Rollup merge of #128430 - Zalathar:print-pat, r=Nadrieril

Use a separate pattern type for `rustc_pattern_analysis` diagnostics

The pattern-analysis code needs to print patterns, as part of its user-visible diagnostics. But it never actually tries to print "real" patterns! Instead, it only ever prints synthetic patterns that it has reconstructed from its own internal represenations.

We can therefore simultaneously remove two obstacles to changing `thir::Pat`, by having the pattern-analysis code use its own dedicated type for building printable patterns, and then making `thir::Pat` not printable at all.

r? `@Nadrieril`

Author: matthiaskrgr

compiler/rustc_middle/src/thir.rs

@@ -28,7 +28,7 @@ use rustc_middle::ty::{
     TyCtxt, UpvarArgs,
 };
 use rustc_span::def_id::LocalDefId;
-use rustc_span::{sym, ErrorGuaranteed, Span, Symbol, DUMMY_SP};
+use rustc_span::{ErrorGuaranteed, Span, Symbol};
 use rustc_target::abi::{FieldIdx, Integer, Size, VariantIdx};
 use rustc_target::asm::InlineAsmRegOrRegClass;
 use tracing::instrument;
@@ -597,10 +597,6 @@ pub struct Pat<'tcx> {
 }
 
 impl<'tcx> Pat<'tcx> {
-    pub fn wildcard_from_ty(ty: Ty<'tcx>) -> Self {
-        Pat { ty, span: DUMMY_SP, kind: PatKind::Wild }
-    }
-
     pub fn simple_ident(&self) -> Option<Symbol> {
         match self.kind {
             PatKind::Binding {
@@ -1073,186 +1069,6 @@ impl<'tcx> PatRangeBoundary<'tcx> {
     }
 }
 
