Merge #4065

4065: Complete unqualified enum names in patterns and expressions r=matklad a=nathanwhit

This PR implements the completion described in #4014.
The result looks like so for patterns:
<img width="542" alt="Screen Shot 2020-04-20 at 3 53 55 PM" src="https://user-images.githubusercontent.com/17734409/79794010-8f529400-831f-11ea-9673-f838aa9bc962.png">

and for `expr`s:
<img width="620" alt="Screen Shot 2020-04-21 at 3 51 24 PM" src="https://user-images.githubusercontent.com/17734409/79908784-d73ded80-83e9-11ea-991d-921f0cb27e6f.png">


I'm not confident that the completion text itself is very robust, as it will unconditionally add completions for enum variants with the form `Enum::Variant`. This means (I believe) it would still suggest `Enum::Variant` even if the local name is changed i.e. `use Enum as Foo` or the variants are brought into scope such as through `use Enum::*`.

Co-authored-by: nathanwhit <nathan.whitaker01@gmail.com>

crates/ra_ide/src/completion/complete_unqualified_path.rs

@@ -4,20 +4,23 @@ use hir::ScopeDef;
 use test_utils::tested_by;
 
 use crate::completion::{CompletionContext, Completions};
+use hir::{Adt, ModuleDef};
 use ra_syntax::AstNode;
 
 pub(super) fn complete_unqualified_path(acc: &mut Completions, ctx: &CompletionContext) {
-    if !ctx.is_trivial_path {
+    if (!ctx.is_trivial_path && !ctx.is_pat_binding_or_const)
-        return;
-    }
-
-    if ctx.is_pat_binding_or_const
         || ctx.record_lit_syntax.is_some()
         || ctx.record_pat_syntax.is_some()
     {
         return;
     }
 
+    complete_enum_variants(acc, ctx);
+
+    if ctx.is_pat_binding_or_const {
+        return;
+    }
+
     ctx.scope().process_all_names(&mut |name, res| {
         if ctx.use_item_syntax.is_some() {
             if let (ScopeDef::Unknown, Some(name_ref)) = (&res, &ctx.name_ref_syntax) {
@@ -31,6 +34,24 @@ pub(super) fn complete_unqualified_path(acc: &mut Completions, ctx: &CompletionC
     });
 }
 
+fn complete_enum_variants(acc: &mut Completions, ctx: &CompletionContext) {
+    if let Some(ty) = ctx.expected_type_of(&ctx.token.parent()) {
+        if let Some(Adt::Enum(enum_data)) = ty.as_adt() {
+            let variants = enum_data.variants(ctx.db);
+            let module = enum_data.module(ctx.db);
+            for variant in variants {
+                if let Some(path) = module.find_use_path(ctx.db, ModuleDef::from(variant)) {
+                    // Variants with trivial paths are already added by the existing completion logic,
+                    // so we should avoid adding these twice
+                    if path.segments.len() > 1 {
+                        acc.add_enum_variant(ctx, variant, Some(path.to_string()));
+                    }
+                }
+            }
+        }
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use insta::assert_debug_snapshot;
@@ -82,7 +103,7 @@ mod tests {
                 }
                 "
             ),
-            @r###"[]"###
+            @"[]"
         );
     }
 
