dev-cmd/cat: support setting bat theme via environment variable

Library/Homebrew/dev-cmd/cat.rb

@@ -32,6 +32,7 @@ module Homebrew
     cd HOMEBREW_REPOSITORY
     pager = if Homebrew::EnvConfig.bat?
       ENV["BAT_CONFIG_PATH"] = Homebrew::EnvConfig.bat_config_path
+      ENV["BAT_THEME"] = Homebrew::EnvConfig.bat_theme
       ensure_formula_installed!(
         "bat",
         reason:           "displaying <formula>/<cask> source",

Library/Homebrew/env_config.rb

@@ -44,6 +44,10 @@ module Homebrew
         description:  "Use this as the `bat` configuration file.",
         default_text: "`$HOME/.config/bat/config`.",
       },
+      HOMEBREW_BAT_THEME:                        {
+        description:  "Use this as the `bat` theme for syntax highlighting.",
+        default_text: "`$BAT_THEME`.",
+      },
       HOMEBREW_BOOTSNAP:                         {
         description: "If set, use Bootsnap to speed up repeated `brew` calls. "\
                      "A no-op when using Homebrew's vendored, relocatable Ruby on macOS (as it doesn't work).",

bin/brew

@@ -75,7 +75,7 @@ HOMEBREW_LIBRARY="${HOMEBREW_REPOSITORY}/Library"
 
 # Copy and export all HOMEBREW_* variables previously mentioned in
 # manpage or used elsewhere by Homebrew.
-for VAR in BROWSER DISPLAY EDITOR NO_COLOR PATH TMUX DBUS_SESSION_BUS_ADDRESS
+for VAR in BAT_THEME BROWSER DISPLAY EDITOR NO_COLOR PATH TMUX DBUS_SESSION_BUS_ADDRESS
 do
   # Skip if variable value is empty.
   [[ -z "${!VAR}" ]] && continue

docs/Manpage.md

@@ -1953,6 +1953,11 @@ example, run `export HOMEBREW_NO_INSECURE_REDIRECT=1` rather than just
 
   *Default:* `$HOME/.config/bat/config`.
 
+- `HOMEBREW_BAT_THEME`
+  <br>Use this as the `bat` theme for syntax highlighting.
+
+  *Default:* `$BAT_THEME`.
+
 - `HOMEBREW_BOOTSNAP`
   <br>If set, use Bootsnap to speed up repeated `brew` calls. A no-op when using Homebrew's vendored, relocatable Ruby on macOS (as it doesn't work).
 

manpages/brew.1

@@ -2772,6 +2772,15 @@ Use this as the \fBbat\fR configuration file\.
 \fIDefault:\fR \fB$HOME/\.config/bat/config\fR\.
 .
 .TP
+\fBHOMEBREW_BAT_THEME\fR
+.
+.br
+Use this as the \fBbat\fR theme for syntax highlighting\.
+.
+.IP
+\fIDefault:\fR \fB$BAT_THEME\fR\.
+.
+.TP
 \fBHOMEBREW_BOOTSNAP\fR
 .
 .br