Auto merge of #65324 - Centril:organize-syntax, r=petrochenkov

Split libsyntax apart

In this PR the general idea is to separate the AST, parser, and friends by a more data / logic structure (tho not fully realized!) by separating out the parser and macro expansion code from libsyntax. Specifically have now three crates instead of one (libsyntax):

- libsyntax:

   - concrete syntax tree (`syntax::ast`)

   - definition of tokens and token-streams (`syntax::{token, tokenstream}`) -- used by `syntax::ast`

   - visitors (`syntax::visit`, `syntax::mut_visit`)

   - shared definitions between `libsyntax_expand`

   - feature gating (`syntax::feature_gate`) -- we could possibly move this out to its own crater later.

   - attribute and meta item utilities, including used-marking (`syntax::attr`)

   - pretty printer (`syntax::print`) -- this should possibly be moved out later. For now I've reduced down the dependencies to a single essential one which could be broken via `ParseSess`. This entails that e.g. `Debug` impls for `Path` cannot reference the pretty printer.

   - definition of `ParseSess` (`syntax::sess`) -- this is used by `syntax::{attr, print, feature_gate}` and is a common definition used by the parser and other things like librustc.

   - the `syntax::source_map` -- this includes definitions used by `syntax::ast` and other things but could ostensibly be moved `syntax_pos` since that is more related to this module.

   - a smattering of misc utilities not sufficiently important to itemize -- some of these could be moved to where they are used (often a single place) but I wanted to limit the scope of this PR.

- librustc_parse:

   - parser (`rustc_parse::parser`) -- reading a file and such are defined in the crate root tho.

   - lexer (`rustc_parse::lexer`)

   - validation of meta grammar (post-expansion) in (`rustc_parse::validate_attr`)

- libsyntax_expand -- this defines the infra for macro expansion and conditional compilation but this is not libsyntax_ext; we might want to merge them later but currently libsyntax_expand is depended on by librustc_metadata which libsyntax_ext is not.

   - conditional compilation (`syntax_expand::config`) -- moved from `syntax::config` to here

   - the bulk of this crate is made up of the old `syntax::ext`

r? @estebank

1 files changed, 2 insertions, 2 deletions

diff --git a/src/libsyntax/util/parser.rs b/src/libsyntax/util/parser.rs
index edb708d7e97..df72fdc8014 100644
--- a/src/libsyntax/util/parser.rs
+++ b/src/libsyntax/util/parser.rs
@@ -69,7 +69,7 @@ pub enum Fixity {
 
 impl AssocOp {
     /// Creates a new AssocOP from a token
-    crate fn from_token(t: &Token) -> Option<AssocOp> {
+    pub fn from_token(t: &Token) -> Option<AssocOp> {
         use AssocOp::*;
         match t.kind {
             token::BinOpEq(k) => Some(AssignOp(k)),
@@ -358,7 +358,7 @@ impl ExprPrecedence {
 }
 
 /// In `let p = e`, operators with precedence `<=` this one requires parenthesis in `e`.
-crate fn prec_let_scrutinee_needs_par() -> usize {
+pub fn prec_let_scrutinee_needs_par() -> usize {
     AssocOp::LAnd.precedence()
 }