manifest: warn if path of rerun-if-changed=PATH does not point to exi…

…sting file.

Fixes rust-lang#6003

src/cargo/core/compiler/fingerprint.rs

@@ -599,6 +599,17 @@ fn build_script_local_fingerprints<'a, 'cfg>(
     // dependencies.
     let deps = &cx.build_explicit_deps[unit];
     let output = deps.build_script_output.clone();
+
+    // check if rerun_if_changed paths corresponds to existing files and warn if not (#6003)
+    for path in &deps.rerun_if_changed {
+        if !path.exists() {
+            cx.bcx.config.shell().warn(format!(
+                "\"cargo:rerun-if-changed\" file \"{}\" not found.",
+                path.display()
+            ))?;
+        }
+    }
+
     if deps.rerun_if_changed.is_empty() && deps.rerun_if_env_changed.is_empty() {
         debug!("old local fingerprints deps");
         let s = pkg_fingerprint(&cx.bcx, unit.pkg)?;
@@ -630,6 +641,7 @@ fn local_fingerprints_deps(
 
     for var in deps.rerun_if_env_changed.iter() {
         let val = env::var(var).ok();
+        // check if the vlu
         local.push(LocalFingerprint::EnvBased(var.clone(), val));
     }
 

tests/testsuite/build_script.rs

@@ -2338,6 +2338,8 @@ fn rebuild_only_on_explicit_paths() {
     p.cargo("build -v")
         .with_stderr(
             "\
+[WARNING] \"cargo:rerun-if-changed\" file \"foo\" not found.
+[WARNING] \"cargo:rerun-if-changed\" file \"bar\" not found.
 [COMPILING] foo v0.5.0 ([..])
 [RUNNING] `[..]/build-script-build`
 [RUNNING] `rustc [..] src/lib.rs [..]`
@@ -2350,7 +2352,7 @@ fn rebuild_only_on_explicit_paths() {
     File::create(p.root().join("bar")).unwrap();
     sleep_ms(1000); // make sure the to-be-created outfile has a timestamp distinct from the infiles
 
-    // now the exist, so run once, catch the mtime, then shouldn't run again
+    // now they exist, so run once, catch the mtime, then shouldn't run again
     println!("run with");
     p.cargo("build -v")
         .with_stderr(
@@ -2403,6 +2405,7 @@ fn rebuild_only_on_explicit_paths() {
     p.cargo("build -v")
         .with_stderr(
             "\
+[WARNING] \"cargo:rerun-if-changed\" file \"bar\" not found.
 [COMPILING] foo v0.5.0 ([..])
 [RUNNING] `[..]/build-script-build`
 [RUNNING] `rustc [..] src/lib.rs [..]`