patch 8.2.0427: it is not possible to check for a typo in a feature name

Problem:    It is not possible to check for a typo in a feature name.
Solution:   Add an extra argument to has().

runtime/doc/eval.txt

@@ -1,4 +1,4 @@
-*eval.txt*	For Vim version 8.2.  Last change: 2020 Mar 16
+*eval.txt*	For Vim version 8.2.  Last change: 2020 Mar 22
 
 
 		  VIM REFERENCE MANUAL	  by Bram Moolenaar
@@ -2515,7 +2515,7 @@ glob({expr} [, {nosuf} [, {list} [, {alllinks}]]])
 glob2regpat({expr})		String	convert a glob pat into a search pat
 globpath({path}, {expr} [, {nosuf} [, {list} [, {alllinks}]]])
 				String	do glob({expr}) for all dirs in {path}
-has({feature})			Number	|TRUE| if feature {feature} supported
+has({feature} [, {check}])	Number	|TRUE| if feature {feature} supported
 has_key({dict}, {key})		Number	|TRUE| if {dict} has entry {key}
 haslocaldir([{winnr} [, {tabnr}]])
 				Number	|TRUE| if the window executed |:lcd|
@@ -4358,8 +4358,8 @@ feedkeys({string} [, {mode}])				*feedkeys()*
 		'L'	Lowlevel input.  Only works for Unix or when using the
 			GUI. Keys are used as if they were coming from the
 			terminal.  Other flags are not used.  *E980*
-			When a CTRL-C interrupts it sets the internal
+			When a CTRL-C interrupts and 't' is included it sets
-			"got_int" flag.
+			the internal "got_int" flag.
 		'i'	Insert the string instead of appending (see above).
 		'x'	Execute commands until typeahead is empty.  This is
 			similar to using ":normal!".  You can call feedkeys()
@@ -5828,10 +5828,20 @@ globpath({path}, {expr} [, {nosuf} [, {list} [, {alllinks}]]])
 			GetExpr()->globpath(&rtp)
 <
 							*has()*
-has({feature})	The result is a Number, which is 1 if the feature {feature} is
+has({feature} [, {check}])
-		supported, zero otherwise.  The {feature} argument is a
+		When {check} is omitted or is zero: The result is a Number,
-		string.  See |feature-list| below.
+		which is 1 if the feature {feature} is supported, zero
+		otherwise.  The {feature} argument is a string, case is
+		ignored.  See |feature-list| below.
+
+		When {check} is present and not zero: The result is a Number,
+		which is 1 if the feature {feature} could ever be supported,
+		zero otherwise.  This is useful to check for a typo in
+		{feature}.  Keep in mind that an older Vim version will not
+		know about a feature added later.
+
 		Also see |exists()|.
+
 		Note that to skip code that has a syntax error when the
 		feature is not available, Vim may skip the rest of the line
 		and miss a following `endif`.  Therfore put the `endif` on a

src/testdir/check.vim

@@ -6,6 +6,9 @@ command -nargs=1 MissingFeature throw 'Skipped: ' .. <args> .. ' feature missing
 " Command to check for the presence of a feature.
 command -nargs=1 CheckFeature call CheckFeature(<f-args>)
 func CheckFeature(name)
+  if !has(a:name, 1)
+    throw 'Checking for non-existent feature ' .. a:name
+  endif
   if !has(a:name)
     MissingFeature a:name
   endif

src/testdir/test_functions.vim

@@ -20,6 +20,14 @@ func Test_00_bufexists()
   call assert_equal(0, bufexists('Xfoo'))
 endfunc
 
+func Test_has()
+  call assert_equal(1, has('eval'))
+  call assert_equal(1, has('eval', 1))
+
+  call assert_equal(0, has('nonexistent'))
+  call assert_equal(0, has('nonexistent', 1))
+endfunc
+
 func Test_empty()
   call assert_equal(1, empty(''))
   call assert_equal(0, empty('a'))
@@ -1586,7 +1594,7 @@ func Test_confirm()
   call assert_equal(2, a)
 
   " confirm() should return 0 when pressing CTRL-C.
-  call feedkeys("\<C-c>", 'L')
+  call feedkeys("\<C-C>", 'L')
   let a = confirm('Are you sure?', "&Yes\n&No")
   call assert_equal(0, a)
 

src/version.c

@@ -738,6 +738,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    427,
 /**/
     426,
 /**/