bpo-40280: Skip socket, fork, subprocess tests on Emscripten (GH-31986)

- Add requires_fork and requires_subprocess to more tests
- Skip extension import tests if dlopen is not available
- Don't assume that _testcapi is a shared extension
- Skip a lot of socket tests that don't work on Emscripten
- Skip mmap tests, mmap emulation is incomplete
- venv does not work yet
- Cannot get libc from executable

The "entire" test suite is now passing on Emscripten with EMSDK from git head (91 suites are skipped).

1 files changed, 40 insertions, 2 deletions

diff --git a/configure.ac b/configure.ac
index 7a37ad2..4afc898 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1659,6 +1659,13 @@ if test "$Py_LTO" = 'true' ; then
           ;;
       esac
       ;;
+    *emcc*)
+      if test "$Py_LTO_POLICY" != "default"; then
+        AC_MSG_ERROR([emcc supports only default lto.])
+      fi
+      LTOFLAGS="-flto"
+      LTOCFLAGS="-flto"
+      ;;
     *gcc*)
       if test $Py_LTO_POLICY = thin
       then
@@ -1861,15 +1868,33 @@ then
 fi
 
 # WASM flags
+# TODO: Add -s MAIN_MODULE=2 for dlopen() support.
+# The option disables code elimination, which increases code size of main
+# binary. All objects must be built with -fPIC.
 AS_CASE([$ac_sys_system/$ac_sys_emscripten_target],
   [Emscripten/browser], [
-    LDFLAGS_NODIST="$LDFLAGS_NODIST -s ASSERTIONS=1 -s ALLOW_MEMORY_GROWTH=1 --preload-file \$(WASM_ASSETS_DIR)"
+    LDFLAGS_NODIST="$LDFLAGS_NODIST -s ALLOW_MEMORY_GROWTH=1"
+    LINKFORSHARED="--preload-file \$(WASM_ASSETS_DIR)"
     WASM_ASSETS_DIR=".\$(prefix)"
     WASM_STDLIB="\$(WASM_ASSETS_DIR)/local/lib/python\$(VERSION)/os.py"
+    dnl separate-dwarf does not seem to work in Chrome DevTools Support.
+    if test "$Py_DEBUG" = 'true'; then
+      LDFLAGS_NODIST="$LDFLAGS_NODIST -s ASSERTIONS=1"
+      LINKFORSHARED="$LINKFORSHARED -gsource-map --emit-symbol-map"
+    else
+      LINKFORSHARED="$LINKFORSHARED -O2 -g0"
+    fi
   ],
   [Emscripten/node], [
-    LDFLAGS_NODIST="$LDFLAGS_NODIST -s ASSERTIONS=1 -s ALLOW_MEMORY_GROWTH=1 -s NODERAWFS=1 -s EXIT_RUNTIME=1 -s USE_PTHREADS -s PROXY_TO_PTHREAD"
+    LDFLAGS_NODIST="$LDFLAGS_NODIST -s ALLOW_MEMORY_GROWTH=1 -s NODERAWFS=1 -s USE_PTHREADS=1"
+    LINKFORSHARED="-s PROXY_TO_PTHREAD=1 -s EXIT_RUNTIME=1"
     CFLAGS_NODIST="$CFLAGS_NODIST -pthread"
+    if test "$Py_DEBUG" = 'true'; then
+      LDFLAGS_NODIST="$LDFLAGS_NODIST -s ASSERTIONS=1"
+      LINKFORSHARED="$LINKFORSHARED -gseparate-dwarf --emit-symbol-map"
+    else
+      LINKFORSHARED="$LINKFORSHARED -O2 -gseparate-dwarf"
+    fi
   ],
   [WASI/*], [
     AC_DEFINE([_WASI_EMULATED_SIGNAL], [1], [Define to 1 if you want to emulate signals on WASI])
@@ -2880,6 +2905,10 @@ then
 	Linux*|GNU*|QNX*|VxWorks*|Haiku*)
 		LDSHARED='$(CC) -shared'
 		LDCXXSHARED='$(CXX) -shared';;
+	Emscripten*)
+		LDSHARED='$(CC) -shared -s SIDE_MODULE=1'
+		LDCXXSHARED='$(CXX) -shared -s SIDE_MODULE=1'
+    ;;
 	FreeBSD*)
 		if [[ "`$CC -dM -E - </dev/null | grep __ELF__`" != "" ]]
 		then
@@ -4354,6 +4383,10 @@ PKG_CHECK_MODULES([ZLIB], [zlib >= 1.2.0], [
   ], [have_zlib=no])
 ])
 
+if test "$have_zlib" = "yes" -a "$ac_sys_system" = "Emscripten" -a "$ZLIB_LIBS" = "-lz"; then
+  ZLIB_LIBS="-s USE_ZLIB=1"
+fi
+
 dnl binascii can use zlib for optimized crc32.
 AS_VAR_IF([have_zlib], [yes], [
   BINASCII_CFLAGS="-DUSE_ZLIB_CRC32 $ZLIB_CFLAGS"
@@ -4372,6 +4405,11 @@ PKG_CHECK_MODULES([BZIP2], [bzip2], [have_bzip2=yes], [
   ], [have_bzip2=no])
 ])
 
+if test "$have_bzip2" = "yes" -a "$ac_sys_system" = "Emscripten" -a "$BZIP2_LIBS" = "-lbz2"; then
+  BZIP2_LIBS="-s USE_BZIP2=1"
+fi
+
+
 PKG_CHECK_MODULES([LIBLZMA], [liblzma], [have_liblzma=yes], [
   AC_CHECK_HEADERS([lzma.h], [
     WITH_SAVE_ENV([