Add hasLocationInfo for Types

It returns a dummy location except for named types with a type
declaration in the source.

Author: owen-mc

go/ql/lib/semmle/go/Types.qll

@@ -154,6 +154,23 @@ class Type extends @type {
    * Gets a basic textual representation of this type.
    */
   string toString() { result = this.getName() }
+
+  /**
+   * Holds if this element is at the specified location.
+   * The location spans column `startcolumn` of line `startline` to
+   * column `endcolumn` of line `endline` in file `filepath`.
+   * For more information, see
+   * [Locations](https://codeql.github.com/docs/writing-codeql-queries/providing-locations-in-codeql-queries/).
+   */
+  predicate hasLocationInfo(
+    string filepath, int startline, int startcolumn, int endline, int endcolumn
+  ) {
+    filepath = "" and
+    startline = 0 and
+    startcolumn = 0 and
+    endline = 0 and
+    endcolumn = 0
+  }
 }
 
 /** An invalid type. */
@@ -997,6 +1014,17 @@ class NamedType extends @namedtype, CompositeType {
   }
 
   override Type getUnderlyingType() { result = this.getBaseType().getUnderlyingType() }
+
+  override predicate hasLocationInfo(
+    string filepath, int startline, int startcolumn, int endline, int endcolumn
+  ) {
+    exists(DeclaredType dt |
+      dt.getType() = this and
+      // Note that if the type declaration isn't in the source that we have
+      // then we use a dummy location.
+      dt.hasLocationInfo(filepath, startline, startcolumn, endline, endcolumn)
+    )
+  }
 }
 
 /**