Reuse const rendering from rustdoc in rmeta encoding

Author: saethlin

compiler/rustc_metadata/src/lib.rs

@@ -42,6 +42,6 @@ pub mod locator;
 
 pub use fs::{emit_wrapper_file, METADATA_FILENAME};
 pub use native_libs::find_native_static_library;
-pub use rmeta::{encode_metadata, EncodedMetadata, METADATA_HEADER};
+pub use rmeta::{encode_metadata, rendered_const, EncodedMetadata, METADATA_HEADER};
 
 fluent_messages! { "../messages.ftl" }

compiler/rustc_metadata/src/rmeta/encoder.rs

@@ -17,8 +17,8 @@ use rustc_hir::def_id::{
     CrateNum, DefId, DefIndex, LocalDefId, CRATE_DEF_ID, CRATE_DEF_INDEX, LOCAL_CRATE,
 };
 use rustc_hir::definitions::DefPathData;
-use rustc_hir::intravisit;
 use rustc_hir::lang_items::LangItem;
+use rustc_hir_pretty::id_to_string;
 use rustc_middle::middle::debugger_visualizer::DebuggerVisualizerFile;
 use rustc_middle::middle::dependency_format::Linkage;
 use rustc_middle::middle::exported_symbols::{
@@ -1614,7 +1614,7 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
                     record!(self.tables.mir_const_qualif[def_id.to_def_id()] <- qualifs);
                     let body_id = tcx.hir().maybe_body_owned_by(def_id);
                     if let Some(body_id) = body_id {
-                        let const_data = self.encode_rendered_const_for_body(body_id);
+                        let const_data = rendered_const(self.tcx, body_id);
                         record!(self.tables.rendered_const[def_id.to_def_id()] <- const_data);
                     }
                 }
@@ -1682,14 +1682,6 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
         }
     }
 
