replace_if_let_with_match: don't assume sad pattern

crates/assists/src/handlers/replace_if_let_with_match.rs

@@ -5,7 +5,7 @@ use syntax::{
     ast::{
         self,
         edit::{AstNodeEdit, IndentLevel},
-        make,
+        make, Pat,
     },
     AstNode,
 };
@@ -66,7 +66,13 @@ pub(crate) fn replace_if_let_with_match(acc: &mut Assists, ctx: &AssistContext)
                         .sema
                         .type_of_pat(&pat)
                         .and_then(|ty| TryEnum::from_ty(&ctx.sema, &ty))
-                        .map(|it| it.sad_pattern())
+                        .map(|it| {
+                            if does_pat_match_variant(&pat, &it.sad_pattern()) {
+                                it.happy_pattern()
+                            } else {
+                                it.sad_pattern()
+                            }
+                        })
                         .unwrap_or_else(|| make::wildcard_pat().into());
                     let else_expr = unwrap_trivial_block(else_block);
                     make::match_arm(vec![pattern], else_expr)
@@ -81,6 +87,26 @@ pub(crate) fn replace_if_let_with_match(acc: &mut Assists, ctx: &AssistContext)
     )
 }
 
+fn does_pat_match_variant(pat: &Pat, var: &Pat) -> bool {
+    let first_node_text = |pat: &Pat| pat.syntax().first_child().map(|node| node.text());
+
+    let pat_head = match pat {
+        Pat::IdentPat(bind_pat) => {
+            if let Some(p) = bind_pat.pat() {
+                first_node_text(&p)
+            } else {
+                return pat.syntax().text() == var.syntax().text();
+            }
+        }
+        pat => first_node_text(pat),
+    };
+
+    let var_head = first_node_text(var);
+    println!("{:?} {:?}", pat_head, var_head);
+
+    pat_head == var_head
+}
+
 // Assist: replace_match_with_if_let
 //
 // Replaces a binary `match` with a wildcard pattern and no guards with an `if let` expression.
@@ -278,6 +304,36 @@ fn foo(x: Option<i32>) {
         );
     }
 
+    #[test]
+    fn special_case_inverted_option() {
+        check_assist(
+            replace_if_let_with_match,
+            r#"
+enum Option<T> { Some(T), None }
+use Option::*;
+
+fn foo(x: Option<i32>) {
+    $0if let None = x {
+        println!("none")
+    } else {
+        println!("some")
+    }
+}
+           "#,
+            r#"
+enum Option<T> { Some(T), None }
+use Option::*;
+
+fn foo(x: Option<i32>) {
+    match x {
+        None => println!("none"),
+        Some(_) => println!("some"),
+    }
+}
+           "#,
+        );
+    }
+
     #[test]
     fn special_case_result() {
         check_assist(
@@ -308,6 +364,36 @@ fn foo(x: Result<i32, ()>) {
         );
     }
 
+    #[test]
+    fn special_case_inverted_result() {
+        check_assist(
+            replace_if_let_with_match,
+            r#"
+enum Result<T, E> { Ok(T), Err(E) }
+use Result::*;
+
+fn foo(x: Result<i32, ()>) {
+    $0if let Err(x) = x {
+        println!("{}", x)
+    } else {
+        println!("ok")
+    }
+}
+           "#,
+            r#"
+enum Result<T, E> { Ok(T), Err(E) }
+use Result::*;
+
+fn foo(x: Result<i32, ()>) {
+    match x {
+        Err(x) => println!("{}", x),
+        Ok(_) => println!("ok"),
+    }
+}
+           "#,
+        );
+    }
+
     #[test]
     fn nested_indent() {
         check_assist(

crates/ide_db/src/ty_filter.rs

@@ -49,6 +49,21 @@ impl TryEnum {
         }
     }
 
+    pub fn happy_pattern(self) -> ast::Pat {
+        match self {
+            TryEnum::Result => make::tuple_struct_pat(
+                make::path_unqualified(make::path_segment(make::name_ref("Ok"))),
+                iter::once(make::wildcard_pat().into()),
+            )
+            .into(),
+            TryEnum::Option => make::tuple_struct_pat(
+                make::path_unqualified(make::path_segment(make::name_ref("Some"))),
+                iter::once(make::wildcard_pat().into()),
+            )
+            .into(),
+        }
+    }
+
     fn type_name(self) -> &'static str {
         match self {
             TryEnum::Result => "Result",