Task alias validation during training mode (#886)

* Attempt to validate task alias
* Validate allowed options for --task alias
* Update comment in aliases.cpp
* Show allowed values for alias

Co-authored-by: Roman Grundkiewicz <rgrundkiewicz@gmail.com>

4 files changed, 21 insertions, 2 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 169a1a5e..4c624954 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -49,6 +49,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Fixed loading binary models on architectures where `size_t` != `uint64_t`.
 - Missing float template specialisation for elem::Plus
 - Broken links to MNIST data sets
+- Enforce validation for the task alias in training mode.
 
 ### Changed
 - Optimize LSH for speed by treating is as a shortlist generator. No option changes in decoder
diff --git a/src/common/aliases.cpp b/src/common/aliases.cpp
index 0be26a8c..36613327 100644
--- a/src/common/aliases.cpp
+++ b/src/common/aliases.cpp
@@ -19,6 +19,8 @@ namespace marian {
  * As aliases are key-value pairs by default, values are compared as std::string. 
  * If the command line option corresponding to the alias is a vector, the alias 
  * will be triggered if the requested value exists in that vector at least once.
+ * By design if an option value that is not defined for that alias option below
+ * is used, the CLI parser will abort with 'unknown value for alias' error.
  *
  * @see CLIWrapper::alias()
  *
diff --git a/src/common/cli_wrapper.cpp b/src/common/cli_wrapper.cpp
index 9a5a1a2c..211dd0b9 100644
--- a/src/common/cli_wrapper.cpp
+++ b/src/common/cli_wrapper.cpp
@@ -132,8 +132,14 @@ void CLIWrapper::parseAliases() {
   if(aliases_.empty())
     return;
 
+  // Find the set of values allowed for each alias option.
+  // Later we will check and abort if an alias option has an unknown value.
+  std::unordered_map<std::string, std::unordered_set<std::string>> allowedAliasValues;
+  for(auto &&alias : aliases_)
+    allowedAliasValues[alias.key].insert(alias.value);
+
   // Iterate all known aliases, each alias has a key, value, and config
-  for(const auto &alias : aliases_) {
+  for(auto &&alias : aliases_) {
     // Check if the alias option exists in the config (it may come from command line or a config
     // file)
     if(config_[alias.key]) {
@@ -145,6 +151,15 @@ void CLIWrapper::parseAliases() {
       bool expand = false;
       if(config_[alias.key].IsSequence()) {
         auto aliasOpts = config_[alias.key].as<std::vector<std::string>>();
+        // Abort if an alias option has an unknown value, i.e. value that has not been defined
+        // in common/aliases.cpp
+        for(auto &&aliasOpt : aliasOpts)
+          if(allowedAliasValues[alias.key].count(aliasOpt) == 0) {
+            std::vector<std::string> allowedOpts(allowedAliasValues[alias.key].begin(),
+                                                 allowedAliasValues[alias.key].end());
+            ABORT("Unknown value '" + aliasOpt + "' for alias option --" + alias.key + ". "
+                  "Allowed values: " + utils::join(allowedOpts, ", "));
+          }
         expand = std::find(aliasOpts.begin(), aliasOpts.end(), alias.value) != aliasOpts.end();
       } else {
         expand = config_[alias.key].as<std::string>() == alias.value;
diff --git a/src/common/config_parser.cpp b/src/common/config_parser.cpp
index 30d77e36..8da9520c 100644
--- a/src/common/config_parser.cpp
+++ b/src/common/config_parser.cpp
@@ -557,7 +557,8 @@ void ConfigParser::addOptionsTraining(cli::CLIWrapper& cli) {
   addSuboptionsULR(cli);
 
   cli.add<std::vector<std::string>>("--task",
-     "Use predefined set of options. Possible values: transformer, transformer-big");
+     "Use predefined set of options. Possible values: transformer-base, transformer-big, "
+     "transformer-base-prenorm, transformer-big-prenorm");
   cli.switchGroup(previous_group);
   // clang-format on
 }