1 files changed, 92 insertions, 0 deletions
diff --git a/compiler/rustc_builtin_macros/src/standard_library_imports.rs b/compiler/rustc_builtin_macros/src/standard_library_imports.rs
new file mode 100644
index 000000000..09ad5f9b3
--- /dev/null
+++ b/compiler/rustc_builtin_macros/src/standard_library_imports.rs
@@ -0,0 +1,92 @@
+use rustc_ast as ast;
+use rustc_expand::base::{ExtCtxt, ResolverExpand};
+use rustc_expand::expand::ExpansionConfig;
+use rustc_session::Session;
+use rustc_span::edition::Edition::*;
+use rustc_span::hygiene::AstPass;
+use rustc_span::symbol::{kw, sym, Ident, Symbol};
+use rustc_span::DUMMY_SP;
+
+pub fn inject(
+    mut krate: ast::Crate,
+    resolver: &mut dyn ResolverExpand,
+    sess: &Session,
+) -> ast::Crate {
+    let edition = sess.parse_sess.edition;
+
+    // the first name in this list is the crate name of the crate with the prelude
+    let names: &[Symbol] = if sess.contains_name(&krate.attrs, sym::no_core) {
+        return krate;
+    } else if sess.contains_name(&krate.attrs, sym::no_std) {
+        if sess.contains_name(&krate.attrs, sym::compiler_builtins) {
+            &[sym::core]
+        } else {
+            &[sym::core, sym::compiler_builtins]
+        }
+    } else {
+        &[sym::std]
+    };
+
+    let expn_id = resolver.expansion_for_ast_pass(
+        DUMMY_SP,
+        AstPass::StdImports,
+        &[sym::prelude_import],
+        None,
+    );
+    let span = DUMMY_SP.with_def_site_ctxt(expn_id.to_expn_id());
+    let call_site = DUMMY_SP.with_call_site_ctxt(expn_id.to_expn_id());
+
+    let ecfg = ExpansionConfig::default("std_lib_injection".to_string());
+    let cx = ExtCtxt::new(sess, ecfg, resolver, None);
+
+    // .rev() to preserve ordering above in combination with insert(0, ...)
+    for &name in names.iter().rev() {
+        let ident = if edition >= Edition2018 {
+            Ident::new(name, span)
+        } else {
+            Ident::new(name, call_site)
+        };
+        krate.items.insert(
+            0,
+            cx.item(
+                span,
+                ident,
+                vec![cx.attribute(cx.meta_word(span, sym::macro_use))],
+                ast::ItemKind::ExternCrate(None),
+            ),
+        );
+    }
+
+    // The crates have been injected, the assumption is that the first one is
+    // the one with the prelude.
+    let name = names[0];
+
+    let root = (edition == Edition2015).then(|| kw::PathRoot);
+
+    let import_path = root
+        .iter()
+        .chain(&[name, sym::prelude])
+        .chain(&[match edition {
+            Edition2015 => sym::rust_2015,
+            Edition2018 => sym::rust_2018,
+            Edition2021 => sym::rust_2021,
+            Edition2024 => sym::rust_2024,
+        }])
+        .map(|&symbol| Ident::new(symbol, span))
+        .collect();
+
+    let use_item = cx.item(
+        span,
+        Ident::empty(),
+        vec![cx.attribute(cx.meta_word(span, sym::prelude_import))],
+        ast::ItemKind::Use(ast::UseTree {
+            prefix: cx.path(span, import_path),
+            kind: ast::UseTreeKind::Glob,
+            span,
+        }),
+    );
+
+    krate.items.insert(0, use_item);
+
+    krate
+}