Treat write errors in markdown doc generation

This code was already using io.Writer, but was completely ignoring write
errors.

The most worrying part is how GenMarkdownTreeCustom used an unnecessary
buffer to then dump all of its contents on a file, and instead of
returning an error on file creation/writing, it would just exit the
entire program.

doc/md_docs.go

@@ -14,7 +14,6 @@
 package doc
 
 import (
-	"bytes"
 	"fmt"
 	"io"
 	"os"
@@ -25,29 +24,38 @@ import (
 	"github.com/spf13/cobra"
 )
 
-func printOptions(out io.Writer, cmd *cobra.Command, name string) {
+func printOptions(w io.Writer, cmd *cobra.Command, name string) error {
 	flags := cmd.NonInheritedFlags()
-	flags.SetOutput(out)
+	flags.SetOutput(w)
 	if flags.HasFlags() {
-		fmt.Fprintf(out, "### Options\n\n```\n")
+		if _, err := fmt.Fprintf(w, "### Options\n\n```\n"); err != nil {
+			return err
+		}
 		flags.PrintDefaults()
-		fmt.Fprintf(out, "```\n\n")
+		if _, err := fmt.Fprintf(w, "```\n\n"); err != nil {
+			return err
+		}
 	}
 
 	parentFlags := cmd.InheritedFlags()
-	parentFlags.SetOutput(out)
+	parentFlags.SetOutput(w)
 	if parentFlags.HasFlags() {
-		fmt.Fprintf(out, "### Options inherited from parent commands\n\n```\n")
+		if _, err := fmt.Fprintf(w, "### Options inherited from parent commands\n\n```\n"); err != nil {
-		parentFlags.PrintDefaults()
+			return err
-		fmt.Fprintf(out, "```\n\n")
 		}
+		parentFlags.PrintDefaults()
+		if _, err := fmt.Fprintf(w, "```\n\n"); err != nil {
+			return err
+		}
+	}
+	return nil
 }
 
-func GenMarkdown(cmd *cobra.Command, out io.Writer) {
+func GenMarkdown(cmd *cobra.Command, w io.Writer) error {
-	GenMarkdownCustom(cmd, out, func(s string) string { return s })
+	return GenMarkdownCustom(cmd, w, func(s string) string { return s })
 }
 
-func GenMarkdownCustom(cmd *cobra.Command, out io.Writer, linkHandler func(string) string) {
+func GenMarkdownCustom(cmd *cobra.Command, w io.Writer, linkHandler func(string) string) error {
 	name := cmd.CommandPath()
 
 	short := cmd.Short
@@ -56,29 +64,49 @@ func GenMarkdownCustom(cmd *cobra.Command, out io.Writer, linkHandler func(strin
 		long = short
 	}
 
-	fmt.Fprintf(out, "## %s\n\n", name)
+	if _, err := fmt.Fprintf(w, "## %s\n\n", name); err != nil {
-	fmt.Fprintf(out, "%s\n\n", short)
+		return err
-	fmt.Fprintf(out, "### Synopsis\n\n")
+	}
-	fmt.Fprintf(out, "\n%s\n\n", long)
+	if _, err := fmt.Fprintf(w, "%s\n\n", short); err != nil {
+		return err
+	}
+	if _, err := fmt.Fprintf(w, "### Synopsis\n\n"); err != nil {
+		return err
+	}
+	if _, err := fmt.Fprintf(w, "\n%s\n\n", long); err != nil {
+		return err
+	}
 
 	if cmd.Runnable() {
-		fmt.Fprintf(out, "```\n%s\n```\n\n", cmd.UseLine())
+		if _, err := fmt.Fprintf(w, "```\n%s\n```\n\n", cmd.UseLine()); err != nil {
+			return err
+		}
 	}
 
 	if len(cmd.Example) > 0 {
-		fmt.Fprintf(out, "### Examples\n\n")
+		if _, err := fmt.Fprintf(w, "### Examples\n\n"); err != nil {
-		fmt.Fprintf(out, "```\n%s\n```\n\n", cmd.Example)
+			return err
+		}
+		if _, err := fmt.Fprintf(w, "```\n%s\n```\n\n", cmd.Example); err != nil {
+			return err
+		}
 	}
 
