compose: warn before sending with empty subject

Ask user whether they want to abort before sending if the subject header
is empty and they have enabled the warn-empty-subject config option.

Signed-off-by: Jason Cox <me@jasoncarloscox.com>
Acked-by: Tim Culverhouse <tim@timculverhouse.com>

6 files changed, 41 insertions, 11 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index b293b869..53208c19 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -8,6 +8,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 ### Added
 
 - Colorize can style diff chunk function names with `diff_chunk_func`.
+- Warn before sending emails with an empty subject with `empty-subject-warning`
+  in `aerc.conf`.
 
 ## [0.15.2](https://git.sr.ht/~rjarry/aerc/refs/0.15.2) - 2023-05-11
 
diff --git a/commands/compose/send.go b/commands/compose/send.go
index d43f28ea..eeea96cd 100644
--- a/commands/compose/send.go
+++ b/commands/compose/send.go
@@ -109,12 +109,17 @@ func (Send) Execute(aerc *widgets.Aerc, args []string) error {
 	log.Debugf("send config rcpts: %s", ctx.rcpts)
 	log.Debugf("send config domain: %s", ctx.domain)
 
-	warn, err := composer.ShouldWarnAttachment()
-	if err != nil || warn {
-		msg := "You may have forgotten an attachment."
-		if err != nil {
-			log.Warnf("failed to check for a forgotten attachment: %v", err)
-			msg = "Failed to check for a forgotten attachment."
+	warnSubject := composer.ShouldWarnSubject()
+	warnAttachment := composer.ShouldWarnAttachment()
+	if warnSubject || warnAttachment {
+		var msg string
+		switch {
+		case warnSubject && warnAttachment:
+			msg = "The subject is empty, and you may have forgotten an attachment."
+		case warnSubject:
+			msg = "The subject is empty."
+		default:
+			msg = "You may have forgotten an attachment."
 		}
 
 		prompt := widgets.NewPrompt(
diff --git a/config/aerc.conf b/config/aerc.conf
index cb720e07..800e6ec6 100644
--- a/config/aerc.conf
+++ b/config/aerc.conf
@@ -417,6 +417,11 @@
 # Default: true
 #reply-to-self=true
 
+# Warn before sending an email with an empty subject.
+#
+# Default: false
+#empty-subject-warning=false
+
 #
 # Warn before sending an email that matches the specified regexp but does not
 # have any attachments. Leave empty to disable this feature.
diff --git a/config/compose.go b/config/compose.go
index 70533453..017b9efb 100644
--- a/config/compose.go
+++ b/config/compose.go
@@ -13,6 +13,7 @@ type ComposeConfig struct {
 	AddressBookCmd      string         `ini:"address-book-cmd"`
 	ReplyToSelf         bool           `ini:"reply-to-self" default:"true"`
 	NoAttachmentWarning *regexp.Regexp `ini:"no-attachment-warning" parse:"ParseNoAttachmentWarning"`
+	EmptySubjectWarning bool           `ini:"empty-subject-warning"`
 	FilePickerCmd       string         `ini:"file-picker-cmd"`
 	FormatFlowed        bool           `ini:"format-flowed"`
 }
diff --git a/doc/aerc-config.5.scd b/doc/aerc-config.5.scd
index 5a04288a..aff57729 100644
--- a/doc/aerc-config.5.scd
+++ b/doc/aerc-config.5.scd
@@ -571,6 +571,11 @@ These options are configured in the *[compose]* section of _aerc.conf_.
 
 	Default: _true_
 
+*empty-subject-warning* = _true_|_false_
+	Warn before sending an email with an empty subject.
+
+	Default: _false_
+
 *no-attachment-warning* = _<regexp>_
 	Specifies a regular expression against which an email's body should be
 	tested before sending an email with no attachment. If the regexp
diff --git a/widgets/compose.go b/widgets/compose.go
index 1e7450e9..4735782b 100644
--- a/widgets/compose.go
+++ b/widgets/compose.go
@@ -853,24 +853,36 @@ func (c *Composer) WriteMessage(header *mail.Header, writer io.Writer) error {
 	}
 }
 
-func (c *Composer) ShouldWarnAttachment() (bool, error) {
+func (c *Composer) ShouldWarnAttachment() bool {
 	regex := config.Compose.NoAttachmentWarning
 
 	if regex == nil || len(c.attachments) > 0 {
-		return false, nil
+		return false
 	}
 
 	err := c.reloadEmail()
 	if err != nil {
-		return false, errors.Wrap(err, "reloadEmail")
+		log.Warnf("failed to check for a forgotten attachment (reloadEmail): %v", err)
+		return true
 	}
 
 	body, err := io.ReadAll(c.email)
 	if err != nil {
-		return false, errors.Wrap(err, "io.ReadAll")
+		log.Warnf("failed to check for a forgotten attachment (io.ReadAll): %v", err)
+		return true
+	}
+
+	return regex.Match(body)
+}
+
+func (c *Composer) ShouldWarnSubject() bool {
+	if !config.Compose.EmptySubjectWarning {
+		return false
 	}
 
-	return regex.Match(body), nil
+	// ignore errors because the raw header field is sufficient here
+	subject, _ := c.header.Subject()
+	return len(subject) == 0
 }
 
 func writeMsgImpl(c *Composer, header *mail.Header, writer io.Writer) error {