Update diagnostic message

compiler/rustc_session/messages.ftl

@@ -25,7 +25,7 @@ session_feature_diagnostic_help =
     add `#![feature({$feature})]` to the crate attributes to enable
 
 session_feature_suggest_upgrade_compiler =
-    this compiler is version {$version} built on {$date}, consider upgrading?
+    this compiler was built on {$date}; consider upgrading if it is out of date
 
 session_file_is_not_writeable = output file {$file} is not writeable -- check its permissions
 

compiler/rustc_session/src/errors.rs

@@ -34,16 +34,14 @@ pub struct FeatureDiagnosticForIssue {
 #[derive(Subdiagnostic)]
 #[note(session_feature_suggest_upgrade_compiler)]
 pub struct SuggestUpgradeCompiler {
-    version: &'static str,
     date: &'static str,
 }
 
 impl SuggestUpgradeCompiler {
-    pub fn new() -> Self {
-        let version = option_env!("CFG_VERSION").unwrap_or("unknown");
-        let date = option_env!("CFG_VER_DATE").unwrap_or("unknown");
+    pub fn new() -> Option<Self> {
+        let date = option_env!("CFG_VER_DATE")?;
 
-        Self { version, date }
+        Some(Self { date })
     }
 }
 

compiler/rustc_session/src/parse.rs

@@ -185,7 +185,9 @@ pub fn add_feature_diagnostics_for_issue(
             err.subdiagnostic(FeatureDiagnosticHelp { feature });
         }
 
-        err.subdiagnostic(SuggestUpgradeCompiler::new());
+        if let Some(suggestion) = SuggestUpgradeCompiler::new() {
+            err.subdiagnostic(suggestion);
+        }
     }
 }