feat: add etl package

.agents/docs/2026-10-13-add-etl-plan.md

@@ -0,0 +1,15 @@
+# Add compat.etl
+
+ETL 20.49.0 is a MIT-licensed header-only upstream release. A generated C
+anchor gives mcpp a library target and exposes the original include directory.
+The three platform entries share the pinned archive and SHA-256. No optional
+compiled sources exist, so no sources-only features are advertised.
+
+The GLOBAL URL is kept as a plain string; CN users fall back to upstream
+until a byte-identical mirror is published. The example redirects compat to
+this checkout and asserts fixed-capacity vector and queue ordering.
+
+Local validation: mcpp 2026.10.1.2, gcc 16.1.0, `mcpp test -p etl`:
+`test result ok. 1 passed; 0 failed`. The original LLVM CI failure belonged
+to eui-neo-tray, which used setenv without stdlib.h; the follow-up includes
+that declaration so the already selected CI member compiles correctly.

README.md

@@ -63,6 +63,7 @@ the online index; open a PR and confirm CI is green.
 A PR runs lint and tests only the workspace members that depend on the changed descriptors; after the merge,
 `deploy-site` publishes the site.
 
+Additional example: [`compat.etl`](pkgs/c/compat.etl.lua) — Header-only; [`consumer test`](tests/examples/etl/mcpp.toml).
 Additional example: [`compat.richdem`](pkgs/c/compat.richdem.lua) — C++ sources, serial terrain analysis; [`consumer test`](tests/examples/richdem/mcpp.toml).
 
 ## Documentation

README.zh-CN.md

@@ -59,6 +59,7 @@ agent(如 Claude Code)即可:
 
 提交 PR 后,CI 执行 lint,并只测试依赖了被修改描述符的 workspace 成员;合并后,`deploy-site` 发布站点。
 
+新增示例: [`compat.etl`](pkgs/c/compat.etl.lua) — Header-only; [`消费测试`](tests/examples/etl/mcpp.toml)。
 新增示例: [`compat.richdem`](pkgs/c/compat.richdem.lua) — C++ sources, serial terrain analysis; [`消费测试`](tests/examples/richdem/mcpp.toml)。
 
 ## 文档

mcpp.toml

@@ -180,6 +180,7 @@ members = [
     "tests/examples/httplib-zstd",
     "tests/examples/msdfgen",
     "tests/examples/gtl",
+    "tests/examples/etl",
     "tests/examples/galay",
     "tests/examples/miniaudio",
     "tests/examples/nanosvg",

pkgs/c/compat.etl.lua

@@ -0,0 +1,56 @@
+-- Form B inline descriptor for the Embedded Template Library (ETL), a
+-- header-only collection of fixed-capacity containers and utilities for
+-- resource-constrained systems.
+--
+-- The upstream CMake target is INTERFACE-only and exposes `include/`, so a
+-- small C anchor gives mcpp a buildable library target while consumers use
+-- headers such as `<etl/vector.h>`.
+--
+-- ETL supports older language modes, but this package is built by mcpp, whose
+-- supported C++ standard starts at C++20. The package therefore uses C++23
+-- for its anchor and remains compatible with C++20 consumers.
+package = {
+    spec        = "1",
+    namespace   = "compat",
+    name        = "etl",
+    description = "Embedded Template Library — fixed-capacity containers and utilities (header-only)",
+    licenses    = {"MIT"},
+    repo        = "https://github.com/ETLCPP/etl",
+    type        = "package",
+
+    xpm = {
+        linux = {
+            ["20.49.0"] = {
+                url    = "https://github.com/ETLCPP/etl/archive/refs/tags/20.49.0.tar.gz",
+                sha256 = "b3e7a5544795ec8f4a1b2ab46f6e88fdb78be5a07738f008ce11dd37ed14b6e4",
+            },
+        },
+        macosx = {
+            ["20.49.0"] = {
+                url    = "https://github.com/ETLCPP/etl/archive/refs/tags/20.49.0.tar.gz",
+                sha256 = "b3e7a5544795ec8f4a1b2ab46f6e88fdb78be5a07738f008ce11dd37ed14b6e4",
+            },
+        },
+        windows = {
+            ["20.49.0"] = {
+                url    = "https://github.com/ETLCPP/etl/archive/refs/tags/20.49.0.tar.gz",
+                sha256 = "b3e7a5544795ec8f4a1b2ab46f6e88fdb78be5a07738f008ce11dd37ed14b6e4",
+            },
+        },
+    },
+
+    mcpp = {
+        language     = "c++23",
+        import_std   = false,
+        c_standard   = "c11",
+        include_dirs = { "*/include" },
+        generated_files = {
+            ["mcpp_generated/etl_anchor.c"] = [==[
+int mcpp_compat_etl_headers_anchor(void) { return 0; }
+]==],
+        },
+        sources = { "mcpp_generated/etl_anchor.c" },
+        targets = { ["etl"] = { kind = "lib" } },
+        deps    = {},
+    },
+}

tests/examples/etl/mcpp.toml

@@ -0,0 +1,11 @@
+# ETL test project: exercise a fixed-capacity vector and a queue without
+# requiring dynamic allocation from the library.
+[package]
+name = "etl-tests"
+version = "0.1.0"
+
+[dependencies.compat]
+etl = "20.49.0"
+
+[indices]
+compat = { path = "../../.." }

tests/examples/etl/tests/containers.cpp

@@ -0,0 +1,29 @@
+// compat.etl — exercise ETL's fixed-capacity containers and their observable
+// capacity/ordering behaviour.
+#include <etl/queue.h>
+#include <etl/vector.h>
+
+int main() {
+    etl::vector<int, 4> values;
+    values.push_back(3);
+    values.push_back(1);
+    values.push_back(4);
+
+    if (values.size() != 3 || values.capacity() != 4 ||
+        values[0] != 3 || values[2] != 4) {
+        return 1;
+    }
+
+    etl::queue<int, 4> queue;
+    queue.push(10);
+    queue.push(20);
+    if (queue.front() != 10 || queue.back() != 20) {
+        return 2;
+    }
+    queue.pop();
+    if (queue.front() != 20 || queue.size() != 1) {
+        return 3;
+    }
+
+    return 0;
+}

tests/examples/eui-neo-tray/tests/tray.cpp

@@ -42,6 +42,7 @@
 
 #if defined(__linux__)
 #include <limits.h>
+#include <stdlib.h>
 #include <unistd.h>
 #endif