--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gcc/d/dmd/imphint.c	Thu Feb 13 11:34:05 2020 +0900
@@ -0,0 +1,52 @@
+
+/* Compiler implementation of the D programming language
+ * Copyright (C) 2010-2019 by The D Language Foundation, All Rights Reserved
+ * written by Walter Bright
+ * http://www.digitalmars.com
+ * Distributed under the Boost Software License, Version 1.0.
+ * http://www.boost.org/LICENSE_1_0.txt
+ * https://github.com/D-Programming-Language/dmd/blob/master/src/imphint.c
+ */
+
+
+#include "root/dsystem.h"
+
+#include "mars.h"
+
+/******************************************
+ * Looks for undefined identifier s to see
+ * if it might be undefined because an import
+ * was not specified.
+ * Not meant to be a comprehensive list of names in each module,
+ * just the most common ones.
+ */
+
+const char *importHint(const char *s)
+{
+    static const char *modules[] =
+    {   "core.stdc.stdio",
+        "std.stdio",
+        "std.math",
+        NULL
+    };
+    static const char *names[] =
+    {
+        "printf", NULL,
+        "writeln", NULL,
+        "sin", "cos", "sqrt", "fabs", NULL,
+    };
+    int m = 0;
+    for (int n = 0; modules[m]; n++)
+    {
+        const char *p = names[n];
+        if (p == NULL)
+        {
+            m++;
+            continue;
+        }
+        assert(modules[m]);
+        if (strcmp(s, p) == 0)
+            return modules[m];
+    }
+    return NULL;        // didn't find it
+}