Completition for type name? #3418

Iterate through TupleStructPat's until a MatchArm if
one exists. Store in a new is_pat_bind_and_path bool
and allow the `complete_scope` to find matches.

Added some tests to ensure it works in simple and nested cases.

Author: slyngbaek

crates/ra_ide/src/completion/complete_scope.rs

@@ -3,7 +3,7 @@
 use crate::completion::{CompletionContext, Completions};
 
 pub(super) fn complete_scope(acc: &mut Completions, ctx: &CompletionContext) {
-    if !ctx.is_trivial_path {
+    if !ctx.is_trivial_path && !ctx.is_pat_binding_and_path {
         return;
     }
 
@@ -20,6 +20,111 @@ mod tests {
         do_completion(ra_fixture, CompletionKind::Reference)
     }
 
+    #[test]
+    fn nested_bind_pat_and_path() {
+        assert_debug_snapshot!(
+            do_reference_completion(
+                r"
+                enum First {
+                    A,
+                    B,
+                }
+                enum Second {
+                    A(First),
+                    B(First),
+                }
+                fn quux(x: Option<Option<Second>>>) {
+                    match x {
+                        None => (),
+                        Some(Some(Second(Fi<|>))) => (),
+                    }
+                }
+                "
+            ),
+            @r###"
+            [
+                CompletionItem {
+                    label: "First",
+                    source_range: [363; 365),
+                    delete: [363; 365),
+                    insert: "First",
+                    kind: Enum,
+                },
+                CompletionItem {
+                    label: "Second",
+                    source_range: [363; 365),
+                    delete: [363; 365),
+                    insert: "Second",
+                    kind: Enum,
+                },
+                CompletionItem {
+                    label: "quux(…)",
+                    source_range: [363; 365),
+                    delete: [363; 365),
+                    insert: "quux(${1:x})$0",
+                    kind: Function,
+                    lookup: "quux",
+                    detail: "fn quux(x: Option<Option<Second>>)",
+                },
+            ]
+            "###
+        );
+    }
+
+    #[test]
+    fn bind_pat_and_path() {
+        assert_debug_snapshot!(
+            do_reference_completion(
+                r"
+                enum Enum {
+                    A,
+                    B,
+                }
+                fn quux(x: Option<Enum>) {
+                    match x {
+                        None => (),
+                        Some(en<|>) => (),
+                    }
+                }
+                "
+            ),
+            @r###"
+            [
+                CompletionItem {
+                    label: "Enum",
+                    source_range: [231; 233),
+                    delete: [231; 233),
+                    insert: "Enum",
+                    kind: Enum,
+                },
+                CompletionItem {
+                    label: "None",
+                    source_range: [231; 233),
+                    delete: [231; 233),
+                    insert: "None",
+                    kind: Binding,
+                },
+                CompletionItem {
+                    label: "quux(…)",
+                    source_range: [231; 233),
+                    delete: [231; 233),
+                    insert: "quux(${1:x})$0",
+                    kind: Function,
+                    lookup: "quux",
+                    detail: "fn quux(x: Option<Enum>)",
+                },
+                CompletionItem {
+                    label: "x",
+                    source_range: [231; 233),
+                    delete: [231; 233),
+                    insert: "x",
+                    kind: Binding,
+                },
+            ]
+            "###
+        );
+    }
+
     #[test]
     fn completes_bindings_from_let() {
         assert_debug_snapshot!(

crates/ra_ide/src/completion/completion_context.rs

@@ -36,6 +36,9 @@ pub(crate) struct CompletionContext<'a> {
     /// 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 bind battern which may also be part of a path.
+    // if let Some(En<|>) = Some(Enum::A)
+    pub(super) is_pat_binding_and_path: 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).
@@ -95,6 +98,7 @@ impl<'a> CompletionContext<'a> {
             impl_def: None,
             is_param: false,
             is_pat_binding: false,
+            is_pat_binding_and_path: false,
             is_trivial_path: false,
             path_prefix: None,
             after_if: false,
@@ -186,12 +190,20 @@ impl<'a> CompletionContext<'a> {
         // suggest declaration names, see `CompletionKind::Magic`.
         if let Some(name) = find_node_at_offset::<ast::Name>(&file_with_fake_ident, offset) {
             if let Some(bind_pat) = name.syntax().ancestors().find_map(ast::BindPat::cast) {
-                let parent = bind_pat.syntax().parent();
+                let mut parent = bind_pat.syntax().parent();
                 if parent.clone().and_then(ast::MatchArm::cast).is_some()
-                    || parent.and_then(ast::Condition::cast).is_some()
+                    || parent.clone().and_then(ast::Condition::cast).is_some()
                 {
                     self.is_pat_binding = true;
                 }
+
+                while let Some(_) = parent.clone().and_then(ast::TupleStructPat::cast) {
+                    parent = parent.and_then(|p| p.parent());
+                    if parent.clone().and_then(ast::MatchArm::cast).is_some() {
+                        self.is_pat_binding_and_path = true;
+                        break;
+                    }
+                }
             }
             if is_node::<ast::Param>(name.syntax()) {
                 self.is_param = true;