-    fn encode_rendered_const_for_body(&mut self, body_id: hir::BodyId) -> String {
-        let hir = self.tcx.hir();
-        let body = hir.body(body_id);
-        rustc_hir_pretty::to_string(&(&hir as &dyn intravisit::Map<'_>), |s| {
-            s.print_expr(&body.value)
-        })
-    }
-
     #[instrument(level = "debug", skip(self))]
     fn encode_info_for_macro(&mut self, def_id: LocalDefId) {
         let tcx = self.tcx;
@@ -2291,3 +2283,97 @@ pub fn provide(providers: &mut Providers) {
         ..*providers
     }
 }
+
+/// Build a textual representation of an unevaluated constant expression.
+///
+/// If the const expression is too complex, an underscore `_` is returned.
+/// For const arguments, it's `{ _ }` to be precise.
+/// This means that the output is not necessarily valid Rust code.
+///
+/// Currently, only
+///
+/// * literals (optionally with a leading `-`)
+/// * unit `()`
+/// * blocks (`{ … }`) around simple expressions and
+/// * paths without arguments
+///
+/// are considered simple enough. Simple blocks are included since they are
+/// necessary to disambiguate unit from the unit type.
+/// This list might get extended in the future.
+///
+/// Without this censoring, in a lot of cases the output would get too large
+/// and verbose. Consider `match` expressions, blocks and deeply nested ADTs.
+/// Further, private and `doc(hidden)` fields of structs would get leaked
+/// since HIR datatypes like the `body` parameter do not contain enough
+/// semantic information for this function to be able to hide them –
+/// at least not without significant performance overhead.
+///
+/// Whenever possible, prefer to evaluate the constant first and try to
+/// use a different method for pretty-printing. Ideally this function
+/// should only ever be used as a fallback.
+pub fn rendered_const<'tcx>(tcx: TyCtxt<'tcx>, body: hir::BodyId) -> String {
+    let hir = tcx.hir();
+    let value = &hir.body(body).value;
+
+    #[derive(PartialEq, Eq)]
+    enum Classification {
+        Literal,
+        Simple,
+        Complex,
+    }
+
+    use Classification::*;
+
+    fn classify(expr: &hir::Expr<'_>) -> Classification {
+        match &expr.kind {
+            hir::ExprKind::Unary(hir::UnOp::Neg, expr) => {
+                if matches!(expr.kind, hir::ExprKind::Lit(_)) { Literal } else { Complex }
+            }
+            hir::ExprKind::Lit(_) => Literal,
+            hir::ExprKind::Tup([]) => Simple,
+            hir::ExprKind::Block(hir::Block { stmts: [], expr: Some(expr), .. }, _) => {
+                if classify(expr) == Complex { Complex } else { Simple }
+            }
+            // Paths with a self-type or arguments are too “complex” following our measure since
+            // they may leak private fields of structs (with feature `adt_const_params`).
+            // Consider: `<Self as Trait<{ Struct { private: () } }>>::CONSTANT`.
+            // Paths without arguments are definitely harmless though.
+            hir::ExprKind::Path(hir::QPath::Resolved(_, hir::Path { segments, .. })) => {
+                if segments.iter().all(|segment| segment.args.is_none()) { Simple } else { Complex }
+            }
+            // FIXME: Claiming that those kinds of QPaths are simple is probably not true if the Ty
+            //        contains const arguments. Is there a *concise* way to check for this?
+            hir::ExprKind::Path(hir::QPath::TypeRelative(..)) => Simple,
+            // FIXME: Can they contain const arguments and thus leak private struct fields?
+            hir::ExprKind::Path(hir::QPath::LangItem(..)) => Simple,
+            _ => Complex,
+        }
+    }
+
+    let classification = classify(value);
+
+    if classification == Literal
+    && !value.span.from_expansion()
+    && let Ok(snippet) = tcx.sess.source_map().span_to_snippet(value.span) {
+        // For literals, we avoid invoking the pretty-printer and use the source snippet instead to
+        // preserve certain stylistic choices the user likely made for the sake legibility like
+        //
+        // * hexadecimal notation
+        // * underscores
+        // * character escapes
+        //
+        // FIXME: This passes through `-/*spacer*/0` verbatim.
+        snippet
+    } else if classification == Simple {
+        // Otherwise we prefer pretty-printing to get rid of extraneous whitespace, comments and
+        // other formatting artifacts.
+        id_to_string(&hir, body.hir_id)
+    } else if tcx.def_kind(hir.body_owner_def_id(body).to_def_id()) == DefKind::AnonConst {
+        // FIXME: Omit the curly braces if the enclosing expression is an array literal
+        //        with a repeated element (an `ExprKind::Repeat`) as in such case it
+        //        would not actually need any disambiguation.
+        "{ _ }".to_owned()
+    } else {
+        "_".to_owned()
+    }
+}

compiler/rustc_metadata/src/rmeta/mod.rs

@@ -42,7 +42,7 @@ pub use decoder::provide_extern;
 use decoder::DecodeContext;
 pub(crate) use decoder::{CrateMetadata, CrateNumMap, MetadataBlob};
 use encoder::EncodeContext;
-pub use encoder::{encode_metadata, EncodedMetadata};
+pub use encoder::{encode_metadata, rendered_const, EncodedMetadata};
 use rustc_span::hygiene::SyntaxContextData;
 
 mod decoder;

src/librustdoc/clean/types.rs

@@ -22,6 +22,7 @@ use rustc_hir::lang_items::LangItem;
 use rustc_hir::{BodyId, Mutability};
 use rustc_hir_analysis::check::intrinsic::intrinsic_operation_unsafety;
 use rustc_index::IndexVec;
+use rustc_metadata::rendered_const;
 use rustc_middle::ty::fast_reject::SimplifiedType;
 use rustc_middle::ty::{self, TyCtxt, Visibility};
 use rustc_resolve::rustdoc::{add_doc_fragment, attrs_to_doc_fragments, inner_docs, DocFragment};
@@ -35,7 +36,7 @@ use rustc_target::spec::abi::Abi;
 use crate::clean::cfg::Cfg;
 use crate::clean::external_path;
 use crate::clean::inline::{self, print_inlined_const};
-use crate::clean::utils::{is_literal_expr, print_const_expr, print_evaluated_const};
+use crate::clean::utils::{is_literal_expr, print_evaluated_const};
 use crate::core::DocContext;
 use crate::formats::cache::Cache;
 use crate::formats::item_type::ItemType;
@@ -2086,7 +2087,7 @@ impl Discriminant {
     /// Will be `None` in the case of cross-crate reexports, and may be
     /// simplified
     pub(crate) fn expr(&self, tcx: TyCtxt<'_>) -> Option<String> {
-        self.expr.map(|body| print_const_expr(tcx, body))
+        self.expr.map(|body| rendered_const(tcx, body))
     }
     /// Will always be a machine readable number, without underscores or suffixes.
     pub(crate) fn value(&self, tcx: TyCtxt<'_>) -> String {
@@ -2326,7 +2327,7 @@ impl ConstantKind {
             ConstantKind::TyConst { ref expr } => expr.to_string(),
             ConstantKind::Extern { def_id } => print_inlined_const(tcx, def_id),
             ConstantKind::Local { body, .. } | ConstantKind::Anonymous { body } => {
-                print_const_expr(tcx, body)
+                rendered_const(tcx, body)
             }
         }
     }

