Change the logging level and other improvement.

src/cargo/ops/cargo_package.rs

@@ -342,15 +342,9 @@ fn build_ar_list(
         if let Some(custome_build_path) = t.src_path().path() {
             let abs_custome_build_path =
                 paths::normalize_path(&pkg.root().join(custome_build_path));
-            if abs_custome_build_path.is_file() {
-                if !abs_custome_build_path
-                    .ancestors()
-                    .any(|ancestor| ancestor == pkg.root())
-                {
-                    warn_custom_build_file_not_in_package(pkg, &abs_custome_build_path, t, &ws)?
-                }
-            } else {
-                warn_on_nonexistent_file(&pkg, &custome_build_path, "build", &ws)?
+            if !abs_custome_build_path.is_file() || !abs_custome_build_path.starts_with(pkg.root())
+            {
+                error_custom_build_file_not_in_package(pkg, &abs_custome_build_path, t, &ws)?
             }
         }
     }
@@ -429,21 +423,33 @@ fn warn_on_nonexistent_file(
     ))
 }
 
-fn warn_custom_build_file_not_in_package(
+fn error_custom_build_file_not_in_package(
     pkg: &Package,
     path: &Path,
     target: &Target,
     ws: &Workspace<'_>,
 ) -> CargoResult<()> {
+    let tip = {
+        if path.is_file() {
+            format!("the source file of {:?} target `{}` doesn't appear to be a path inside of the package.\n\
+            It is at `{}`, whereas the root the package is `{}`.\n",
+            target.kind(), target.name(), path.display(), pkg.root().display()
+            )
+        } else {
+            format!(
+                "the source file of {:?} target `{}` doesn't appear to exist.\n",
+                target.kind(),
+                target.name()
+            )
+        }
+    };
     let msg = format!(
-        "the source file of {:?} target `{}` doesn't appear to be a path inside of the package.\n\
-        It is at {}, whereas the root the package is {}.\n\
+        "{}\
         This may cause issue during packaging, as modules resolution and resources included via macros are often relative to the path of source files.\n\
         Please update the `build` setting in the manifest at `{}` and point to a path inside the root of the package.",
-        target.kind(), target.name(), path.display(), pkg.root().display(),  pkg.manifest_path().display()
+        tip,  pkg.manifest_path().display()
     );
-
-    ws.config().shell().warn(&msg)
+    ws.config().shell().error(&msg)
 }
 
 /// Construct `Cargo.lock` for the package to be published.

tests/testsuite/package.rs

@@ -3306,55 +3306,45 @@ fn init_and_add_inner_target(p: ProjectBuilder) -> ProjectBuilder {
 }
 
 #[cargo_test]
-fn custom_build_warning() {
+fn build_script_outside_pkg_root() {
     let p = project()
         .file(
             "Cargo.toml",
             r#"
-        [package]
-        name = "foo"
-        version = "0.0.1"
-        license = "MIT"
-        description = "foo"
-        authors = []
-        build = "../t_custom_build/custom_build.rs"
-        "#,
+    [package]
+    name = "foo"
+    version = "0.0.1"
+    license = "MIT"
+    description = "foo"
+    authors = []
+    build = "../t_custom_build/custom_build.rs"
+    "#,
         )
         .file("src/main.rs", "fn main() {}")
         .build();
-    p.cargo("package -l")
-        .with_stderr(format!(
-            "\
+    let mut expect_msg = String::from("\
 warning: manifest has no documentation, homepage or repository.
 See https://doc.rust-lang.org/cargo/reference/manifest.html#package-metadata for more info.
-warning: build `{}/../t_custom_build/custom_build.rs` does not appear to exist.
-Please update the build setting in the manifest at `{}/Cargo.toml`
-This may become a hard error in the future.
-",
-            p.root().display(),
-            p.root().display()
-        ))
-        .run();
+error: the source file of \"custom-build\" target `build-script-custom_build` doesn't appear to exist.
+This may cause issue during packaging, as modules resolution and resources included via macros are often relative to the path of source files.
+Please update the `build` setting in the manifest at `[CWD]/Cargo.toml` and point to a path inside the root of the package.
+");
+    // custom_build.rs does not exist
+    p.cargo("package -l").with_stderr(&expect_msg).run();
 
-    // crate custom_build.rs outside the package root
+    // custom_build.rs outside the package root
     let custom_build_root = p.root().parent().unwrap().join("t_custom_build");
     _ = fs::create_dir(&custom_build_root).unwrap();
     _ = fs::write(&custom_build_root.join("custom_build.rs"), "fn main() {}");
-
-    p.cargo("package -l")
-        .with_stderr(format!(
-            "\
+    expect_msg = format!(
+        "\
 warning: manifest has no documentation, homepage or repository.
 See https://doc.rust-lang.org/cargo/reference/manifest.html#package-metadata for more info.
-warning: the source file of \"custom-build\" target `build-script-custom_build` doesn't appear to be a path inside of the package.
-It is at {}/t_custom_build/custom_build.rs, whereas the root the package is {}.
+error: the source file of \"custom-build\" target `build-script-custom_build` doesn't appear to be a path inside of the package.
+It is at `{}/t_custom_build/custom_build.rs`, whereas the root the package is `[CWD]`.
 This may cause issue during packaging, as modules resolution and resources included via macros are often relative to the path of source files.
-Please update the `build` setting in the manifest at `{}/Cargo.toml` and point to a path inside the root of the package.
-",
-p.root().parent().unwrap().display(),
-            p.root().display(),
-            p.root().display()
-        ))
-        .run();
+Please update the `build` setting in the manifest at `[CWD]/Cargo.toml` and point to a path inside the root of the package.
+", p.root().parent().unwrap().display());
+    p.cargo("package -l").with_stderr(&expect_msg).run();
     _ = fs::remove_dir_all(&custom_build_root).unwrap();
 }