2 files changed, 117 insertions, 0 deletions

diff --git a/crates/ra_assists/src/lib.rs b/crates/ra_assists/src/lib.rs
index 4c330c907..a2998ae59 100644
--- a/crates/ra_assists/src/lib.rs
+++ b/crates/ra_assists/src/lib.rs
@@ -101,6 +101,7 @@ mod split_import;
 mod remove_dbg;
 pub mod auto_import;
 mod add_missing_impl_members;
+mod move_guard_to_arm_body;
 
 fn all_assists<DB: HirDatabase>() -> &'static [fn(AssistCtx<DB>) -> Option<Assist>] {
     &[
@@ -120,6 +121,7 @@ fn all_assists<DB: HirDatabase>() -> &'static [fn(AssistCtx<DB>) -> Option<Assis
         add_missing_impl_members::add_missing_impl_members,
         add_missing_impl_members::add_missing_default_members,
         inline_local_variable::inline_local_varialbe,
+        move_guard_to_arm_body::move_guard_to_arm_body,
     ]
 }
 
diff --git a/crates/ra_assists/src/move_guard_to_arm_body.rs b/crates/ra_assists/src/move_guard_to_arm_body.rs
new file mode 100644
index 000000000..a8ca19f5d
--- /dev/null
+++ b/crates/ra_assists/src/move_guard_to_arm_body.rs
@@ -0,0 +1,115 @@
+use hir::db::HirDatabase;
+use ra_syntax::{
+    TextUnit,
+    SyntaxElement,
+    ast::{MatchArm, AstNode, AstToken},
+    ast,
+};
+
+use crate::{AssistCtx, Assist, AssistId};
+
+pub(crate) fn move_guard_to_arm_body(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+    let match_arm = ctx.node_at_offset::<MatchArm>()?;
+    let guard = match_arm.guard()?;
+    let space_before_guard = guard.syntax().prev_sibling_or_token();
+
+    let guard_conditions = guard.expr()?;
+    let arm_expr = match_arm.expr()?;
+    let buf = format!("if {} {{ {} }}", guard_conditions.syntax().text(), arm_expr.syntax().text());
+
+    ctx.add_action(AssistId("move_guard_to_arm_body"), "move guard to arm body", |edit| {
+        edit.target(guard.syntax().range());
+        let offseting_amount = match space_before_guard {
+            Some(SyntaxElement::Token(tok)) => {
+                if let Some(_) = ast::Whitespace::cast(tok) {
+                    let ele = space_before_guard.unwrap().range();
+                    edit.delete(ele);
+                    ele.len()
+                } else {
+                    TextUnit::from(0)
+                }
+            }
+            _ => TextUnit::from(0),
+        };
+
+        edit.delete(guard.syntax().range());
+        edit.replace_node_and_indent(arm_expr.syntax(), buf);
+        edit.set_cursor(arm_expr.syntax().range().start() + TextUnit::from(3) - offseting_amount);
+    });
+    ctx.build()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    use crate::helpers::{ check_assist, check_assist_target };
+
+    #[test]
+    fn move_guard_to_arm_body_target() {
+        check_assist_target(
+            move_guard_to_arm_body,
+            r#"
+            fn f() {
+                let t = 'a';
+                let chars = "abcd";
+                match t {
+                    '\r' <|>if chars.clone().next() == Some('\n') => false,
+                    _ => true
+                }
+            }
+            "#,
+            r#"if chars.clone().next() == Some('\n')"#,
+        );
+    }
+
+    #[test]
+    fn move_guard_to_arm_body_works() {
+        check_assist(
+            move_guard_to_arm_body,
+            r#"
+            fn f() {
+                let t = 'a';
+                let chars = "abcd";
+                match t {
+                    '\r' <|>if chars.clone().next() == Some('\n') => false,
+                    _ => true
+                }
+            }
+            "#,
+            r#"
+            fn f() {
+                let t = 'a';
+                let chars = "abcd";
+                match t {
+                    '\r' => if chars.clone().next() == Some('\n') { <|>false },
+                    _ => true
+                }
+            }
+            "#,
+        );
+    }
+
+    #[test]
+    fn move_guard_to_arm_body_works_complex_match() {
+        check_assist(
+            move_guard_to_arm_body,
+            r#"
+            fn f() {
+                match x {
+                    <|>y @ 4 | y @ 5    if y > 5 => true,
+                    _ => false
+                }
+            }
+            "#,
+            r#"
+            fn f() {
+                match x {
+                    y @ 4 | y @ 5 => if y > 5 { <|>true },
+                    _ => false
+                }
+            }
+            "#,
+        );
+    }
+}