compatibility code for gpt2 in 20a and 20b - use should not need to checkout other git commits when using these versions

Author: bwdGitHub

+gpt2/+internal/getSupportFilePath.m

@@ -7,6 +7,10 @@
 arguments
     fileName (1,1) string
 end
+if ismember(version('-release'),["2020a","2020b"])
+    filePath = legacySupportFilePath(fileName);
+    return
+end
 sd = matlab.internal.examples.utils.getSupportFileDir();
 localFileDir = {"data","networks"};%#ok
 localFile = fullfile(sd,"nnet",localFileDir{:},fileName);
@@ -15,4 +19,37 @@
 end
 fileURL = strjoin([localFileDir,fileName],"/");
 filePath = matlab.internal.examples.downloadSupportFile("nnet",fileURL);
+end
+
+function filePath = legacySupportFilePath(fileName)
+% For releases before matlab.internal.examples.downloadSupportFile,
+% use manual download code. We save to the repo's root directory instead of
+% the userpath.
+% Create directories for the model.
+modelType = 'gpt2-355M';
+modelDirectory = fullfile(fileparts(mfilename('fullpath')),'..','..',modelType);
+filePath = fullfile(modelDirectory,fileName);
+iCreateDirectoryIfItDoesNotExist(modelDirectory);
+
+iDownloadFileIfItDoesNotExist( ...
+    filePath, ...
+    "https://ssd.mathworks.com/supportfiles/nnet/data/networks/"+fileName );
+end
+
+function iCreateDirectoryIfItDoesNotExist(directory)
+if ~exist(directory, 'dir')
+    fprintf('Creating directory ''%s''...\n', directory);
+    mkdir(directory);
+else
+    fprintf('Skipped creating directory ''%s'' as it already exists\n', directory);
+end
+end
+
+function iDownloadFileIfItDoesNotExist(destination, source)
+if ~exist(destination, 'file')
+    fprintf('Downloading file ''%s'' ...\n', destination);
+    websave(destination, source);
+else
+    fprintf('Skipped downloading file ''%s'' as it already exists\n', destination);
+end
 end