Auto merge of rust-lang#79472 - Aaron1011:new-remove-pretty-print-hack, r=petrochenkov

Replace pretty-print/compare/retokenize hack with targeted workarounds

Based on rust-lang#78296
cc rust-lang#43081

The 'pretty-print/compare/retokenize' hack is used to try to avoid passing an outdated `TokenStream` to a proc-macro when the underlying AST is modified in some way (e.g. cfg-stripping before derives). Unfortunately, retokenizing throws away spans (including hygiene information), which causes issues of its own. Every improvement to the accuracy of the pretty-print/retokenize comparison has resulted in non-trivial ecosystem breakage due to hygiene changes. In extreme cases, users deliberately wrote unhygienic `macro_rules!` macros (likely because they did not realize that the compiler's behavior was a bug).

Additionaly, the comparison between the original and pretty-printed/retoknized token streams comes at a non-trivial runtime cost, as shown by rust-lang#79338

This PR removes the pretty-print/compare/retokenize logic from `nt_to_tokenstream`. We only discard the original `TokenStream` under two circumstances:
* Inner attributes are used (detected by examining the AST)
* `cfg`/`cfg_attr` processing modifies the AST. This is detected by making the visitor update a flag when it performs a modification, instead of trying to detect the modification after-the-fact. Note that a 'matching' `cfg` (e.g. `#[cfg(not(FALSE)]`) does not actually get removed from the AST, allowing us to preserve the original `TokenStream`.

In all other cases, we preserve the original `TokenStream`.

This could use a bit of refactoring/renaming - opening for a Crater run.

r? `@ghost`

Author: bors

compiler/rustc_ast/src/tokenstream.rs

@@ -44,6 +44,12 @@ pub enum TokenTree {
     Delimited(DelimSpan, DelimToken, TokenStream),
 }
 
+#[derive(Copy, Clone)]
+pub enum CanSynthesizeMissingTokens {
+    Yes,
+    No,
+}
+
 // Ensure all fields of `TokenTree` is `Send` and `Sync`.
 #[cfg(parallel_compiler)]
 fn _dummy()

compiler/rustc_ast_lowering/src/lib.rs

@@ -37,7 +37,7 @@
 
 use rustc_ast::node_id::NodeMap;
 use rustc_ast::token::{self, DelimToken, Nonterminal, Token};
-use rustc_ast::tokenstream::{DelimSpan, TokenStream, TokenTree};
+use rustc_ast::tokenstream::{CanSynthesizeMissingTokens, DelimSpan, TokenStream, TokenTree};
 use rustc_ast::visit::{self, AssocCtxt, Visitor};
 use rustc_ast::walk_list;
 use rustc_ast::{self as ast, *};
@@ -206,7 +206,8 @@ pub trait ResolverAstLowering {
     ) -> LocalDefId;
 }
 
-type NtToTokenstream = fn(&Nonterminal, &ParseSess, Span) -> TokenStream;
+type NtToTokenstream =
+    fn(&Nonterminal, &ParseSess, Span, CanSynthesizeMissingTokens) -> TokenStream;
 
 /// Context of `impl Trait` in code, which determines whether it is allowed in an HIR subtree,
 /// and if so, what meaning it has.
@@ -393,6 +394,47 @@ enum AnonymousLifetimeMode {
     PassThrough,
 }
 