@@ -1109,4 +1130,182 @@ mod tests {
         "###
         );
     }
+    #[test]
+    fn completes_enum_variant_matcharm() {
+        assert_debug_snapshot!(
+            do_reference_completion(
+                r"
+                enum Foo {
+                    Bar,
+                    Baz,
+                    Quux
+                }
+
+                fn main() {
+                    let foo = Foo::Quux;
+
+                    match foo {
+                        Qu<|>
+                    }
+                }
+                "
+            ),
+            @r###"
+        [
+            CompletionItem {
+                label: "Foo",
+                source_range: [248; 250),
+                delete: [248; 250),
+                insert: "Foo",
+                kind: Enum,
+            },
+            CompletionItem {
+                label: "Foo::Bar",
+                source_range: [248; 250),
+                delete: [248; 250),
+                insert: "Foo::Bar",
+                kind: EnumVariant,
+                detail: "()",
+            },
+            CompletionItem {
+                label: "Foo::Baz",
+                source_range: [248; 250),
+                delete: [248; 250),
+                insert: "Foo::Baz",
+                kind: EnumVariant,
+                detail: "()",
+            },
+            CompletionItem {
+                label: "Foo::Quux",
+                source_range: [248; 250),
+                delete: [248; 250),
+                insert: "Foo::Quux",
+                kind: EnumVariant,
+                detail: "()",
+            },
+        ]
+        "###
+        )
+    }
+
+    #[test]
+    fn completes_enum_variant_iflet() {
+        assert_debug_snapshot!(
+            do_reference_completion(
+                r"
+                enum Foo {
+                    Bar,
+                    Baz,
+                    Quux
+                }
+
+                fn main() {
+                    let foo = Foo::Quux;
+
+                    if let Qu<|> = foo {
+
+                    }
+                }
+                "
+            ),
+            @r###"
+        [
+            CompletionItem {
+                label: "Foo",
+                source_range: [219; 221),
+                delete: [219; 221),
+                insert: "Foo",
+                kind: Enum,
+            },
+            CompletionItem {
+                label: "Foo::Bar",
+                source_range: [219; 221),
+                delete: [219; 221),
+                insert: "Foo::Bar",
+                kind: EnumVariant,
+                detail: "()",
+            },
+            CompletionItem {
+                label: "Foo::Baz",
+                source_range: [219; 221),
+                delete: [219; 221),
+                insert: "Foo::Baz",
+                kind: EnumVariant,
+                detail: "()",
+            },
+            CompletionItem {
+                label: "Foo::Quux",
+                source_range: [219; 221),
+                delete: [219; 221),
+                insert: "Foo::Quux",
+                kind: EnumVariant,
+                detail: "()",
+            },
+        ]
+        "###
+        )
+    }
+
+    #[test]
+    fn completes_enum_variant_basic_expr() {
+        assert_debug_snapshot!(
+            do_reference_completion(
+                r"
+                enum Foo {
+                    Bar,
+                    Baz,
+                    Quux
+                }
+
+                fn main() {
+                    let foo: Foo = Q<|>
+                }
+                "
+            ),
+            @r###"
+        [
+            CompletionItem {
+                label: "Foo",
+                source_range: [185; 186),
+                delete: [185; 186),
+                insert: "Foo",
+                kind: Enum,
+            },
+            CompletionItem {
+                label: "Foo::Bar",
+                source_range: [185; 186),
+                delete: [185; 186),
+                insert: "Foo::Bar",
+                kind: EnumVariant,
+                detail: "()",
+            },
+            CompletionItem {
+                label: "Foo::Baz",
+                source_range: [185; 186),
+                delete: [185; 186),
+                insert: "Foo::Baz",
+                kind: EnumVariant,
+                detail: "()",
+            },
+            CompletionItem {
+                label: "Foo::Quux",
+                source_range: [185; 186),
+                delete: [185; 186),
+                insert: "Foo::Quux",
+                kind: EnumVariant,
+                detail: "()",
+            },
+            CompletionItem {
+                label: "main()",
+                source_range: [185; 186),
+                delete: [185; 186),
+                insert: "main()$0",
+                kind: Function,
+                lookup: "main",
+                detail: "fn main()",
+            },
+        ]
+        "###
+        )
+    }
 }

crates/ra_ide/src/completion/completion_context.rs

@@ -1,6 +1,6 @@
 //! FIXME: write short doc here
 
-use hir::{Semantics, SemanticsScope};
+use hir::{Semantics, SemanticsScope, Type};
 use ra_db::SourceDatabase;
 use ra_ide_db::RootDatabase;
 use ra_syntax::{
@@ -168,6 +168,17 @@ impl<'a> CompletionContext<'a> {
         self.sema.scope_at_offset(&self.token.parent(), self.offset)
     }
 
+    pub(crate) fn expected_type_of(&self, node: &SyntaxNode) -> Option<Type> {
+        for ancestor in node.ancestors() {
+            if let Some(pat) = ast::Pat::cast(ancestor.clone()) {
+                return self.sema.type_of_pat(&pat);
+            } else if let Some(expr) = ast::Expr::cast(ancestor) {
+                return self.sema.type_of_expr(&expr);
+            }
+        }
+        None
+    }
+
     fn fill(
         &mut self,
         original_file: &SyntaxNode,