C++: Extend jump-to-def support to template instantiations.

This commit extends developers ability to use jump-to-def in C/C++ files opened in the VSCode extension.
Before, jump-to-def starting with code in a template instantiation did not work.

Furthermore, this fixes a bug, as the list of all references of a location did not include template instantiations.

cpp/ql/src/definitions.ql

@@ -9,5 +9,5 @@
 import definitions
 
 from Top e, Top def, string kind
-where def = definitionOf(e, kind)
+where def = definitionOf(e, kind, false)
 select e, def, kind

cpp/ql/src/definitions.qll

@@ -77,9 +77,9 @@ predicate hasLocationInfo_Include(Include i, string path, int sl, int sc, int el
 
 /** Holds if `e` is a source or a target of jump-to-definition. */
 predicate interestingElement(Element e) {
-  exists(definitionOf(e, _))
+  exists(definitionOf(e, _, true))
   or
-  e = definitionOf(_, _)
+  e = definitionOf(_, _, true)
 }
 
 /**
@@ -124,6 +124,10 @@ private predicate constructorCallTypeMention(ConstructorCall cc, TypeMention tm)
 
 /**
  * Gets an element, of kind `kind`, that element `e` uses, if any.
+ * If `includeTemplateInstantiations` is set, include information for
+ * elements `e` that are inside of template instantiations.
+ * Doing so yields multiple definitions for a single location, which can be
+ * undesirably. For example, lgtm.com does not support that.
  *
  * The `kind` is a string representing what kind of use it is:
  *  - `"M"` for function and method calls
@@ -133,7 +137,7 @@ private predicate constructorCallTypeMention(ConstructorCall cc, TypeMention tm)
  *  - `"I"` for import / include directives
  */
 cached
-Top definitionOf(Top e, string kind) {
+Top definitionOf(Top e, string kind, boolean includeTemplateInstantiations) {
   (
     // call -> function called
     kind = "M" and
@@ -197,14 +201,12 @@ Top definitionOf(Top e, string kind) {
     // exclude nested macro invocations, as they will overlap with
     // the top macro invocation.
     not exists(e.(MacroAccess).getParentInvocation()) and
-    // exclude results from template instantiations, as:
-    // (1) these dependencies will often be caused by a choice of
-    // template parameter, which is non-local to this part of code; and
-    // (2) overlapping results pointing to different locations will
-    // be very common.
-    // It's possible we could allow a subset of these dependencies
-    // in future, if we're careful to ensure the above don't apply.
-    not e.isFromTemplateInstantiation(_)
+    (
+      includeTemplateInstantiations = true
+      or
+      includeTemplateInstantiations = false and
+      not e.isFromTemplateInstantiation(_)
+    )
   ) and
   // Some entities have many locations. This can arise for an external
   // function that is frequently declared but not defined, or perhaps

cpp/ql/src/localDefinitions.ql

@@ -1,7 +1,7 @@
 /**
  * @name Jump-to-definition links
  * @description Generates use-definition pairs that provide the data
- *              for jump-to-definition in the code viewer.
+ *              for jump-to-definition in the code viewer of VSCode.
  * @kind definitions
  * @id cpp/ide-jump-to-definition
  * @tags ide-contextual-queries/local-definitions
@@ -12,5 +12,5 @@ import definitions
 external string selectedSourceFile();
 
 from Top e, Top def, string kind
-where def = definitionOf(e, kind) and e.getFile() = getEncodedFile(selectedSourceFile())
+where def = definitionOf(e, kind, true) and e.getFile() = getEncodedFile(selectedSourceFile())
 select e, def, kind

cpp/ql/src/localReferences.ql

@@ -1,7 +1,7 @@
 /**
  * @name Find-references links
  * @description Generates use-definition pairs that provide the data
- *              for find-references in the code viewer.
+ *              for find-references in the code viewer of VSCode.
  * @kind definitions
  * @id cpp/ide-find-references
  * @tags ide-contextual-queries/local-references
@@ -12,5 +12,5 @@ import definitions
 external string selectedSourceFile();
 
 from Top e, Top def, string kind
-where def = definitionOf(e, kind) and def.getFile() = getEncodedFile(selectedSourceFile())
+where def = definitionOf(e, kind, true) and def.getFile() = getEncodedFile(selectedSourceFile())
 select e, def, kind

cpp/ql/test/query-tests/definitions/locationInfo.ql

@@ -4,7 +4,7 @@ import definitions
  * An element that is the source of a jump-to-definition link.
  */
 class Link extends Top {
-  Link() { exists(definitionOf(this, _)) }
+  Link() { exists(definitionOf(this, _, false)) }
 }
 
 /**
@@ -31,7 +31,7 @@ predicate linkLocationInfo(Link e, string filepath, int begin, int end) {
  * Gets a string describing a problem with a `Link`.
  */
 string issues(Link e) {
-  strictcount(Top def | def = definitionOf(e, _)) > 1 and
+  strictcount(Top def | def = definitionOf(e, _, false)) > 1 and
   result = "has more than one definition"
   or
   exists(string filepath1, int begin1, int end1, Link e2, string filepath2, int begin2, int end2 |