feat(comp): Bring in Cobra's zsh and fish scripts

These scripts also contain all bug fixes PR that have yet to be merged
in Cobra.

Signed-off-by: Marc Khouzam <marc.khouzam@montreal.ca>

cmd/helm/completion.go

@@ -24,6 +24,7 @@ import (
 	"github.com/spf13/cobra"
 
 	"helm.sh/helm/v3/cmd/helm/require"
+	"helm.sh/helm/v3/internal/completion"
 )
 
 const completionDesc = `
@@ -173,12 +174,7 @@ fi
 }
 
 func runCompletionZsh(out io.Writer, cmd *cobra.Command) error {
-	var err error
-	if disableCompDescriptions {
-		err = cmd.Root().GenZshCompletionNoDesc(out)
-	} else {
-		err = cmd.Root().GenZshCompletion(out)
-	}
+	err := completion.GenZshCompletion(out, !disableCompDescriptions)
 
 	// In case the user renamed the helm binary (e.g., to be able to run
 	// both helm2 and helm3), we hook the new binary name to the completion function
@@ -199,7 +195,7 @@ compdef _helm %[1]s
 }
 
 func runCompletionFish(out io.Writer, cmd *cobra.Command) error {
-	return cmd.Root().GenFishCompletion(out, !disableCompDescriptions)
+	return completion.GenFishCompletion(out, !disableCompDescriptions)
 }
 