-impl<'tcx> Pat<'tcx> {
-    /// Prints a [`Pat`] to an owned string, for user-facing diagnostics.
-    ///
-    /// If we ever switch over to storing subpatterns as `PatId`, this will also
-    /// need to take a context that can resolve IDs to subpatterns.
-    pub fn to_string(&self) -> String {
-        format!("{}", self.display())
-    }
-
-    /// Used internally by [`fmt::Display`] for [`PatDisplay`].
-    fn display(&self) -> PatDisplay<'_, 'tcx> {
-        PatDisplay { pat: self }
-    }
-}
-
-/// Wrapper around [`&Pat<'tcx>`][`Pat`] that implements [`fmt::Display`].
-///
-/// If we ever switch over to storing subpatterns as `PatId`, this will also
-/// need to hold a context that can resolve IDs to subpatterns.
-struct PatDisplay<'pat, 'tcx> {
-    pat: &'pat Pat<'tcx>,
-}
-
-impl<'pat, 'tcx> fmt::Display for PatDisplay<'pat, 'tcx> {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        let &Self { pat } = self;
-
-        // Printing lists is a chore.
-        let mut first = true;
-        let mut start_or_continue = |s| {
-            if first {
-                first = false;
-                ""
-            } else {
-                s
-            }
-        };
-        let mut start_or_comma = || start_or_continue(", ");
-
-        match pat.kind {
-            PatKind::Wild => write!(f, "_"),
-            PatKind::Never => write!(f, "!"),
-            PatKind::AscribeUserType { ref subpattern, .. } => {
-                write!(f, "{}: _", subpattern.display())
-            }
-            PatKind::Binding { name, mode, ref subpattern, .. } => {
-                f.write_str(mode.prefix_str())?;
-                write!(f, "{name}")?;
-                if let Some(ref subpattern) = *subpattern {
-                    write!(f, " @ {}", subpattern.display())?;
-                }
-                Ok(())
-            }
-            PatKind::Variant { ref subpatterns, .. } | PatKind::Leaf { ref subpatterns } => {
-                let variant_and_name = match pat.kind {
-                    PatKind::Variant { adt_def, variant_index, .. } => ty::tls::with(|tcx| {
-                        let variant = adt_def.variant(variant_index);
-                        let adt_did = adt_def.did();
-                        let name = if tcx.get_diagnostic_item(sym::Option) == Some(adt_did)
-                            || tcx.get_diagnostic_item(sym::Result) == Some(adt_did)
-                        {
-                            variant.name.to_string()
-                        } else {
-                            format!("{}::{}", tcx.def_path_str(adt_def.did()), variant.name)
-                        };
-                        Some((variant, name))
-                    }),
-                    _ => pat.ty.ty_adt_def().and_then(|adt_def| {
-                        if !adt_def.is_enum() {
-                            ty::tls::with(|tcx| {
-                                Some((adt_def.non_enum_variant(), tcx.def_path_str(adt_def.did())))
-                            })
-                        } else {
-                            None
-                        }
-                    }),
-                };
-
-                if let Some((variant, name)) = &variant_and_name {
-                    write!(f, "{name}")?;
-
-                    // Only for Adt we can have `S {...}`,
-                    // which we handle separately here.
-                    if variant.ctor.is_none() {
-                        write!(f, " {{ ")?;
-
-                        let mut printed = 0;
-                        for p in subpatterns {
-                            if let PatKind::Wild = p.pattern.kind {
-                                continue;
-                            }
-                            let name = variant.fields[p.field].name;
-                            write!(f, "{}{}: {}", start_or_comma(), name, p.pattern.display())?;
-                            printed += 1;
-                        }
-
-                        let is_union = pat.ty.ty_adt_def().is_some_and(|adt| adt.is_union());
-                        if printed < variant.fields.len() && (!is_union || printed == 0) {
-                            write!(f, "{}..", start_or_comma())?;
-                        }
-
-                        return write!(f, " }}");
-                    }
-                }
-
-                let num_fields =
-                    variant_and_name.as_ref().map_or(subpatterns.len(), |(v, _)| v.fields.len());
-                if num_fields != 0 || variant_and_name.is_none() {
-                    write!(f, "(")?;
-                    for i in 0..num_fields {
-                        write!(f, "{}", start_or_comma())?;
-
-                        // Common case: the field is where we expect it.
-                        if let Some(p) = subpatterns.get(i) {
-                            if p.field.index() == i {
-                                write!(f, "{}", p.pattern.display())?;
-                                continue;
-                            }
-                        }
-
-                        // Otherwise, we have to go looking for it.
-                        if let Some(p) = subpatterns.iter().find(|p| p.field.index() == i) {
-                            write!(f, "{}", p.pattern.display())?;
-                        } else {
-                            write!(f, "_")?;
-                        }
-                    }
-                    write!(f, ")")?;
-                }
-
-                Ok(())
-            }
-            PatKind::Deref { ref subpattern } => {
-                match pat.ty.kind() {
-                    ty::Adt(def, _) if def.is_box() => write!(f, "box ")?,
-                    ty::Ref(_, _, mutbl) => {
-                        write!(f, "&{}", mutbl.prefix_str())?;
-                    }
-                    _ => bug!("{} is a bad Deref pattern type", pat.ty),
-                }
-                write!(f, "{}", subpattern.display())
-            }
-            PatKind::DerefPattern { ref subpattern, .. } => {
-                write!(f, "deref!({})", subpattern.display())
-            }
-            PatKind::Constant { value } => write!(f, "{value}"),
-            PatKind::InlineConstant { def: _, ref subpattern } => {
-                write!(f, "{} (from inline const)", subpattern.display())
-            }
-            PatKind::Range(ref range) => write!(f, "{range}"),
-            PatKind::Slice { ref prefix, ref slice, ref suffix }
-            | PatKind::Array { ref prefix, ref slice, ref suffix } => {
-                write!(f, "[")?;
-                for p in prefix.iter() {
-                    write!(f, "{}{}", start_or_comma(), p.display())?;
-                }
-                if let Some(ref slice) = *slice {
-                    write!(f, "{}", start_or_comma())?;
-                    match slice.kind {
-                        PatKind::Wild => {}
-                        _ => write!(f, "{}", slice.display())?,
-                    }
-                    write!(f, "..")?;
-                }
-                for p in suffix.iter() {
-                    write!(f, "{}{}", start_or_comma(), p.display())?;
-                }
-                write!(f, "]")
-            }
-            PatKind::Or { ref pats } => {
-                for pat in pats.iter() {
-                    write!(f, "{}{}", start_or_continue(" | "), pat.display())?;
-                }
-                Ok(())
-            }
-            PatKind::Error(_) => write!(f, "<error>"),
-        }
-    }
-}
-
 // Some nodes are used a lot. Make sure they don't unintentionally get bigger.
 #[cfg(target_pointer_width = "64")]
 mod size_asserts {

