1 files changed, 100 insertions, 0 deletions
diff --git a/src/tools/rust-analyzer/crates/ide-assists/src/handlers/replace_let_with_if_let.rs b/src/tools/rust-analyzer/crates/ide-assists/src/handlers/replace_let_with_if_let.rs
new file mode 100644
index 000000000..c2be4593b
--- /dev/null
+++ b/src/tools/rust-analyzer/crates/ide-assists/src/handlers/replace_let_with_if_let.rs
@@ -0,0 +1,100 @@
+use std::iter::once;
+
+use ide_db::ty_filter::TryEnum;
+use syntax::{
+    ast::{
+        self,
+        edit::{AstNodeEdit, IndentLevel},
+        make,
+    },
+    AstNode, T,
+};
+
+use crate::{AssistContext, AssistId, AssistKind, Assists};
+
+// Assist: replace_let_with_if_let
+//
+// Replaces `let` with an `if let`.
+//
+// ```
+// # enum Option<T> { Some(T), None }
+//
+// fn main(action: Action) {
+//     $0let x = compute();
+// }
+//
+// fn compute() -> Option<i32> { None }
+// ```
+// ->
+// ```
+// # enum Option<T> { Some(T), None }
+//
+// fn main(action: Action) {
+//     if let Some(x) = compute() {
+//     }
+// }
+//
+// fn compute() -> Option<i32> { None }
+// ```
+pub(crate) fn replace_let_with_if_let(acc: &mut Assists, ctx: &AssistContext<'_>) -> Option<()> {
+    let let_kw = ctx.find_token_syntax_at_offset(T![let])?;
+    let let_stmt = let_kw.parent().and_then(ast::LetStmt::cast)?;
+    let init = let_stmt.initializer()?;
+    let original_pat = let_stmt.pat()?;
+
+    let target = let_kw.text_range();
+    acc.add(
+        AssistId("replace_let_with_if_let", AssistKind::RefactorRewrite),
+        "Replace let with if let",
+        target,
+        |edit| {
+            let ty = ctx.sema.type_of_expr(&init);
+            let happy_variant = ty
+                .and_then(|ty| TryEnum::from_ty(&ctx.sema, &ty.adjusted()))
+                .map(|it| it.happy_case());
+            let pat = match happy_variant {
+                None => original_pat,
+                Some(var_name) => {
+                    make::tuple_struct_pat(make::ext::ident_path(var_name), once(original_pat))
+                        .into()
+                }
+            };
+
+            let block =
+                make::ext::empty_block_expr().indent(IndentLevel::from_node(let_stmt.syntax()));
+            let if_ = make::expr_if(make::expr_let(pat, init).into(), block, None);
+            let stmt = make::expr_stmt(if_);
+
+            edit.replace_ast(ast::Stmt::from(let_stmt), ast::Stmt::from(stmt));
+        },
+    )
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::check_assist;
+
+    use super::*;
+
+    #[test]
+    fn replace_let_unknown_enum() {
+        check_assist(
+            replace_let_with_if_let,
+            r"
+enum E<T> { X(T), Y(T) }
+
+fn main() {
+    $0let x = E::X(92);
+}
+            ",
+            r"
+enum E<T> { X(T), Y(T) }
+
+fn main() {
+    if let x = E::X(92) {
+    }
+}
+            ",
+        )
+    }
+}