strip_test: build executables with debug symbols (#90)

On Darwin, it seems that the plugin's default compiler and linker flags
generate executables that are already pretty stripped, to the extent
that `-Wl,-S -Wl,-x` doesn't do anything meaningful to all of them (e.g.
the stripped and unstripped shared objects have identical file sizes and
contain the same number of symbols). Guarantee that the linker has
symbols to strip by emitting debug symbols; that way, the tests can
ensure that the unstripped executables contain them, and the stripped
ones don't.

This also removes the run-time dependency on `file(1)`, which might not
be present (e.g. on Alpine); `nm(1)` is part of both GNU binutils and
LLVM, and is therefore much more likely to be installed if GCC or Clang
are installed.

Author: chrisnovakovic

test/strip/BUILD

@@ -3,6 +3,16 @@ subinclude(
     "//build_defs:cc",
 )
 
+package(
+    cc = {
+        # This is slightly contrived, but Mach-O executables always contain at least one symbol, even when stripped.
+        # Emitting debug symbols ensures that Mach-O executables contain superfluous symbols that can later be stripped,
+        # thus providing a clear distinction between stripped and unstripped executables for our tests.
+        "default_opt_cflags": CONFIG.CC.DEFAULT_OPT_CFLAGS + ["-g"],
+        "default_opt_cppflags": CONFIG.CC.DEFAULT_OPT_CPPFLAGS + ["-g"],
+    },
+)
+
 binary_linker_flags = [
     "-L" + package_name(),
     "-rpath '%s'" % ("@executable_path" if CONFIG.OS == "darwin" else "$ORIGIN"),
@@ -21,7 +31,7 @@ for strip in [True, False]:
         linker_flags = [f"-install_name @rpath/libc_so_{stripped}.so"] if CONFIG.OS == "darwin" else [],
         strip = strip,
     )
-    data[f"c_binary_{stripped}"] = c_binary(
+    data[f"c_{stripped}"] = c_binary(
         name = f"c_binary_{stripped}",
         srcs = ["binary.c"],
         hdrs = ["so.h"],
@@ -37,21 +47,35 @@ for strip in [True, False]:
         linker_flags = [f"-install_name @rpath/libcc_so_{stripped}.so"] if CONFIG.OS == "darwin" else [],
         strip = strip,
     )
-    data[f"cc_binary_{stripped}"] = cc_binary(
+    data[f"cc_{stripped}"] = cc_binary(
         name = f"cc_binary_{stripped}",
         srcs = ["binary.cpp"],
         linker_flags = binary_linker_flags + [f"-lcc_so_{stripped}"],
         strip = strip,
         deps = [f":cc_so_{stripped}"],
     )
 
+# Ensure the executables still function as expected after being stripped.
+test_cmd = ["for i in $DATA_C_STRIPPED $DATA_CC_STRIPPED $DATA_C_UNSTRIPPED $DATA_CC_UNSTRIPPED; do test $($i) = 42; done"]
+
+if CONFIG.TARGET_OS == "darwin":
+    test_cmd += [
+        # `nm -a` should show that the unstripped executables contain debug symbols ("-")...
+        "for i in $DATA_C_SO_UNSTRIPPED $DATA_C_UNSTRIPPED $DATA_CC_UNSTRIPPED; do nm -a $i | grep -qF ' - '; done",
+        # ...but that the stripped executables don't.
+        "for i in $DATA_C_SO_STRIPPED $DATA_C_STRIPPED $DATA_CC_STRIPPED; do ! nm -a $i | grep -qF ' - '; done",
+    ]
+else:
+    test_cmd += [
+        # `nm -a` should show that the unstripped executables contain at least one symbol...
+        "for i in $DATA_C_SO_UNSTRIPPED $DATA_C_UNSTRIPPED $DATA_CC_UNSTRIPPED; do ! nm -a $i 2>&1 | grep -qF 'no symbols'; done",
+        # ...but that the stripped executables contain none.
+        "for i in $DATA_C_SO_STRIPPED $DATA_C_STRIPPED $DATA_CC_STRIPPED; do nm -a $i 2>&1 | grep -qF 'no symbols'; done",
+    ]
+
 gentest(
     name = "strip_test",
-    test_cmd = [
-        "for i in $DATA_C_BINARY_STRIPPED $DATA_CC_BINARY_STRIPPED $DATA_C_BINARY_UNSTRIPPED $DATA_CC_BINARY_UNSTRIPPED; do test $($i) = 42; done",
-        "for i in $DATA_C_SO_UNSTRIPPED $DATA_C_BINARY_UNSTRIPPED $DATA_CC_BINARY_UNSTRIPPED; do file $i | grep -q 'not stripped'; done",
-        "for i in $DATA_C_SO_STRIPPED $DATA_C_BINARY_STRIPPED $DATA_CC_BINARY_STRIPPED; do file $i | grep -q ', stripped'; done",
-    ],
+    test_cmd = test_cmd,
     data = data,
     exit_on_error = True,
     no_test_output = True,