Update terminal-width flag.

Author: ehuss

src/cargo/core/compiler/mod.rs

@@ -793,11 +793,11 @@ fn add_error_format_and_color(cx: &Context<'_, '_>, cmd: &mut ProcessBuilder) {
         ) {
             // Terminal width explicitly provided - only useful for testing.
             (Some(Some(width)), _) => {
-                cmd.arg(format!("-Zterminal-width={}", width));
+                cmd.arg(format!("--diagnostic-width={}", width));
             }
             // Terminal width was not explicitly provided but flag was provided - common case.
             (Some(None), Some(width)) => {
-                cmd.arg(format!("-Zterminal-width={}", width));
+                cmd.arg(format!("--diagnostic-width={}", width));
             }
             // User didn't opt-in.
             _ => (),

tests/testsuite/build.rs

@@ -6107,7 +6107,7 @@ fn target_directory_backup_exclusion() {
 #[cargo_test]
 fn simple_terminal_width() {
     if !is_nightly() {
-        // --terminal-width is unstable
+        // --diagnostic-width is stabilized in 1.64
         return;
     }
     let p = project()