Add syntax highlighting for Nix package manager

Based on PHP. It is not ideal yet but much better than nothing.

rc/filetype/nix.kak

@@ -0,0 +1,115 @@
+# Nix package manager language
+# https://nixos.org/nix/manual/
+
+# Detection
+# ‾‾‾‾‾‾‾‾‾
+
+hook global BufCreate .*[.](nix) %{
+    set-option buffer filetype nix
+}
+
+# Initialization
+# ‾‾‾‾‾‾‾‾‾‾‾‾‾‾
+
+hook global WinSetOption filetype=nix %{
+    require-module nix
+
+    hook window ModeChange insert:.* -group nix-trim-indent  nix-trim-indent
+    hook window InsertChar .* -group nix-indent nix-indent-on-char
+    hook window InsertChar \n -group nix-indent nix-indent-on-new-line
+
+    hook -once -always window WinSetOption filetype=.* %{ remove-hooks window nix-.+ }
+}
+
+hook -group nix-highlight global WinSetOption filetype=nix %{
+    add-highlighter window/nix ref nix
+    hook -once -always window WinSetOption filetype=.* %{ remove-highlighter window/nix }
+}
+
+provide-module nix %(
+
+# Highlighters
+# ‾‾‾‾‾‾‾‾‾‾‾‾
+
+add-highlighter shared/nix regions
+add-highlighter shared/nix/code  default-region group
+# Define strings. They can contain interpolated nix code,
+# which itself can contain strings.
+# Note that we currently cannot properly support nesting of the same-delimiter strings
+# because of https://github.com/mawww/kakoune/issues/1670
+add-highlighter shared/nix/double_string region '"'    (?<!\\)(?:\\\\)*"         regions
+# this is hard one: it is terminated by '', but ''$, ''\* and ''' are escapes.
+add-highlighter shared/nix/indent_string region "''"   (?<!')(?:''')*''(?![\\'$]) regions
+add-highlighter shared/nix/comment1      region '#'    '$'                       fill comment
+add-highlighter shared/nix/comment2      region /\*    \*/                       fill comment
+
+
+#add-highlighter shared/nix/code/ regex "([a-zA-Z_][a-zA-Z0-9-_.]*)\s*([=])" 1:variable
+add-highlighter shared/nix/code/ regex "(\b|-)[0-9]*\.?[0-9eE]+\b" 0:value
+
+add-highlighter shared/nix/double_string/str default-region fill string
+add-highlighter shared/nix/double_string/variable region -recurse \{ (?<!\\)(\\\\)*\$\{ \} ref nix
+add-highlighter shared/nix/indent_string/str default-region fill string
+# FIXME: the opening regex is not ideal. See https://nixos.org/nix/manual/#idm140737317975776
+# It should usually match "${", should match "'''${" (as "'''" is escaped itself),
+# but should not match "''${" and "''\${".
+# Seems that negative lookbehind semantics is not enough for some complex cases.
+add-highlighter shared/nix/indent_string/variable region -recurse \{ (?<![^']'')\$\{ \} ref nix
+
+add-highlighter shared/nix/code/ regex \b(true|false|null|let|in|with|if|then|else)\b 0:keyword
+add-highlighter shared/nix/code/ regex \b(rec)\b\s*\{ 1:keyword
+# Those are builtin functions available in global scope.
+# They should not be assigned to.
+add-highlighter shared/nix/code/ regex '[^.]\s*\b(builtins|inherit|baseNameOf|derivation|dirOf|fetchTarball|import|isNull|map|removeAttrs|throw|toString)\b\s*[^=]' 1:builtin
+
+add-highlighter shared/nix/code/ regex '\b\s*(\.)\s*\b'  1:operator
+add-highlighter shared/nix/code/ regex '-'         0:operator
+add-highlighter shared/nix/code/ regex '\?'        0:operator
+add-highlighter shared/nix/code/ regex '\+\+=?'    0:operator
+add-highlighter shared/nix/code/ regex '(\*|/|\+)' 0:operator
+add-highlighter shared/nix/code/ regex '!'         0:operator
+add-highlighter shared/nix/code/ regex '//=?'      0:operator
+add-highlighter shared/nix/code/ regex '[<>]=?\??' 0:operator
+add-highlighter shared/nix/code/ regex '(==|!=)'   0:operator
+add-highlighter shared/nix/code/ regex '(&&|\|\|)' 0:operator
+add-highlighter shared/nix/code/ regex '->'        0:operator
+add-highlighter shared/nix/code/ regex \bor\b      0:operator
+
+# override any operators matched before
+# path:
+add-highlighter shared/nix/code/ regex '\s(\.?\.?/[-A-Za-z0-9/_+.]+)[;?]?' 1:meta
+# imported path:
+add-highlighter shared/nix/code/ regex <[-A-Za-z0-9/_+.]+> 0:meta
+# RFC 2396 URIs can be used without quoting. Strangely, "string" ends URL but ''indented'' one doesn't
+# List of prohibited characters was tested manually in nix-repl as it is not properly documented.
+add-highlighter shared/nix/code/ regex '([^:/?#\s]+):([^#(){}\[\]";`|\s\\]+)' 0:string
+
+# Commands
+# ‾‾‾‾‾‾‾‾
+
+define-command -hidden nix-trim-indent %{
+    # remove trailing white spaces
+    try %{ execute-keys -draft -itersel <a-x> s \h+$ <ret> d }
+}
+
+define-command -hidden nix-indent-on-char %<
+    evaluate-commands -draft -itersel %<
+        # align closer token to its opener when alone on a line
+        try %/ execute-keys -draft <a-h> <a-k> ^\h+[]}]$ <ret> m s \A|.\z <ret> 1<a-&> /
+    >
+>
+
+define-command -hidden nix-indent-on-new-line %<
+    evaluate-commands -draft -itersel %<
+        # copy // comments prefix and following white spaces
+        try %{ execute-keys -draft k <a-x> s ^\h*\K#\h* <ret> y gh j P }
+        # preserve previous line indent
+        try %{ execute-keys -draft \; K <a-&> }
+        # filter previous line
+        try %{ execute-keys -draft k : nix-trim-indent <ret> }
+        # indent after lines beginning / ending with opener token
+        try %_ execute-keys -draft k <a-x> <a-k> ^\h*[[{]|[[{]$ <ret> j <a-gt> _
+    >
+>
+
+)