11 files changed, 71 insertions, 12 deletions
diff --git a/src/nvim/eval/funcs.c b/src/nvim/eval/funcs.c
index c5fa0f12cc..b56034b92d 100644
--- a/src/nvim/eval/funcs.c
+++ b/src/nvim/eval/funcs.c
@@ -95,7 +95,6 @@ PRAGMA_DIAG_POP
 
 
 static char *e_listarg = N_("E686: Argument of %s must be a List");
-static char *e_stringreq = N_("E928: String required");
 static char *e_invalwindow = N_("E957: Invalid window number");
 
 /// Dummy va_list for passing to vim_snprintf
@@ -1877,10 +1876,12 @@ static void f_eventhandler(typval_T *argvars, typval_T *rettv, FunPtr fptr)
  */
 static void f_executable(typval_T *argvars, typval_T *rettv, FunPtr fptr)
 {
-  const char *name = tv_get_string(&argvars[0]);
+  if (tv_check_for_string(&argvars[0]) == FAIL) {
+    return;
+  }
 
   // Check in $PATH and also check directly if there is a directory name
-  rettv->vval.v_number = os_can_exe(name, NULL, true);
+  rettv->vval.v_number = os_can_exe(tv_get_string(&argvars[0]), NULL, true);
 }
 
 typedef struct {
@@ -1984,10 +1985,13 @@ static void f_execute(typval_T *argvars, typval_T *rettv, FunPtr fptr)
 /// "exepath()" function
 static void f_exepath(typval_T *argvars, typval_T *rettv, FunPtr fptr)
 {
-  const char *arg = tv_get_string(&argvars[0]);
+  if (tv_check_for_string(&argvars[0]) == FAIL) {
+    return;
+  }
+
   char *path = NULL;
 
-  (void)os_can_exe(arg, &path, true);
+  (void)os_can_exe(tv_get_string(&argvars[0]), &path, true);
 
   rettv->v_type = VAR_STRING;
   rettv->vval.v_string = (char_u *)path;
diff --git a/src/nvim/eval/typval.c b/src/nvim/eval/typval.c
index b62820fecc..02d32a4f86 100644
--- a/src/nvim/eval/typval.c
+++ b/src/nvim/eval/typval.c
@@ -2953,6 +2953,19 @@ float_T tv_get_float(const typval_T *const tv)
   return 0;
 }
 
+// Give an error and return FAIL unless "tv" is a non-empty string.
+int tv_check_for_string(const typval_T *const tv)
+  FUNC_ATTR_NONNULL_ALL FUNC_ATTR_WARN_UNUSED_RESULT FUNC_ATTR_PURE
+{
+  if (tv->v_type != VAR_STRING
+      || tv->vval.v_string == NULL
+      || *tv->vval.v_string == NUL) {
+    EMSG(_(e_stringreq));
+    return FAIL;
+  }
+  return OK;
+}
+
 /// Get the string value of a "stringish" VimL object.
 ///
 /// @param[in]  tv  Object to get value of.
diff --git a/src/nvim/globals.h b/src/nvim/globals.h
index e0853e900f..c53c1546a4 100644
--- a/src/nvim/globals.h
+++ b/src/nvim/globals.h
@@ -935,6 +935,7 @@ EXTERN char_u e_readonly[] INIT(= N_(
     "E45: 'readonly' option is set (add ! to override)"));
 EXTERN char_u e_readonlyvar[] INIT(= N_(
     "E46: Cannot change read-only variable \"%.*s\""));
+EXTERN char_u e_stringreq[] INIT(= N_("E928: String required"));
 EXTERN char_u e_dictreq[] INIT(= N_("E715: Dictionary required"));
 EXTERN char_u e_toomanyarg[] INIT(= N_(
     "E118: Too many arguments for function: %s"));
diff --git a/test/functional/eval/executable_spec.lua b/test/functional/eval/executable_spec.lua
index a1cf056907..28aefb72e5 100644
--- a/test/functional/eval/executable_spec.lua
+++ b/test/functional/eval/executable_spec.lua
@@ -2,6 +2,7 @@ local helpers = require('test.functional.helpers')(after_each)
 local eq, clear, call, iswin, write_file, command =
   helpers.eq, helpers.clear, helpers.call, helpers.iswin, helpers.write_file,
   helpers.command
+local exc_exec = helpers.exc_exec
 local eval = helpers.eval
 