compiler/rustc_pattern_analysis/src/rustc.rs

@@ -7,7 +7,7 @@ use rustc_hir::HirId;
 use rustc_index::{Idx, IndexVec};
 use rustc_middle::middle::stability::EvalResult;
 use rustc_middle::mir::{self, Const};
-use rustc_middle::thir::{self, FieldPat, Pat, PatKind, PatRange, PatRangeBoundary};
+use rustc_middle::thir::{self, Pat, PatKind, PatRange, PatRangeBoundary};
 use rustc_middle::ty::layout::IntegerExt;
 use rustc_middle::ty::{
     self, FieldDef, OpaqueTypeKey, ScalarInt, Ty, TyCtxt, TypeVisitableExt, VariantDef,
@@ -26,6 +26,8 @@ use crate::pat_column::PatternColumn;
 use crate::usefulness::{compute_match_usefulness, PlaceValidity};
 use crate::{errors, Captures, PatCx, PrivateUninhabitedField};
 
+mod print;
+
 // Re-export rustc-specific versions of all these types.
 pub type Constructor<'p, 'tcx> = crate::constructor::Constructor<RustcPatCtxt<'p, 'tcx>>;
 pub type ConstructorSet<'p, 'tcx> = crate::constructor::ConstructorSet<RustcPatCtxt<'p, 'tcx>>;
@@ -773,8 +775,9 @@ impl<'p, 'tcx: 'p> RustcPatCtxt<'p, 'tcx> {
         }
     }
 
-    /// Convert back to a `thir::Pat` for diagnostic purposes.
-    fn hoist_pat_range(&self, range: &IntRange, ty: RevealedTy<'tcx>) -> Pat<'tcx> {
+    /// Convert to a [`print::Pat`] for diagnostic purposes.
+    fn hoist_pat_range(&self, range: &IntRange, ty: RevealedTy<'tcx>) -> print::Pat<'tcx> {
+        use print::{Pat, PatKind};
         use MaybeInfiniteInt::*;
         let cx = self;
         let kind = if matches!((range.lo, range.hi), (NegInfinity, PosInfinity)) {
@@ -808,19 +811,20 @@ impl<'p, 'tcx: 'p> RustcPatCtxt<'p, 'tcx> {
             PatKind::Range(Box::new(PatRange { lo, hi, end, ty: ty.inner() }))
         };
 
-        Pat { ty: ty.inner(), span: DUMMY_SP, kind }
+        Pat { ty: ty.inner(), kind }
     }
 
     /// Prints a [`WitnessPat`] to an owned string, for diagnostic purposes.
     pub fn print_witness_pat(&self, pat: &WitnessPat<'p, 'tcx>) -> String {
-        // This works by converting the witness pattern back to a `thir::Pat`
+        // This works by converting the witness pattern to a `print::Pat`
         // and then printing that, but callers don't need to know that.
         self.hoist_witness_pat(pat).to_string()
     }
 
