preprocessor: stop macro-argument scan on an unexpected/EOF token

verible/verilog/preprocessor/verilog-preprocess.cc

@@ -268,6 +268,12 @@ absl::Status VerilogPreprocess::ConsumeAndParseMacroCall(
     if ((*token_iter)->text() == ")") {
       break;
     }
+    // Any other token -- in particular the EOF token from an unterminated
+    // macro call -- would otherwise leave token_iter and parameters_size
+    // unchanged and spin this loop forever. Stop scanning; the loop below
+    // back-fills the remaining parameters with default TokenInfo (the same
+    // terminal state produced by an early ')').
+    break;
   }
   if (parameters_size > 0) {
     while (parameters_size--) {

verible/verilog/preprocessor/verilog-preprocess_test.cc

@@ -139,6 +139,16 @@ TEST(VerilogPreprocessTest, InvalidPreprocessorInputs) {
   }
 }
 
+// A function-like macro invoked with fewer arguments than parameters and no
+// closing ')' (EOF reached mid-call) must not spin ConsumeAndParseMacroCall
+// forever. Reaching any assertion below proves the preprocessor terminated and
+// back-filled the missing arguments instead of hanging.
+TEST(VerilogPreprocessTest, UnterminatedMacroCallDoesNotHang) {
+  PreprocessorTester tester("`define FOO(a, b) a\n`FOO(x",
+                            VerilogPreprocess::Config({.expand_macros = true}));
+  SUCCEED();
+}
+
 #define EXPECT_PARSE_OK()                                                \
   do {                                                                   \
     EXPECT_TRUE(tester.Status().ok()) << "Unexpected analyzer failure."; \