build(windows): restore tee.exe on Windows #36363

Problem:
Neovim no longer ships with a tee binary on Windows, which breaks
functionality for the :grep and :make commands.

    nvim --clean
    :grep foo or :make
    "tee is not recognized as an internal or external command"

Solution:
Include a simple, no-dependency tee.c source file in the src/ directory.
Update CMakeLists.txt to build a tee executable alongside neovim during
the build process, and ensure the tee.exe program appears alongside the
neovim executable in the bin/ directory so that it is accessible for
:grep and :make.

tee.c was obtained from the vim codebase:
https://github.com/vim/vim/blob/master/src/tee/tee.c

And we modified it to fix performance issues.

Testing:

    nvim --clean
    :grep foo or :make, after setting a file to the makeprg option.
    Verify that :grep results and error output from a compiler appear in the message pane.

ref https://github.com/neovim/neovim/issues/32431
fix https://github.com/neovim/neovim/issues/32504

Other tee options:
- [tee-win32](https://github.com/dEajL3kA/tee-win32): MIT. However,
  I couldn't get it to build on my machine even after updating its
  makefile to call my install of MSVC. It's also super optimized and
  uses some processor intrinsics for multithreading.
- [gnu coreutils tee](https://gnuwin32.sourceforge.net/packages/coreutils.htm):
  (Windows coreutils contains a tee.c. Last updated 2005. Did not build
  immediately on my machine; we'd have to determine which definitions
  from elsewhere in coreutils tee.c needs and incorporate them somehow.
- [WinTee](https://github.com/mpderbec/WinTee): Has no license. Last
  updated 11 years ago. Relies on Visual Studio to build.

Co-authored-by: Justin M. Keyes <justinkz@gmail.com>

CMakeLists.txt

@@ -312,6 +312,7 @@ add_custom_target(nvim ALL)
 add_dependencies(nvim nvim_bin nvim_runtime_deps nvim_runtime)
 
 add_subdirectory(src/nvim)
+add_subdirectory(src/tee)
 add_subdirectory(cmake.config)
 add_subdirectory(runtime)
 add_subdirectory(test)

src/nvim/CMakeLists.txt

@@ -423,6 +423,7 @@ list(SORT NVIM_SOURCES)
 list(SORT NVIM_HEADERS)
 
 list(APPEND UNCRUSTIFY_NVIM_SOURCES ${NVIM_SOURCES} ${NVIM_HEADERS})
+list(APPEND UNCRUSTIFY_NVIM_SOURCES ${PROJECT_SOURCE_DIR}/src/tee/tee.c)
 
 foreach(sfile ${NVIM_SOURCES})
   get_filename_component(f ${sfile} NAME)
@@ -454,6 +455,7 @@ foreach(hfile ${NVIM_HEADERS})
 endforeach()
 
 list(APPEND LINT_NVIM_SOURCES ${NVIM_SOURCES} ${NVIM_HEADERS})
+list(APPEND LINT_NVIM_SOURCES ${PROJECT_SOURCE_DIR}/src/tee/tee.c)
 
 # Log level (NVIM_LOG_DEBUG in log.h)
 if(CI_BUILD)

src/tee/CMakeLists.txt

@@ -0,0 +1,10 @@
+add_executable(tee tee.c)
+
+# tee has to be in the same directory as the nvim executable
+set_target_properties(tee PROPERTIES
+  RUNTIME_OUTPUT_DIRECTORY "${CMAKE_BINARY_DIR}/bin"
+)
+
+install(TARGETS tee
+  RUNTIME DESTINATION "${CMAKE_INSTALL_BINDIR}"
+)