-    /// Convert back to a `thir::Pat` for diagnostic purposes. This panics for patterns that don't
+    /// Convert to a [`print::Pat`] for diagnostic purposes. This panics for patterns that don't
     /// appear in diagnostics, like float ranges.
-    fn hoist_witness_pat(&self, pat: &WitnessPat<'p, 'tcx>) -> Pat<'tcx> {
+    fn hoist_witness_pat(&self, pat: &WitnessPat<'p, 'tcx>) -> print::Pat<'tcx> {
+        use print::{FieldPat, Pat, PatKind};
         let cx = self;
         let is_wildcard = |pat: &Pat<'_>| matches!(pat.kind, PatKind::Wild);
         let mut subpatterns = pat.iter_fields().map(|p| Box::new(cx.hoist_witness_pat(p)));
@@ -840,15 +844,15 @@ impl<'p, 'tcx: 'p> RustcPatCtxt<'p, 'tcx> {
                     // the pattern is a box pattern.
                     PatKind::Deref { subpattern: subpatterns.next().unwrap() }
                 }
-                ty::Adt(adt_def, args) => {
+                ty::Adt(adt_def, _args) => {
                     let variant_index = RustcPatCtxt::variant_index_for_adt(&pat.ctor(), *adt_def);
                     let subpatterns = subpatterns
                         .enumerate()
                         .map(|(i, pattern)| FieldPat { field: FieldIdx::new(i), pattern })
                         .collect();
 
                     if adt_def.is_enum() {
-                        PatKind::Variant { adt_def: *adt_def, args, variant_index, subpatterns }
+                        PatKind::Variant { adt_def: *adt_def, variant_index, subpatterns }
                     } else {
                         PatKind::Leaf { subpatterns }
                     }
@@ -885,7 +889,7 @@ impl<'p, 'tcx: 'p> RustcPatCtxt<'p, 'tcx> {
                             }
                         }
                         let suffix: Box<[_]> = subpatterns.collect();
-                        let wild = Pat::wildcard_from_ty(pat.ty().inner());
+                        let wild = Pat { ty: pat.ty().inner(), kind: PatKind::Wild };
                         PatKind::Slice {
                             prefix: prefix.into_boxed_slice(),
                             slice: Some(Box::new(wild)),
@@ -906,7 +910,7 @@ impl<'p, 'tcx: 'p> RustcPatCtxt<'p, 'tcx> {
             }
         };
 
-        Pat { ty: pat.ty().inner(), span: DUMMY_SP, kind }
+        Pat { ty: pat.ty().inner(), kind }
     }
 }
 
@@ -1003,12 +1007,11 @@ impl<'p, 'tcx: 'p> PatCx for RustcPatCtxt<'p, 'tcx> {
         }
         // `pat` is an exclusive range like `lo..gap`. `gapped_with` contains ranges that start with
         // `gap+1`.
-        let suggested_range: thir::Pat<'_> = {
+        let suggested_range: String = {
             // Suggest `lo..=gap` instead.
-            let mut suggested_range = thir_pat.clone();
-            let thir::PatKind::Range(range) = &mut suggested_range.kind else { unreachable!() };
-            range.end = rustc_hir::RangeEnd::Included;
-            suggested_range
+            let mut suggested_range = PatRange::clone(range);
+            suggested_range.end = rustc_hir::RangeEnd::Included;
+            suggested_range.to_string()
         };
         let gap_as_pat = self.hoist_pat_range(&gap, *pat.ty());
         if gapped_with.is_empty() {
@@ -1023,7 +1026,7 @@ impl<'p, 'tcx: 'p> PatCx for RustcPatCtxt<'p, 'tcx> {
                     // That's the gap that isn't covered.
                     max: gap_as_pat.to_string(),
                     // Suggest `lo..=max` instead.
-                    suggestion: suggested_range.to_string(),
+                    suggestion: suggested_range,
                 },
             );
         } else {
@@ -1037,15 +1040,15 @@ impl<'p, 'tcx: 'p> PatCx for RustcPatCtxt<'p, 'tcx> {
                     // That's the gap that isn't covered.
                     gap: gap_as_pat.to_string(),
                     // Suggest `lo..=gap` instead.
-                    suggestion: suggested_range.to_string(),
+                    suggestion: suggested_range,
                     // All these ranges skipped over `gap` which we think is probably a
                     // mistake.
                     gap_with: gapped_with
                         .iter()
                         .map(|pat| errors::GappedRange {
                             span: pat.data().span,
                             gap: gap_as_pat.to_string(),
-                            first_range: thir_pat.to_string(),
+                            first_range: range.to_string(),
                         })
                         .collect(),
                 },