Add Locations library and move language independent files to 'codeql'

ql/src/codeql/Locations.qll

@@ -0,0 +1,53 @@
+/** Provides classes for working with locations. */
+
+import files.FileSystem
+
+/**
+ * A location as given by a file, a start line, a start column,
+ * an end line, and an end column.
+ *
+ * For more information about locations see [LGTM locations](https://lgtm.com/help/ql/locations).
+ */
+class Location extends @location {
+  /** Gets the file for this location. */
+  File getFile() { locations_default(this, result, _, _, _, _) }
+
+  /** Gets the 1-based line number (inclusive) where this location starts. */
+  int getStartLine() { locations_default(this, _, result, _, _, _) }
+
+  /** Gets the 1-based column number (inclusive) where this location starts. */
+  int getStartColumn() { locations_default(this, _, _, result, _, _) }
+
+  /** Gets the 1-based line number (inclusive) where this location ends. */
+  int getEndLine() { locations_default(this, _, _, _, result, _) }
+
+  /** Gets the 1-based column number (inclusive) where this location ends. */
+  int getEndColumn() { locations_default(this, _, _, _, _, result) }
+
+  /** Gets the number of lines covered by this location. */
+  int getNumLines() { result = getEndLine() - getStartLine() + 1 }
+
+  /** Gets a textual representation of this element. */
+  string toString() {
+    exists(string filepath, int startline, int startcolumn, int endline, int endcolumn |
+      hasLocationInfo(filepath, startline, startcolumn, endline, endcolumn) and
+      result = filepath + "@" + startline + ":" + startcolumn + ":" + endline + ":" + endcolumn
+    )
+  }
+
+  /**
+   * 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
+   * [LGTM locations](https://lgtm.com/help/ql/locations).
+   */
+  predicate hasLocationInfo(
+    string filepath, int startline, int startcolumn, int endline, int endcolumn
+  ) {
+    exists(File f |
+      locations_default(this, f, startline, startcolumn, endline, endcolumn) and
+      filepath = f.getAbsolutePath()
+    )
+  }
+}