src/tee/tee.c

@@ -0,0 +1,130 @@
+// tee.c - pipe fitting
+//
+//      Copyright (c) 1996, Paul Slootman
+//
+//      Author: Paul Slootman
+//                      (paul@wurtel.hobby.nl, paul@murphy.nl, paulS@toecompst.nl)
+//      Modifications for MSVC: Yasuhiro Matsumoto
+//      Modifications for Neovim: https://github.com/neovim/neovim/pull/36363
+//
+//      This source code is released into the public domain. It is provided on an
+//      as-is basis and no responsibility is accepted for its failure to perform
+//      as expected. It is worth at least as much as you paid for it!
+//
+//
+// tee reads stdin, and writes what it reads to each of the specified
+// files. The primary reason of existence for this version is a quick
+// and dirty implementation to distribute with Vim, to make one of the
+// most useful features of Vim possible on OS/2: quickfix.
+//
+// Of course, not using tee but instead redirecting make's output directly
+// into a temp file and then processing that is possible, but if we have a
+// system capable of correctly piping (unlike DOS, for example), why not
+// use it as well as possible? This tee should also work on other systems,
+// but it's not been tested there, only on OS/2.
+//
+// tee is also available in the GNU shellutils package, which is available
+// precompiled for OS/2. That one probably works better.
+
+#ifndef _MSC_VER
+# include <unistd.h>
+#endif
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#ifdef _WIN32
+# define sysconf(x) - 1
+#endif
+
+void usage(void)
+{
+  fprintf(stderr,
+          "Neotee: a web-scale fork of tee\n"
+          "Usage:\n"
+          "\ttee [-a] file ... file_n\n"
+          "\n"
+          "\t-a\tappend to files instead of truncating\n"
+          "\n"
+          "Tee reads its input, and writes to each of the specified files,\n"
+          "as well as to the standard output.\n"
+          "\n"
+          "Shipped with Nvim 0.12+ for use with :make, :grep, :!, etc.\n");
+}
+
+int main(int argc, char *argv[])
+{
+  int append = 0;
+  size_t numfiles;
+  int maxfiles;
+  FILE **filepointers;
+  int i;
+  char buf[65536];
+  int n;
+  int optnr = 1;
+
+  for (i = 1; i < argc; i++) {
+    if (argv[i][0] != '-') {
+      break;
+    }
+    if (!strcmp(argv[i], "-a")) {
+      append++;
+    } else {
+      usage();
+      exit(2);
+    }
+    optnr++;
+  }
+
+  numfiles = argc - optnr;
+
+  if (numfiles == 0) {
+    usage();
+    exit(2);
+  }
+
+  maxfiles = sysconf(_SC_OPEN_MAX);       // or fill in 10 or so
+  if (maxfiles < 0) {
+    maxfiles = 10;
+  }
+  if (numfiles + 3 > maxfiles) {  // +3 accounts for stdin, out, err
+    fprintf(stderr, "There is a limit of max %d files.\n", maxfiles - 3);
+    exit(1);
+  }
+  filepointers = calloc(numfiles, sizeof(FILE *));  // NOLINT
+  if (filepointers == NULL) {
+    fprintf(stderr, "Error allocating memory for %ld files\n", (long)numfiles);
+    exit(1);
+  }
+  for (i = 0; i < numfiles; i++) {
+    filepointers[i] = fopen(argv[i + optnr], append ? "ab" : "wb");
+    if (filepointers[i] == NULL) {
+      fprintf(stderr, "Can't open \"%s\"\n", argv[i + optnr]);
+      exit(1);
+    }
+  }
+#ifdef _WIN32
+  setmode(fileno(stdin),  O_BINARY);
+  fflush(stdout);  // needed for _fsetmode(stdout)
+  setmode(fileno(stdout),  O_BINARY);
+  setvbuf(stdout, NULL, _IONBF, 0);  // unbuffered for immediate output
+#endif
+
+  while ((n = fread(buf, 1, sizeof(buf), stdin)) > 0) {
+    fwrite(buf, 1, n, stdout);
+    for (i = 0; i < numfiles; i++) {
+      if (filepointers[i]) {
+        fwrite(buf, 1, n, filepointers[i]);
+      }
+    }
+    fflush(stdout);
+  }
+  for (i = 0; i < numfiles; i++) {
+    if (filepointers[i]) {
+      fclose(filepointers[i]);
+    }
+  }
+
+  exit(0);
+}