Correct highlighting of abbreviations

Abbreviation highlighting cannot use the snapshot environment because we do
not know up-front which variables to capture. Will revisit this later.

src/expand.cpp

@@ -1207,6 +1207,12 @@ maybe_t<wcstring> expand_abbreviation(const wcstring &src, const environment_t &
     return none();
 }
 
+maybe_t<wcstring> expand_abbreviation(const wcstring &src) {
+    // FIXME: We use the principal environment stack because we don't know which variables need to
+    // be captured in a snapshot.
+    return expand_abbreviation(src, env_stack_t::principal());
+}
+
 std::map<wcstring, wcstring> get_abbreviations() {
     // TODO: try to make this cheaper
     const auto &vars = env_stack_t::principal();

src/expand.h

@@ -161,6 +161,7 @@ wcstring replace_home_directory_with_tilde(const wcstring &str, const environmen
 /// Abbreviation support. Expand src as an abbreviation, returning the expanded form if found,
 /// none() if not.
 maybe_t<wcstring> expand_abbreviation(const wcstring &src, const environment_t &vars);
+maybe_t<wcstring> expand_abbreviation(const wcstring &src);
 
 /// \return a snapshot of all abbreviations as a map abbreviation->expansion.
 std::map<wcstring, wcstring> get_abbreviations();

src/highlight.cpp

@@ -1015,7 +1015,7 @@ static bool command_is_valid(const wcstring &cmd, enum parse_statement_decoratio
     if (!is_valid && function_ok) is_valid = function_exists_no_autoload(cmd, vars);
 
     // Abbreviations
-    if (!is_valid && abbreviation_ok) is_valid = expand_abbreviation(cmd, vars).has_value();
+    if (!is_valid && abbreviation_ok) is_valid = expand_abbreviation(cmd).has_value();
 
     // Regular commands
     if (!is_valid && command_ok) is_valid = path_get_path(cmd, NULL, vars);