[ulib][c] Begin soft migration of files to /strings

llvm/llvm-project#118899 began the process of
moving files from /string to /strings. This CL likewise introduces the
/strings directory to Fuchsia's build machinery and performs the first
step in migrating the needed targets to /strings.

Since it's expected that we'll need to repeat this process as more
targets are migrated to strings/ in the future, this CL introduces a
(temporary) exec_script that can be used as an example for future CL
migrations, to make it easier and faster to detect file changes (but
note the exec_script gets cleaned up after each migration, as is done
in Ia8de544a2695125f888544071b08f37906fe381d).

Bug: 383347626
Change-Id: I81b66e1f5ec01f240ed8cf1f601764eb89ed6cff
Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1172248
Reviewed-by: David Fang <[email protected]>
Commit-Queue: Auto-Submit <[email protected]>
Fuchsia-Auto-Submit: Caslyn Tonelli <[email protected]>

Author: Caslyn

.gn

@@ -47,6 +47,9 @@ exec_script_whitelist = [
   "//build/toolchain/default_concurrent_jobs.gni",
   "//build/toolchain/zircon/zircon_toolchain.gni",
   "//zircon/kernel/arch/x86/phys/BUILD.gn",
+
+  # TODO(https://fxbug.dev/383347626): This is temporary to perform soft-migration.
+  "//zircon/system/ulib/c/string/file_exists_check.gni",
 ]
 
 check_system_includes = true

zircon/system/ulib/c/BUILD.gn

@@ -11,6 +11,7 @@ import("//build/toolchain/ifs_shared_library.gni")
 import("//build/zircon/migrated_targets.gni")
 import("libc.gni")
 import("libc_toolchain.gni")
+import("string/file_exists_check.gni")
 
 assert(libc == get_path_info(get_path_info(".", "abspath"), "dir"),
        get_path_info(get_path_info(".", "abspath"), "dir"))
@@ -34,8 +35,14 @@ libc_testonly_components = []
 
 if (use_llvm_libc_string_functions) {
   libc_components += [ "string" ]
+  if (!file_exists_in_string) {
+    libc_components += [ "strings" ]
+  }
 } else {
   libc_testonly_components += [ "string" ]
+  if (!file_exists_in_string) {
+    libc_testonly_components += [ "strings" ]
+  }
 }
 
 group("components") {

zircon/system/ulib/c/string/BUILD.gn

@@ -3,14 +3,20 @@
 # found in the LICENSE file.
 
 import("../libc.gni")
+import("file_exists_check.gni")
 
 llvm_libc_group("string") {
   deps = [
-    ":compat",
     ":mem",
     ":str",
   ]
 
+  # TODO(https://fxbug.dev/383347626): these files are moved from string/ to
+  # strings/ after llvm rev 431ea2d076f8a5ca35b2c293dd5d62f5ce083f45
+  if (file_exists_in_string) {
+    deps += [ ":compat" ]
+  }
+
   # TODO(https://fxbug.dev/42053650): not yet using the llvm-libc versions of these
   non_test_deps = [
     "//zircon/third_party/ulib/musl/src/string:strerror_r",
@@ -176,12 +182,10 @@ llvm_libc_source_set("minimal-str") {
 
 llvm_libc_source_set("str") {
   functions = [
-    "strcasecmp",
     "strcasestr",
     "strcoll",
     "strxfrm",
     "strdup",
-    "strncasecmp",
     "strndup",
     "strtok",
     "strtok_r",
@@ -193,6 +197,15 @@ llvm_libc_source_set("str") {
   ]
 
   deps = [ ":minimal-str" ]
+
+  # TODO(https://fxbug.dev/383347626): these files are moved from string/ to
+  # strings/ after llvm rev 431ea2d076f8a5ca35b2c293dd5d62f5ce083f45
+  if (file_exists_in_string) {
+    functions += [
+      "strncasecmp",
+      "strcasecmp",
+    ]
+  }
 }
 
 llvm_libc_source_set("strsignalerror") {
@@ -239,32 +252,36 @@ llvm_libc_source_set("StringUtil") {
   ]
 }
 
-llvm_libc_source_set("compat") {
-  functions = [
-    "bcmp",
-    "bcopy",
-    "bzero",
-    "index",
-    "rindex",
-  ]
-
-  deps = [ ":swab" ]
-}
+if (file_exists_in_string) {
+  llvm_libc_source_set("compat") {
+    functions = [
+      "bcmp",
+      "bcopy",
+      "bzero",
+      "index",
+      "rindex",
+    ]
+
+    deps = [ ":swab" ]
+  }
 
-# This lives in libc/src/unistd upstream because it's declared in <unistd.h>
-# but it's really a compat string function, so we include it here instead.
-llvm_libc_source_set("swab") {
-  dir = "unistd"
-  functions = [ "swab" ]
+  # This lives in libc/src/unistd upstream because it's declared in <unistd.h>
+  # but it's really a compat string function, so we include it here instead.
+  llvm_libc_source_set("swab") {
+    dir = "unistd"
+    functions = [ "swab" ]
+  }
 }
 
 # This provides an archive library of the universally safe string functions.
 # When built outside the "user.libc" environment, these always define only
 # hidden-visibility symbols and should be safe in any build environment.
 static_library("hermetic") {
   complete_static_lib = true
-  deps = [
-    ":compat",
-    ":minimal-str",
-  ]
+  deps = [ ":minimal-str" ]
+  if (file_exists_in_string) {
+    deps += [ ":compat" ]
+  } else {
+    deps += [ "//zircon/system/ulib/c/strings:compat" ]
+  }
 }

zircon/system/ulib/c/string/file_exists.sh

@@ -0,0 +1,13 @@
+#! /bin/sh
+# Copyright 2024 The Fuchsia Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+# This script prints "true" if the file exists, else "false".
+
+file="$1"
+if test -f "$file"; then
+  echo "true"
+else
+  echo "false"
+fi

zircon/system/ulib/c/string/file_exists_check.gni

@@ -0,0 +1,10 @@
+# Copyright 2024 The Fuchsia Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+# TODO(https://fxbug.dev/383347626): soft-migration of source file location
+# changes. This exec_script is temporary, used only during this migration.
+file = "//third_party/llvm-libc/src/src/string/bcmp.cpp"
+file_exists_in_string = exec_script("file_exists.sh",
+                                    [ rebase_path("$file", root_build_dir) ],
+                                    "value")

zircon/system/ulib/c/strings/BUILD.gn

@@ -0,0 +1,41 @@
+# Copyright 2024 The Fuchsia Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+import("../libc.gni")
+import("../string/file_exists_check.gni")
+
+if (!file_exists_in_string) {
+  llvm_libc_group("strings") {
+    deps = [
+      ":compat",
+      ":str",
+    ]
+  }
+
+  llvm_libc_source_set("str") {
+    functions = [
+      "strcasecmp",
+      "strncasecmp",
+    ]
+  }
+
+  llvm_libc_source_set("compat") {
+    functions = [
+      "bcmp",
+      "bcopy",
+      "bzero",
+      "index",
+      "rindex",
+    ]
+
+    deps = [ ":swab" ]
+  }
+
+  # This lives in libc/src/unistd upstream because it's declared in <unistd.h>
+  # but it's really a compat string function, so we include it here instead.
+  llvm_libc_source_set("swab") {
+    dir = "unistd"
+    functions = [ "swab" ]
+  }
+}