 func runCompletionPowershell(out io.Writer, cmd *cobra.Command) error {

internal/completion/fish_completion.go

@@ -0,0 +1,192 @@
+package completion
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+
+	"github.com/spf13/cobra"
+)
+
+// GenFishCompletion generates the Fish completion script
+func GenFishCompletion(w io.Writer, includeDesc bool) error {
+	compCmd := cobra.ShellCompRequestCmd
+	if !includeDesc {
+		compCmd = cobra.ShellCompNoDescRequestCmd
+	}
+	buf := new(bytes.Buffer)
+	buf.WriteString(fmt.Sprintf(`# Helm's own fish completion
+
+function __helm_debug
+    set file "$BASH_COMP_DEBUG_FILE"
+    if test -n "$file"
+        echo "$argv" >> $file
+    end
+end
+
+function __helm_perform_completion
+    __helm_debug "Starting __helm_perform_completion"
+
+    set args (string split -- " " (commandline -c))
+    set lastArg "$args[-1]"
+
+    __helm_debug "args: $args"
+    __helm_debug "last arg: $lastArg"
+
+    set emptyArg ""
+    if test -z "$lastArg"
+        __helm_debug "Setting emptyArg"
+        set emptyArg \"\"
+    end
+    __helm_debug "emptyArg: $emptyArg"
+
+    if not type -q "$args[1]"
+        # This can happen when "complete --do-complete helm" is called when running this script.
+        __helm_debug "Cannot find $args[1]. No completions."
+        return
+    end
+
+    set requestComp "$args[1] %[1]s $args[2..-1] $emptyArg"
+    __helm_debug "Calling $requestComp"
+
+    set results (eval $requestComp 2> /dev/null)
+    set comps $results[1..-2]
+    set directiveLine $results[-1]
+
+    # For Fish, when completing a flag with an = (e.g., <program> -n=<TAB>)
+    # completions must be prefixed with the flag
+    set flagPrefix (string match -r -- '-.*=' "$lastArg")
+
+    __helm_debug "Comps: $comps"
+    __helm_debug "DirectiveLine: $directiveLine"
+    __helm_debug "flagPrefix: $flagPrefix"
+
+    for comp in $comps
+        printf "%%s%%s\n" "$flagPrefix" "$comp"
+    end
+
+    printf "%%s\n" "$directiveLine"
+end
+
+# This function does two things:
+# - Obtain the completions and store them in the global __helm_comp_results
+# - Return false if file completion should be performed
+function __helm_prepare_completions
+    __helm_debug ""
+    __helm_debug "========= starting completion logic =========="
+
+    # Start fresh
+    set --erase __helm_comp_results
+
+    set results (__helm_perform_completion)
+    __helm_debug "Completion results: $results"
+
+    if test -z "$results"
+        __helm_debug "No completion, probably due to a failure"
+        # Might as well do file completion, in case it helps
+        return 1
+    end
+
+    set directive (string sub --start 2 $results[-1])
+    set --global __helm_comp_results $results[1..-2]
+
+    __helm_debug "Completions are: $__helm_comp_results"
+    __helm_debug "Directive is: $directive"
+
+    set shellCompDirectiveError %[2]d
+    set shellCompDirectiveNoSpace %[3]d
+    set shellCompDirectiveNoFileComp %[4]d
+    set shellCompDirectiveFilterFileExt %[5]d
+    set shellCompDirectiveFilterDirs %[6]d
+
+    if test -z "$directive"
+        set directive 0
+    end
+
+    set compErr (math (math --scale 0 $directive / $shellCompDirectiveError) %% 2)
+    if test $compErr -eq 1
+        __helm_debug "Received error directive: aborting."
+        # Might as well do file completion, in case it helps
+        return 1
+    end
+
+    set filefilter (math (math --scale 0 $directive / $shellCompDirectiveFilterFileExt) %% 2)
+    set dirfilter (math (math --scale 0 $directive / $shellCompDirectiveFilterDirs) %% 2)
+    if test $filefilter -eq 1; or test $dirfilter -eq 1
+        __helm_debug "File extension filtering or directory filtering not supported"
+        # Do full file completion instead
+        return 1
+    end
+
+    set nospace (math (math --scale 0 $directive / $shellCompDirectiveNoSpace) %% 2)
+    set nofiles (math (math --scale 0 $directive / $shellCompDirectiveNoFileComp) %% 2)
+
+    __helm_debug "nospace: $nospace, nofiles: $nofiles"
+
+    # If we want to prevent a space, or if file completion is NOT disabled,
+    # we need to count the number of valid completions.
+    # To do so, we will filter on prefix as the completions we have received
+    # may not already be filtered so as to allow fish to math on different
+    # criteria than prefix.
+    if test $nospace -ne 0; or test $nofiles -eq 0
+        set prefix (commandline -t)
+        __helm_debug "prefix: $prefix"
+
+        set completions
+        for comp in $__helm_comp_results
+            if test (string match -e -r "^$prefix" "$comp")
+                set -a completions $comp
+            end
+        end
+        set --global __helm_comp_results $completions
+        __helm_debug "Filtered completions are: $__helm_comp_results"
+
+        # Important not to quote the variable for count to work
+        set numComps (count $__helm_comp_results)
+        __helm_debug "numComps: $numComps"
+
+        if test $numComps -eq 1; and test $nospace -ne 0
+            # To support the "nospace" directive we trick the shell
+            # by outputting an extra, longer completion.
+            # We must first split on \t to get rid of the descriptions because
+            # the extra character we add to the fake second completion must be
+            # before the description.  We don't need descriptions anyway since
+            # there is only a single real completion which the shell will expand
+            # immediately.
+            __helm_debug "Adding second completion to perform nospace directive"
+            set split (string split --max 1 \t $__helm_comp_results[1])
+            set --global __helm_comp_results $split[1] $split[1].
+            __helm_debug "Completions are now: $__helm_comp_results"
+        end
+
+        if test $numComps -eq 0; and test $nofiles -eq 0
+            # To be consistent with bash and zsh, we only trigger file
+            # completion when there are no other completions
+            __helm_debug "Requesting file completion"
+            return 1
+        end
+    end
+
+    return 0
+end
+
+# Since Fish completions are only loaded once the user triggers them, we trigger them ourselves
+# so we can properly delete any completions provided by another script.
+# The space after the the program name is essential to trigger completion for the program
+# and not completion of the program name itself.
+complete --do-complete "helm " > /dev/null 2>&1
+# Using '> /dev/null 2>&1' since '&>' is not supported in older versions of fish.
+
+# Remove any pre-existing completions for the program since we will be handling all of them.
+complete -c helm -e
+
+# The call to __helm_prepare_completions will setup __helm_comp_results
+# which provides the program's completion choices.
+complete -c helm -n '__helm_prepare_completions' -f -a '$__helm_comp_results'
+`, compCmd,
+		cobra.ShellCompDirectiveError, cobra.ShellCompDirectiveNoSpace, cobra.ShellCompDirectiveNoFileComp,
+		cobra.ShellCompDirectiveFilterFileExt, cobra.ShellCompDirectiveFilterDirs))
+
+	_, err := buf.WriteTo(w)
+	return err
+}