Move detection to be in the fingerprint code

src/cargo/core/compiler/fingerprint/dirty_reason.rs

@@ -29,6 +29,7 @@ pub enum DirtyReason {
     MetadataChanged,
     ConfigSettingsChanged,
     CompileKindChanged,
+    EnvConfigChanged,
     LocalLengthsChanged,
     PrecalculatedComponentsChanged {
         old: String,
@@ -172,6 +173,9 @@ impl DirtyReason {
             DirtyReason::CompileKindChanged => {
                 s.dirty_because(unit, "the rustc compile kind changed")
             }
+            DirtyReason::EnvConfigChanged => {
+                s.dirty_because(unit, "the environment variable changed")
+            },
             DirtyReason::LocalLengthsChanged => {
                 s.dirty_because(unit, "the local lengths changed")?;
                 s.note(

src/cargo/core/compiler/fingerprint/mod.rs

@@ -420,8 +420,14 @@ pub fn prepare_target(
     let mtime_on_use = build_runner.bcx.gctx.cli_unstable().mtime_on_use;
     let dirty_reason = compare_old_fingerprint(unit, &loc, &*fingerprint, mtime_on_use, force);
 
-    let Some(dirty_reason) = dirty_reason else {
-        return Ok(Job::new_fresh());
+    let dirty_reason = match dirty_reason {
+        Some(dr) => dr,
+        None => {
+            let Some(dr) = env_config_modified(bcx.gctx) else {
+                return Ok(Job::new_fresh());
+            };
+            dr
+        },
     };
 
     // We're going to rebuild, so ensure the source of the crate passes all
@@ -2231,3 +2237,17 @@ pub fn parse_rustc_dep_info(rustc_dep_info: &Path) -> CargoResult<RustcDepInfo>
         Ok(ret)
     }
 }
+
+/// Detects if environment variables from config `[env]` is newly modified.
+fn env_config_modified(gctx: &crate::GlobalContext) -> Option<DirtyReason> {
+    for (key, value) in gctx.env_config().unwrap().iter() {
+        if !gctx.env().any(|(k, _)| k == key) {
+            continue;
+        }
+
+        if !value.is_force() && gctx.env().find(|(k, _)| k == key).is_some() {
+            return Some(DirtyReason::EnvConfigChanged);
+        }
+    }
+    None
+}

src/cargo/core/compiler/mod.rs

@@ -191,7 +191,7 @@ fn compile<'gctx>(
         let force = exec.force_rebuild(unit) || force_rebuild;
         let mut job = fingerprint::prepare_target(build_runner, unit, force)?;
         job.before(
-            if job.freshness().is_dirty() || env_config_modified(bcx.gctx)? {
+            if job.freshness().is_dirty() {
                 let work = if unit.mode.is_doc() || unit.mode.is_doc_scrape() {
                     rustdoc(build_runner, unit)?
                 } else {
@@ -1928,21 +1928,6 @@ fn should_include_scrape_units(bcx: &BuildContext<'_, '_>, unit: &Unit) -> bool
     unit.mode.is_doc() && bcx.scrape_units.len() > 0 && bcx.ws.unit_needs_doc_scrape(unit)
 }
 
-/// Detects if environment variables from config `[env]` is newly modified.
-fn env_config_modified(gctx: &crate::GlobalContext) -> CargoResult<bool> {
-    for (key, value) in gctx.env_config()?.iter() {
-        if !gctx.env().any(|(k, _)| k == key) {
-            continue;
-        }
-
-        if !value.is_force() && gctx.env().find(|(k, _)| k == key).is_some() {
-            return Ok(true);
-        }
-    }
-
-    Ok(false)
-}
-
 /// Gets the file path of function call information output from `rustdoc`.
 fn scrape_output_path(build_runner: &BuildRunner<'_, '_>, unit: &Unit) -> CargoResult<PathBuf> {
     assert!(unit.mode.is_doc() || unit.mode.is_doc_scrape());