From 02533ffdda609f1960f66ef72f593826d801d482 Mon Sep 17 00:00:00 2001
From: Mura Li <2606021+typeless@users.noreply.github.com>
Date: Mon, 27 Jul 2026 13:00:34 +0800
Subject: [PATCH] Order discovered variants by name, not by interning order
 (fixes #175)

discover_variants ended with std::sort(result.begin(), result.end()) on a
Vec<StringId>. StringId is an enum class over the interning handle, and the names
are interned in read_directory order, so the sort ordered by raw readdir order.
Same defect as #171, at the second and last site that reads a directory into
StringIds and treats handle order as name order.

Its one consumer is the build-directory hint, so the damage is cosmetic -- the
order never reaches %f, command identity, or anything persisted -- but the same
tree listed its candidates differently on different machines:

  before: found: build-yankee, build-mike, build-charlie, build-bravo, build-alpha, build-zeta
  after:  found: build-alpha, build-bravo, build-charlie, build-mike, build-yankee, build-zeta

(readdir order was yankee mike charlie bravo alpha zeta.)

The test fixes interning order rather than trusting the filesystem to enumerate
out of order, as the #171 test does.

The remaining std::sort calls over StringId -- cmd_build.cpp, context.cpp,
scheduler.cpp, glob_expand_all's exclusion list -- are sort+unique or
binary_search set structures, where handle order is order-agnostic by
construction. cmd_show.cpp and multi_variant.cpp already sort through pool.get.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TLob4Ef3qyMd3Dnp9q3XmA
---
 src/core/layout.cpp       |  3 ++-
 test/unit/test_layout.cpp | 37 +++++++++++++++++++++++++++++++++++++
 2 files changed, 39 insertions(+), 1 deletion(-)

diff --git a/src/core/layout.cpp b/src/core/layout.cpp
index 70b3f859..a4a9b0da 100644
--- a/src/core/layout.cpp
+++ b/src/core/layout.cpp
@@ -218,7 +218,8 @@ auto discover_variants(
         }
     }
 
-    std::sort(result.begin(), result.end());
+    // StringId order is interning order, i.e. readdir order, not name order.
+    std::ranges::sort(result, {}, [&pool](StringId id) { return pool.get(id); });
     return result;
 }
 
diff --git a/test/unit/test_layout.cpp b/test/unit/test_layout.cpp
index 9f0e8bab..e6a418cf 100644
--- a/test/unit/test_layout.cpp
+++ b/test/unit/test_layout.cpp
@@ -6,9 +6,11 @@
 #include "pup/core/layout.hpp"
 #include "pup/core/string_pool.hpp"
 
+#include <array>
 #include <filesystem>
 #include <fstream>
 #include <random>
+#include <vector>
 
 namespace fs = std::filesystem;
 
@@ -199,3 +201,38 @@ TEST_CASE("discover_layout from build directory", "[e2e][layout]")
         REQUIRE(fs::canonical(std::string(global_pool().get(result->output_root))) == fs::canonical(tmp.path() / "build").string());
     }
 }
+
+SCENARIO("discover_variants orders variants by name, not by interning order", "[e2e][layout]")
+{
+    GIVEN("build directories whose names were interned in reverse-lexicographic order")
+    {
+        // Names unique to this test, so the interning below decides their handles.
+        auto const names = std::array<std::string_view, 4> {
+            "dvar_alpha",
+            "dvar_bravo",
+            "dvar_mike",
+            "dvar_zeta",
+        };
+
+        auto tmp = TempDir {};
+        tmp.create_file("Tupfile.ini");
+        for (auto name : names) {
+            tmp.create_file(fs::path { name } / "tup.config");
+        }
+        for (auto i = names.size(); i-- > 0;) {
+            (void)global_pool().intern(names[i]);
+        }
+
+        WHEN("the source root is scanned for variants")
+        {
+            THEN("the variants are in lexicographic name order")
+            {
+                auto found = std::vector<std::string_view> {};
+                for (auto id : pup::discover_variants(tmp.path().string())) {
+                    found.push_back(global_pool().get(id));
+                }
+                REQUIRE(found == std::vector<std::string_view>(names.begin(), names.end()));
+            }
+        }
+    }
+}