+struct TokenStreamLowering<'a> {
+    parse_sess: &'a ParseSess,
+    synthesize_tokens: CanSynthesizeMissingTokens,
+    nt_to_tokenstream: NtToTokenstream,
+}
+
+impl<'a> TokenStreamLowering<'a> {
+    fn lower_token_stream(&mut self, tokens: TokenStream) -> TokenStream {
+        tokens.into_trees().flat_map(|tree| self.lower_token_tree(tree).into_trees()).collect()
+    }
+
+    fn lower_token_tree(&mut self, tree: TokenTree) -> TokenStream {
+        match tree {
+            TokenTree::Token(token) => self.lower_token(token),
+            TokenTree::Delimited(span, delim, tts) => {
+                TokenTree::Delimited(span, delim, self.lower_token_stream(tts)).into()
+            }
+        }
+    }
+
+    fn lower_token(&mut self, token: Token) -> TokenStream {
+        match token.kind {
+            token::Interpolated(nt) => {
+                let tts = (self.nt_to_tokenstream)(
+                    &nt,
+                    self.parse_sess,
+                    token.span,
+                    self.synthesize_tokens,
+                );
+                TokenTree::Delimited(
+                    DelimSpan::from_single(token.span),
+                    DelimToken::NoDelim,
+                    self.lower_token_stream(tts),
+                )
+                .into()
+            }
+            _ => TokenTree::Token(token).into(),
+        }
+    }
+}
+
 struct ImplTraitTypeIdVisitor<'a> {
     ids: &'a mut SmallVec<[NodeId; 1]>,
 }
@@ -955,40 +997,49 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         match *args {
             MacArgs::Empty => MacArgs::Empty,
             MacArgs::Delimited(dspan, delim, ref tokens) => {
-                MacArgs::Delimited(dspan, delim, self.lower_token_stream(tokens.clone()))
-            }
-            MacArgs::Eq(eq_span, ref tokens) => {
-                MacArgs::Eq(eq_span, self.lower_token_stream(tokens.clone()))
-            }
-        }
-    }
-
-    fn lower_token_stream(&mut self, tokens: TokenStream) -> TokenStream {
-        tokens.into_trees().flat_map(|tree| self.lower_token_tree(tree).into_trees()).collect()
-    }
-
-    fn lower_token_tree(&mut self, tree: TokenTree) -> TokenStream {
-        match tree {
-            TokenTree::Token(token) => self.lower_token(token),
-            TokenTree::Delimited(span, delim, tts) => {
-                TokenTree::Delimited(span, delim, self.lower_token_stream(tts)).into()
+                // This is either a non-key-value attribute, or a `macro_rules!` body.
+                // We either not have any nonterminals present (in the case of an attribute),
+                // or have tokens available for all nonterminals in the case of a nested
+                // `macro_rules`: e.g:
+                //
+                // ```rust
+                // macro_rules! outer {
+                //     ($e:expr) => {
+                //         macro_rules! inner {
+                //             () => { $e }
+                //         }
+                //     }
+                // }
+                // ```
+                //
+                // In both cases, we don't want to synthesize any tokens
+                MacArgs::Delimited(
+                    dspan,
+                    delim,
+                    self.lower_token_stream(tokens.clone(), CanSynthesizeMissingTokens::No),
+                )
             }
+            // This is an inert key-value attribute - it will never be visible to macros
+            // after it gets lowered to HIR. Therefore, we can synthesize tokens with fake
+            // spans to handle nonterminals in `#[doc]` (e.g. `#[doc = $e]`).
+            MacArgs::Eq(eq_span, ref tokens) => MacArgs::Eq(
+                eq_span,
+                self.lower_token_stream(tokens.clone(), CanSynthesizeMissingTokens::Yes),
+            ),
         }
     }
 
-    fn lower_token(&mut self, token: Token) -> TokenStream {
-        match token.kind {
-            token::Interpolated(nt) => {
-                let tts = (self.nt_to_tokenstream)(&nt, &self.sess.parse_sess, token.span);
-                TokenTree::Delimited(
-                    DelimSpan::from_single(token.span),
-                    DelimToken::NoDelim,
-                    self.lower_token_stream(tts),
-                )
-                .into()
-            }
-            _ => TokenTree::Token(token).into(),
+    fn lower_token_stream(
+        &self,
+        tokens: TokenStream,
+        synthesize_tokens: CanSynthesizeMissingTokens,
+    ) -> TokenStream {
+        TokenStreamLowering {
+            parse_sess: &self.sess.parse_sess,
+            synthesize_tokens,
+            nt_to_tokenstream: self.nt_to_tokenstream,
         }
+        .lower_token_stream(tokens)
     }
 
     /// Given an associated type constraint like one of these:

compiler/rustc_expand/src/base.rs

@@ -2,8 +2,8 @@ use crate::expand::{self, AstFragment, Invocation};
 use crate::module::DirectoryOwnership;
 
 use rustc_ast::ptr::P;
-use rustc_ast::token;
-use rustc_ast::tokenstream::TokenStream;
+use rustc_ast::token::{self, Nonterminal};
+use rustc_ast::tokenstream::{CanSynthesizeMissingTokens, TokenStream};
 use rustc_ast::visit::{AssocCtxt, Visitor};
 use rustc_ast::{self as ast, Attribute, NodeId, PatKind};
 use rustc_attr::{self as attr, Deprecation, HasAttrs, Stability};
@@ -119,8 +119,8 @@ impl Annotatable {
         }
     }
 
