patch 8.0.1832: cannot use :unlet for an environment variablev8.0.1832

Problem:    Cannot use :unlet for an environment variable.
Solution:   Make it work.  Use unsetenv() if available. (Ken Takata,
            closes #2855)

9 files changed, 63 insertions, 2 deletions

diff --git a/runtime/doc/eval.txt b/runtime/doc/eval.txt
index 050b48960a..730a5d11c4 100644
--- a/runtime/doc/eval.txt
+++ b/runtime/doc/eval.txt
@@ -9939,6 +9939,14 @@ This does NOT work: >
 			variables are automatically deleted when the function
 			ends.
 
+:unl[et] ${env-name} ...			*:unlet-environment* *:unlet-$*
+			Remove environment variable {env-name}.
+			Can mix {name} and ${env-name} in one :unlet command.
+			No error message is given for a non-existing
+			variable, also without !.
+			If the system does not support deleting an environment
+			variable, it is made emtpy.
+
 :lockv[ar][!] [depth] {name} ...			*:lockvar* *:lockv*
 			Lock the internal variable {name}.  Locking means that
 			it can no longer be changed (until it is unlocked).
diff --git a/src/auto/configure b/src/auto/configure
index e65884c80a..1628b940e3 100755
--- a/src/auto/configure
+++ b/src/auto/configure
@@ -12609,7 +12609,7 @@ for ac_func in fchdir fchown fchmod fsync getcwd getpseudotty \
 	getpgid setpgid setsid sigaltstack sigstack sigset sigsetjmp sigaction \
 	sigprocmask sigvec strcasecmp strerror strftime stricmp strncasecmp \
 	strnicmp strpbrk strtol tgetent towlower towupper iswupper \
-	usleep utime utimes mblen ftruncate
+	usleep utime utimes mblen ftruncate unsetenv
 do :
   as_ac_var=`$as_echo "ac_cv_func_$ac_func" | $as_tr_sh`
 ac_fn_c_check_func "$LINENO" "$ac_func" "$as_ac_var"
diff --git a/src/config.h.in b/src/config.h.in
index 7d6122058f..00117cf8ca 100644
--- a/src/config.h.in
+++ b/src/config.h.in
@@ -211,6 +211,7 @@
 #undef HAVE_TOWLOWER
 #undef HAVE_TOWUPPER
 #undef HAVE_ISWUPPER
+#undef HAVE_UNSETENV
 #undef HAVE_USLEEP
 #undef HAVE_UTIME
 #undef HAVE_BIND_TEXTDOMAIN_CODESET
diff --git a/src/configure.ac b/src/configure.ac
index cfc3b1be1b..107c170ecb 100644
--- a/src/configure.ac
+++ b/src/configure.ac
@@ -3709,7 +3709,7 @@ AC_CHECK_FUNCS(fchdir fchown fchmod fsync getcwd getpseudotty \
 	getpgid setpgid setsid sigaltstack sigstack sigset sigsetjmp sigaction \
 	sigprocmask sigvec strcasecmp strerror strftime stricmp strncasecmp \
 	strnicmp strpbrk strtol tgetent towlower towupper iswupper \
-	usleep utime utimes mblen ftruncate)
+	usleep utime utimes mblen ftruncate unsetenv)
 AC_FUNC_FSEEKO
 
 dnl define _LARGE_FILES, _FILE_OFFSET_BITS and _LARGEFILE_SOURCE when
diff --git a/src/eval.c b/src/eval.c
index b787474d10..2ba9e82a80 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -2758,6 +2758,20 @@ ex_unletlock(
 
     do
     {
+	if (*arg == '$')
+	{
+	    char_u    *name = ++arg;
+
+	    if (get_env_len(&arg) == 0)
+	    {
+		EMSG2(_(e_invarg2), name - 1);
+		return;
+	    }
+	    vim_unsetenv(name);
+	    arg = skipwhite(arg);
+	    continue;
+	}
+
 	/* Parse the name and find the end. */
 	name_end = get_lval(arg, NULL, &lv, TRUE, eap->skip || error, 0,
 							     FNE_CHECK_START);
diff --git a/src/misc1.c b/src/misc1.c
index 6c77f4b0d2..1ab55f0862 100644
--- a/src/misc1.c
+++ b/src/misc1.c
@@ -4479,6 +4479,17 @@ remove_tail(char_u *p, char_u *pend, char_u *name)
     return pend;
 }
 
+    void
+vim_unsetenv(char_u *var)
+{
+#ifdef HAVE_UNSETENV
+    unsetenv((char *)var);
+#else
+    mch_setenv((char *)var, "", 0);
+#endif
+}
+
+
 /*
  * Our portable version of setenv.
  */
diff --git a/src/proto/misc1.pro b/src/proto/misc1.pro
index 4e299e5f9a..4b613e6b1a 100644
--- a/src/proto/misc1.pro
+++ b/src/proto/misc1.pro
@@ -60,6 +60,7 @@ void expand_env(char_u *src, char_u *dst, int dstlen);
 void expand_env_esc(char_u *srcp, char_u *dst, int dstlen, int esc, int one, char_u *startstr);
 char_u *vim_getenv(char_u *name, int *mustfree);
 void vim_setenv(char_u *name, char_u *val);
+void vim_unsetenv(char_u *name);
 char_u *get_env_name(expand_T *xp, int idx);
 char_u *get_users(expand_T *xp, int idx);
 int match_user(char_u *name);
diff --git a/src/testdir/test_unlet.vim b/src/testdir/test_unlet.vim
index c20b0beb7f..6636f6d66b 100644
--- a/src/testdir/test_unlet.vim
+++ b/src/testdir/test_unlet.vim
@@ -21,3 +21,27 @@ endfunc
 func Test_unlet_fails()
   call assert_fails('unlet v:["count"]', 'E46:')
 endfunc
+
+func Test_unlet_env()
+  let envcmd = has('win32') ? 'set' : 'env'
+
+  let $FOOBAR = 'test'
+  let found = 0
+  for kv in split(system(envcmd), "\r*\n")
+    if kv == 'FOOBAR=test'
+      let found = 1
+    endif
+  endfor
+  call assert_equal(1, found)
+
+  unlet $FOOBAR
+  let found = 0
+  for kv in split(system(envcmd), "\r*\n")
+    if kv == 'FOOBAR=test'
+      let found = 1
+    endif
+  endfor
+  call assert_equal(0, found)
+
+  unlet $MUST_NOT_BE_AN_ERROR
+endfunc
diff --git a/src/version.c b/src/version.c
index ac41ff30fb..080ba72e38 100644
--- a/src/version.c
+++ b/src/version.c
@@ -762,6 +762,8 @@ static char *(features[]) =
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1832,
+/**/
     1831,
 /**/
     1830,