4 files changed, 160 insertions, 14 deletions

diff --git a/Cargo.lock b/Cargo.lock
index f8d26192d..eb5247b69 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -876,6 +876,7 @@ name = "ra_assists"
 version = "0.1.0"
 dependencies = [
  "format-buf",
+ "itertools",
  "join_to_string",
  "ra_db",
  "ra_fmt",
diff --git a/crates/ra_assists/Cargo.toml b/crates/ra_assists/Cargo.toml
index d314dc8e6..85adddb5b 100644
--- a/crates/ra_assists/Cargo.toml
+++ b/crates/ra_assists/Cargo.toml
@@ -11,6 +11,7 @@ doctest = false
 format-buf = "1.0.0"
 join_to_string = "0.1.3"
 rustc-hash = "1.1.0"
+itertools = "0.8.2"
 
 ra_syntax = { path = "../ra_syntax" }
 ra_text_edit = { path = "../ra_text_edit" }
diff --git a/crates/ra_assists/src/handlers/fill_match_arms.rs b/crates/ra_assists/src/handlers/fill_match_arms.rs
index fbd6a3ec3..d207c3307 100644
--- a/crates/ra_assists/src/handlers/fill_match_arms.rs
+++ b/crates/ra_assists/src/handlers/fill_match_arms.rs
@@ -2,6 +2,8 @@
 
 use std::iter;
 
+use itertools::Itertools;
+
 use hir::{Adt, HasSource, Semantics};
 use ra_ide_db::RootDatabase;
 
@@ -39,13 +41,6 @@ pub(crate) fn fill_match_arms(ctx: AssistCtx) -> Option<Assist> {
     let match_arm_list = match_expr.match_arm_list()?;
 
     let expr = match_expr.expr()?;
-    let enum_def = resolve_enum_def(&ctx.sema, &expr)?;
-    let module = ctx.sema.scope(expr.syntax()).module()?;
-
-    let variants = enum_def.variants(ctx.db);
-    if variants.is_empty() {
-        return None;
-    }
 
     let mut arms: Vec<MatchArm> = match_arm_list.arms().collect();
     if arms.len() == 1 {
@@ -54,13 +49,40 @@ pub(crate) fn fill_match_arms(ctx: AssistCtx) -> Option<Assist> {
         }
     }
 
-    let db = ctx.db;
-    let missing_arms: Vec<MatchArm> = variants
-        .into_iter()
-        .filter_map(|variant| build_pat(db, module, variant))
-        .filter(|variant_pat| is_variant_missing(&mut arms, variant_pat))
-        .map(|pat| make::match_arm(iter::once(pat), make::expr_unit()))
-        .collect();
+    let module = ctx.sema.scope(expr.syntax()).module()?;
+
+    let missing_arms: Vec<MatchArm> = if let Some(enum_def) = resolve_enum_def(&ctx.sema, &expr) {
+        let variants = enum_def.variants(ctx.db);
+
+        variants
+            .into_iter()
+            .filter_map(|variant| build_pat(ctx.db, module, variant))
+            .filter(|variant_pat| is_variant_missing(&mut arms, variant_pat))
+            .map(|pat| make::match_arm(iter::once(pat), make::expr_unit()))
+            .collect()
+    } else if let Some(enum_defs) = resolve_tuple_of_enum_def(&ctx.sema, &expr) {
+        // partial fill not currently supported for tuple of enums
+        if !arms.is_empty() {
+            return None;
+        }
+
+        enum_defs
+            .into_iter()
+            .map(|enum_def| enum_def.variants(ctx.db))
+            .multi_cartesian_product()
+            .map(|variants| {
+                let patterns = variants
+                    .into_iter()
+                    .filter_map(|variant| build_pat(ctx.db, module, variant))
+                    .collect::<Vec<_>>();
+                ast::Pat::from(make::tuple_pat(patterns))
+            })
+            .filter(|variant_pat| is_variant_missing(&mut arms, variant_pat))
+            .map(|pat| make::match_arm(iter::once(pat), make::expr_unit()))
+            .collect()
+    } else {
+        return None;
+    };
 
     if missing_arms.is_empty() {
         return None;
@@ -104,6 +126,22 @@ fn resolve_enum_def(sema: &Semantics<RootDatabase>, expr: &ast::Expr) -> Option<
     })
 }
 
