fix(new): Only suggest bin.name for valid crate names

Validate crate names are a superset of valid package names which also
try to work for `--extern`.

Fixes #16396

Author: epage

src/cargo/ops/cargo_new.rs

@@ -181,7 +181,8 @@ fn check_name(
     };
     let bin_help = || {
         let mut help = String::from(name_help);
-        if has_bin && !name.is_empty() {
+        // Only suggest `bin.name` for valid crate names because it is used for `--crate`
+        if has_bin && validate_crate_name(name) {
             help.push_str(&format!(
                 "\n\
                 help: to name the binary \"{name}\", use a valid package \
@@ -274,6 +275,23 @@ fn check_name(
     Ok(())
 }
 
+// Taken from <https://github.com/rust-lang/rust/blob/693f365667a97b24cb40173bc2801eb66ea53020/compiler/rustc_session/src/output.rs#L49-L79>
+fn validate_crate_name(name: &str) -> bool {
+    if name.is_empty() {
+        return false;
+    }
+
+    for c in name.chars() {
+        if c.is_alphanumeric() || c == '-' || c == '_' {
+            continue;
+        } else {
+            return false;
+        }
+    }
+
+    true
+}
+
 /// Checks if the path contains any invalid PATH env characters.
 fn check_path(path: &Path, shell: &mut Shell) -> CargoResult<()> {
     // warn if the path contains characters that will break `env::join_paths`

tests/testsuite/cargo_init/invalid_dir_name/stderr.term.svg

@@ -170,12 +170,6 @@ fn invalid_characters() {
 [ERROR] invalid character `.` in package name: `foo.rs`, characters must be Unicode XID characters (numbers, `-`, `_`, or most letters)
 [NOTE] the directory name is used as the package name
 [HELP] to override the package name, pass `--name <pkgname>`
-[HELP] to name the binary "foo.rs", use a valid package name, and set the binary name to be different from the package. This can be done by setting the binary filename to `src/bin/foo.rs.rs` or change the name in Cargo.toml with:
-
-    [[bin]]
-    name = "foo.rs"
-    path = "src/main.rs"
-
 
 "#]])
         .run();