-    crate fn into_tokens(self, sess: &ParseSess) -> TokenStream {
-        let nt = match self {
+    crate fn into_nonterminal(self) -> Nonterminal {
+        match self {
             Annotatable::Item(item) => token::NtItem(item),
             Annotatable::TraitItem(item) | Annotatable::ImplItem(item) => {
                 token::NtItem(P(item.and_then(ast::AssocItem::into_item)))
@@ -137,8 +137,11 @@ impl Annotatable {
             | Annotatable::Param(..)
             | Annotatable::StructField(..)
             | Annotatable::Variant(..) => panic!("unexpected annotatable"),
-        };
-        nt_to_tokenstream(&nt, sess, DUMMY_SP)
+        }
+    }
+
+    crate fn into_tokens(self, sess: &ParseSess) -> TokenStream {
+        nt_to_tokenstream(&self.into_nonterminal(), sess, DUMMY_SP, CanSynthesizeMissingTokens::No)
     }
 
     pub fn expect_item(self) -> P<ast::Item> {

compiler/rustc_expand/src/config.rs

@@ -29,6 +29,7 @@ use smallvec::SmallVec;
 pub struct StripUnconfigured<'a> {
     pub sess: &'a Session,
     pub features: Option<&'a Features>,
+    pub modified: bool,
 }
 
 fn get_features(
@@ -199,7 +200,7 @@ fn get_features(
 
 // `cfg_attr`-process the crate's attributes and compute the crate's features.
 pub fn features(sess: &Session, mut krate: ast::Crate) -> (ast::Crate, Features) {
-    let mut strip_unconfigured = StripUnconfigured { sess, features: None };
+    let mut strip_unconfigured = StripUnconfigured { sess, features: None, modified: false };
 
     let unconfigured_attrs = krate.attrs.clone();
     let diag = &sess.parse_sess.span_diagnostic;
@@ -243,7 +244,12 @@ const CFG_ATTR_NOTE_REF: &str = "for more information, visit \
 impl<'a> StripUnconfigured<'a> {
     pub fn configure<T: HasAttrs>(&mut self, mut node: T) -> Option<T> {
         self.process_cfg_attrs(&mut node);
-        self.in_cfg(node.attrs()).then_some(node)
+        if self.in_cfg(node.attrs()) {
+            Some(node)
+        } else {
+            self.modified = true;
+            None
+        }
     }
 
     /// Parse and expand all `cfg_attr` attributes into a list of attributes
@@ -270,6 +276,9 @@ impl<'a> StripUnconfigured<'a> {
             return vec![attr];
         }
 
+        // A `#[cfg_attr]` either gets removed, or replaced with a new attribute
+        self.modified = true;
+
         let (cfg_predicate, expanded_attrs) = match self.parse_cfg_attr(&attr) {
             None => return vec![],
             Some(r) => r,

compiler/rustc_expand/src/expand.rs

@@ -12,7 +12,7 @@ use rustc_ast::ptr::P;
 use rustc_ast::token;
 use rustc_ast::tokenstream::TokenStream;
 use rustc_ast::visit::{self, AssocCtxt, Visitor};
-use rustc_ast::{self as ast, AttrItem, Block, LitKind, NodeId, PatKind, Path};
+use rustc_ast::{self as ast, AttrItem, AttrStyle, Block, LitKind, NodeId, PatKind, Path};
 use rustc_ast::{ItemKind, MacArgs, MacCallStmt, MacStmtStyle, StmtKind, Unsafe};
 use rustc_ast_pretty::pprust;
 use rustc_attr::{self as attr, is_builtin_attr, HasAttrs};
@@ -522,12 +522,29 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                         item.visit_attrs(|attrs| attrs.retain(|a| !a.has_name(sym::derive)));
                         (item, Vec::new())
                     } else {
-                        let mut item = StripUnconfigured {
+                        let mut visitor = StripUnconfigured {
                             sess: self.cx.sess,
                             features: self.cx.ecfg.features,
-                        }
-                        .fully_configure(item);
+                            modified: false,
+                        };
+                        let mut item = visitor.fully_configure(item);
                         item.visit_attrs(|attrs| attrs.retain(|a| !a.has_name(sym::derive)));
+                        if visitor.modified && !derives.is_empty() {
+                            // Erase the tokens if cfg-stripping modified the item
+                            // This will cause us to synthesize fake tokens
+                            // when `nt_to_tokenstream` is called on this item.
+                            match &mut item {
+                                Annotatable::Item(item) => item.tokens = None,
+                                Annotatable::Stmt(stmt) => {
+                                    if let StmtKind::Item(item) = &mut stmt.kind {
+                                        item.tokens = None
+                                    } else {
+                                        panic!("Unexpected stmt {:?}", stmt);
+                                    }
+                                }
+                                _ => panic!("Unexpected annotatable {:?}", item),
+                            }
+                        }
 
