[changed files] don't fail on non-existent absolute paths

Summary:
When a file is passed to infer through `--changed-files-index` which is
- an absolute path
- the file does not exist

Then the code fails throwing an exception in the function below while trying to relativise the absolute path.

The behaviour on relative paths is to skip missing files, and does not fail because Infer does not attempt to relativise them.

Swallow the exception and skip the file; and so unify the behaviour across relative and absolute paths.

Reviewed By: mityal

Differential Revision: D16279672

fbshipit-source-id: 33b468da7

Author: ngorogiannis

infer/src/base/SourceFile.ml

@@ -169,14 +169,16 @@ let create ?(warn_on_error = true) path =
 
 let changed_sources_from_changed_files changed_files =
   List.fold changed_files ~init:Set.empty ~f:(fun changed_files_set line ->
-      let source_file = create line in
-      let changed_files' = Set.add source_file changed_files_set in
-      (* Add source corresponding to changed header if it exists *)
-      match of_header source_file with
-      | Some src ->
-          Set.add src changed_files'
-      | None ->
-          changed_files' )
+      try
+        let source_file = create line in
+        let changed_files' = Set.add source_file changed_files_set in
+        (* Add source corresponding to changed header if it exists *)
+        match of_header source_file with
+        | Some src ->
+            Set.add src changed_files'
+        | None ->
+            changed_files'
+      with _exn -> changed_files_set )
 
 
 module SQLite = struct