vim-patch:9.1.1936: filetype: Erlang lexical files are not recognized

Problem:  filetype: Erlang lexical files are not recognized
Solution: Detect *.xrl files as leex filetype, include syntax and
          filetype plugins (Jon Parise).

leex is the lexical analyzer generator for Erlang. Its input file format
follows a section-based structure and uses the `.xrl` file extension.

This initial work includes file detection, an ftplugin (which inherits
the Erlang configuration), and a syntax definition.

Reference:
-  https://www.erlang.org/doc/apps/parsetools/leex.html

related: vim/vim#18819
closes: vim/vim#18832

b087c5452b

Co-authored-by: Jon Parise <jon@indelible.org>

runtime/ftplugin/leex.vim

@@ -0,0 +1,14 @@
+" Vim ftplugin file
+" Language:     Leex (Erlang Lexical Analyzer Generator)
+" Maintainer:   Jon Parise <jon@indelible.org>
+" Last Change:  2025 Nov 29
+" Filenames:    *.xrl
+"
+" References:
+" - https://www.erlang.org/doc/apps/parsetools/leex.html
+
+if exists('b:did_ftplugin')
+  finish
+endif
+
+runtime! ftplugin/erlang.vim

runtime/lua/vim/filetype.lua

@@ -705,6 +705,7 @@ local extension = {
   journal = 'ledger',
   ldg = 'ledger',
   ledger = 'ledger',
+  xrl = 'leex',
   leo = 'leo',
   less = 'less',
   lex = 'lex',

runtime/syntax/leex.vim

@@ -0,0 +1,63 @@
+" Vim syntax file
+" Language:     Leex (Erlang Lexical Analyzer Generator)
+" Maintainer:   Jon Parise <jon@indelible.org>
+" Last Change:  2025 Nov 30
+" Filenames:    *.xrl
+"
+" References:
+" - https://www.erlang.org/doc/apps/parsetools/leex.html
+
+if exists('b:current_syntax')
+  finish
+endif
+
+syn include @leexErlang syntax/erlang.vim
+unlet! b:current_syntax
+
+syn match leexComment "%.*$" contains=@Spell display
+
+syn match leexRegexOperator "[|*+?]" contained display
+syn match leexRegexDelimiter "[()[\]]" contained display
+syn match leexRegexSpecial "[.^$\\]" contained display
+syn match leexRegexEscape '\\\%([bfnrtevsd]\|\o\{1,3}\|x\x\{2}\|x{\x\+}\|.\)' contained display
+syn match leexRegexRange "\[[^\]]*\]" contains=leexRegexDelimiter,leexRegexEscape contained display
+
+" Macro definitions: NAME = VALUE
+syn match leexMacroName "^\s*\zs\h\w*\ze\s\+=\s\+" contained nextgroup=leexMacroEquals skipwhite display
+syn match leexMacroEquals "=" contained nextgroup=leexMacroValue skipwhite display
+syn match leexMacroValue "\S\+" contained contains=leexRegexOperator,leexRegexDelimiter,leexRegexSpecial,leexRegexEscape,leexRegexRange,leexMacroRef display
+syn match leexMacroRef "{\h\w*}" contained display
+
+" Rule definitions: <Regexp> : <Erlang code>.
+syn match leexRuleRegex "^\s*\zs[^%].\{-}\ze\s\+:" contained contains=leexRegexOperator,leexRegexDelimiter,leexRegexSpecial,leexRegexEscape,leexRegexRange,leexMacroRef nextgroup=leexRuleColon skipwhite display
+syn match leexRuleColon ":" contained nextgroup=leexRuleCode skipwhite skipnl display
+syn region leexRuleCode start="" end="\.\s*\%(%.*\)\?$" skip="^\s*%.*$" contained contains=@leexErlang keepend skipnl skipwhite
+
+" Sections
+syn match leexHeading "^\%(Definitions\|Rules\|Erlang code\)\.$" contained display
+syn region leexDefinitions start="^Definitions\.$" end="^[A-Z][A-Za-z ]*\.$"me=s-1 end="\%$" keepend fold
+  \ contains=leexHeading,leexComment,leexMacroName
+syn region leexRules start="^Rules\.$" end="^[A-Z][A-Za-z ]*\.$"me=s-1 end="\%$" keepend fold
+  \ contains=leexHeading,leexComment,leexRuleRegex
+syn region leexErlangCode start="^Erlang code\.$" end="^[A-Z][A-Za-z ]*\.$"me=s-1 end="\%$" keepend fold
+  \ contains=leexHeading,@leexErlang
+
+hi def link leexComment Comment
+hi def link leexHeading PreProc
+
+hi def link leexRegexOperator Operator
+hi def link leexRegexDelimiter Delimiter
+hi def link leexRegexSpecial Special
+hi def link leexRegexRange String
+hi def link leexRegexEscape SpecialChar
+
+hi def link leexMacroName Identifier
+hi def link leexMacroEquals Operator
+hi def link leexMacroValue String
+hi def link leexMacroRef Macro
+
+hi def link leexRuleColon Operator
+
+syn sync fromstart
+
+let b:current_syntax = 'leex'

test/old/testdir/test_filetype.vim

@@ -437,6 +437,7 @@ func s:GetFilenameChecks() abort
     \ 'ldif': ['file.ldif'],
     \ 'lean': ['file.lean'],
     \ 'ledger': ['file.ldg', 'file.ledger', 'file.journal'],
+    \ 'leex': ['file.xrl'],
     \ 'leo': ['file.leo'],
     \ 'less': ['file.less'],
     \ 'lex': ['file.lex', 'file.l', 'file.lxx', 'file.l++'],