gyp-to-cmake: ldflags and cflags produce broken builds for valid binding.gyp input #481

ldflags support landed in #476, and it shares its path with cflags. Both fields produce broken builds for valid binding.gyp input, and cflags has every problem below except where noted.

Line references are to transformer.ts at ff237c0. The flags go through .flatMap(mapExpansion).map(escapeSpaces) (lines 122-123) and are then joined unquoted into target_compile_options / target_link_options (lines 225-233).

Reproduced by generating a CMakeLists from bindingGypToCmakeLists and building it with CMake 4.4.3 and Ninja on macOS arm64. The ldflags Android result used NDK 27.1.

Problems

1. Flags are emitted on platforms where gyp ignores them

On mac, gyp's make.py takes both flag sets from xcode_settings (GetCflags at line 1416, GetLdflags at line 1717). It only reads the target-level cflags and ldflags on other platforms. We emit them everywhere, so flags written for Linux reach Apple builds.

2. CMake de-duplicates options, which corrupts multi-token flags

3. escapeSpaces turns a multi-word flag into one argument

gyp's QuoteIfNecessary only quotes flags containing ", so a flag with spaces is split by the shell. We keep it as one argument.

The existing tests assert this escaped output as correct, including -DNAME=value\ with\ space for cflags.

4. Flags aren't quoted as CMake arguments

-DGREETING="hi" in cflags builds correctly.

5. gyp's $$ escape isn't unescaped

-Wl,-rpath,'$$ORIGIN' builds, but the rpath is literally '$$ORIGIN'. There's no build error, so it only shows up at runtime. This is specific to ldflags in practice.

6. gyp expansions inside a string aren't handled

isCmdExpansion (line 22) only checks the start of the value, and <(var) isn't handled at all. Both -I<!(pwd)/inc and -I<(module_root_dir)/inc pass straight through and fail with no such file or directory: '('. The same applies to -L in ldflags.

Suggested fix

• Wrap the emitted cflags and ldflags lines in if(NOT APPLE) to match gyp. This has not been tested. Apple builds then get none of these flags until xcode_settings is read.

• Emit all flags for a target as one quoted SHELL: argument, which fixes 2 and 3 and most of 4. This form built correctly on macOS for repeated -include, -framework and -Xlinker groups, for # and (), and for ; when escaped as \;:

  target_compile_options(foo PRIVATE "SHELL:-include a.h -include b.h")
  target_link_options(foo PRIVATE "SHELL:-framework CoreFoundation -framework Foundation")

  Those cases were hand-written and shell-quoted, so the generator still needs an escaping function that handles shell and CMake quoting. It also needs a decision for a flag that really is one argument containing spaces, since word-splitting matches gyp but changes the current -DNAME=value with space behaviour.

• Add tests that run cmake configure on the generated CMakeLists and assert on the flags CMake resolves, in place of comparing strings. No build or addon compile is needed: CMake applies de-duplication and argument parsing at configure time. Generating the example from problem 2 and only configuring gives these link fragments from the File API:

  ["-framework", "CoreFoundation", "Foundation"]

  • Read the result through cmake-file-api (compileCommandFragments and link.commandFragments), added as a dev dependency. compile_commands.json also shows compile flags, but not link flags.
  • This should catch problems 2 to 6 by asserting on the resolved flags and on configure failures. Problem 1 needs an assertion per host, so that the flags are absent on macos-latest and present on ubuntu-latest.
  • project() still detects a compiler during configure, and unit-tests runs on Ubuntu, Windows and macOS, so check that CMake is available on all three. Assertions shouldn't depend on how each toolchain groups fragments.

Not covered

• Not read at all: conditions (Improve gyp-to-cmake to handle "conditions" #98), xcode_settings (OTHER_CFLAGS, OTHER_LDFLAGS), cflags_cc and libraries. Issues Improve gyp-to-cmake to handle "cflags" #99 and Improve gyp-to-cmake to handle "ldflags" #100 can't really close until those are handled.
• sources, include_dirs and defines also use escapeSpaces and unquoted arguments. They weren't tested.
• Not tested: real iOS SDK builds, Windows, the Makefile generator, or a side-by-side build with node-gyp.