src/librustdoc/clean/utils.rs

@@ -14,6 +14,7 @@ use rustc_ast::tokenstream::TokenTree;
 use rustc_hir as hir;
 use rustc_hir::def::{DefKind, Res};
 use rustc_hir::def_id::{DefId, LocalDefId, LOCAL_CRATE};
+use rustc_metadata::rendered_const;
 use rustc_middle::mir;
 use rustc_middle::mir::interpret::ConstValue;
 use rustc_middle::ty::{self, GenericArgKind, GenericArgsRef, TyCtxt};
@@ -253,7 +254,7 @@ pub(crate) fn print_const(cx: &DocContext<'_>, n: ty::Const<'_>) -> String {
     match n.kind() {
         ty::ConstKind::Unevaluated(ty::UnevaluatedConst { def, args: _ }) => {
             let s = if let Some(def) = def.as_local() {
-                print_const_expr(cx.tcx, cx.tcx.hir().body_owned_by(def))
+                rendered_const(cx.tcx, cx.tcx.hir().body_owned_by(def))
             } else {
                 inline::print_inlined_const(cx.tcx, def)
             };
@@ -365,100 +366,6 @@ pub(crate) fn is_literal_expr(tcx: TyCtxt<'_>, hir_id: hir::HirId) -> bool {
     false
 }
 
