From 0f38558435a0f73c4c025b5641bd8e531f063e0c Mon Sep 17 00:00:00 2001
From: mlugg <mlugg@mlugg.co.uk>
Date: Wed, 5 Feb 2025 19:36:14 +0000
Subject: compiler: provide result type to sentinel expression in slice
 operation

Resolves: #21867
---
 lib/std/zig/AstGen.zig | 6 +++++-
 lib/std/zig/Zir.zig    | 8 ++++++++
 2 files changed, 13 insertions(+), 1 deletion(-)

(limited to 'lib/std')

diff --git a/lib/std/zig/AstGen.zig b/lib/std/zig/AstGen.zig
index c105a371ef..d43a837b2f 100644
--- a/lib/std/zig/AstGen.zig
+++ b/lib/std/zig/AstGen.zig
@@ -920,7 +920,10 @@ fn expr(gz: *GenZir, scope: *Scope, ri: ResultInfo, node: Ast.Node.Index) InnerE
             const cursor = maybeAdvanceSourceCursorToMainToken(gz, node);
             const start = try expr(gz, scope, .{ .rl = .{ .coerced_ty = .usize_type } }, full.ast.start);
             const end = if (full.ast.end != 0) try expr(gz, scope, .{ .rl = .{ .coerced_ty = .usize_type } }, full.ast.end) else .none;
-            const sentinel = if (full.ast.sentinel != 0) try expr(gz, scope, .{ .rl = .none }, full.ast.sentinel) else .none;
+            const sentinel = if (full.ast.sentinel != 0) s: {
+                const sentinel_ty = try gz.addUnNode(.slice_sentinel_ty, lhs, node);
+                break :s try expr(gz, scope, .{ .rl = .{ .coerced_ty = sentinel_ty } }, full.ast.sentinel);
+            } else .none;
             try emitDbgStmt(gz, cursor);
             if (sentinel != .none) {
                 const result = try gz.addPlNode(.slice_sentinel, node, Zir.Inst.SliceSentinel{
@@ -2855,6 +2858,7 @@ fn addEnsureResult(gz: *GenZir, maybe_unused_result: Zir.Inst.Ref, statement: As
             .slice_end,
             .slice_sentinel,
             .slice_length,
+            .slice_sentinel_ty,
             .import,
             .switch_block,
             .switch_block_ref,
diff --git a/lib/std/zig/Zir.zig b/lib/std/zig/Zir.zig
index 092a354de6..32872eeabc 100644
--- a/lib/std/zig/Zir.zig
+++ b/lib/std/zig/Zir.zig
@@ -599,6 +599,10 @@ pub const Inst = struct {
         /// Returns a pointer to the subslice.
         /// Uses the `pl_node` field. AST node is the slice syntax. Payload is `SliceLength`.
         slice_length,
+        /// Given a value which is a pointer to the LHS of a slice operation, return the sentinel
+        /// type, used as the result type of the slice sentinel (i.e. `s` in `lhs[a..b :s]`).
+        /// Uses the `un_node` field. AST node is the slice syntax. Operand is `lhs`.
+        slice_sentinel_ty,
         /// Same as `store` except provides a source location.
         /// Uses the `pl_node` union field. Payload is `Bin`.
         store_node,
@@ -1185,6 +1189,7 @@ pub const Inst = struct {
                 .slice_end,
                 .slice_sentinel,
                 .slice_length,
+                .slice_sentinel_ty,
                 .import,
                 .typeof_log2_int_type,
                 .resolve_inferred_alloc,
@@ -1472,6 +1477,7 @@ pub const Inst = struct {
                 .slice_end,
                 .slice_sentinel,
                 .slice_length,
+                .slice_sentinel_ty,
                 .import,
                 .typeof_log2_int_type,
                 .switch_block,
@@ -1702,6 +1708,7 @@ pub const Inst = struct {
                 .slice_end = .pl_node,
                 .slice_sentinel = .pl_node,
                 .slice_length = .pl_node,
+                .slice_sentinel_ty = .un_node,
                 .store_node = .pl_node,
                 .store_to_inferred_ptr = .pl_node,
                 .str = .str,
@@ -4162,6 +4169,7 @@ fn findTrackableInner(
         .slice_end,
         .slice_sentinel,
         .slice_length,
+        .slice_sentinel_ty,
         .store_node,
         .store_to_inferred_ptr,
         .str,
-- 
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