Move standard library injection into libsyntax_ext

2 files changed, 96 insertions, 0 deletions

diff --git a/src/libsyntax_ext/lib.rs b/src/libsyntax_ext/lib.rs
index cd0d0886239..f49c75d7424 100644
--- a/src/libsyntax_ext/lib.rs
+++ b/src/libsyntax_ext/lib.rs
@@ -43,6 +43,7 @@ mod trace_macros;
 
 pub mod plugin_macro_defs;
 pub mod proc_macro_decls;
+pub mod standard_library_imports;
 pub mod test_harness;
 
 pub fn register_builtin_macros(resolver: &mut dyn syntax::ext::base::Resolver, edition: Edition) {
diff --git a/src/libsyntax_ext/standard_library_imports.rs b/src/libsyntax_ext/standard_library_imports.rs
new file mode 100644
index 00000000000..81bb32d79a2
--- /dev/null
+++ b/src/libsyntax_ext/standard_library_imports.rs
@@ -0,0 +1,95 @@
+use syntax::{ast, attr};
+use syntax::edition::Edition;
+use syntax::ext::hygiene::{ExpnId, MacroKind};
+use syntax::ptr::P;
+use syntax::source_map::{ExpnInfo, ExpnKind, dummy_spanned, respan};
+use syntax::symbol::{Ident, Symbol, kw, sym};
+use syntax::tokenstream::TokenStream;
+use syntax_pos::DUMMY_SP;
+
+use std::iter;
+
+pub fn inject(
+    mut krate: ast::Crate, alt_std_name: Option<&str>, edition: Edition
+) -> (ast::Crate, Option<Symbol>) {
+    let rust_2018 = edition >= Edition::Edition2018;
+
+    // the first name in this list is the crate name of the crate with the prelude
+    let names: &[&str] = if attr::contains_name(&krate.attrs, sym::no_core) {
+        return (krate, None);
+    } else if attr::contains_name(&krate.attrs, sym::no_std) {
+        if attr::contains_name(&krate.attrs, sym::compiler_builtins) {
+            &["core"]
+        } else {
+            &["core", "compiler_builtins"]
+        }
+    } else {
+        &["std"]
+    };
+
+    // .rev() to preserve ordering above in combination with insert(0, ...)
+    let alt_std_name = alt_std_name.map(Symbol::intern);
+    for orig_name_str in names.iter().rev() {
+        // HACK(eddyb) gensym the injected crates on the Rust 2018 edition,
+        // so they don't accidentally interfere with the new import paths.
+        let orig_name_sym = Symbol::intern(orig_name_str);
+        let orig_name_ident = Ident::with_empty_ctxt(orig_name_sym);
+        let (rename, orig_name) = if rust_2018 {
+            (orig_name_ident.gensym(), Some(orig_name_sym))
+        } else {
+            (orig_name_ident, None)
+        };
+        krate.module.items.insert(0, P(ast::Item {
+            attrs: vec![attr::mk_attr_outer(
+                DUMMY_SP,
+                attr::mk_attr_id(),
+                attr::mk_word_item(ast::Ident::with_empty_ctxt(sym::macro_use))
+            )],
+            vis: dummy_spanned(ast::VisibilityKind::Inherited),
+            node: ast::ItemKind::ExternCrate(alt_std_name.or(orig_name)),
+            ident: rename,
+            id: ast::DUMMY_NODE_ID,
+            span: DUMMY_SP,
+            tokens: None,
+        }));
+    }
+
+    // the crates have been injected, the assumption is that the first one is the one with
+    // the prelude.
+    let name = names[0];
+
+    let span = DUMMY_SP.fresh_expansion(ExpnId::root(), ExpnInfo::allow_unstable(
+        ExpnKind::Macro(MacroKind::Attr, sym::std_inject), DUMMY_SP, edition,
+        [sym::prelude_import][..].into(),
+    ));
+
+    krate.module.items.insert(0, P(ast::Item {
+        attrs: vec![ast::Attribute {
+            style: ast::AttrStyle::Outer,
+            path: ast::Path::from_ident(ast::Ident::new(sym::prelude_import, span)),
+            tokens: TokenStream::empty(),
+            id: attr::mk_attr_id(),
+            is_sugared_doc: false,
+            span,
+        }],
+        vis: respan(span.shrink_to_lo(), ast::VisibilityKind::Inherited),
+        node: ast::ItemKind::Use(P(ast::UseTree {
+            prefix: ast::Path {
+                segments: iter::once(ast::Ident::with_empty_ctxt(kw::PathRoot))
+                    .chain(
+                        [name, "prelude", "v1"].iter().cloned()
+                            .map(ast::Ident::from_str)
+                    ).map(ast::PathSegment::from_ident).collect(),
+                span,
+            },
+            kind: ast::UseTreeKind::Glob,
+            span,
+        })),
+        id: ast::DUMMY_NODE_ID,
+        ident: ast::Ident::invalid(),
+        span,
+        tokens: None,
+    }));
+
+    (krate, Some(Symbol::intern(name)))
+}