-/// Build a textual representation of an unevaluated constant expression.
-///
-/// If the const expression is too complex, an underscore `_` is returned.
-/// For const arguments, it's `{ _ }` to be precise.
-/// This means that the output is not necessarily valid Rust code.
-///
-/// Currently, only
-///
-/// * literals (optionally with a leading `-`)
-/// * unit `()`
-/// * blocks (`{ … }`) around simple expressions and
-/// * paths without arguments
-///
-/// are considered simple enough. Simple blocks are included since they are
-/// necessary to disambiguate unit from the unit type.
-/// This list might get extended in the future.
-///
-/// Without this censoring, in a lot of cases the output would get too large
-/// and verbose. Consider `match` expressions, blocks and deeply nested ADTs.
-/// Further, private and `doc(hidden)` fields of structs would get leaked
-/// since HIR datatypes like the `body` parameter do not contain enough
-/// semantic information for this function to be able to hide them –
-/// at least not without significant performance overhead.
-///
-/// Whenever possible, prefer to evaluate the constant first and try to
-/// use a different method for pretty-printing. Ideally this function
-/// should only ever be used as a fallback.
-pub(crate) fn print_const_expr(tcx: TyCtxt<'_>, body: hir::BodyId) -> String {
-    let hir = tcx.hir();
-    let value = &hir.body(body).value;
-
-    #[derive(PartialEq, Eq)]
-    enum Classification {
-        Literal,
-        Simple,
-        Complex,
-    }
-
-    use Classification::*;
-
-    fn classify(expr: &hir::Expr<'_>) -> Classification {
-        match &expr.kind {
-            hir::ExprKind::Unary(hir::UnOp::Neg, expr) => {
-                if matches!(expr.kind, hir::ExprKind::Lit(_)) { Literal } else { Complex }
-            }
-            hir::ExprKind::Lit(_) => Literal,
-            hir::ExprKind::Tup([]) => Simple,
-            hir::ExprKind::Block(hir::Block { stmts: [], expr: Some(expr), .. }, _) => {
-                if classify(expr) == Complex { Complex } else { Simple }
-            }
-            // Paths with a self-type or arguments are too “complex” following our measure since
-            // they may leak private fields of structs (with feature `adt_const_params`).
-            // Consider: `<Self as Trait<{ Struct { private: () } }>>::CONSTANT`.
-            // Paths without arguments are definitely harmless though.
-            hir::ExprKind::Path(hir::QPath::Resolved(_, hir::Path { segments, .. })) => {
-                if segments.iter().all(|segment| segment.args.is_none()) { Simple } else { Complex }
-            }
-            // FIXME: Claiming that those kinds of QPaths are simple is probably not true if the Ty
-            //        contains const arguments. Is there a *concise* way to check for this?
-            hir::ExprKind::Path(hir::QPath::TypeRelative(..)) => Simple,
-            // FIXME: Can they contain const arguments and thus leak private struct fields?
-            hir::ExprKind::Path(hir::QPath::LangItem(..)) => Simple,
-            _ => Complex,
-        }
-    }
-
-    let classification = classify(value);
-
-    if classification == Literal
-    && !value.span.from_expansion()
-    && let Ok(snippet) = tcx.sess.source_map().span_to_snippet(value.span) {
-        // For literals, we avoid invoking the pretty-printer and use the source snippet instead to
-        // preserve certain stylistic choices the user likely made for the sake legibility like
-        //
-        // * hexadecimal notation
-        // * underscores
-        // * character escapes
-        //
-        // FIXME: This passes through `-/*spacer*/0` verbatim.
-        snippet
-    } else if classification == Simple {
-        // Otherwise we prefer pretty-printing to get rid of extraneous whitespace, comments and
-        // other formatting artifacts.
-        rustc_hir_pretty::id_to_string(&hir, body.hir_id)
-    } else if tcx.def_kind(hir.body_owner_def_id(body).to_def_id()) == DefKind::AnonConst {
-        // FIXME: Omit the curly braces if the enclosing expression is an array literal
-        //        with a repeated element (an `ExprKind::Repeat`) as in such case it
-        //        would not actually need any disambiguation.
-        "{ _ }".to_owned()
-    } else {
-        "_".to_owned()
-    }
-}
-
 /// Given a type Path, resolve it to a Type using the TyCtxt
 pub(crate) fn resolve_type(cx: &mut DocContext<'_>, path: Path) -> Type {
     debug!("resolve_type({path:?})");

src/librustdoc/json/conversions.rs

@@ -8,14 +8,14 @@ use std::fmt;
 
 use rustc_ast::ast;
 use rustc_hir::{def::CtorKind, def::DefKind, def_id::DefId};
+use rustc_metadata::rendered_const;
 use rustc_middle::ty::{self, TyCtxt};
 use rustc_span::symbol::sym;
 use rustc_span::{Pos, Symbol};
 use rustc_target::spec::abi::Abi as RustcAbi;
 
 use rustdoc_json_types::*;
 
-use crate::clean::utils::print_const_expr;
 use crate::clean::{self, ItemId};
 use crate::formats::item_type::ItemType;
 use crate::json::JsonRenderer;
@@ -805,7 +805,7 @@ impl FromWithTcx<clean::Static> for Static {
         Static {
             type_: stat.type_.into_tcx(tcx),
             mutable: stat.mutability == ast::Mutability::Mut,
-            expr: stat.expr.map(|e| print_const_expr(tcx, e)).unwrap_or_default(),
+            expr: stat.expr.map(|e| rendered_const(tcx, e)).unwrap_or_default(),
         }
     }
 }

tests/rustdoc/show-const-contents.rs

@@ -47,7 +47,7 @@ pub struct MyTypeWithStr(&'static str);
 // @!hasraw show_const_contents/constant.MY_TYPE_WITH_STR.html '; //'
 pub const MY_TYPE_WITH_STR: MyTypeWithStr = MyTypeWithStr("show this");
 
-// @hasraw show_const_contents/constant.PI.html '= 3.14159265358979323846264338327950288f32;'
+// @hasraw show_const_contents/constant.PI.html '= 3.14159265358979323846264338327950288_f32;'
 // @hasraw show_const_contents/constant.PI.html '; // 3.14159274f32'
 pub use std::f32::consts::PI;