From ff982a1e677251ccb3a4bb90ab9f3e7f91e40f67 Mon Sep 17 00:00:00 2001
From: Claude <claude@anthropic.com>
Date: Mon, 19 Oct 2026 00:05:38 +0700
Subject: [PATCH] t27o: rust_std.t27 function test coverage 88 % -> 100 %
 (Closes #10550)

One test names digits_upto, parse_unsigned, parse_signed, sum_u64,
sum_usize, sum_i32 and sum_f32 directly: both sides of every bound, a
lone sign, i64::MIN, u64::MAX exactly, an empty slice. t27c coverage 59
of 59; t27b 11/11; test-report 11/11 with 0 vacuous; a mutant of the
digits_upto overflow guard fails it (and one existing test).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
---
 .trinity/seals/t27o_T27oRustStd.json | 20 ++++++++---------
 specs/tools/t27o/rust_std.t27        | 32 ++++++++++++++++++++++++++++
 2 files changed, 42 insertions(+), 10 deletions(-)

diff --git a/.trinity/seals/t27o_T27oRustStd.json b/.trinity/seals/t27o_T27oRustStd.json
index 8137a05e69..c9298463cc 100644
--- a/.trinity/seals/t27o_T27oRustStd.json
+++ b/.trinity/seals/t27o_T27oRustStd.json
@@ -1,5 +1,5 @@
 {
-  "built_by": "t27c-bootstrap@0.5.2+262746089",
+  "built_by": "t27c-bootstrap@0.5.2+9b556b7c3",
   "closure": [
     {
       "spec": "specs/hosting/toolchain.t27",
@@ -15,27 +15,27 @@
     }
   ],
   "config": "gen=c,rust,verilog,zig;tests=zig",
-  "gen_hash_c": "sha256:2761293642eb099cc257c46cabb57edbcc63ce841f17c8392272c26a3c197256",
-  "gen_hash_rust": "sha256:455339c3be513e911ec8bbea8d4bab01b77bc3d6799dea488edccacd95147e64",
-  "gen_hash_verilog": "sha256:a15e71febb0aec7f75316957883dd7316168bf680b33c9aba0cd8fcda57433e4",
-  "gen_hash_zig": "sha256:29dc623cc1b486c76c74e3929f358c6808dfce7c80112b89204a53174ce44133",
+  "gen_hash_c": "sha256:e2f3310cb7a4bc69c3719299098b247d1b4deac743249978de470617b8abc7f1",
+  "gen_hash_rust": "sha256:054308d17bce7b04be20ef206e53be8ec05ff7174609b2598bcadc2dc38cdbd7",
+  "gen_hash_verilog": "sha256:ae1350281fd19042bc344b29572b65a18760f4d1d7f0a7703b1b03be9cd7137e",
+  "gen_hash_zig": "sha256:df61571a23405733bc65b2641f0e32e59098be2cc60f857c963c3a1bfeadb556",
   "module": "T27oRustStd",
   "ring": 12,
   "seal_schema": 2,
-  "sealed_at": "2026-10-12T12:21:08Z",
+  "sealed_at": "2026-10-18T17:04:56Z",
   "sealed_by": "t27c-bootstrap@0.5.2",
-  "spec_hash": "sha256:32ee8d8c4af07ad5db18cc961fc3965e491e806a0a40a6129b82aae40f1e4547",
+  "spec_hash": "sha256:ee1cf77e327861bfa2fe6ae0d4179a610f24e5603d028a53b075739448c0e73a",
   "spec_path": "specs/tools/t27o/rust_std.t27",
   "tests": {
     "failed": 0,
     "failing": [],
     "forced": false,
-    "passed": 10,
-    "total": 10,
+    "passed": 11,
+    "total": 11,
     "vacuous": 0
   },
   "toolchain": {
-    "test_runner": "sha256:1982ae948e24d00c5d221ccec12dfce1eb01204b53e37b0f857f93b16d64629d",
+    "test_runner": "sha256:8512b80da533b79289110fca4a65f3336abd7a059ca4b72ea595d5e33ff8ad10",
     "zig": "0.16.0"
   }
 }
\ No newline at end of file
diff --git a/specs/tools/t27o/rust_std.t27 b/specs/tools/t27o/rust_std.t27
index 8da0f0a809..fd32d895e6 100644
--- a/specs/tools/t27o/rust_std.t27
+++ b/specs/tools/t27o/rust_std.t27
@@ -1409,3 +1409,35 @@ test std_strip_prefix_suffix_are_option_slices {
     assert(!starts_with_digit("x1"));
     assert(!starts_with_digit(""));
 }
+
+// The helpers the parse_* fns share, and the sums no other test named (t27c coverage: 52 of 59 fns
+// before this test, #10522). Each bound is checked on both sides: the largest value that parses and
+// the first one that does not.
+test std_parse_helpers_and_the_other_sums_named_directly {
+    assert(digits_upto("123", 0, 999).? == 123);
+    assert(digits_upto("123", 1, 999).? == 23);
+    assert(digits_upto("999", 0, 999).? == 999);
+    assert(digits_upto("1000", 0, 999) == null);
+    assert(digits_upto("12a", 0, 999) == null);
+    assert(digits_upto("12", 2, 999) == null);
+    assert(parse_unsigned("+42", 100).? == 42);
+    assert(parse_unsigned("100", 100).? == 100);
+    assert(parse_unsigned("101", 100) == null);
+    assert(parse_unsigned("-42", 100) == null);
+    assert(parse_unsigned("+", 100) == null);
+    assert(parse_signed("-128", 127).? == -128);
+    assert(parse_signed("-129", 127) == null);
+    assert(parse_signed("+127", 127).? == 127);
+    assert(parse_signed("128", 127) == null);
+    assert(parse_signed("-", 127) == null);
+    assert(parse_signed("-9223372036854775808", 9223372036854775807).? == -9223372036854775807 - 1);
+    const a : [3]u64 = [1, 2, 18446744073709551612];
+    assert(sum_u64(a[0 .. 3]) == 18446744073709551615);
+    assert(sum_u64(a[0 .. 0]) == 0);
+    const b : [2]usize = [3, 4];
+    assert(sum_usize(b[0 .. 2]) == 7);
+    const c : [3]i32 = [-5, 7, -2147483646];
+    assert(sum_i32(c[0 .. 3]) == -2147483644);
+    const d : [3]f32 = [0.5, 1.25, -2.0];
+    assert(sum_f32(d[0 .. 3]) == -0.25);
+}