Merge pull request #1689 from xlsynth:cdleary/2024-11-01-ellipsis-requires-type-context

PiperOrigin-RevId: 693812992

Author: copybara-github

xls/dslx/type_system/deduce_expr.cc

@@ -139,6 +139,18 @@ absl::StatusOr<std::unique_ptr<Type>> DeduceArray(const Array* node,
       member_types[0]->CloneToUnique(), member_types_dim);
 
   if (node->type_annotation() == nullptr) {
+    if (node->has_ellipsis()) {
+      const Span array_obrack_span(node->span().start(), node->span().start());
+      return TypeInferenceErrorStatus(
+          array_obrack_span, inferred.get(),
+          absl::StrFormat(
+              "Array has ellipsis (`...`) but does not have a type annotation; "
+              "please add a type annotation to indicate how many elements to "
+              "expand to; for example: `%s[N]:%s`",
+              inferred->element_type().ToString(), node->ToString()),
+          ctx->file_table());
+    }
+
     return inferred;
   }
 

xls/dslx/type_system/typecheck_module_test.cc

@@ -2027,6 +2027,18 @@ TEST(TypecheckErrorTest, ArrayEllipsisNoTrailingElement) {
                          "repeat; please add at least one element")));
 }
 
+TEST(TypecheckErrorTest, ArrayEllipsisNoLeadingTypeAnnotation) {
+  EXPECT_THAT(
+      Typecheck(R"(fn main() -> u8[2] {
+    let x: u8[2] = [u8:0, ...];
+    x
+})"),
+      StatusIs(absl::StatusCode::kInvalidArgument,
+               HasSubstr("does not have a type annotation; please add a type "
+                         "annotation to indicate how many elements to expand "
+                         "to; for example: `uN[8][N]:[u8:0, ...]`")));
+}
+
 TEST(TypecheckTest, BadArrayAddition) {
   EXPECT_THAT(Typecheck(R"(
 fn f(a: bits[32][4], b: bits[32][4]) -> bits[32][4] {