3 files changed, 103 insertions, 0 deletions

diff --git a/crates/ra_ide_api/src/completion.rs b/crates/ra_ide_api/src/completion.rs
index fbfd7e3e7..c8022f94f 100644
--- a/crates/ra_ide_api/src/completion.rs
+++ b/crates/ra_ide_api/src/completion.rs
@@ -4,6 +4,7 @@ mod presentation;
 
 mod complete_dot;
 mod complete_struct_literal;
+mod complete_pattern;
 mod complete_fn_param;
 mod complete_keyword;
 mod complete_snippet;
@@ -65,6 +66,7 @@ pub(crate) fn completions(db: &db::RootDatabase, position: FilePosition) -> Opti
     complete_scope::complete_scope(&mut acc, &ctx);
     complete_dot::complete_dot(&mut acc, &ctx);
     complete_struct_literal::complete_struct_literal(&mut acc, &ctx);
+    complete_pattern::complete_pattern(&mut acc, &ctx);
     complete_postfix::complete_postfix(&mut acc, &ctx);
     Some(acc)
 }
diff --git a/crates/ra_ide_api/src/completion/complete_pattern.rs b/crates/ra_ide_api/src/completion/complete_pattern.rs
new file mode 100644
index 000000000..3cf79c080
--- /dev/null
+++ b/crates/ra_ide_api/src/completion/complete_pattern.rs
@@ -0,0 +1,87 @@
+use crate::completion::{CompletionContext, Completions};
+
+/// Completes constats and paths in patterns.
+pub(super) fn complete_pattern(acc: &mut Completions, ctx: &CompletionContext) {
+    if !ctx.is_pat_binding {
+        return;
+    }
+    // TODO: ideally, we should look at the type we are matching against and
+    // suggest variants + auto-imports
+    let names = ctx.resolver.all_names(ctx.db);
+    for (name, res) in names.into_iter() {
+        let r = res.as_ref();
+        let def = match r.take_types().or(r.take_values()) {
+            Some(hir::Resolution::Def(def)) => def,
+            _ => continue,
+        };
+        match def {
+            hir::ModuleDef::Enum(..)
+            | hir::ModuleDef::EnumVariant(..)
+            | hir::ModuleDef::Const(..)
+            | hir::ModuleDef::Module(..) => (),
+            _ => continue,
+        }
+        acc.add_resolution(ctx, name.to_string(), &res)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use insta::assert_debug_snapshot_matches;
+    use crate::completion::{CompletionItem, CompletionKind, do_completion};
+
+    fn complete(code: &str) -> Vec<CompletionItem> {
+        do_completion(code, CompletionKind::Reference)
+    }
+
+    #[test]
+    fn completes_enum_variants_and_modules() {
+        let completions = complete(
+            r"
+            enum E { X }
+            use self::E::X;
+            const Z: E = E::X;
+            mod m {}
+
+            static FOO: E = E::X;
+            struct Bar { f: u32 }
+
+            fn foo() {
+               match E::X {
+                   <|>
+               }
+            }
+            ",
+        );
+        assert_debug_snapshot_matches!(completions, @r###"[
+    CompletionItem {
+        label: "E",
+        source_range: [246; 246),
+        delete: [246; 246),
+        insert: "E",
+        kind: Enum
+    },
+    CompletionItem {
+        label: "X",
+        source_range: [246; 246),
+        delete: [246; 246),
+        insert: "X",
+        kind: EnumVariant
+    },
+    CompletionItem {
+        label: "Z",
+        source_range: [246; 246),
+        delete: [246; 246),
+        insert: "Z",
+        kind: Const
+    },
+    CompletionItem {
+        label: "m",
+        source_range: [246; 246),
+        delete: [246; 246),
+        insert: "m",
+        kind: Module
+    }
+]"###);
+    }
+}
diff --git a/crates/ra_ide_api/src/completion/completion_context.rs b/crates/ra_ide_api/src/completion/completion_context.rs
index d351be054..724d0dfbf 100644
--- a/crates/ra_ide_api/src/completion/completion_context.rs
+++ b/crates/ra_ide_api/src/completion/completion_context.rs
@@ -23,6 +23,9 @@ pub(crate) struct CompletionContext<'a> {
     pub(super) use_item_syntax: Option<&'a ast::UseItem>,
     pub(super) struct_lit_syntax: Option<&'a ast::StructLit>,
     pub(super) is_param: bool,
+    /// If a name-binding or reference to a const in a pattern.
+    /// Irrefutable patterns (like let) are excluded.
+    pub(super) is_pat_binding: bool,
     /// A single-indent path, like `foo`. `::foo` should not be considered a trivial path.
     pub(super) is_trivial_path: bool,
     /// If not a trivial, path, the prefix (qualifier).
@@ -58,6 +61,7 @@ impl<'a> CompletionContext<'a> {
             use_item_syntax: None,
             struct_lit_syntax: None,
             is_param: false,
+            is_pat_binding: false,
             is_trivial_path: false,
             path_prefix: None,
             after_if: false,
@@ -102,12 +106,22 @@ impl<'a> CompletionContext<'a> {
         // Otherwise, see if this is a declaration. We can use heuristics to
         // suggest declaration names, see `CompletionKind::Magic`.
         if let Some(name) = find_node_at_offset::<ast::Name>(file.syntax(), offset) {
+            if is_node::<ast::BindPat>(name.syntax()) {
+                let bind_pat = name.syntax().ancestors().find_map(ast::BindPat::cast).unwrap();
+                let parent = bind_pat.syntax().parent();
+                if parent.and_then(ast::MatchArm::cast).is_some()
+                    || parent.and_then(ast::Condition::cast).is_some()
+                {
+                    self.is_pat_binding = true;
+                }
+            }
             if is_node::<ast::Param>(name.syntax()) {
                 self.is_param = true;
                 return;
             }
         }
     }
+
     fn classify_name_ref(&mut self, original_file: &'a SourceFile, name_ref: &ast::NameRef) {
         let name_range = name_ref.syntax().range();
         if name_ref.syntax().parent().and_then(ast::NamedField::cast).is_some() {