Rollup merge of rust-lang#87082 - michaelwoerister:const-in-debuginfo…

…-type-names-fix, r=oli-obk,wesleywiser

Handle non-integer const generic parameters in debuginfo type names.

This PR fixes an ICE introduced by rust-lang#85269 which started emitting const generic arguments for debuginfo names but did not cover the case where such an argument could not be evaluated to a flat string of bits.

The fix implemented in this PR is very basic: If `try_eval_bits()` fails for the constant in question, we fall back to generating a stable hash of the constant and emit that instead. This way we get a (virtually) unique name and side step the problem of generating a string representation of a potentially complex value.

The downside is that the generated name will be rather opaque. E.g. the regression test adds a function `const_generic_fn_non_int<()>` which is then rendered as `const_generic_fn_non_int<{CONST#fe3cfa0214ac55c7}>`. I think it's an open question how to deal with this more gracefully.

I'd be interested in ideas on how to do this better.

r? ``@wesleywiser``

cc ``@dpaoliello`` (do you see any problems with this approach?)
cc ``@Mark-Simulacrum`` & ``@nagisa`` (who I've seen comment on debuginfo issues recently -- anyone else?)

Fixes rust-lang#86893

compiler/rustc_codegen_ssa/src/debuginfo/type_names.rs

@@ -12,12 +12,15 @@
 // * `"` is treated as the start of a string.
 
 use rustc_data_structures::fx::FxHashSet;
+use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
 use rustc_hir::definitions::{DefPathData, DefPathDataName, DisambiguatedDefPathData};
+use rustc_middle::ich::NodeIdHashingMode;
+use rustc_middle::ty::layout::IntegerExt;
 use rustc_middle::ty::subst::{GenericArgKind, SubstsRef};
 use rustc_middle::ty::{self, AdtDef, Ty, TyCtxt};
-use rustc_target::abi::{TagEncoding, Variants};
+use rustc_target::abi::{Integer, TagEncoding, Variants};
 
 use std::fmt::Write;
 
@@ -47,7 +50,7 @@ pub fn push_debuginfo_type_name<'tcx>(
 ) {
     // When targeting MSVC, emit C++ style type names for compatibility with
     // .natvis visualizers (and perhaps other existing native debuggers?)
-    let cpp_like_names = tcx.sess.target.is_like_msvc;
+    let cpp_like_names = cpp_like_names(tcx);
 
     match *t.kind() {
         ty::Bool => output.push_str("bool"),
@@ -424,16 +427,14 @@ fn push_unqualified_item_name(
     disambiguated_data: DisambiguatedDefPathData,
     output: &mut String,
 ) {
-    let cpp_like_names = tcx.sess.target.is_like_msvc;
-
     match disambiguated_data.data {
         DefPathData::CrateRoot => {
             output.push_str(&tcx.crate_name(def_id.krate).as_str());
         }
         DefPathData::ClosureExpr if tcx.generator_kind(def_id).is_some() => {
             // Generators look like closures, but we want to treat them differently
             // in the debug info.
-            if cpp_like_names {
+            if cpp_like_names(tcx) {
                 write!(output, "generator${}", disambiguated_data.disambiguator).unwrap();
             } else {
                 write!(output, "{{generator#{}}}", disambiguated_data.disambiguator).unwrap();
@@ -444,7 +445,7 @@ fn push_unqualified_item_name(
                 output.push_str(&name.as_str());
             }
             DefPathDataName::Anon { namespace } => {
-                if cpp_like_names {
+                if cpp_like_names(tcx) {
                     write!(output, "{}${}", namespace, disambiguated_data.disambiguator).unwrap();
                 } else {
                     write!(output, "{{{}#{}}}", namespace, disambiguated_data.disambiguator)
@@ -478,19 +479,14 @@ fn push_generic_params_internal<'tcx>(
         match type_parameter {
             GenericArgKind::Type(type_parameter) => {
                 push_debuginfo_type_name(tcx, type_parameter, true, output, visited);
-                output.push_str(", ");
-            }
-            GenericArgKind::Const(const_parameter) => match const_parameter.val {
-                ty::ConstKind::Param(param) => write!(output, "{}, ", param.name).unwrap(),
-                _ => write!(
-                    output,
-                    "0x{:x}, ",
-                    const_parameter.eval_bits(tcx, ty::ParamEnv::reveal_all(), const_parameter.ty)
-                )
-                .unwrap(),
-            },
+            }
+            GenericArgKind::Const(ct) => {
+                push_const_param(tcx, ct, output);
+            }
             other => bug!("Unexpected non-erasable generic: {:?}", other),
         }
+
+        output.push_str(", ");
     }
 
     output.pop();
@@ -499,6 +495,51 @@ fn push_generic_params_internal<'tcx>(
     push_close_angle_bracket(tcx, output);
 }
 
