Handle not let if expressions in replace_if_let_with_match

crates/ide_assists/src/handlers/replace_if_let_with_match.rs

@@ -1,5 +1,6 @@
 use std::iter::{self, successors};
 
+use either::Either;
 use ide_db::{ty_filter::TryEnum, RootDatabase};
 use syntax::{
     ast::{
@@ -53,17 +54,30 @@ pub(crate) fn replace_if_let_with_match(acc: &mut Assists, ctx: &AssistContext)
     });
     let scrutinee_to_be_expr = if_expr.condition()?.expr()?;
 
-    let mut pat_bodies = Vec::new();
+    let mut pat_seen = false;
+    let mut cond_bodies = Vec::new();
     for if_expr in if_exprs {
         let cond = if_expr.condition()?;
         let expr = cond.expr()?;
+        let cond = match cond.pat() {
+            Some(pat) => {
                 if scrutinee_to_be_expr.syntax().text() != expr.syntax().text() {
                     // Only if all condition expressions are equal we can merge them into a match
                     return None;
+                } else {
+                    pat_seen = true;
+                    Either::Left(pat)
                 }
-        let pat = cond.pat()?;
+            }
+            None => Either::Right(expr),
+        };
         let body = if_expr.then_branch()?;
-        pat_bodies.push((pat, body));
+        cond_bodies.push((cond, body));
+    }
+
+    if !pat_seen {
+        // Don't offer turning an if (chain) without patterns into a match
+        return None;
     }
 
     let target = if_expr.syntax().text_range();
@@ -76,8 +90,8 @@ pub(crate) fn replace_if_let_with_match(acc: &mut Assists, ctx: &AssistContext)
                 let else_arm = {
                     match else_block {
                         Some(else_block) => {
-                            let pattern = match &*pat_bodies {
+                            let pattern = match &*cond_bodies {
-                                [(pat, _)] => ctx
+                                [(Either::Left(pat), _)] => ctx
                                     .sema
                                     .type_of_pat(&pat)
                                     .and_then(|ty| TryEnum::from_ty(&ctx.sema, &ty))
@@ -99,19 +113,30 @@ pub(crate) fn replace_if_let_with_match(acc: &mut Assists, ctx: &AssistContext)
                         ),
                     }
                 };
-                let arms = pat_bodies
+                let arms = cond_bodies
                     .into_iter()
                     .map(|(pat, body)| {
                         let body = body.reset_indent().indent(IndentLevel(1));
-                        make::match_arm(vec![pat], unwrap_trivial_block(body))
+                        match pat {
+                            Either::Left(pat) => {
+                                make::match_arm(iter::once(pat), unwrap_trivial_block(body))
+                            }
+                            Either::Right(expr) => make::match_arm_with_guard(
+                                iter::once(make::wildcard_pat().into()),
+                                expr,
+                                unwrap_trivial_block(body),
+                            ),
+                        }
                     })
                     .chain(iter::once(else_arm));
                 let match_expr = make::expr_match(scrutinee_to_be_expr, make::match_arm_list(arms));
                 match_expr.indent(IndentLevel::from_node(if_expr.syntax()))
             };
 
-            let expr =
+            let has_preceding_if_expr =
-                if if_expr.syntax().parent().map_or(false, |it| ast::IfExpr::can_cast(it.kind())) {
+                if_expr.syntax().parent().map_or(false, |it| ast::IfExpr::can_cast(it.kind()));
+            let expr = if has_preceding_if_expr {
+                // make sure we replace the `else if let ...` with a block so we don't end up with `else expr`
                 make::block_expr(None, Some(match_expr)).into()
             } else {
                 match_expr
@@ -210,7 +235,19 @@ fn is_pat_wildcard_or_sad(sema: &hir::Semantics<RootDatabase>, pat: &ast::Pat) -
 mod tests {
     use super::*;
 
-    use crate::tests::{check_assist, check_assist_target};
+    use crate::tests::{check_assist, check_assist_not_applicable, check_assist_target};
+
+    #[test]
+    fn test_if_let_with_match_unapplicable_for_simple_ifs() {
+        check_assist_not_applicable(
+            replace_if_let_with_match,
+            r#"
+fn main() {
+    if $0true {} else if false {} else {}
+}
+"#,
+        )
+    }
 
     #[test]
     fn test_if_let_with_match_no_else() {
@@ -223,7 +260,8 @@ pub fn foo(&self) {
             self.foo();
         }
     }
-}           "#,
+}
+"#,
             r#"
 impl VariantData {
     pub fn foo(&self) {
@@ -234,7 +272,8 @@ pub fn foo(&self) {
             _ => (),
         }
     }
-}           "#,
+}
+"#,
         )
     }
 
@@ -249,19 +288,23 @@ pub fn is_struct(&self) -> bool {
             true
         } else if let VariantData::Tuple(..) = *self {
             false
+        } else if cond() {
+            true
         } else {
             bar(
                 123
             )
         }
     }
-}           "#,
+}
+"#,
             r#"
 impl VariantData {
     pub fn is_struct(&self) -> bool {
         match *self {
             VariantData::Struct(..) => true,
             VariantData::Tuple(..) => false,
+            _ if cond() => true,
             _ => {
                     bar(
                         123
@@ -269,7 +312,8 @@ pub fn is_struct(&self) -> bool {
                 }
         }
     }
-}           "#,
+}
+"#,
         )
     }
 
@@ -288,7 +332,8 @@ pub fn is_struct(&self) -> bool {
             false
         }
     }
-}           "#,
+}
+"#,
             r#"
 impl VariantData {
     pub fn is_struct(&self) -> bool {
@@ -301,7 +346,8 @@ pub fn is_struct(&self) -> bool {
         }
 }
     }
-}           "#,
+}
+"#,
         )
     }
 

crates/syntax/src/ast/make.rs

@@ -430,6 +430,19 @@ fn from_text(text: &str) -> ast::MatchArm {
     }
 }
 
+pub fn match_arm_with_guard(
+    pats: impl IntoIterator<Item = ast::Pat>,
+    guard: ast::Expr,
+    expr: ast::Expr,
+) -> ast::MatchArm {
+    let pats_str = pats.into_iter().join(" | ");
+    return from_text(&format!("{} if {} => {}", pats_str, guard, expr));
+
+    fn from_text(text: &str) -> ast::MatchArm {
+        ast_from_text(&format!("fn f() {{ match () {{{}}} }}", text))
+    }
+}
+
 pub fn match_arm_list(arms: impl IntoIterator<Item = ast::MatchArm>) -> ast::MatchArmList {
     let arms_str = arms
         .into_iter()