                         invocations.reserve(derives.len());
                         let derive_placeholders = derives
@@ -622,7 +639,11 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
 
         let invocations = {
             let mut collector = InvocationCollector {
-                cfg: StripUnconfigured { sess: &self.cx.sess, features: self.cx.ecfg.features },
+                cfg: StripUnconfigured {
+                    sess: &self.cx.sess,
+                    features: self.cx.ecfg.features,
+                    modified: false,
+                },
                 cx: self.cx,
                 invocations: Vec::new(),
                 monotonic: self.monotonic,
@@ -716,7 +737,15 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                 SyntaxExtensionKind::Attr(expander) => {
                     self.gate_proc_macro_input(&item);
                     self.gate_proc_macro_attr_item(span, &item);
-                    let tokens = item.into_tokens(&self.cx.sess.parse_sess);
+                    let tokens = match attr.style {
+                        AttrStyle::Outer => item.into_tokens(&self.cx.sess.parse_sess),
+                        // FIXME: Properly collect tokens for inner attributes
+                        AttrStyle::Inner => rustc_parse::fake_token_stream(
+                            &self.cx.sess.parse_sess,
+                            &item.into_nonterminal(),
+                            span,
+                        ),
+                    };
                     let attr_item = attr.unwrap_normal_item();
                     if let MacArgs::Eq(..) = attr_item.args {
                         self.cx.span_err(span, "key-value macro attributes are not supported");

compiler/rustc_expand/src/proc_macro.rs

@@ -3,7 +3,7 @@ use crate::proc_macro_server;
 
 use rustc_ast::ptr::P;
 use rustc_ast::token;
-use rustc_ast::tokenstream::{TokenStream, TokenTree};
+use rustc_ast::tokenstream::{CanSynthesizeMissingTokens, TokenStream, TokenTree};
 use rustc_ast::{self as ast, *};
 use rustc_data_structures::sync::Lrc;
 use rustc_errors::{struct_span_err, Applicability, ErrorReported};
@@ -94,7 +94,12 @@ impl MultiItemModifier for ProcMacroDerive {
         let input = if item.pretty_printing_compatibility_hack() {
             TokenTree::token(token::Interpolated(Lrc::new(item)), DUMMY_SP).into()
         } else {
-            nt_to_tokenstream(&item, &ecx.sess.parse_sess, DUMMY_SP)
+            nt_to_tokenstream(
+                &item,
+                &ecx.sess.parse_sess,
+                DUMMY_SP,
+                CanSynthesizeMissingTokens::Yes,
+            )
         };
 
         let server = proc_macro_server::Rustc::new(ecx);

compiler/rustc_expand/src/proc_macro_server.rs

@@ -2,7 +2,8 @@ use crate::base::ExtCtxt;
 
 use rustc_ast as ast;
 use rustc_ast::token;
-use rustc_ast::tokenstream::{self, DelimSpan, Spacing::*, TokenStream, TreeAndSpacing};
+use rustc_ast::tokenstream::{self, CanSynthesizeMissingTokens};
+use rustc_ast::tokenstream::{DelimSpan, Spacing::*, TokenStream, TreeAndSpacing};
 use rustc_ast_pretty::pprust;
 use rustc_data_structures::sync::Lrc;
 use rustc_errors::Diagnostic;
@@ -178,7 +179,7 @@ impl FromInternal<(TreeAndSpacing, &'_ ParseSess, &'_ mut Vec<Self>)>
                 {
                     TokenTree::Ident(Ident::new(sess, name.name, is_raw, name.span))
                 } else {
-                    let stream = nt_to_tokenstream(&nt, sess, span);
+                    let stream = nt_to_tokenstream(&nt, sess, span, CanSynthesizeMissingTokens::No);
                     TokenTree::Group(Group {
                         delimiter: Delimiter::None,
                         stream,