interpret: call caller_location logic the same way codegen does, and share some code

compiler/rustc_const_eval/src/util/caller_location.rs

@@ -0,0 +1,63 @@
+use rustc_hir::LangItem;
+use rustc_middle::mir;
+use rustc_middle::ty::layout::LayoutOf;
+use rustc_middle::ty::{self, TyCtxt};
+use rustc_span::{source_map::DUMMY_SP, symbol::Symbol};
+use rustc_type_ir::Mutability;
+
+use crate::const_eval::{mk_eval_cx, CanAccessStatics, CompileTimeEvalContext};
+use crate::interpret::*;
+
+/// Allocate a `const core::panic::Location` with the provided filename and line/column numbers.
+fn alloc_caller_location<'mir, 'tcx>(
+    ecx: &mut CompileTimeEvalContext<'mir, 'tcx>,
+    filename: Symbol,
+    line: u32,
+    col: u32,
+) -> MPlaceTy<'tcx> {
+    let loc_details = ecx.tcx.sess.opts.unstable_opts.location_detail;
+    // This can fail if rustc runs out of memory right here. Trying to emit an error would be
+    // pointless, since that would require allocating more memory than these short strings.
+    let file = if loc_details.file {
+        ecx.allocate_str(filename.as_str(), MemoryKind::CallerLocation, Mutability::Not).unwrap()
+    } else {
+        // FIXME: This creates a new allocation each time. It might be preferable to
+        // perform this allocation only once, and re-use the `MPlaceTy`.
+        // See https://github.com/rust-lang/rust/pull/89920#discussion_r730012398
+        ecx.allocate_str("<redacted>", MemoryKind::CallerLocation, Mutability::Not).unwrap()
+    };
+    let line = if loc_details.line { Scalar::from_u32(line) } else { Scalar::from_u32(0) };
+    let col = if loc_details.column { Scalar::from_u32(col) } else { Scalar::from_u32(0) };
+
+    // Allocate memory for `CallerLocation` struct.
+    let loc_ty = ecx
+        .tcx
+        .type_of(ecx.tcx.require_lang_item(LangItem::PanicLocation, None))
+        .instantiate(*ecx.tcx, ecx.tcx.mk_args(&[ecx.tcx.lifetimes.re_erased.into()]));
+    let loc_layout = ecx.layout_of(loc_ty).unwrap();
+    let location = ecx.allocate(loc_layout, MemoryKind::CallerLocation).unwrap();
+
+    // Initialize fields.
+    ecx.write_immediate(file.to_ref(ecx), &ecx.project_field(&location, 0).unwrap())
+        .expect("writing to memory we just allocated cannot fail");
+    ecx.write_scalar(line, &ecx.project_field(&location, 1).unwrap())
+        .expect("writing to memory we just allocated cannot fail");
+    ecx.write_scalar(col, &ecx.project_field(&location, 2).unwrap())
+        .expect("writing to memory we just allocated cannot fail");
+
+    location
+}
+
+pub(crate) fn const_caller_location_provider(
+    tcx: TyCtxt<'_>,
+    (file, line, col): (Symbol, u32, u32),
+) -> mir::ConstValue<'_> {
+    trace!("const_caller_location: {}:{}:{}", file, line, col);
+    let mut ecx = mk_eval_cx(tcx, DUMMY_SP, ty::ParamEnv::reveal_all(), CanAccessStatics::No);
+
+    let loc_place = alloc_caller_location(&mut ecx, file, line, col);
+    if intern_const_alloc_recursive(&mut ecx, InternKind::Constant, &loc_place).is_err() {
+        bug!("intern_const_alloc_recursive should not error in this case")
+    }
+    mir::ConstValue::Scalar(Scalar::from_maybe_pointer(loc_place.ptr(), &tcx))
+}

compiler/rustc_const_eval/src/util/mod.rs

@@ -1,6 +1,7 @@
 use rustc_middle::mir;
 
 mod alignment;
+pub(crate) mod caller_location;
 mod check_validity_requirement;
 mod compare_types;
 mod type_name;