2026.9.8.1: a package's host modules are ordered by what they import

一个 host-module 包贡献的那些单元,过去按**路径**排序:lib root 在前,其余按
`std::set<path>` 的字母序。而 `build_program.cppm` 是一边编译一边累积模块旗标的,
每个单元只看得见排在它前面的那些 BMI。于是 `rules/spirv.cppm` 排在
`src/declare.cppm` 之前,一个 import 了本包共享单元的成员先被编译,失败于:

    failed to read compiled module: No such file or directory
    note: imports must be built before being imported

**两个方向都复现过**:把共享单元改个名让它的路径排在前面,同一个包就构建通过。所以
成因是那次排序,不是别的。

它的代价不是一次失败,而是一个基于误读的设计决定
------------------------------------------------

`mcpp:plugins` 把这个失败读成「第二个单元根本不会被编译成 host module」,于是把成员
共享的一切都折进 lib root,让它从约二十行涨到约七百行(该包设计文档 §13.1.1 把这笔
代价记了下来,连同那个错误的成因)。真正的成因是一次排序。

修法
----

按 import 图拓扑排序,并以**路径序做稳定次序**:没有包内 import 时结果与今天逐字相同,
只有在今天已经坏掉的情形下才不同 —— 对既有包严格更安全。

`declared_imports` 与它旁边的 `declared_interface_name` 同形:按行、认注释、刻意浅。
它回答的是「本包哪些单元必须排在这个之前」,任何不是本包单元的名字由调用方丢弃。它不是
模块扫描器的替代品。

环留给编译器报。那是 ill-formed C++,编译器会点名那两个单元;在这里拒绝只会把同一个
事实报在更差的位置,而顺序错这件事无论如何已经不可能发生了。

判据
----

e2e 633 两条腿:

  1. 一条**完全逆序**的链 —— 三个单元的 import 序与路径序恰好相反。路径排序下每一个
     都排在它 import 的东西前面;import 排序下每一个都排在后面。除了顺序没有别的东西
     决定它建不建得起来。判据是三个模块共同算出的那个值,经 `mcpp::warning` 输出 ——
     那是构建成功时唯一会被打印的构建程序通道。

  2. 包内无 import 的情形必须保持原次序。不是装饰:一个忽略原次序的拓扑排序可以吐出
     任意合法序,于是今天能用的包会被无理由重排,而且是静默的。

把修复退回路径排序,第一条腿如实变红。

Author: speak-agent

CHANGELOG.md

@@ -5,6 +5,58 @@
 
 ## [Unreleased]
 
+## [2026.9.8.1] - 2026-09-08
+
+### 一个包的 host module,按它们互相 import 的顺序编译
+
+一个 host-module 包贡献的那些单元,过去按**路径**排序:lib root 在前,其余按
+`std::set<path>` 的字母序。而 `build_program.cppm` 是一边编译一边累积模块旗标的,
+每个单元只看得见排在它前面的那些 BMI。于是 `rules/spirv.cppm` 排在
+`src/surface.cppm` 之前,一个 import 了本包共享单元的成员先被编译,失败于:
+
+```
+failed to read compiled module: No such file or directory
+note: imports must be built before being imported
+```
+
+**两个方向都复现过**:把共享单元改个名让它的路径排在前面,同一个包就构建通过。所以
+成因是那次排序,不是别的。
+
+**它的代价不是一次失败,而是一个基于误读的设计决定。** `mcpp:plugins` 把这个失败读成
+「第二个单元根本不会被编译成 host module」,于是把成员共享的一切都折进 lib root,
+让它从约二十行涨到约七百行。真正的成因是一次排序。
+
+现在按 import 图拓扑排序,并以**路径序做稳定次序**:没有包内 import 时结果与今天逐字
+相同,只有在今天已经坏掉的情形下才不同。环留给编译器报——那是 ill-formed C++,编译器
+会点名那两个单元,在这里拒绝只会把同一个事实报在更差的位置。
+
+判据是 e2e 633 的两条腿:一条**完全逆序**的链(路径序与 import 序恰好相反),以及一个
+包内无 import 的包必须保持原次序。把修复退回路径排序,第一条腿如实变红。
+
+### `device_extensions` 与 `rule_module` 不再被报成 unsupported
+
+这两个键在同一个解析器里往上约四十行就被读进 `featureDeviceExtensions` 与
+`featureRuleModule`,而且 prepare 在消费者激活该 feature 时会读它们——它们正是「新增一门
+设备语言不需要引擎发版」的全部依据。它们只是没被加进 `kKnownFeatureKeys`,于是引擎对
+一个它刚刚用过的键打印「unsupported key (ignored)」。
+
+比消息错更坏:它在**建议包作者删掉让规则生效的那两行**。
+
+没被发现是因为规则包平时走的 host-module 路径不打印 schema 警告;而**普通**构建会打印。
+`tools = [...]` 让规则包的普通构建成为常态,这条噪音于是浮上来。
+
+### 撤回:一条曾经加上的编译依赖通道
+
+本版早先的草案加过 `mcpp::recompile_if_changed`(协议 9),用来声明「编译某个源文件时
+读到、却没有任何 depfile 会报告」的依赖——`.incbin` 就是这种。它工作正常,判据齐备。
+
+**它被撤回,因为原型证明它不必要。** 那条依赖用引擎已有的唯一图原语就能表达:让生成
+`.S` 的那一步成为一条 `mcpp::action`,载荷是它的**声明输入**。载荷一变,action 重跑;
+没有 `restat`,其 output 被视为新的;汇编边随之重跑。实测 `bytes=64 -> 192`,零引擎改动。
+
+协议因此保持在 8。发一条只有一个使用者、而那个使用者本可以不需要它的协议面,是永久成本
+换一次便利。
+
 ## [2026.9.7.1] - 2026-09-07
 
