--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/clang/test/Preprocessor/_Pragma-in-macro-arg.cpp	Thu Feb 13 15:10:13 2020 +0900
@@ -0,0 +1,22 @@
+// RUN: %clang_cc1 %s -verify -Wconversion
+
+#define P(X) _Pragma(#X)
+#define V(X) X
+
+#define X \
+  P(clang diagnostic push) \
+  P(clang diagnostic ignored "-Wconversion") \
+  ) = 1.2; \
+  P(clang diagnostic pop)
+
+void f() {
+  int a = 1.2; // expected-warning {{changes value}}
+
+  // Note, we intentionally enter a tentatively-parsed context here to trigger
+  // regular use of lookahead. This would go wrong if _Pragma checking in macro
+  // argument pre-expansion also tries to use token lookahead.
+  int (b
+  V(X)
+
+  int c = 1.2; // expected-warning {{changes value}}
+}