+fn resolve_tuple_of_enum_def(
+    sema: &Semantics<RootDatabase>,
+    expr: &ast::Expr,
+) -> Option<Vec<hir::Enum>> {
+    Some(
+        sema.type_of_expr(&expr)?
+            .tuple_fields(sema.db)
+            .iter()
+            .map(|ty| match ty.as_adt() {
+                Some(Adt::Enum(e)) => e,
+                _ => panic!("handle the case of tuple containing non-enum"),
+            })
+            .collect(),
+    )
+}
+
 fn build_pat(db: &RootDatabase, module: hir::Module, var: hir::EnumVariant) -> Option<ast::Pat> {
     let path = crate::ast_transform::path_to_ast(module.find_use_path(db, var.into())?);
 
@@ -308,6 +346,103 @@ mod tests {
     }
 
     #[test]
+    fn fill_match_arms_tuple_of_enum() {
+        check_assist(
+            fill_match_arms,
+            r#"
+            enum A {
+                One,
+                Two,
+            }
+            enum B {
+                One,
+                Two,
+            }
+
+            fn main() {
+                let a = A::One;
+                let b = B::One;
+                match (a<|>, b) {}
+            }
+            "#,
+            r#"
+            enum A {
+                One,
+                Two,
+            }
+            enum B {
+                One,
+                Two,
+            }
+
+            fn main() {
+                let a = A::One;
+                let b = B::One;
+                match <|>(a, b) {
+                    (A::One, B::One) => (),
+                    (A::One, B::Two) => (),
+                    (A::Two, B::One) => (),
+                    (A::Two, B::Two) => (),
+                }
+            }
+            "#,
+        );
+    }
+
+    #[test]
+    fn fill_match_arms_tuple_of_enum_partial() {
+        check_assist_not_applicable(
+            fill_match_arms,
+            r#"
+            enum A {
+                One,
+                Two,
+            }
+            enum B {
+                One,
+                Two,
+            }
+
+            fn main() {
+                let a = A::One;
+                let b = B::One;
+                match (a<|>, b) {
+                    (A::Two, B::One) => (),
+                }
+            }
+            "#,
+        );
+    }
+
+    #[test]
+    fn fill_match_arms_tuple_of_enum_not_applicable() {
+        check_assist_not_applicable(
+            fill_match_arms,
+            r#"
+            enum A {
+                One,
+                Two,
+            }
+            enum B {
+                One,
+                Two,
+            }
+
+            fn main() {
+                let a = A::One;
+                let b = B::One;
+                match (a<|>, b) {
+                    (A::Two, B::One) => (),
+                    (A::One, B::One) => (),
+                    (A::One, B::Two) => (),
+                    (A::Two, B::Two) => (),
+                }
+            }
+            "#,
+        );
+    }
+
+    #[test]
     fn test_fill_match_arm_refs() {
         check_assist(
             fill_match_arms,
diff --git a/crates/ra_syntax/src/ast/make.rs b/crates/ra_syntax/src/ast/make.rs
index 9f6f1cc53..9d8ed6238 100644
--- a/crates/ra_syntax/src/ast/make.rs
+++ b/crates/ra_syntax/src/ast/make.rs
@@ -136,6 +136,15 @@ pub fn placeholder_pat() -> ast::PlaceholderPat {
     }
 }
 
+pub fn tuple_pat(pats: impl IntoIterator<Item = ast::Pat>) -> ast::TuplePat {
+    let pats_str = pats.into_iter().map(|p| p.syntax().to_string()).join(", ");
+    return from_text(&format!("({})", pats_str));
+
+    fn from_text(text: &str) -> ast::TuplePat {
+        ast_from_text(&format!("fn f({}: ())", text))
+    }
+}
+
 pub fn tuple_struct_pat(
     path: ast::Path,
     pats: impl IntoIterator<Item = ast::Pat>,