Fix theme config for json output (so cargo can use it)

Author: estebank

compiler/rustc_errors/src/json.rs

@@ -11,7 +11,7 @@
 
 use crate::emitter::{
     should_show_source_code, ColorConfig, Destination, Emitter, HumanEmitter,
-    HumanReadableErrorType,
+    HumanReadableErrorType, OutputTheme,
 };
 use crate::registry::Registry;
 use crate::translation::{to_fluent_args, Translate};
@@ -362,6 +362,11 @@ impl Diagnostic {
             .terminal_url(je.terminal_url)
             .ui_testing(je.ui_testing)
             .ignored_directories_in_source_blocks(je.ignored_directories_in_source_blocks.clone())
+            .theme(if let HumanReadableErrorType::Unicode(_) = je.json_rendered {
+                OutputTheme::Unicode
+            } else {
+                OutputTheme::Ascii
+            })
             .emit_diagnostic(diag);
         let buf = Arc::try_unwrap(buf.0).unwrap().into_inner().unwrap();
         let buf = String::from_utf8(buf).unwrap();

compiler/rustc_session/src/config.rs

@@ -1677,6 +1677,9 @@ pub fn parse_json(early_dcx: &EarlyDiagCtxt, matches: &getopts::Matches) -> Json
         for sub_option in option.split(',') {
             match sub_option {
                 "diagnostic-short" => json_rendered = HumanReadableErrorType::Short,
+                "diagnostic-unicode" => {
+                    json_rendered = HumanReadableErrorType::Unicode;
+                }
                 "diagnostic-rendered-ansi" => json_color = ColorConfig::Always,
                 "artifacts" => json_artifact_notifications = true,
                 "unused-externs" => json_unused_externs = JsonUnusedExterns::Loud,