repl: fix multi-line attribute set in variable binding (issue #16310)

src/libcmd/repl.cc

@@ -902,7 +902,13 @@ ExprAttrs * NixRepl::parseReplBindings(std::string s)
     // Try parsing as bindings
     try {
         return state->parseReplBindings(s, basePath, staticEnv);
-    } catch (ParseError &) {
+    } catch (ParseError & e) {
+        // If the input is incomplete (e.g. `a = {` without closing `}`),
+        // signal the main loop to prompt for continuation instead of falling
+        // through to expression evaluation (which would produce a confusing
+        // "unexpected '='" error).
+        if (isIncompleteInput(e))
+            throw IncompleteReplExpr(e.msg());
     }
 
     // Try with semicolon appended (for `inherit foo` shorthand)

tests/functional/suites/repl/cases/multiline-attrset-binding.expected

@@ -0,0 +1,9 @@
+Nix <nix version>
+Type :? for help.
+
+nix-repl> a = {
+        >   b = 1;
+        > }
+
+nix-repl> a
+{ b = 1; }

tests/functional/suites/repl/cases/multiline-attrset-binding.in

@@ -0,0 +1,5 @@
+# COM: Multi-line attribute set in binding should trigger continuation (issue #16310)
+a = {
+  b = 1;
+}
+a

tests/functional/suites/repl/cases/multiline-attrset-expr.expected

@@ -0,0 +1,7 @@
+Nix <nix version>
+Type :? for help.
+
+nix-repl> {
+        >   x = 1;
+        > }
+{ x = 1; }

tests/functional/suites/repl/cases/multiline-attrset-expr.in

@@ -0,0 +1,4 @@
+# COM: Multi-line attribute set expression (not binding) should still trigger continuation (issue #16310)
+{
+  x = 1;
+}