 ### 四条通道,都是「规则包知道而引擎收不到」的形状

mcpp.toml

@@ -1,6 +1,6 @@
 [package]
 name        = "mcpp"
-version = "2026.9.7.1"
+version = "2026.9.8.1"
 description = "Modern C++ build & package management tool"
 license     = "Apache-2.0"
 authors     = ["mcpp-community"]

modules/buildmcpp/src/provisions.cppm

@@ -357,6 +357,68 @@ inline std::string declared_interface_name(std::string_view source)
     return {};
 }
 
+// The module names a unit IMPORTS, for ordering one package's host modules
+// among themselves.
+//
+// WHY THIS EXISTS. The units a host-module package contributes used to be
+// compiled in PATH order, and a package whose members share a unit could
+// therefore be handed to the compiler in an order the compiler cannot accept:
+// `rules/spirv.cppm` sorts before `src/surface.cppm`, so a member importing
+// the shared unit failed with "failed to read compiled module ... imports must
+// be built before being imported". Measured, and measured in both directions:
+// renaming the shared unit so its path sorted first made the same package
+// build. The cost of not having this was a design decision made against the
+// wrong cause -- a collection folded everything its members shared into the lib
+// root, taking it from about twenty lines to about seven hundred, because the
+// ordering was read as "a second unit is not compiled at all".
+//
+// Deliberately line-based and deliberately shallow, matching
+// `declared_interface_name` above: this answers "which units of THIS package
+// must precede this one", and every name that is not another unit of the same
+// package is discarded by the caller. It is not a substitute for the module
+// scanner, which answers a much harder question about the build graph proper.
+//
+// `export import` counts -- it is an import. A partition import (`import :p;`)
+// does not: a partition is not a unit compiled alone under a name of its own,
+// which is the same reason `declared_interface_name` rejects one.
+inline std::vector<std::string> declared_imports(std::string_view source)
+{
+    auto is_name = [](char c) {
+        return (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z')
+            || (c >= '0' && c <= '9') || c == '_' || c == '.';
+    };
+    auto is_ws = [](char c) { return c == ' ' || c == '\t' || c == '\r'; };
+    std::vector<std::string> out;
+    std::size_t lineStart = 0;
+    while (lineStart < source.size()) {
+        auto eol = source.find('\n', lineStart);
+        if (eol == std::string_view::npos) eol = source.size();
+        auto line = source.substr(lineStart, eol - lineStart);
+        lineStart = eol + 1;
+
+        std::size_t i = 0;
+        while (i < line.size() && is_ws(line[i])) ++i;
+        if (line.substr(i).starts_with("//")) continue;
+        if (line.substr(i).starts_with("export")) {
+            i += 6;
+            if (i >= line.size() || !is_ws(line[i])) continue;
+            while (i < line.size() && is_ws(line[i])) ++i;
+        }
+        if (!line.substr(i).starts_with("import")) continue;
+        i += 6;
+        if (i >= line.size() || !is_ws(line[i])) continue;
+        while (i < line.size() && is_ws(line[i])) ++i;
+        std::size_t start = i;
+        while (i < line.size() && is_name(line[i])) ++i;
+        if (i == start) continue;                 // `import :part;`, `import <h>;`
+        std::string name(line.substr(start, i - start));
+        while (i < line.size() && is_ws(line[i])) ++i;
+        if (i >= line.size() || line[i] != ';') continue;
+        out.push_back(std::move(name));
+    }
+    return out;
+}
+
 // One host module as registered for one consumer's build program.
 struct HostModule {
     std::string           module;     // what `import` in build.mcpp addresses

