patch 9.0.0196: finding value in list may require a for loop

Problem:    Finding value in list may require a for loop.
Solution:   Add indexof(). (Yegappan Lakshmanan, closes #10903)
diff --git a/src/testdir/test_listdict.vim b/src/testdir/test_listdict.vim
index 1a6a1d0..2c4e5c7 100644
--- a/src/testdir/test_listdict.vim
+++ b/src/testdir/test_listdict.vim
@@ -1446,4 +1446,49 @@
   unlockvar d
 endfunc
 
+" Test for the indexof() function
+func Test_indexof()
+  let l = [#{color: 'red'}, #{color: 'blue'}, #{color: 'green'}]
+  call assert_equal(0, indexof(l, {i, v -> v.color == 'red'}))
+  call assert_equal(2, indexof(l, {i, v -> v.color == 'green'}))
+  call assert_equal(-1, indexof(l, {i, v -> v.color == 'grey'}))
+  call assert_equal(1, indexof(l, "v:val.color == 'blue'"))
+  call assert_equal(-1, indexof(l, "v:val.color == 'cyan'"))
+
+  let l = [#{n: 10}, #{n: 10}, #{n: 20}]
+  call assert_equal(0, indexof(l, "v:val.n == 10", #{startidx: 0}))
+  call assert_equal(1, indexof(l, "v:val.n == 10", #{startidx: -2}))
+  call assert_equal(-1, indexof(l, "v:val.n == 10", #{startidx: 4}))
+  call assert_equal(-1, indexof(l, "v:val.n == 10", #{startidx: -4}))
+  call assert_equal(0, indexof(l, "v:val.n == 10", test_null_dict()))
+
+  call assert_equal(-1, indexof([], {i, v -> v == 'a'}))
+  call assert_equal(-1, indexof(test_null_list(), {i, v -> v == 'a'}))
+  call assert_equal(-1, indexof(l, test_null_string()))
+  call assert_equal(-1, indexof(l, test_null_function()))
+
+  " failure cases
+  call assert_fails('let i = indexof(l, "v:val == ''cyan''")', 'E735:')
+  call assert_fails('let i = indexof(l, "color == ''cyan''")', 'E121:')
+  call assert_fails('let i = indexof(l, {})', 'E1256:')
+  call assert_fails('let i = indexof({}, "v:val == 2")', 'E1226:')
+  call assert_fails('let i = indexof([], "v:val == 2", [])', 'E1206:')
+
+  func TestIdx(k, v)
+    return a:v.n == 20
+  endfunc
+  call assert_equal(2, indexof(l, function("TestIdx")))
+  delfunc TestIdx
+  func TestIdx(k, v)
+    return {}
+  endfunc
+  call assert_fails('let i = indexof(l, function("TestIdx"))', 'E728:')
+  delfunc TestIdx
+  func TestIdx(k, v)
+    throw "IdxError"
+  endfunc
+  call assert_fails('let i = indexof(l, function("TestIdx"))', 'E605:')
+  delfunc TestIdx
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab