[DSLX:fmt] Fix handling of inline comment on unary operation.

The unary operation was not tagged with the correct position data from the
original source text, so the comment emission process was getting confused.

Fixes #1372

PiperOrigin-RevId: 623587102

xls/dslx/fmt/ast_fmt_test.cc

@@ -1181,6 +1181,14 @@ struct Foo {
 )");
 }
 
+TEST_F(ModuleFmtTest, UnaryWithCommentGithub1372) {
+  Run(
+      R"(fn main(x: bool) -> bool {
+    !x  // Gotta negate it!
+}
+)");
+}
+
 TEST_F(ModuleFmtTest, StructDefTwoParametrics) {
   const std::string_view kProgram =
       "pub struct Point<M: u32, N: u32> { x: bits[M], y: bits[N] }\n";

xls/dslx/frontend/parser.cc

@@ -1615,7 +1615,7 @@ absl::StatusOr<Expr*> Parser::ParseTermLhs(Bindings& outer_bindings,
       default:
         LOG(FATAL) << "Inconsistent unary operation token kind.";
     }
-    Span span(start_pos, GetPos());
+    Span span(tok.span().start(), arg->span().limit());
     lhs = module_->Make<Unop>(span, unop_kind, arg);
   } else if (peek->IsTypeKeyword() ||
              (peek->kind() == TokenKind::kIdentifier &&

xls/dslx/frontend/parser_test.cc

@@ -969,7 +969,10 @@ TEST_F(ParserTest, LocalConstBinding) {
   EXPECT_EQ(definer, const_let);
 }
 
-TEST_F(ParserTest, ParenthesizedUnop) { RoundTripExpr("(!x)", {"x"}); }
+TEST_F(ParserTest, ParenthesizedUnop) {
+  Expr* e = RoundTripExpr("(!x)", {"x"});
+  EXPECT_EQ(e->span().ToString(), "test.x:1:2-1:4");
+}
 
 TEST_F(ParserTest, BitSliceOfCall) { RoundTripExpr("id(x)[0:8]", {"id", "x"}); }