src: do not call path.back() when it is empty

[zcbenz]

Fix a crash when running tests with the GN build of node:

../out/Debug/node test/parallel/test-cli-permission-multiple-allow.js

Crash trace:

$ lldb ../out/Debug/node
(lldb) target create "../out/Debug/node"
Current executable set to '/Users/zcbenz/codes/node_with_gn/out/Debug/node' (arm64).
(lldb) run --experimental-permission --allow-fs-write /Users/zcbenz/codes/node_with_gn/node/tmp --allow-fs-write /Users/zcbenz/codes/node_with_gn/node/other-path -e 'console.log(process.permission.has("fs.write"));'
Process 28010 launched: '/Users/zcbenz/codes/node_with_gn/out/Debug/node' (arm64)
../../third_party/gn/third_party/libc++/src/include/string:1364: assertion !empty() failed: string::back(): string is empty
Process 28010 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = signal SIGABRT
frame #0: 0x000000018b88e0dc libsystem_kernel.dylib`__pthread_kill + 8
libsystem_kernel.dylib`:
-> 0x18b88e0dc <+8>: b.lo 0x18b88e0fc ; <+40>
0x18b88e0e0 <+12>: pacibsp 0x18b88e0e4 <+16>: stp x29, x30, [sp, #-0x10]!
0x18b88e0e8 <+20>: mov x29, sp
Target 0: (node) stopped.
(lldb) bt
* thread #1, queue = 'com.apple.main-thread', stop reason = signal SIGABRT
* frame #0: 0x000000018b88e0dc libsystem_kernel.dylib`__pthread_kill + 8
frame #1: 0x000000018b8c5cc0 libsystem_pthread.dylib`pthread_kill + 288
frame #2: 0x000000018b7d1a40 libsystem_c.dylib`abort + 180
frame #3: 0x0000000103ddb5bc node`std::__Cr::__libcpp_verbose_abort(format="%s") at verbose_abort.cpp:74:3
frame #4: 0x00000001004f0ef8 node`std::__Cr::basic_string<char, std::__Cr::char_traits<char>, std::__Cr::allocator<char>>::back(this="") const at string:1364:5
frame #5: 0x000000010070bfd4 node`node::PathResolve(env=0x0000000134898a00, paths=size=1) at path.cc:269:55
frame #6: 0x000000010070cd0c node`(anonymous namespace)::is_tree_granted(env=0x0000000134898a00, granted_tree=0x00006000006b44e8, param="") at fs_permission.cc:58:32
frame #7: 0x000000010070cc2c node`node::permission::FSPermission::is_granted(this=0x00006000006b44d8, env=0x0000000134898a00, perm=kFileSystemWrite, param="") const at fs_permission.cc:168:15
frame #8: 0x00000001000e0d10 node`node::permission::Permission::is_scope_granted(this=0x0000000134898f78, env=0x0000000134898a00, permission=kFileSystemWrite, res="") const at permission.h:83:33
frame #9: 0x0000000100714878 node`node::permission::(anonymous namespace)::Has(v8::FunctionCallbackInfo<v8::Value> const&) [inlined] node::permission::Permission::is_granted(this=0x0000000134898f78, env=0x0000000134898a00, permission=kFileSystemWrite, res="") const at permission.h:56:12
frame #10: 0x0000000100714844 node`node::permission::(anonymous namespace)::Has(args=0x000000016fdfa658) at permission.cc:58:55

Crash was introduced by #54224.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.23%. Comparing base (4f88179) to head (9edbef8).
Report is 123 commits behind head on main.

Additional details and impacted files

@@ Coverage Diff @@## main #55072 +/- ##
==========================================
- Coverage 88.23% 88.23% -0.01% 
==========================================
Files 652 652 Lines 183920 183920 Branches 35863 35868 +5 ==========================================
- Hits 162286 162280 -6 + Misses 14913 14912 -1 - Partials 6721 6728 +7 

Files with missing lines	Coverage Δ
src/path.cc	67.39% <100.00%> (ø)

... and 21 files with indirect coverage changes

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/62680/

[targos]

Could we add a regression test?

[zcbenz]

Could we add a regression test?

The crash only happens when building with a newer version of libc++ that asserts on calling back() on an empty string, for the official build I don't see a way to test this.

[nodejs-github-bot]

Landed in 773e7c6