Merge #3019

3019: Better cursor placement when merging arms r=matklad a=matklad



Co-authored-by: Aleksey Kladov <aleksey.kladov@gmail.com>

crates/ra_assists/src/assists/merge_match_arms.rs

@@ -1,6 +1,12 @@
-use crate::{Assist, AssistCtx, AssistId, TextRange, TextUnit};
+use std::iter::successors;
+
 use hir::db::HirDatabase;
-use ra_syntax::ast::{AstNode, MatchArm};
+use ra_syntax::{
+    ast::{self, AstNode},
+    Direction, TextUnit,
+};
+
+use crate::{Assist, AssistCtx, AssistId, TextRange};
 
 // Assist: merge_match_arms
 //
@@ -27,62 +33,80 @@ use ra_syntax::ast::{AstNode, MatchArm};
 // }
 // ```
 pub(crate) fn merge_match_arms(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
-    let current_arm = ctx.find_node_at_offset::<MatchArm>()?;
-
-    // We check if the following match arm matches this one. We could, but don't,
-    // compare to the previous match arm as well.
-    let next = current_arm.syntax().next_sibling();
-    let next_arm = MatchArm::cast(next?)?;
-
+    let current_arm = ctx.find_node_at_offset::<ast::MatchArm>()?;
     // Don't try to handle arms with guards for now - can add support for this later
-    if current_arm.guard().is_some() || next_arm.guard().is_some() {
+    if current_arm.guard().is_some() {
         return None;
     }
-
     let current_expr = current_arm.expr()?;
-    let next_expr = next_arm.expr()?;
+    let current_text_range = current_arm.syntax().text_range();
 
-    // Check for match arm equality by comparing lengths and then string contents
-    if current_expr.syntax().text_range().len() != next_expr.syntax().text_range().len() {
+    enum CursorPos {
+        InExpr(TextUnit),
+        InPat(TextUnit),
+    }
+    let cursor_pos = ctx.frange.range.start();
+    let cursor_pos = if current_expr.syntax().text_range().contains(cursor_pos) {
+        CursorPos::InExpr(current_text_range.end() - cursor_pos)
+    } else {
+        CursorPos::InPat(cursor_pos)
+    };
+
+    // We check if the following match arms match this one. We could, but don't,
+    // compare to the previous match arm as well.
+    let arms_to_merge = successors(Some(current_arm), next_arm)
+        .take_while(|arm| {
+            if arm.guard().is_some() {
+                return false;
+            }
+            match arm.expr() {
+                Some(expr) => expr.syntax().text() == current_expr.syntax().text(),
+                None => false,
+            }
+        })
+        .collect::<Vec<_>>();
+
+    if arms_to_merge.len() <= 1 {
         return None;
     }
-    if current_expr.syntax().text() != next_expr.syntax().text() {
-        return None;
-    }
-
-    let cursor_to_end = current_arm.syntax().text_range().end() - ctx.frange.range.start();
 
     ctx.add_assist(AssistId("merge_match_arms"), "Merge match arms", |edit| {
-        fn contains_placeholder(a: &MatchArm) -> bool {
-            a.pats().any(|x| match x {
-                ra_syntax::ast::Pat::PlaceholderPat(..) => true,
-                _ => false,
-            })
-        }
-
-        let pats = if contains_placeholder(&current_arm) || contains_placeholder(&next_arm) {
+        let pats = if arms_to_merge.iter().any(contains_placeholder) {
             "_".into()
         } else {
-            let ps: Vec<String> = current_arm
-                .pats()
+            arms_to_merge
+                .iter()
+                .flat_map(ast::MatchArm::pats)
                 .map(|x| x.syntax().to_string())
-                .chain(next_arm.pats().map(|x| x.syntax().to_string()))
-                .collect();
-            ps.join(" | ")
+                .collect::<Vec<String>>()
+                .join(" | ")
         };
 
         let arm = format!("{} => {}", pats, current_expr.syntax().text());
-        let offset = TextUnit::from_usize(arm.len()) - cursor_to_end;
 
-        let start = current_arm.syntax().text_range().start();
-        let end = next_arm.syntax().text_range().end();
+        let start = arms_to_merge.first().unwrap().syntax().text_range().start();
+        let end = arms_to_merge.last().unwrap().syntax().text_range().end();
 
-        edit.target(current_arm.syntax().text_range());
+        edit.target(current_text_range);
+        edit.set_cursor(match cursor_pos {
+            CursorPos::InExpr(back_offset) => start + TextUnit::from_usize(arm.len()) - back_offset,
+            CursorPos::InPat(offset) => offset,
+        });
         edit.replace(TextRange::from_to(start, end), arm);
-        edit.set_cursor(start + offset);
     })
 }
 
+fn contains_placeholder(a: &ast::MatchArm) -> bool {
+    a.pats().any(|x| match x {
+        ra_syntax::ast::Pat::PlaceholderPat(..) => true,
+        _ => false,
+    })
+}
+
+fn next_arm(arm: &ast::MatchArm) -> Option<ast::MatchArm> {
+    arm.syntax().siblings(Direction::Next).skip(1).find_map(ast::MatchArm::cast)
+}
+
 #[cfg(test)]
 mod tests {
     use super::merge_match_arms;
@@ -184,6 +208,37 @@ mod tests {
         );
     }
 
+    #[test]
+    fn merges_all_subsequent_arms() {
+        check_assist(
+            merge_match_arms,
+            r#"
+            enum X { A, B, C, D, E }
+
+            fn main() {
+                match X::A {
+                    X::A<|> => 92,
+                    X::B => 92,
+                    X::C => 92,
+                    X::D => 62,
+                    _ => panic!(),
+                }
+            }
+            "#,
+            r#"
+            enum X { A, B, C, D, E }
+
+            fn main() {
+                match X::A {
+                    X::A<|> | X::B | X::C => 92,
+                    X::D => 62,
+                    _ => panic!(),
+                }
+            }
+            "#,
+        )
+    }
+
     #[test]
     fn merge_match_arms_rejects_guards() {
         check_assist_not_applicable(