[ENH] give more meaningful error messsages when failing to read json (#…

…582)

* add warning mentioning which json files could not be read

* add file not found erro

+bids/+util/jsondecode.m

@@ -33,20 +33,48 @@
         ismember(exist('jsondecode', 'file'), [2 3]); % jsonstuff / Matlab-compatible implementation
   end
 
+  if ~exist(file, 'file')
+    msg = sprintf('Unable to read file ''%s'': file not found', file);
+    bids.internal.error_handling(mfilename(), 'FileNotFound', ...
+                                 msg, false);
+  end
+
   if has_jsondecode
-    value = jsondecode(fileread(file));
+    try
+      value = jsondecode(fileread(file));
+    catch ME
+      warning_cannot_read_json(file);
+      rethrow(ME);
+    end
 
     % JSONio
   elseif exist('jsonread', 'file') == 3
-    value = jsonread(file, varargin{:});
+    try
+      value = jsonread(file, varargin{:});
+    catch ME
+      warning_cannot_read_json(file);
+      rethrow(ME);
+    end
 
     % SPM12
   elseif exist('spm_jsonread', 'file') == 3
-    value = spm_jsonread(file, varargin{:});
+    try
+      value = spm_jsonread(file, varargin{:});
+    catch ME
+      warning_cannot_read_json(file);
+      rethrow(ME);
+    end
 
   else
     url = 'https://github.com/gllmflndn/JSONio';
     error('JSON library required: install JSONio from: %s', url);
+
   end
 
 end
+
+function warning_cannot_read_json(file)
+  msg = sprintf('Could not read file:\n%s', file);
+  bids.internal.error_handling(mfilename(), 'CannotReadJson', ...
+                               msg, true, true);
+end

requirements.txt

@@ -1,4 +1,4 @@
-miss_hit==0.9.35
+miss_hit
 pre-commit
 jupyterlab
 octave_kernel

tests/tests_utils/test_json_decode.m

@@ -0,0 +1,31 @@
+function test_suite = test_json_decode %#ok<*STOUT>
+  try % assignment of 'localfunctions' is necessary in Matlab >= 2016
+    test_functions = localfunctions(); %#ok<*NASGU>
+  catch % no problem; early Matlab versions can use initTestSuite fine
+  end
+  initTestSuite;
+end
+
+function test_json_decode_file_not_found()
+
+  % write dummy faulty json
+
+  filename = fullfile(temp_dir, 'foo.json');
+  assertExceptionThrown(@() bids.util.jsondecode(filename), ...
+                        'jsondecode:FileNotFound');
+
+end
+
+function test_json_decode_parse_error()
+
+  % write dummy faulty json
+
+  filename = fullfile(temp_dir, 'wrong.json');
+  fid = fopen(filename, 'Wt');
+  fprintf(fid, '{"foo": "bla"');
+  fclose(fid);
+
+  assertWarning(@() bids.util.jsondecode(filename), ...
+                'jsondecode:CannotReadJson');
+
+end