Auto merge of rust-lang#130599 - jieyouxu:snake_case_binary_cleanup, r=petrochenkov

Explain why `non_snake_case` is skipped for binary crates and cleanup tests

- Explain `non_snake_case` lint is skipped for bin crate names because binaries are not intended to be distributed or consumed like library crates (rust-lang#45127).
- Coalesce the bunch of tests into a single one but with revisions, which is easier to compare the differences for `non_snake_case` behavior with respect to crate types.

Follow-up to rust-lang#121749 with some more comments and test cleanup.

cc `@saethlin` who bumped into one of the tests and was confused why it was `only-x86_64-unknown-linux-gnu`.

Author: bors

compiler/rustc_lint/src/nonstandard_style.rs

@@ -332,6 +332,9 @@ impl<'tcx> LateLintPass<'tcx> for NonSnakeCase {
             return;
         }
 
+        // Issue #45127: don't enforce `snake_case` for binary crates as binaries are not intended
+        // to be distributed and depended on like libraries. The lint is not suppressed for cdylib
+        // or staticlib because it's not clear what the desired lint behavior for those are.
         if cx.tcx.crate_types().iter().all(|&crate_type| crate_type == CrateType::Executable) {
             return;
         }

src/tools/compiletest/src/command-list.rs

@@ -56,6 +56,7 @@ const KNOWN_DIRECTIVE_NAMES: &[&str] = &[
     "ignore-horizon",
     "ignore-i686-pc-windows-gnu",
     "ignore-i686-pc-windows-msvc",
+    "ignore-i686-unknown-linux-musl",
     "ignore-illumos",
     "ignore-ios",
     "ignore-linux",