compat.expat 改为静态:host tool 链接它才能真的跑起来

pkgs/c/compat.expat.lua

@@ -86,7 +86,33 @@ package = {
             "lib/xmlrole.c",
         },
 
-        targets = { ["expat"] = { kind = "shared", soname = "libexpat.so.1" } },
+        -- STATIC, unlike compat.libdrm's shared build, and the difference is
+        -- not an oversight.
+        --
+        -- libdrm is shared because Mesa's payload has DT_NEEDED on
+        -- `libdrm.so.2` and the two must be ONE mapping — libdrm keeps mutable
+        -- file-static state (`drmHashTable`, `nr_fds`, `connection`) over a
+        -- shared set of fds, so a second copy is a split ledger. Expat has no
+        -- equivalent: every bit of parser state hangs off the XML_Parser the
+        -- caller owns, so a consumer that merges these objects while Mesa loads
+        -- the payload's libexpat.so.1 is not sharing anything to corrupt.
+        --
+        -- And there is a concrete reason to prefer static here. Expat's only
+        -- consumer in this index is `freedesktop.wayland-scanner`, a
+        -- `kind = "bin"` HOST TOOL that mcpp builds in a sub-build and then
+        -- RUNS during another package's build.mcpp. A host tool linking a
+        -- shared dependency comes out with a DT_NEEDED nothing satisfies —
+        -- mcpp does not stage the .so beside the tool, and the sub-build's
+        -- bin/ holds the executable alone:
+        --
+        --     wayland-scanner: error while loading shared libraries:
+        --     libexpat.so.1: cannot open shared object file
+        --
+        -- That reproduces only on a machine without a graphics stack: with
+        -- Mesa installed the tool's RPATH reaches `<registry>/subos/default/lib`
+        -- and silently binds to `xim:expat`'s copy instead — the WRONG library,
+        -- succeeding. Static removes the question.
+        targets = { ["expat"] = { kind = "lib" } },
         deps    = {},
 
         generated_files = {

tests/examples/expat/tests/xml.cpp

@@ -97,17 +97,22 @@ int main()
     }
 
     // ── 4. It is THIS build that ran ─────────────────────────────────────
+    // The package is `kind = "lib"`, so these objects are merged into the
+    // consumer and dladdr reports the EXECUTABLE. The check that matters is
+    // the same either way: the code that just parsed must not have come from
+    // the ecosystem's `xim:expat`, which is present whenever Mesa is and would
+    // otherwise answer silently.
     {
         Dl_info info{};
         const bool located =
             ::dladdr(reinterpret_cast<void *>(&XML_ParserCreate), &info) != 0
             && info.dli_fname != nullptr;
-        check(located, "dladdr locates the loaded libexpat");
+        check(located, "dladdr locates the code that parsed");
         if (located) {
             const std::string from = info.dli_fname;
-            std::printf("   loaded from: %s\n", from.c_str());
+            std::printf("   resolved from: %s\n", from.c_str());
             check(from.find("xim-x-expat") == std::string::npos,
-                  "the loaded libexpat is not the ecosystem payload's copy");
+                  "it is not the ecosystem payload's libexpat");
         }
     }