4 files changed, 48 insertions, 6 deletions
diff --git a/src/nvim/os/env.c b/src/nvim/os/env.c
index 747a34d8ce..4707b0a326 100644
--- a/src/nvim/os/env.c
+++ b/src/nvim/os/env.c
@@ -831,3 +831,43 @@ char_u *get_env_name(expand_T *xp, int idx)
   return NULL;
 }
 
+/// Appends the head of `fname` to $PATH and sets it in the environment.
+///
+/// @param fname  Full path whose parent directory will be appended to $PATH.
+///
+/// @return true if `path` was appended-to
+bool os_setenv_append_path(const char *fname)
+  FUNC_ATTR_NONNULL_ALL
+{
+#ifdef WIN32
+// 8191 (plus NUL) is considered the practical maximum.
+# define MAX_ENVPATHLEN 8192
+#else
+// No prescribed maximum on unix.
+# define MAX_ENVPATHLEN INT_MAX
+#endif
+  if (!path_is_absolute_path((char_u *)fname)) {
+    EMSG2(_(e_intern2), "os_setenv_append_path()");
+    return false;
+  }
+  const char *tail = (char *)path_tail_with_sep((char_u *)fname);
+  const char *dir = (char *)vim_strnsave((char_u *)fname,
+                                         (size_t)(tail - fname));
+  const char *path = os_getenv("PATH");
+  const size_t pathlen = path ? strlen(path) : 0;
+  const size_t newlen = pathlen + strlen(dir) + 2;
+  if (newlen < MAX_ENVPATHLEN) {
+    char *temp = xmalloc(newlen);
+    if (pathlen == 0) {
+      temp[0] = NUL;
+    } else {
+      xstrlcpy(temp, path, newlen);
+      xstrlcat(temp, ENV_SEPSTR, newlen);
+    }
+    xstrlcat(temp, dir, newlen);
+    os_setenv("PATH", temp, 1);
+    xfree(temp);
+    return true;
+  }
+  return false;
+}
diff --git a/src/nvim/os/fs.c b/src/nvim/os/fs.c
index b3d838c01a..4ca67d1f1a 100644
--- a/src/nvim/os/fs.c
+++ b/src/nvim/os/fs.c
@@ -224,7 +224,7 @@ bool os_can_exe(const char_u *name, char_u **abspath, bool use_path)
   if (!use_path || path_is_absolute_path(name)
       || (name[0] == '.'
           && (name[1] == '/' || (name[1] == '.' && name[2] == '/')))) {
-#if WIN32
+#ifdef WIN32
     bool ok = is_executable(name);
 #else
     // Must have path separator, cannot execute files in the current directory.
@@ -255,7 +255,7 @@ static bool is_executable(const char_u *name)
     return false;
   }
 
-#if WIN32
+#ifdef WIN32
   // Windows does not have exec bit; just check if the file exists and is not
   // a directory.
   return (S_ISREG(mode));
@@ -281,7 +281,7 @@ static bool is_executable_in_path(const char_u *name, char_u **abspath)
 #ifdef WIN32
   // Prepend ".;" to $PATH.
   size_t pathlen = strlen(path_env);
-  char *path = memcpy(xmallocz(pathlen + 3), ".;", 2);
+  char *path = memcpy(xmallocz(pathlen + 3), "." ENV_SEPSTR, 2);
   memcpy(path + 2, path_env, pathlen);
 #else
   char *path = xstrdup(path_env);
@@ -1027,7 +1027,7 @@ shortcut_end:
 int os_translate_sys_error(int sys_errno) {
 #ifdef HAVE_UV_TRANSLATE_SYS_ERROR
   return uv_translate_sys_error(sys_errno);
-#elif WIN32
+#elif defined(WIN32)
   // TODO(equalsraf): libuv does not yet expose uv_translate_sys_error()
   // in its public API, include a version here until it can be used.
   // See https://github.com/libuv/libuv/issues/79
diff --git a/src/nvim/os/unix_defs.h b/src/nvim/os/unix_defs.h
index 690a39c3cd..c98aa88bfa 100644
--- a/src/nvim/os/unix_defs.h
+++ b/src/nvim/os/unix_defs.h
@@ -16,7 +16,8 @@
 // Special wildcards that need to be handled by the shell.
 #define SPECIAL_WILDCHAR "`'{"
 
-// Separator character for environment variables.
+// Character that separates entries in $PATH.
 #define ENV_SEPCHAR ':'
+#define ENV_SEPSTR  ":"
 
 #endif  // NVIM_OS_UNIX_DEFS_H
diff --git a/src/nvim/os/win_defs.h b/src/nvim/os/win_defs.h
index 6a29f86e79..8de896c490 100644
--- a/src/nvim/os/win_defs.h
+++ b/src/nvim/os/win_defs.h
@@ -20,8 +20,9 @@
 
 #define FNAME_ILLEGAL "\"*?><|"
 
-// Separator character for environment variables.
+// Character that separates entries in $PATH.
 #define ENV_SEPCHAR ';'
+#define ENV_SEPSTR  ";"
 
 #define USE_CRNL