From 39a5f228d13ad04e05b502d871bffa7f4c8b40c3 Mon Sep 17 00:00:00 2001
From: Pavel Avgustinov <pavel@semmle.com>
Date: Thu, 27 Sep 2018 10:25:28 +0100
Subject: [PATCH 1/2] Definitions: Only emit links for canonical type mentions

---
 cpp/ql/src/definitions.qll | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/cpp/ql/src/definitions.qll b/cpp/ql/src/definitions.qll
index b067c22040ce..6f8ca88dbca2 100644
--- a/cpp/ql/src/definitions.qll
+++ b/cpp/ql/src/definitions.qll
@@ -126,6 +126,28 @@ private cached predicate constructorCallTypeMention(ConstructorCall cc, TypeMent
   )
 }
 
+/**
+ * We sometimes produce many type mentions at the same location that
+ * refer to the same type. For the purposes of providing a definition
+ * link, we only want one of them.
+ */
+private module TypeMentions {
+  private
+  predicate identity(TypeMention a, TypeMention b) { a = b }
+
+  private
+  int id(TypeMention a) = equivalenceRelation(identity/2)(a, result)
+
+  private
+  TypeMention minMentionIdAt(Location l, Type t) {
+    result = min(TypeMention m | l = m.getLocation() and t = m.getMentionedType() | m order by id(m))
+  }
+
+  predicate isCanonical(TypeMention m) {
+    m = minMentionIdAt(_, _)
+  }
+}
+
 /**
  * Gets an element, of kind `kind`, that element `e` uses, if any.
  *
@@ -156,7 +178,9 @@ Top definitionOf(Top e, string kind) {
     ) or (
       // type mention -> type
       kind = "T" and
+      TypeMentions::isCanonical(e) and
       e.(TypeMention).getMentionedType() = result and
+      not result instanceof ClassTemplateInstantiation and
       not constructorCallTypeMention(_, e) and // handled elsewhere
       // Multiple type mentions can be generated when a typedef is used, and
       // in such cases we want to exclude all but the originating typedef.
@@ -177,6 +201,7 @@ Top definitionOf(Top e, string kind) {
       //  - using the location of the type mention, since it's
       //    tighter that the location of the function call.
       kind = "M" and
+      TypeMentions::isCanonical(e) and
       exists(ConstructorCall cc |
         constructorCallTypeMention(cc, e) and
         result = cc.getTarget()

From 382c7efcd9818793dbaa2a57674a23010eaab9fb Mon Sep 17 00:00:00 2001
From: Pavel Avgustinov <pavgust@users.noreply.github.com>
Date: Thu, 27 Sep 2018 13:57:28 +0100
Subject: [PATCH 2/2] Reintroduce definition links for template instantiations

---
 cpp/ql/src/definitions.qll | 1 -
 1 file changed, 1 deletion(-)

diff --git a/cpp/ql/src/definitions.qll b/cpp/ql/src/definitions.qll
index 6f8ca88dbca2..2625e085f90f 100644
--- a/cpp/ql/src/definitions.qll
+++ b/cpp/ql/src/definitions.qll
@@ -180,7 +180,6 @@ Top definitionOf(Top e, string kind) {
       kind = "T" and
       TypeMentions::isCanonical(e) and
       e.(TypeMention).getMentionedType() = result and
-      not result instanceof ClassTemplateInstantiation and
       not constructorCallTypeMention(_, e) and // handled elsewhere
       // Multiple type mentions can be generated when a typedef is used, and
       // in such cases we want to exclude all but the originating typedef.