1 files changed, 308 insertions, 0 deletions

diff --git a/crates/ra_assists/src/handlers/move_guard.rs b/crates/ra_assists/src/handlers/move_guard.rs
new file mode 100644
index 000000000..2b91ce7c4
--- /dev/null
+++ b/crates/ra_assists/src/handlers/move_guard.rs
@@ -0,0 +1,308 @@
+use ra_syntax::{
+    ast,
+    ast::{AstNode, AstToken, IfExpr, MatchArm},
+    TextUnit,
+};
+
+use crate::{Assist, AssistCtx, AssistId};
+
+// Assist: move_guard_to_arm_body
+//
+// Moves match guard into match arm body.
+//
+// ```
+// enum Action { Move { distance: u32 }, Stop }
+//
+// fn handle(action: Action) {
+//     match action {
+//         Action::Move { distance } <|>if distance > 10 => foo(),
+//         _ => (),
+//     }
+// }
+// ```
+// ->
+// ```
+// enum Action { Move { distance: u32 }, Stop }
+//
+// fn handle(action: Action) {
+//     match action {
+//         Action::Move { distance } => if distance > 10 { foo() },
+//         _ => (),
+//     }
+// }
+// ```
+pub(crate) fn move_guard_to_arm_body(ctx: AssistCtx) -> Option<Assist> {
+    let match_arm = ctx.find_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_assist(AssistId("move_guard_to_arm_body"), "Move guard to arm body", |edit| {
+        edit.target(guard.syntax().text_range());
+        let offseting_amount = match space_before_guard.and_then(|it| it.into_token()) {
+            Some(tok) => {
+                if let Some(_) = ast::Whitespace::cast(tok.clone()) {
+                    let ele = tok.text_range();
+                    edit.delete(ele);
+                    ele.len()
+                } else {
+                    TextUnit::from(0)
+                }
+            }
+            _ => TextUnit::from(0),
+        };
+
+        edit.delete(guard.syntax().text_range());
+        edit.replace_node_and_indent(arm_expr.syntax(), buf);
+        edit.set_cursor(
+            arm_expr.syntax().text_range().start() + TextUnit::from(3) - offseting_amount,
+        );
+    })
+}
+
+// Assist: move_arm_cond_to_match_guard
+//
+// Moves if expression from match arm body into a guard.
+//
+// ```
+// enum Action { Move { distance: u32 }, Stop }
+//
+// fn handle(action: Action) {
+//     match action {
+//         Action::Move { distance } => <|>if distance > 10 { foo() },
+//         _ => (),
+//     }
+// }
+// ```
+// ->
+// ```
+// enum Action { Move { distance: u32 }, Stop }
+//
+// fn handle(action: Action) {
+//     match action {
+//         Action::Move { distance } if distance > 10 => foo(),
+//         _ => (),
+//     }
+// }
+// ```
+pub(crate) fn move_arm_cond_to_match_guard(ctx: AssistCtx) -> Option<Assist> {
+    let match_arm: MatchArm = ctx.find_node_at_offset::<MatchArm>()?;
+    let last_match_pat = match_arm.pats().last()?;
+
+    let arm_body = match_arm.expr()?;
+    let if_expr: IfExpr = IfExpr::cast(arm_body.syntax().clone())?;
+    let cond = if_expr.condition()?;
+    let then_block = if_expr.then_branch()?;
+
+    // Not support if with else branch
+    if let Some(_) = if_expr.else_branch() {
+        return None;
+    }
+    // Not support moving if let to arm guard
+    if let Some(_) = cond.pat() {
+        return None;
+    }
+
+    let buf = format!(" if {}", cond.syntax().text());
+
+    ctx.add_assist(
+        AssistId("move_arm_cond_to_match_guard"),
+        "Move condition to match guard",
+        |edit| {
+            edit.target(if_expr.syntax().text_range());
+            let then_only_expr = then_block.block().and_then(|it| it.statements().next()).is_none();
+
+            match &then_block.block().and_then(|it| it.expr()) {
+                Some(then_expr) if then_only_expr => {
+                    edit.replace(if_expr.syntax().text_range(), then_expr.syntax().text())
+                }
+                _ => edit.replace(if_expr.syntax().text_range(), then_block.syntax().text()),
+            }
+
+            edit.insert(last_match_pat.syntax().text_range().end(), buf);
+            edit.set_cursor(last_match_pat.syntax().text_range().end() + TextUnit::from(1));
+        },
+    )
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    use crate::helpers::{check_assist, check_assist_not_applicable, 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
+                }
+            }
+            "#,
+        );
+    }
+
+    #[test]
+    fn move_arm_cond_to_match_guard_works() {
+        check_assist(
+            move_arm_cond_to_match_guard,
+            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_arm_cond_to_match_guard_if_let_not_works() {
+        check_assist_not_applicable(
+            move_arm_cond_to_match_guard,
+            r#"
+            fn f() {
+                let t = 'a';
+                let chars = "abcd";
+                match t {
+                    '\r' => if let Some(_) = chars.clone().next() { <|>false },
+                    _ => true
+                }
+            }
+            "#,
+        );
+    }
+
+    #[test]
+    fn move_arm_cond_to_match_guard_if_empty_body_works() {
+        check_assist(
+            move_arm_cond_to_match_guard,
+            r#"
+            fn f() {
+                let t = 'a';
+                let chars = "abcd";
+                match t {
+                    '\r' => if chars.clone().next().is_some() { <|> },
+                    _ => true
+                }
+            }
+            "#,
+            r#"
+            fn f() {
+                let t = 'a';
+                let chars = "abcd";
+                match t {
+                    '\r' <|>if chars.clone().next().is_some() => {  },
+                    _ => true
+                }
+            }
+            "#,
+        );
+    }
+
+    #[test]
+    fn move_arm_cond_to_match_guard_if_multiline_body_works() {
+        check_assist(
+            move_arm_cond_to_match_guard,
+            r#"
+            fn f() {
+                let mut t = 'a';
+                let chars = "abcd";
+                match t {
+                    '\r' => if chars.clone().next().is_some() {
+                        t = 'e';<|>
+                        false
+                    },
+                    _ => true
+                }
+            }
+            "#,
+            r#"
+            fn f() {
+                let mut t = 'a';
+                let chars = "abcd";
+                match t {
+                    '\r' <|>if chars.clone().next().is_some() => {
+                        t = 'e';
+                        false
+                    },
+                    _ => true
+                }
+            }
+            "#,
+        );
+    }
+}