vim-patch:8.2.0893: assert_equalfile() does not take a third argument

Problem:    Assert_equalfile() does not take a third argument.
Solution:   Implement the third argument. (Gary Johnson)
fb517bac23

runtime/doc/eval.txt

@@ -2019,11 +2019,12 @@ argidx()			Number	current index in the argument list
 arglistid([{winnr} [, {tabnr}]]) Number	argument list id
 argv({nr} [, {winid}])		String	{nr} entry of the argument list
 argv([-1, {winid}])		List	the argument list
+asin({expr})			Float	arc sine of {expr}
 assert_beeps({cmd})		Number	assert {cmd} causes a beep
 assert_equal({exp}, {act} [, {msg}])
 				Number	assert {exp} is equal to {act}
-assert_equalfile({fname-one}, {fname-two})
+assert_equalfile({fname-one}, {fname-two} [, {msg}])
-				Number	assert file contents is equal
+				Number	assert file contents are equal
 assert_exception({error} [, {msg}])
 				Number	assert {error} is in v:exception
 assert_fails({cmd} [, {error}])	Number	assert {cmd} fails
@@ -2039,7 +2040,6 @@ assert_notmatch({pat}, {text} [, {msg}])
 				Number	assert {pat} not matches {text}
 assert_report({msg})		Number	report a test failure
 assert_true({actual} [, {msg}])	Number	assert {actual} is true
-asin({expr})			Float	arc sine of {expr}
 atan({expr})			Float	arc tangent of {expr}
 atan2({expr}, {expr})		Float   arc tangent of {expr1} / {expr2}
 browse({save}, {title}, {initdir}, {default})
@@ -2630,7 +2630,7 @@ assert_equal({expected}, {actual}, [, {msg}])
 	test.vim line 12: Expected 'foo' but got 'bar' ~
 
 							*assert_equalfile()*
-assert_equalfile({fname-one}, {fname-two})
+assert_equalfile({fname-one}, {fname-two} [, {msg}])
 		When the files {fname-one} and {fname-two} do not contain
 		exactly the same text an error message is added to |v:errors|.
 		Also see |assert-return|.

src/nvim/eval.c

@@ -5739,6 +5739,12 @@ int assert_equalfile(typval_T *argvars)
   }
   if (IObuff[0] != NUL) {
     prepare_assert_error(&ga);
+    if (argvars[2].v_type != VAR_UNKNOWN) {
+      char *const tofree = encode_tv2echo(&argvars[2], NULL);
+      ga_concat(&ga, (char_u *)tofree);
+      xfree(tofree);
+      ga_concat(&ga, (char_u *)": ");
+    }
     ga_concat(&ga, IObuff);
     assert_error(&ga);
     ga_clear(&ga);

src/nvim/eval.lua

@@ -28,7 +28,7 @@ return {
     asin={args=1, func="float_op_wrapper", data="&asin"},  -- WJMc
     assert_beeps={args={1, 2}},
     assert_equal={args={2, 3}},
-    assert_equalfile={args=2},
+    assert_equalfile={args={2, 3}},
     assert_exception={args={1, 2}},
     assert_fails={args={1, 3}},
     assert_false={args={1, 2}},

src/nvim/eval/funcs.c

@@ -415,7 +415,7 @@ static void f_assert_equal(typval_T *argvars, typval_T *rettv, FunPtr fptr)
   rettv->vval.v_number = assert_equal_common(argvars, ASSERT_EQUAL);
 }
 
-// "assert_equalfile(fname-one, fname-two)" function
+// "assert_equalfile(fname-one, fname-two[, msg])" function
 static void f_assert_equalfile(typval_T *argvars, typval_T *rettv, FunPtr fptr)
 {
   rettv->vval.v_number = assert_equalfile(argvars);

src/nvim/testdir/test_assert.vim

@@ -31,6 +31,10 @@ func Test_assert_equalfile()
   call assert_match("difference at byte 4", v:errors[0])
   call remove(v:errors, 0)
 
+  call assert_equal(1, assert_equalfile('Xone', 'Xtwo', 'a message'))
+  call assert_match("a message: difference at byte 4", v:errors[0])
+  call remove(v:errors, 0)
+
   call delete('Xone')
   call delete('Xtwo')
 endfunc