+fn push_const_param<'tcx>(tcx: TyCtxt<'tcx>, ct: &'tcx ty::Const<'tcx>, output: &mut String) {
+    match ct.val {
+        ty::ConstKind::Param(param) => {
+            write!(output, "{}", param.name)
+        }
+        _ => match ct.ty.kind() {
+            ty::Int(ity) => {
+                let bits = ct.eval_bits(tcx, ty::ParamEnv::reveal_all(), ct.ty);
+                let val = Integer::from_int_ty(&tcx, *ity).size().sign_extend(bits) as i128;
+                write!(output, "{}", val)
+            }
+            ty::Uint(_) => {
+                let val = ct.eval_bits(tcx, ty::ParamEnv::reveal_all(), ct.ty);
+                write!(output, "{}", val)
+            }
+            ty::Bool => {
+                let val = ct.try_eval_bool(tcx, ty::ParamEnv::reveal_all()).unwrap();
+                write!(output, "{}", val)
+            }
+            _ => {
+                // If we cannot evaluate the constant to a known type, we fall back
+                // to emitting a stable hash value of the constant. This isn't very pretty
+                // but we get a deterministic, virtually unique value for the constant.
+                let hcx = &mut tcx.create_stable_hashing_context();
+                let mut hasher = StableHasher::new();
+                hcx.while_hashing_spans(false, |hcx| {
+                    hcx.with_node_id_hashing_mode(NodeIdHashingMode::HashDefPath, |hcx| {
+                        ct.val.hash_stable(hcx, &mut hasher);
+                    });
+                });
+                // Let's only emit 64 bits of the hash value. That should be plenty for
+                // avoiding collisions and will make the emitted type names shorter.
+                let hash: u64 = hasher.finish();
+
+                if cpp_like_names(tcx) {
+                    write!(output, "CONST${:x}", hash)
+                } else {
+                    write!(output, "{{CONST#{:x}}}", hash)
+                }
+            }
+        },
+    }
+    .unwrap();
+}
+
 pub fn push_generic_params<'tcx>(tcx: TyCtxt<'tcx>, substs: SubstsRef<'tcx>, output: &mut String) {
     let mut visited = FxHashSet::default();
     push_generic_params_internal(tcx, substs, output, &mut visited);
@@ -507,9 +548,13 @@ pub fn push_generic_params<'tcx>(tcx: TyCtxt<'tcx>, substs: SubstsRef<'tcx>, out
 fn push_close_angle_bracket<'tcx>(tcx: TyCtxt<'tcx>, output: &mut String) {
     // MSVC debugger always treats `>>` as a shift, even when parsing templates,
     // so add a space to avoid confusion.
-    if tcx.sess.target.is_like_msvc && output.ends_with('>') {
+    if cpp_like_names(tcx) && output.ends_with('>') {
         output.push(' ')
     };
 
     output.push('>');
 }
+
+fn cpp_like_names(tcx: TyCtxt<'_>) -> bool {
+    tcx.sess.target.is_like_msvc
+}

src/test/debuginfo/function-names.rs

@@ -33,6 +33,13 @@
 // Generator
 // Generators don't seem to appear in GDB's symbol table.
 
+// Const generic parameter
+// gdb-command:info functions -q function_names::const_generic_fn.*
+// gdb-check:[...]static fn function_names::const_generic_fn_bool();
+// gdb-check:[...]static fn function_names::const_generic_fn_non_int();
+// gdb-check:[...]static fn function_names::const_generic_fn_signed_int();
+// gdb-check:[...]static fn function_names::const_generic_fn_unsigned_int();
+
 // === CDB TESTS ===================================================================================
 
 // Top-level function
@@ -65,10 +72,18 @@
 // cdb-command:x a!function_names::*::generator*
 // cdb-check:[...] a!function_names::main::generator$1 (void)
 
+// Const generic parameter
+// cdb-command:x a!function_names::const_generic_fn*
+// cdb-check:[...] a!function_names::const_generic_fn_bool<false> (void)
+// cdb-check:[...] a!function_names::const_generic_fn_non_int<CONST$fe3cfa0214ac55c7> (void)
+// cdb-check:[...] a!function_names::const_generic_fn_signed_int<-7> (void)
+// cdb-check:[...] a!function_names::const_generic_fn_unsigned_int<14> (void)
+
 #![allow(unused_variables)]
 #![feature(omit_gdb_pretty_printer_section)]
 #![omit_gdb_pretty_printer_section]
-#![feature(generators, generator_trait)]
+#![feature(const_generics, generators, generator_trait)]
+#![allow(incomplete_features)] // for const_generics
 
 use Mod1::TestTrait2;
 use std::ops::Generator;
@@ -97,6 +112,12 @@ fn main() {
     // Generator
     let mut generator = || { yield; return; };
     Pin::new(&mut generator).resume(());
+
+    // Const generic functions
+    const_generic_fn_bool::<false>();
+    const_generic_fn_non_int::<{()}>();
+    const_generic_fn_signed_int::<-7>();
+    const_generic_fn_unsigned_int::<14>();
 }
 
 struct TestStruct1;
@@ -173,3 +194,8 @@ fn generic_func<T>(value: T) -> T {
 
     value
 }
+
+fn const_generic_fn_bool<const C: bool>() {}
+fn const_generic_fn_non_int<const C: ()>() {}
+fn const_generic_fn_signed_int<const C: i64>() {}
+fn const_generic_fn_unsigned_int<const C: u32>() {}