-	printOptions(out, cmd, name)
+	if err := printOptions(w, cmd, name); err != nil {
+		return err
+	}
 	if hasSeeAlso(cmd) {
-		fmt.Fprintf(out, "### SEE ALSO\n")
+		if _, err := fmt.Fprintf(w, "### SEE ALSO\n"); err != nil {
+			return err
+		}
 		if cmd.HasParent() {
 			parent := cmd.Parent()
 			pname := parent.CommandPath()
 			link := pname + ".md"
 			link = strings.Replace(link, " ", "_", -1)
-			fmt.Fprintf(out, "* [%s](%s)\t - %s\n", pname, linkHandler(link), parent.Short)
+			if _, err := fmt.Fprintf(w, "* [%s](%s)\t - %s\n", pname, linkHandler(link), parent.Short); err != nil {
+				return err
+			}
 			cmd.VisitParents(func(c *cobra.Command) {
 				if c.DisableAutoGenTag {
 					cmd.DisableAutoGenTag = c.DisableAutoGenTag
@@ -96,48 +124,51 @@ func GenMarkdownCustom(cmd *cobra.Command, out io.Writer, linkHandler func(strin
 			cname := name + " " + child.Name()
 			link := cname + ".md"
 			link = strings.Replace(link, " ", "_", -1)
-			fmt.Fprintf(out, "* [%s](%s)\t - %s\n", cname, linkHandler(link), child.Short)
+			if _, err := fmt.Fprintf(w, "* [%s](%s)\t - %s\n", cname, linkHandler(link), child.Short); err != nil {
+				return err
+			}
+		}
+		if _, err := fmt.Fprintf(w, "\n"); err != nil {
+			return err
 		}
-		fmt.Fprintf(out, "\n")
 	}
 	if !cmd.DisableAutoGenTag {
-		fmt.Fprintf(out, "###### Auto generated by spf13/cobra on %s\n", time.Now().Format("2-Jan-2006"))
+		if _, err := fmt.Fprintf(w, "###### Auto generated by spf13/cobra on %s\n", time.Now().Format("2-Jan-2006")); err != nil {
+			return err
 		}
+	}
+	return nil
 }
 
-func GenMarkdownTree(cmd *cobra.Command, dir string) {
+func GenMarkdownTree(cmd *cobra.Command, dir string) error {
 	identity := func(s string) string { return s }
 	emptyStr := func(s string) string { return "" }
-	GenMarkdownTreeCustom(cmd, dir, emptyStr, identity)
+	return GenMarkdownTreeCustom(cmd, dir, emptyStr, identity)
 }
 
-func GenMarkdownTreeCustom(cmd *cobra.Command, dir string, filePrepender, linkHandler func(string) string) {
+func GenMarkdownTreeCustom(cmd *cobra.Command, dir string, filePrepender, linkHandler func(string) string) error {
 	for _, c := range cmd.Commands() {
 		if !c.IsAvailableCommand() || c.IsHelpCommand() {
 			continue
 		}
-		GenMarkdownTreeCustom(c, dir, filePrepender, linkHandler)
+		if err := GenMarkdownTreeCustom(c, dir, filePrepender, linkHandler); err != nil {
+			return err
+		}
 	}
-	out := new(bytes.Buffer)
-
-	GenMarkdownCustom(cmd, out, linkHandler)
 
 	filename := cmd.CommandPath()
 	filename = dir + strings.Replace(filename, " ", "_", -1) + ".md"
-	outFile, err := os.Create(filename)
+	f, err := os.Create(filename)
 	if err != nil {
-		fmt.Println(err)
+		return err
-		os.Exit(1)
 	}
-	defer outFile.Close()
+	defer f.Close()
-	_, err = outFile.WriteString(filePrepender(filename))
+
-	if err != nil {
+	if _, err := io.WriteString(f, filePrepender(filename)); err != nil {
-		fmt.Println(err)
+		return err
-		os.Exit(1)
 	}
-	_, err = outFile.Write(out.Bytes())
+	if err := GenMarkdownCustom(cmd, f, linkHandler); err != nil {
-	if err != nil {
+		return err
-		fmt.Println(err)
-		os.Exit(1)
 	}
+	return nil
 }

doc/md_docs.md

@@ -39,13 +39,13 @@ This will write the markdown doc for ONLY "cmd" into the out, buffer.
 Both `GenMarkdown` and `GenMarkdownTree` have alternate versions with callbacks to get some control of the output:
 
 ```go
-func GenMarkdownTreeCustom(cmd *Command, dir string, filePrepender, linkHandler func(string) string) {
+func GenMarkdownTreeCustom(cmd *Command, dir string, filePrepender, linkHandler func(string) string) error {
     //...
 }
 ```
 
 ```go
-func GenMarkdownCustom(cmd *Command, out *bytes.Buffer, linkHandler func(string) string) {
+func GenMarkdownCustom(cmd *Command, out *bytes.Buffer, linkHandler func(string) string) error {
     //...
 }
 ```

doc/md_docs_test.go

@@ -21,7 +21,9 @@ func TestGenMdDoc(t *testing.T) {
 	out := new(bytes.Buffer)
 
 	// We generate on s subcommand so we have both subcommands and parents
-	GenMarkdown(cmdEcho, out)
+	if err := GenMarkdown(cmdEcho, out); err != nil {
+		t.Fatal(err)
+	}
 	found := out.String()
 
 	// Our description
@@ -75,7 +77,9 @@ func TestGenMdNoTag(t *testing.T) {
 	cmdRootWithRun.PersistentFlags().StringVarP(&flags2a, "rootflag", "r", "two", strtwoParentHelp)
 	out := new(bytes.Buffer)
 
-	GenMarkdown(c, out)
+	if err := GenMarkdown(c, out); err != nil {
+		t.Fatal(err)
+	}
 	found := out.String()
 
 	unexpected := "Auto generated"