Add the codegen-source-order option

Author: ywxt

compiler/rustc_session/src/options.rs

@@ -2172,6 +2172,8 @@ options! {
         "emit runtime checks for contract pre- and post-conditions (default: no)"),
     coverage_options: CoverageOptions = (CoverageOptions::default(), parse_coverage_options, [TRACKED],
         "control details of coverage instrumentation"),
+    codegen_source_order: bool = (false, parse_bool, [UNTRACKED],
+        "emit mono items in the order of spans in source files (default: no)"),
     crate_attr: Vec<String> = (Vec::new(), parse_string_push, [TRACKED],
         "inject the given attribute in the crate"),
     cross_crate_inline_threshold: InliningThreshold = (InliningThreshold::Sometimes(100), parse_inlining_threshold, [TRACKED],

src/doc/unstable-book/src/compiler-flags/codegen-source-order.md

@@ -0,0 +1,17 @@
+# `codegen-source-order`
+
+---
+
+This feature allows you to have a predictive and
+deterministic order for items after codegen.
+
+For every `CodegenUnit`, local `MonoItem`s would
+be sorted by `(Span, DefPath, SymbolName)`, which
+makes codegen tests rely on the order of items in
+source files work.
+
+Note: If you would like to use it, you have to
+manually sort items that are generated by a macro
+in lexicographical order in source files, because
+of the same spans owned by all items of a macro.
+So we have to distinguish them by `DefPath`s.