fix: Improve zsh completion script generator (#219)

* `shellCommand` stores output in a local array that is passed
  to `_describe` to handle spaces and other punctuation in
  the shell command output

* elide the help abstract if it is empty, as it confuses
  the zsh completion system

* set the `_<commandName>_commandname` to `$words[1]`, which
  is the full name of the command used to invoke the completion.
  This ensures invocations like `./build/debug/math` ...
  as passed on to the `_custom_completion` command.

Author: stuartcarnie

Sources/ArgumentParser/Completions/ZshCompletionsGenerator.swift

@@ -17,7 +17,7 @@ struct ZshCompletionsGenerator {
     return """
     #compdef \(type._commandName)
     local context state state_descr line
-    _\(type._commandName)_commandname="\(type._commandName)"
+    _\(type._commandName)_commandname=$words[1]
     typeset -A opt_args
 
     \(generateCompletionFunction([type]))
@@ -118,8 +118,12 @@ extension String {
 }
 
 extension ArgumentDefinition {
-  var zshCompletionAbstract: String? {
-    help.help?.abstract.zshEscapingSingleQuotes()
+  var zshCompletionAbstract: String {
+    guard
+        let abstract = help.help?.abstract,
+        !abstract.isEmpty
+        else { return "" }
+    return "[\(abstract.zshEscapingSingleQuotes())]"
   }
 
   func zshCompletionString(_ commands: [ParsableCommand.Type]) -> String? {
@@ -137,14 +141,14 @@ extension ArgumentDefinition {
       line = ""
     case 1:
       line = """
-      \(names[0].synopsisString)[\(zshCompletionAbstract ?? "")]
+      \(names[0].synopsisString)\(zshCompletionAbstract)
       """
     default:
       let synopses = names.map { $0.synopsisString }
       line = """
       (\(synopses.joined(separator: " ")))'\
       {\(synopses.joined(separator: ","))}\
-      '[\(zshCompletionAbstract ?? "")]
+      '\(zshCompletionAbstract)
       """
     }
 
@@ -170,7 +174,7 @@ extension ArgumentDefinition {
       return "(" + list.joined(separator: " ") + ")"
 
     case .shellCommand(let command):
-      return "{_describe '' $(\(command))}"
+      return "{local -a list; list=(${(f)\"$(\(command))\"}); _describe '''' list}"
 
     case .custom:
       // Generate a call back into the command to retrieve a completions list

Tests/ArgumentParserExampleTests/MathExampleTests.swift

@@ -327,7 +327,7 @@ complete -F _math math
 private let zshCompletionScriptText = """
 #compdef math
 local context state state_descr line
-_math_commandname="math"
+_math_commandname=$words[1]
 typeset -A opt_args
 
 _math() {
@@ -466,14 +466,14 @@ _math_stats_quantiles() {
         ':one-of-four:(alphabet alligator branch braggart)'
         ':custom-arg:{_custom_completion $_math_commandname ---completion stats quantiles -- customArg $words}'
         ':values:'
-        '--test-success-exit-code[]'
-        '--test-failure-exit-code[]'
-        '--test-validation-exit-code[]'
-        '--test-custom-exit-code[]:test-custom-exit-code:'
-        '--file[]:file:_files -g '"'"'*.txt *.md'"'"''
-        '--directory[]:directory:_files -/'
-        '--shell[]:shell:{_describe '' $(head -100 /usr/share/dict/words | tail -50)}'
-        '--custom[]:custom:{_custom_completion $_math_commandname ---completion stats quantiles -- --custom $words}'
+        '--test-success-exit-code'
+        '--test-failure-exit-code'
+        '--test-validation-exit-code'
+        '--test-custom-exit-code:test-custom-exit-code:'
+        '--file:file:_files -g '"'"'*.txt *.md'"'"''
+        '--directory:directory:_files -/'
+        '--shell:shell:{local -a list; list=(${(f)"$(head -100 /usr/share/dict/words | tail -50)"}); _describe '''' list}'
+        '--custom:custom:{_custom_completion $_math_commandname ---completion stats quantiles -- --custom $words}'
         '(-h --help)'{-h,--help}'[Print help information.]'
     )
     _arguments -w -s -S $args[@] && ret=0

Tests/ArgumentParserUnitTests/CompletionScriptTests.swift

@@ -112,19 +112,19 @@ extension CompletionScriptTests {
 private let zshBaseCompletions = """
 #compdef base
 local context state state_descr line
-_base_commandname="base"
+_base_commandname=$words[1]
 typeset -A opt_args
 
 _base() {
     integer ret=1
     local -a args
     args+=(
         '--name[The user'"'"'s name.]:name:'
-        '--kind[]:kind:(one two custom-three)'
-        '--other-kind[]:other-kind:(1 2 3)'
-        '--path1[]:path1:_files'
-        '--path2[]:path2:_files'
-        '--path3[]:path3:(a b c)'
+        '--kind:kind:(one two custom-three)'
+        '--other-kind:other-kind:(1 2 3)'
+        '--path1:path1:_files'
+        '--path2:path2:_files'
+        '--path3:path3:(a b c)'
         '(-h --help)'{-h,--help}'[Print help information.]'
     )
     _arguments -w -s -S $args[@] && ret=0