Auto merge of #38736 - xen0n:save-the-save-analysis, r=alexcrichton

rustbuild: save the save analysis

Fixes #38734. ~~call me the nightly firefighter~~

r? @alexcrichton

src/bootstrap/lib.rs

@@ -521,7 +521,7 @@ impl Build {
                  .env(format!("CFLAGS_{}", target), self.cflags(target).join(" "));
         }
 
-        if self.config.channel == "nightly" && compiler.stage == 2 {
+        if self.config.channel == "nightly" && compiler.is_final_stage(self) {
             cargo.env("RUSTC_SAVE_ANALYSIS", "api".to_string());
         }
 
@@ -922,4 +922,13 @@ impl<'a> Compiler<'a> {
     fn is_snapshot(&self, build: &Build) -> bool {
         self.stage == 0 && self.host == build.config.build
     }
+
+    /// Returns if this compiler should be treated as a final stage one in the
+    /// current build session.
+    /// This takes into account whether we're performing a full bootstrap or
+    /// not; don't directly compare the stage with `2`!
+    fn is_final_stage(&self, build: &Build) -> bool {
+        let final_stage = if build.config.full_bootstrap { 2 } else { 1 };
+        self.stage >= final_stage
+    }
 }