Allow `!` operator in variable expansions

Fixes #21

corpus/literals.txt

@@ -56,6 +56,7 @@ echo $# $* $@
 Variable expansions
 =============================
 
+echo ${!abc}
 echo ${abc}
 echo ${abc:-def}
 echo ${abc:- }
@@ -65,6 +66,7 @@ echo ${abc:
 ---
 
 (program
+  (command (command_name (word)) (expansion (variable_name)))
   (command (command_name (word)) (expansion (variable_name)))
   (command (command_name (word)) (expansion (variable_name) (word)))
   (command (command_name (word)) (expansion (variable_name)))

grammar.js

@@ -437,7 +437,7 @@ module.exports = grammar({
 
     expansion: $ => seq(
       '${',
-      optional('#'),
+      optional(choice('#', '!')),
       choice(
         seq(
           $.variable_name,

script/known-failures.txt

@@ -9,7 +9,6 @@ examples/bash-it/completion/available/docker-compose.completion.bash
 examples/bash-it/completion/available/jboss7.completion.bash
 examples/bash-it/completion/available/gh.completion.bash
 examples/bash-it/completion/available/bundler.completion.bash
-examples/bash-it/completion/available/gradle.completion.bash
 examples/bash-it/completion/available/drush.completion.bash
 examples/bash-it/completion/available/hub.completion.bash
 examples/bash-it/completion/available/docker-machine.completion.bash
@@ -17,7 +16,6 @@ examples/bash-it/completion/available/git.completion.bash
 examples/bash-it/completion/available/vagrant.completion.bash
 examples/bash-it/completion/available/defaults.completion.bash
 examples/bash-it/completion/available/packer.completion.bash
-examples/bash-it/completion/available/salt.completion.bash
 examples/bash-it/completion/available/vault.completion.bash
 examples/bash-it/completion/available/docker.completion.bash
 examples/bash-it/completion/available/tmux.completion.bash
@@ -26,14 +24,12 @@ examples/bash-it/completion/available/apm.completion.bash
 examples/bash-it/completion/available/git_flow.completion.bash
 examples/bash-it/lib/preexec.bash
 examples/bash-it/lib/composure.bash
-examples/bash-it/lib/search.bash
 examples/bash-it/test_lib/bats-support/src/lang.bash
 examples/bash-it/test_lib/bats-support/src/output.bash
 examples/bash-it/test_lib/bats-assert/src/assert.bash
 examples/bash-it/themes/hawaii50/hawaii50.theme.bash
 examples/bash-it/themes/dulcie/dulcie.theme.bash
 examples/bash-it/themes/colors.theme.bash
-examples/bash-it/themes/rana/rana.theme.bash
 examples/bash-it/themes/morris/morris.theme.bash
 examples/bash-it/themes/powerline/powerline.base.bash
 examples/bash-it/themes/base.theme.bash

src/grammar.json

@@ -1774,8 +1774,17 @@
           "type": "CHOICE",
           "members": [
             {
-              "type": "STRING",
-              "value": "#"
+              "type": "CHOICE",
+              "members": [
+                {
+                  "type": "STRING",
+                  "value": "#"
+                },
+                {
+                  "type": "STRING",
+                  "value": "!"
+                }
+              ]
             },
             {
               "type": "BLANK"