 describe('executable()', function()
@@ -10,6 +11,20 @@ describe('executable()', function()
   it('returns 1 for commands in $PATH', function()
     local exe = iswin() and 'ping' or 'ls'
     eq(1, call('executable', exe))
+    command('let $PATH = fnamemodify("./test/functional/fixtures/bin", ":p")')
+    eq(1, call('executable', 'null'))
+    eq(1, call('executable', 'true'))
+    eq(1, call('executable', 'false'))
+  end)
+
+  it('fails for invalid values', function()
+    for _, input in ipairs({'""', 'v:null', 'v:true', 'v:false', '{}', '[]'}) do
+      eq('Vim(call):E928: String required', exc_exec('call executable('..input..')'))
+    end
+    command('let $PATH = fnamemodify("./test/functional/fixtures/bin", ":p")')
+    for _, input in ipairs({'v:null', 'v:true', 'v:false'}) do
+      eq('Vim(call):E928: String required', exc_exec('call executable('..input..')'))
+    end
   end)
 
   it('returns 0 for non-existent files', function()
diff --git a/test/functional/eval/exepath_spec.lua b/test/functional/eval/exepath_spec.lua
index 10a11aeacc..08d2c59af8 100644
--- a/test/functional/eval/exepath_spec.lua
+++ b/test/functional/eval/exepath_spec.lua
@@ -1,14 +1,40 @@
 local helpers = require('test.functional.helpers')(after_each)
 local eq, clear, call, iswin =
   helpers.eq, helpers.clear, helpers.call, helpers.iswin
+local command = helpers.command
+local exc_exec = helpers.exc_exec
+local matches = helpers.matches
 
-describe('exepath() (Windows)', function()
-  if not iswin() then return end  -- N/A for Unix.
+describe('exepath()', function()
+  before_each(clear)
 
-  it('append extension if omitted', function()
-    local filename = 'cmd'
-    local pathext = '.exe'
-    clear({env={PATHEXT=pathext}})
-    eq(call('exepath', filename..pathext), call('exepath', filename))
+  it('returns 1 for commands in $PATH', function()
+    local exe = iswin() and 'ping' or 'ls'
+    local ext_pat = iswin() and '%.EXE$' or '$'
+    matches(exe .. ext_pat, call('exepath', exe))
+    command('let $PATH = fnamemodify("./test/functional/fixtures/bin", ":p")')
+    ext_pat = iswin() and '%.CMD$' or '$'
+    matches('null' .. ext_pat, call('exepath', 'null'))
+    matches('true' .. ext_pat, call('exepath', 'true'))
+    matches('false' .. ext_pat, call('exepath', 'false'))
   end)
+
+  it('fails for invalid values', function()
+    for _, input in ipairs({'""', 'v:null', 'v:true', 'v:false', '{}', '[]'}) do
+      eq('Vim(call):E928: String required', exc_exec('call exepath('..input..')'))
+    end
+    command('let $PATH = fnamemodify("./test/functional/fixtures/bin", ":p")')
+    for _, input in ipairs({'v:null', 'v:true', 'v:false'}) do
+      eq('Vim(call):E928: String required', exc_exec('call exepath('..input..')'))
+    end
+  end)
+
+  if iswin() then
+    it('append extension if omitted', function()
+      local filename = 'cmd'
+      local pathext = '.exe'
+      clear({env={PATHEXT=pathext}})
+      eq(call('exepath', filename..pathext), call('exepath', filename))
+    end)
+  end
 end)
diff --git a/test/functional/fixtures/bin/false b/test/functional/fixtures/bin/false
new file mode 100755
index 0000000000..e69de29bb2
--- /dev/null
+++ b/test/functional/fixtures/bin/false
diff --git a/test/functional/fixtures/bin/false.cmd b/test/functional/fixtures/bin/false.cmd
new file mode 100755
index 0000000000..e69de29bb2
--- /dev/null
+++ b/test/functional/fixtures/bin/false.cmd
diff --git a/test/functional/fixtures/bin/null b/test/functional/fixtures/bin/null
new file mode 100755
index 0000000000..e69de29bb2
--- /dev/null
+++ b/test/functional/fixtures/bin/null
diff --git a/test/functional/fixtures/bin/null.cmd b/test/functional/fixtures/bin/null.cmd
new file mode 100755
index 0000000000..e69de29bb2
--- /dev/null
+++ b/test/functional/fixtures/bin/null.cmd
diff --git a/test/functional/fixtures/bin/true b/test/functional/fixtures/bin/true
new file mode 100755
index 0000000000..e69de29bb2
--- /dev/null
+++ b/test/functional/fixtures/bin/true
diff --git a/test/functional/fixtures/bin/true.cmd b/test/functional/fixtures/bin/true.cmd
new file mode 100755
index 0000000000..e69de29bb2
--- /dev/null
+++ b/test/functional/fixtures/bin/true.cmd