From bd46410419086acd274e33b47d9ae5dc1f678a1b Mon Sep 17 00:00:00 2001
From: Andrew Kelley <andrew@ziglang.org>
Date: Sat, 13 Jan 2024 23:20:33 -0700
Subject: [PATCH] Revert "Merge pull request #18410 from
 dweiller/by-length-slice-bug"

This reverts commit d9d840a33ac8abb0e616de862f592821a7f4a35e, reversing
changes made to a04d4330945565b8d6f298ace993f6954c42d0f3.

This is not an adequate implementation of the missing safety check, as
evidenced by the changes to std.json that are reverted in this commit.

Reopens #18382
Closes #18510
---
 lib/std/json/static.zig                       | 12 ----------
 src/Sema.zig                                  | 24 -------------------
 .../slice_of_array_by-length_oversized.zig    | 19 ---------------
 .../array slice by-length oversized.zig       | 21 ----------------
 4 files changed, 76 deletions(-)
 delete mode 100644 test/cases/compile_errors/slice_of_array_by-length_oversized.zig
 delete mode 100644 test/cases/safety/array slice by-length oversized.zig

diff --git a/lib/std/json/static.zig b/lib/std/json/static.zig
index d4ae6053f4..ea0bb6c0f2 100644
--- a/lib/std/json/static.zig
+++ b/lib/std/json/static.zig
@@ -402,33 +402,21 @@ pub fn innerParse(
                             },
                             .partial_string_escaped_1 => |arr| {
                                 if (i + arr.len > r.len) return error.LengthMismatch;
-                                // tell the compiler that the by-length slice below is valid;
-                                // this assert is required for the inequality to be comptime-known
-                                if (arr.len > r.len) unreachable;
                                 @memcpy(r[i..][0..arr.len], arr[0..]);
                                 i += arr.len;
                             },
                             .partial_string_escaped_2 => |arr| {
                                 if (i + arr.len > r.len) return error.LengthMismatch;
-                                // tell the compiler that the by-length slice below is valid;
-                                // this assert is required for the inequality to be comptime-known
-                                if (arr.len > r.len) unreachable;
                                 @memcpy(r[i..][0..arr.len], arr[0..]);
                                 i += arr.len;
                             },
                             .partial_string_escaped_3 => |arr| {
                                 if (i + arr.len > r.len) return error.LengthMismatch;
-                                // tell the compiler that the by-length slice below is valid;
-                                // this assert is required for the inequality to be comptime-known
-                                if (arr.len > r.len) unreachable;
                                 @memcpy(r[i..][0..arr.len], arr[0..]);
                                 i += arr.len;
                             },
                             .partial_string_escaped_4 => |arr| {
                                 if (i + arr.len > r.len) return error.LengthMismatch;
-                                // tell the compiler that the by-length slice below is valid;
-                                // this assert is required for the inequality to be comptime-known
-                                if (arr.len > r.len) unreachable;
                                 @memcpy(r[i..][0..arr.len], arr[0..]);
                                 i += arr.len;
                             },
diff --git a/src/Sema.zig b/src/Sema.zig
index f66b505e5c..941c91fcd0 100644
--- a/src/Sema.zig
+++ b/src/Sema.zig
@@ -32635,30 +32635,6 @@ fn analyzeSlice(
             if (!end_is_len) {
                 const end = if (by_length) end: {
                     const len = try sema.coerce(block, Type.usize, uncasted_end_opt, end_src);
-                    if (try sema.resolveValue(len)) |slice_len_val| {
-                        const len_s_val = try mod.intValue(
-                            Type.usize,
-                            array_ty.arrayLenIncludingSentinel(mod),
-                        );
-                        if (!(try sema.compareScalar(slice_len_val, .lte, len_s_val, Type.usize))) {
-                            const sentinel_label: []const u8 = if (array_ty.sentinel(mod) != null)
-                                " +1 (sentinel)"
-                            else
-                                "";
-
-                            return sema.fail(
-                                block,
-                                end_src,
-                                "length {} out of bounds for array of length {}{s}",
-                                .{
-                                    slice_len_val.fmtValue(Type.usize, mod),
-                                    len_val.fmtValue(Type.usize, mod),
-                                    sentinel_label,
-                                },
-                            );
-                        }
-                    }
-                    // check len is less than array size if comptime known
                     const uncasted_end = try sema.analyzeArithmetic(block, .add, start, len, src, start_src, end_src, false);
                     break :end try sema.coerce(block, Type.usize, uncasted_end, end_src);
                 } else try sema.coerce(block, Type.usize, uncasted_end_opt, end_src);
diff --git a/test/cases/compile_errors/slice_of_array_by-length_oversized.zig b/test/cases/compile_errors/slice_of_array_by-length_oversized.zig
deleted file mode 100644
index e482197d1a..0000000000
--- a/test/cases/compile_errors/slice_of_array_by-length_oversized.zig
+++ /dev/null
@@ -1,19 +0,0 @@
-export fn entry1() void {
-    var buf: [5]u8 = undefined;
-    var a: u32 = 6;
-    _ = &a;
-    _ = buf[a..][0..10];
-}
-
-export fn entry2() void {
-    var buf: [5]u8 = undefined;
-    const a: u32 = 6;
-    _ = buf[a..][0..10];
-}
-
-// error
-// backend=stage2
-// target=native
-//
-// :5:21: error: length 10 out of bounds for array of length 5
-// :11:21: error: length 10 out of bounds for array of length 5
diff --git a/test/cases/safety/array slice by-length oversized.zig b/test/cases/safety/array slice by-length oversized.zig
deleted file mode 100644
index a8b33e428a..0000000000
--- a/test/cases/safety/array slice by-length oversized.zig	
+++ /dev/null
@@ -1,21 +0,0 @@
-const std = @import("std");
-
-pub fn panic(message: []const u8, stack_trace: ?*std.builtin.StackTrace, _: ?usize) noreturn {
-    _ = stack_trace;
-    if (std.mem.eql(u8, message, "index out of bounds: index 12, len 5")) {
-        std.process.exit(0);
-    }
-    std.process.exit(1);
-}
-
-pub fn main() !void {
-    var buf: [5]u8 = undefined;
-    var a: u32 = 6;
-    _ = &a;
-    _ = buf[a..][0..a];
-    return error.TestFailed;
-}
-
-// run
-// backend=llvm
-// target=native