modules/versioning/src/version.cppm

@@ -31,6 +31,6 @@ import std;
 
 export namespace mcpp {
 
-inline constexpr std::string_view MCPP_VERSION = "2026.9.7.1";
+inline constexpr std::string_view MCPP_VERSION = "2026.9.8.1";
 
 } // namespace mcpp

src/build/prepare.cppm

@@ -7634,17 +7634,82 @@ prepare_build(bool print_fingerprint,
                     }
                 }
                 const auto root = iface.lexically_normal();
+                // ORDERED BY WHAT THEY IMPORT, NOT BY WHERE THEY SIT.
+                //
+                // The compile loop accumulates BMIs in list order, so each
+                // entry sees only what precedes it. Path order was the previous
+                // rule and it is not a valid one: `rules/spirv.cppm` sorts
+                // before `src/surface.cppm`, so a member importing a unit its
+                // package shares was compiled first and failed with "failed to
+                // read compiled module ... imports must be built before being
+                // imported". Reproduced, and reproduced in both directions --
+                // renaming the shared unit so its path sorted first made the
+                // same package build, which is what says the cause is the sort
+                // and nothing else.
+                //
+                // A package that works today is ordered IDENTICALLY: the sort
+                // below keeps path order wherever no import constrains it, so
+                // it differs only where the old order was already broken.
+                struct Unit {
+                    std::filesystem::path        path;
+                    std::string                  name;
+                    std::vector<std::string>     imports;
+                };
+                std::vector<Unit> pending;
                 for (auto const& f : matched) {          // std::set: sorted
                     if (dropped.contains(f)) continue;
                     if (std::filesystem::equivalent(f, root, ec)) continue;
                     std::ifstream is(f);
                     if (!is) continue;
                     std::stringstream buf;
                     buf << is.rdbuf();
-                    auto name = prov::declared_interface_name(buf.str());
+                    auto text = buf.str();
+                    auto name = prov::declared_interface_name(text);
                     if (name.empty()) continue;
-                    push(f, std::move(name));
+                    pending.push_back({f, std::move(name), prov::declared_imports(text)});
                 }
+
+                // Only names this package itself declares constrain anything.
+                // `import std;` and the lib root are already ahead of every
+                // entry here, and a name from another package is ordered by the
+                // cross-package DFS below rather than by this sort.
+                std::map<std::string, std::size_t> byName;
+                for (std::size_t i = 0; i < pending.size(); ++i)
+                    byName.emplace(pending[i].name, i);
+
+                std::vector<char> state(pending.size(), 0);   // 0 new, 1 open, 2 done
+                std::vector<std::size_t> order;
+                order.reserve(pending.size());
+                // Iterative post-order DFS over the path-sorted list: the first
+                // unit that can be emitted is emitted, which is what preserves
+                // path order in the unconstrained case.
+                const auto visit = [&](std::size_t start) {
+                    std::vector<std::pair<std::size_t, std::size_t>> stack{{start, 0}};
+                    while (!stack.empty()) {
+                        auto& [u, k] = stack.back();
+                        if (state[u] == 2) { stack.pop_back(); continue; }
+                        state[u] = 1;
+                        if (k < pending[u].imports.size()) {
+                            auto const& want = pending[u].imports[k++];
+                            auto it = byName.find(want);
+                            // A CYCLE IS LEFT TO THE COMPILER, ON PURPOSE. It
+                            // is ill-formed C++ and the compiler says so with
+                            // the two units named; refusing here would report
+                            // the same fact in a worse place, and getting the
+                            // ordering wrong is no longer possible either way.
+                            if (it != byName.end() && state[it->second] == 0)
+                                stack.push_back({it->second, 0});
+                            continue;
+                        }
+                        state[u] = 2;
+                        order.push_back(u);
+                        stack.pop_back();
+                    }
+                };
+                for (std::size_t i = 0; i < pending.size(); ++i)
+                    if (state[i] == 0) visit(i);
+
+                for (auto i : order) push(pending[i].path, std::move(pending[i].name));
                 return out;
             };
             for (std::size_t c = 0; c < provisionGraph.visible.size(); ++c) {