Add a warning if both package.include and package.exclude are specified.

src/cargo/ops/cargo_package.rs

@@ -56,6 +56,12 @@ pub fn package(ws: &Workspace<'_>, opts: &PackageOpts<'_>) -> CargoResult<Option
 
     verify_dependencies(pkg)?;
 
+    if !pkg.manifest().exclude().is_empty() && !pkg.manifest().include().is_empty() {
+        config.shell().warn(
+            "both package.include and package.exclude are specified; \
+             the exclude list will be ignored",
+        )?;
+    }
     // `list_files` outputs warnings as a side effect, so only do it once.
     let src_files = src.list_files(pkg)?;
 

tests/testsuite/package.rs

@@ -445,6 +445,7 @@ fn include() {
             "\
 [WARNING] manifest has no description[..]
 See https://doc.rust-lang.org/cargo/reference/manifest.html#package-metadata for more info.
+[WARNING] both package.include and package.exclude are specified; the exclude list will be ignored
 [PACKAGING] foo v0.0.1 ([..])
 [ARCHIVING] [..]
 [ARCHIVING] [..]