fix Issue 18480 - dmd 2.079 hangs

Author: timotheecour

src/dmd/access.d

@@ -547,8 +547,8 @@ public Dsymbol mostVisibleOverload(Dsymbol s)
 {
     if (!s.isOverloadable())
         return s;
-
-    Dsymbol next, fstart = s, mostVisible = s;
+    Dsymbol next, fstart = s, mostVisible = s, previous = null;
+    AliasDeclaration adOrig = null;
     for (; s; s = next)
     {
         // void func() {}
@@ -593,7 +593,13 @@ public Dsymbol mostVisibleOverload(Dsymbol s)
                  */
                 auto aliasee = ad.toAlias();
                 if (aliasee.isFuncAliasDeclaration || aliasee.isOverDeclaration)
+                {
+                    if(ad.toChars() == aliasee.toChars())
+                    {
+                        adOrig = ad;
+                    }
                     next = aliasee;
+                }
                 else
                 {
                     /* A simple alias can be at the end of a function or template overload chain.
@@ -613,6 +619,15 @@ public Dsymbol mostVisibleOverload(Dsymbol s)
 
         if (next && mostVisible.prot().isMoreRestrictiveThan(next.prot()))
             mostVisible = next;
+
+        // fixes https://issues.dlang.org/show_bug.cgi?id=18480
+        if(next && next == previous)
+        {
+            assert(adOrig);
+            error(adOrig.loc, "`alias X = X` not allowed (with `X = %s`)", adOrig.toChars());
+            return next;
+        }
+        previous = s;
     }
     return mostVisible;
 }

test/fail_compilation/imports/test18480a.d

@@ -0,0 +1,3 @@
+public import test18480b : TestTemplate;
+alias TestTemplate = TestTemplate;
+

test/fail_compilation/imports/test18480b.d

@@ -0,0 +1 @@
+template TestTemplate() { }

test/fail_compilation/test18480.d

@@ -0,0 +1,13 @@
+/*
+TEST_OUTPUT:
+---
+fail_compilation/imports/test18480a.d(2): Error: alias X = X not allowed (with X = TestTemplate)
+---
+https://issues.dlang.org/show_bug.cgi?id=18480
+*/
+
+import test18480a;
+
+alias TestTemplate = test18480a.TestTemplate;
+
+void main() { }