+    let type_name = ty.as_adt()?.name(ctx.sema.db).to_string();
+
+    for (unwrap_type, variant_name) in [("Result", "Ok"), ("Option", "Some")].iter() {
+        if &type_name == unwrap_type {
+            return ctx.add_assist(
+                AssistId("replace_unwrap_with_match"),
+                "Replace unwrap with match",
+                |edit| {
+                    let ok_path =
+                        make::path_unqualified(make::path_segment(make::name_ref(variant_name)));
+                    let it = make::bind_pat(make::name("a")).into();
+                    let ok_tuple = make::tuple_struct_pat(ok_path, iter::once(it)).into();
+
+                    let bind_path = make::path_unqualified(make::path_segment(make::name_ref("a")));
+                    let ok_arm = make::match_arm(iter::once(ok_tuple), make::expr_path(bind_path));
+
+                    let unreachable_call = make::unreachable_macro_call().into();
+                    let err_arm = make::match_arm(
+                        iter::once(make::placeholder_pat().into()),
+                        unreachable_call,
+                    );
+
+                    let match_arm_list = make::match_arm_list(vec![ok_arm, err_arm]);
+                    let match_expr = make::expr_match(caller.clone(), match_arm_list);
+                    let match_expr =
+                        IndentLevel::from_node(method_call.syntax()).increase_indent(match_expr);
+
+                    edit.target(method_call.syntax().text_range());
+                    edit.set_cursor(caller.syntax().text_range().start());
+                    edit.replace_ast::<ast::Expr>(method_call.into(), match_expr);
+                },
+            );
+        }
+    }
+    None
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::helpers::{check_assist, check_assist_target};
+
+    #[test]
+    fn test_replace_result_unwrap_with_match() {
+        check_assist(
+            replace_unwrap_with_match,
+            r"
+enum Result<T, E> { Ok(T), Err(E) }
+fn i<T>(a: T) -> T { a }
+fn main() {
+    let x: Result<i32, i32> = Result::Ok(92);
+    let y = i(x).<|>unwrap();
+}
+            ",
+            r"
+enum Result<T, E> { Ok(T), Err(E) }
+fn i<T>(a: T) -> T { a }
+fn main() {
+    let x: Result<i32, i32> = Result::Ok(92);
+    let y = <|>match i(x) {
+        Ok(a) => a,
+        _ => unreachable!(),
+    };
+}
+            ",
+        )
+    }
+
+    #[test]
+    fn test_replace_option_unwrap_with_match() {
+        check_assist(
+            replace_unwrap_with_match,
+            r"
+enum Option<T> { Some(T), None }
+fn i<T>(a: T) -> T { a }
+fn main() {
+    let x = Option::Some(92);
+    let y = i(x).<|>unwrap();
+}
+            ",
+            r"
+enum Option<T> { Some(T), None }
+fn i<T>(a: T) -> T { a }
+fn main() {
+    let x = Option::Some(92);
+    let y = <|>match i(x) {
+        Some(a) => a,
+        _ => unreachable!(),
+    };
+}
+            ",
+        );
+    }
+
+    #[test]
+    fn test_replace_result_unwrap_with_match_chaining() {
+        check_assist(
+            replace_unwrap_with_match,
+            r"
+enum Result<T, E> { Ok(T), Err(E) }
+fn i<T>(a: T) -> T { a }
+fn main() {
+    let x: Result<i32, i32> = Result::Ok(92);
+    let y = i(x).<|>unwrap().count_zeroes();
+}
+            ",
+            r"
+enum Result<T, E> { Ok(T), Err(E) }
+fn i<T>(a: T) -> T { a }
+fn main() {
+    let x: Result<i32, i32> = Result::Ok(92);
+    let y = <|>match i(x) {
+        Ok(a) => a,
+        _ => unreachable!(),
+    }.count_zeroes();
+}
+            ",
+        )
+    }
+
+    #[test]
+    fn replace_unwrap_with_match_target() {
+        check_assist_target(
+            replace_unwrap_with_match,
+            r"
+enum Option<T> { Some(T), None }
+fn i<T>(a: T) -> T { a }
+fn main() {
+    let x = Option::Some(92);
+    let y = i(x).<|>unwrap();
+}
+            ",
+            r"i(x).unwrap()",
+        );
+    }
+}