Fish completion using Go completion

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

fish_completions.go

@@ -0,0 +1,115 @@
+package cobra
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"os"
+)
+
+func genFishComp(buf *bytes.Buffer, name string, includeDesc bool) {
+	compCmd := CompRequestCmd
+	if includeDesc {
+		compCmd = CompWithDescRequestCmd
+	}
+	buf.WriteString(fmt.Sprintf("# fish completion for %-36s -*- shell-script -*-\n", name))
+	buf.WriteString(fmt.Sprintf(`
+function __%[1]s_debug
+    set file "$BASH_COMP_DEBUG_FILE"
+    if test -n "$file"
+	    echo "$argv" >> $file
+    end
+end
+
+function __%[1]s_handle_completion
+    __%[1]s_debug "Starting __%[1]s_handle_completion with: $argv"
+
+    set -l args (string split " " "$argv")
+
+    __%[1]s_debug "last arg: $args[-1]"
+
+    set -l emptyArg ""
+    if test -z "$args[-1]"
+        __%[1]s_debug "Setting emptyArg"
+        set emptyArg \"\"
+    end
+
+    __%[1]s_debug "emptyArg: $emptyArg"
+	set requestComp "$args[1] %[2]s $args[2..-1] $emptyArg"
+    __%[1]s_debug "Calling $requestComp"
+    eval $requestComp 2> /dev/null
+end
+
+function __%[1]s_get_completions
+    # Use the cache if possible
+	if not set -q __%[1]s_cache_completions
+	   set -g __%[1]s_cache_completions (__%[1]s_handle_completion (commandline))
+       __%[1]s_debug "Populating completion cache with: $__%[1]s_cache_completions"
+    end
+
+	set -l directive (string sub --start 2 $__%[1]s_cache_completions[-1])
+	set -l comps $__%[1]s_cache_completions[1..-2]
+	__%[1]s_debug "Completions are: $comps"
+	__%[1]s_debug "Directive is: $directive"
+
+	set -l compErr (math (math $directive / %[3]d) %% 2)
+	if test $compErr -eq 1
+	   return 0
+	end
+
+	set -l nospace (math (math $directive / %[4]d) %% 2)
+	set -l nofiles (math (math $directive / %[5]d) %% 2)
+
+	__%[1]s_debug "nospace: $nospace, nofiles: $nofiles"
+
+	for i in $comps
+        printf "%%s\n" $i
+	end
+
+	if test (count $comps) -eq 1; and test $nospace -ne 0
+	   # To support the "nospace" directive we trick the shell
+	   # by outputting an extra, longer completion.
+	   printf "%%s\n" $comps[1].
+	end
+
+	# Return true if no file completion should be done
+	test (count $comps) -gt 0; or test $nofiles -ne 0
+end
+
+# Remove any pre-existing completions for the program since we will be handling all of them
+# TODO this cleanup is not sufficient.  Fish completions are only loaded once the user triggers
+# them, so the below deletion will not work as it is run too early.  What else can we do?
+complete -c %[1]s -e
+
+# The order in which the below two lines are defined is very important so that the cache gets
+# properly cleared at the very beginning of completions processing
+#
+# This completion will be run second as complete commands are added FILO.  It should use the cache.
+# It provides file completion choices when appropriate.
+complete -c %[1]s -n 'not __%[1]s_get_completions'
+
+# This completion will be run first as complete commands are added FILO.  It first clears the cache.
+# It provides the program's completion choices.
+complete -c %[1]s -n 'set -e __%[1]s_cache_completions; __%[1]s_get_completions' -f -a '(__%[1]s_get_completions)'
+
+`, name, compCmd, BashCompDirectiveError, BashCompDirectiveNoSpace, BashCompDirectiveNoFileComp))
+}
+
+// GenFishCompletion generates fish completion file and writes to the passed writer.
+func (c *Command) GenFishCompletion(w io.Writer, includeDesc bool) error {
+	buf := new(bytes.Buffer)
+	genFishComp(buf, c.Name(), includeDesc)
+	_, err := buf.WriteTo(w)
+	return err
+}
+
+// GenFishCompletionFile generates fish completion file.
+func (c *Command) GenFishCompletionFile(filename string, includeDesc bool) error {
+	outFile, err := os.Create(filename)
+	if err != nil {
+		return err
+	}
+	defer outFile.Close()
+
+	return c.GenFishCompletion(outFile, includeDesc)
+}

fish_completions.md

@@ -0,0 +1,7 @@
+## Generating Fish Completions for your own cobra.Command
+
+Cobra supports native Fish completions generated from the root `cobra.Command`.  You can use the `command.GenFishCompletion()` or `command.GenFishCompletionFile()` functions. You must provide these functions with a parameter indicating if the completions should be annotated with a description; Cobra will provide the description automatically based on usage information.  You can choose to make this option configurable by your users.
+
+### Limitations
+
+* Custom completions implemented using the `ValidArgsFunction` and `RegisterFlagCompletionFunc()` are supported automatically but the ones implemented in Bash scripting are not.