ui: allow thread arrow customization

The thread prefix appearance is inspired by mutt and has been regarded
by some as too wide and not very aesthetically pleasing. Nevertheless,
it has some technical limitations, like not being able to show if a
thread is folded.

Allow for full customisation of the thread prefix by introducing 14 new
config options.

Dirlist is not affected.

Changelog-added: Thread arrow prefixes are now fully configurable.
Co-authored-by: Robin Jarry <robin@jarry.cc>
Signed-off-by: inwit <inwit@sindominio.net>
Tested-by: Koni Marti <koni.marti@gmail.com>
Acked-by: Robin Jarry <robin@jarry.cc>

1 files changed, 123 insertions, 0 deletions

diff --git a/doc/aerc-config.5.scd b/doc/aerc-config.5.scd
index 1aa9da5f..9ba7a941 100644
--- a/doc/aerc-config.5.scd
+++ b/doc/aerc-config.5.scd
@@ -469,6 +469,129 @@ These options are configured in the *[ui]* section of _aerc.conf_.
 
 	Default: _false_
 
+## THREAD PREFIX CUSTOMIZATION
+
+You can fully customize the thread arrows appearance, which is defined by the
+following configurable prefix parts:
+
+*thread-prefix-tip* = _<string>_
+	Define the arrow head.
+
+	Default: _">"_
+
+*thread-prefix-indent* = _<string>_
+	Define the arrow indentation.
+
+	Default: _" "_
+
+*thread-prefix-stem* = _<string>_
+	Define the vertical extension of the arrow.
+
+	Default: _"│"_
+
+*thread-prefix-limb* = _<string>_
+	Define the horizontal extension of the arrow.
+
+	Default: _""_
+
+*thread-prefix-folded* = _<string>_
+	Define the folded thread indicator.
+
+	Default: _""_
+
+*thread-prefix-unfolded* = _<string>_
+	Define the unfolded thread indicator.
+
+	Default: _""_
+
+*thread-prefix-first-child* = _<string>_
+	Define the first child connector.
+
+	Default: _""_
+
+*thread-prefix-has-siblings* = _<string>_
+	Define the connector used if the message has siblings.
+
+	Default: _├─_
+
+*thread-prefix-lone* = _<string>_
+	Define the connector used if the message has no parents and no children.
+
+	Default: _""_
+
+*thread-prefix-orphan* = _<string>_
+	Define the connector used if the message has no parents and has children.
+
+	Default: _""_
+
+*thread-prefix-last-sibling* = _<string>_
+	Define the connector for the last sibling.
+
+	Default: _└─_
+
+*thread-prefix-last-sibling-reverse* = _<string>_
+	Define the connector for the last sibling in reversed threads.
+
+	Default: _┌─_
+
+*thread-prefix-first-child-reverse* = _<string>_
+
+	Define the arrow appearance by selecting the first child connector in
+	reversed threads.
+
+	Default: _""_
+
+*thread-prefix-orphan-reverse* = _<string>_
+	Customize the reversed threads arrow appearance by selecting the
+	connector used if the message has no parents and has children.
+
+	Default: _""_
+
+
+Default settings (mutt-style):
+
+	```
+	[PATCH aerc v5] ui: allow thread arrow customisation
+	├─>[aerc/patches] build success
+	├─>Re: [PATCH aerc v5] ui: allow thread arrow customisation
+	├─
+	└─>
+	  ├─>
+	  │ ├─>
+	  │ └─>
+	  │   └─>
+	  └─>
+	```
+
+More compact, rounded threads that are also fold-aware:
+
+	```
+	┌[PATCH aerc v5] ui: allow thread arrow customisation
+	├─[aerc/patches] build success
+	├─Re: [PATCH aerc v5] ui: allow thread arrow customisation
+	├+
+	╰┬
+	 ├┬
+	 │├─
+	 │╰┬
+	 │ ╰─
+	 ╰─
+	```
+
+```
+thread-prefix-tip = ""
+thread-prefix-indent = ""
+thread-prefix-stem = "│"
+thread-prefix-limb = "─"
+thread-prefix-folded = "+"
+thread-prefix-unfolded = ""
+thread-prefix-first-child = "┬"
+thread-prefix-has-siblings = "├"
+thread-prefix-orphan = "┌"
+thread-prefix-lone = " "
+thread-prefix-last-sibling = "╰"
+```
+
 ## CONTEXTUAL UI CONFIGURATION
 
 The UI configuration can be specialized for accounts, specific mail