better f-strings highlighting

Taken from hdima/python-syntax#60

Author: lilydjwg

syntax/python.vim

@@ -96,6 +96,7 @@ else
   syn match   pythonStatement   '\<async\s\+def\>' nextgroup=pythonFunction skipwhite
   syn match   pythonStatement   '\<async\s\+with\>'
   syn match   pythonStatement   '\<async\s\+for\>'
+  syn cluster pythonExpression contains=pythonStatement,pythonRepeat,pythonConditional,pythonOperator,pythonNumber,pythonHexNumber,pythonOctNumber,pythonBinNumber,pythonFloat,pythonString,pythonBytes,pythonBoolean,pythonBuiltinObj,pythonBuiltinFunc
 endif
 
 syn region FunctionParameters start='(\zs' end='\ze)' display contains=
@@ -213,10 +214,15 @@ if s:Python2Syntax()
   syn region pythonUniString  start=+[uU]'''+ end=+'''+ keepend contains=pythonBytesEscape,pythonBytesEscapeError,pythonUniEscape,pythonUniEscapeError,pythonDocTest,pythonSpaceError,@Spell
 else
   " Python 3 strings
-  syn region pythonString   start=+f\?'+ skip=+\\\\\|\\'\|\\$+ excludenl end=+'+ end=+$+ keepend contains=pythonBytesEscape,pythonBytesEscapeError,pythonUniEscape,pythonUniEscapeError,@Spell
-  syn region pythonString   start=+f\?"+ skip=+\\\\\|\\"\|\\$+ excludenl end=+"+ end=+$+ keepend contains=pythonBytesEscape,pythonBytesEscapeError,pythonUniEscape,pythonUniEscapeError,@Spell
-  syn region pythonString   start=+f\?"""+ end=+"""+ keepend contains=pythonBytesEscape,pythonBytesEscapeError,pythonUniEscape,pythonUniEscapeError,pythonDocTest2,pythonSpaceError,@Spell
-  syn region pythonString   start=+f\?'''+ end=+'''+ keepend contains=pythonBytesEscape,pythonBytesEscapeError,pythonUniEscape,pythonUniEscapeError,pythonDocTest,pythonSpaceError,@Spell
+  syn region pythonString   start=+'+ skip=+\\\\\|\\'\|\\$+ excludenl end=+'+ end=+$+ keepend contains=pythonBytesEscape,pythonBytesEscapeError,pythonUniEscape,pythonUniEscapeError,@Spell
+  syn region pythonString   start=+"+ skip=+\\\\\|\\"\|\\$+ excludenl end=+"+ end=+$+ keepend contains=pythonBytesEscape,pythonBytesEscapeError,pythonUniEscape,pythonUniEscapeError,@Spell
+  syn region pythonString   start=+"""+ end=+"""+ keepend contains=pythonBytesEscape,pythonBytesEscapeError,pythonUniEscape,pythonUniEscapeError,pythonDocTest2,pythonSpaceError,@Spell
+  syn region pythonString   start=+'''+ end=+'''+ keepend contains=pythonBytesEscape,pythonBytesEscapeError,pythonUniEscape,pythonUniEscapeError,pythonDocTest,pythonSpaceError,@Spell
+
+  syn region pythonFString   start=+[fF]'+ skip=+\\\\\|\\'\|\\$+ excludenl end=+'+ end=+$+ keepend contains=pythonBytesEscape,pythonBytesEscapeError,pythonUniEscape,pythonUniEscapeError,@Spell
+  syn region pythonFString   start=+[fF]"+ skip=+\\\\\|\\"\|\\$+ excludenl end=+"+ end=+$+ keepend contains=pythonBytesEscape,pythonBytesEscapeError,pythonUniEscape,pythonUniEscapeError,@Spell
+  syn region pythonFString   start=+[fF]"""+ end=+"""+ keepend contains=pythonBytesEscape,pythonBytesEscapeError,pythonUniEscape,pythonUniEscapeError,pythonDocTest2,pythonSpaceError,@Spell
+  syn region pythonFString   start=+[fF]'''+ end=+'''+ keepend contains=pythonBytesEscape,pythonBytesEscapeError,pythonUniEscape,pythonUniEscapeError,pythonDocTest,pythonSpaceError,@Spell
 endif
 
 if s:Python2Syntax()
@@ -267,8 +273,9 @@ if s:Enabled('g:python_highlight_string_format')
     syn match pythonStrFormat '{{\|}}' contained containedin=pythonString,pythonUniString,pythonUniRawString,pythonRawString
     syn match pythonStrFormat '{\%(\%([^[:cntrl:][:space:][:punct:][:digit:]]\|_\)\%([^[:cntrl:][:punct:][:space:]]\|_\)*\|\d\+\)\=\%(\.\%([^[:cntrl:][:space:][:punct:][:digit:]]\|_\)\%([^[:cntrl:][:punct:][:space:]]\|_\)*\|\[\%(\d\+\|[^!:\}]\+\)\]\)*\%(![rsa]\)\=\%(:\%({\%(\%([^[:cntrl:][:space:][:punct:][:digit:]]\|_\)\%([^[:cntrl:][:punct:][:space:]]\|_\)*\|\d\+\)}\|\%([^}]\=[<>=^]\)\=[ +-]\=#\=0\=\d*,\=\%(\.\d\+\)\=[bcdeEfFgGnosxX%]\=\)\=\)\=}' contained containedin=pythonString,pythonUniString,pythonUniRawString,pythonRawString
   else
-    syn match pythonStrFormat '{{\|}}' contained containedin=pythonString,pythonRawString
-    syn match pythonStrFormat '{\%(\%([^[:cntrl:][:space:][:punct:][:digit:]]\|_\)\%([^[:cntrl:][:punct:][:space:]]\|_\)*\|\d\+\)\=\%(\.\%([^[:cntrl:][:space:][:punct:][:digit:]]\|_\)\%([^[:cntrl:][:punct:][:space:]]\|_\)*\|\[\%(\d\+\|[^!:\}]\+\)\]\)*\%(![rsa]\)\=\%(:\%({\%(\%([^[:cntrl:][:space:][:punct:][:digit:]]\|_\)\%([^[:cntrl:][:punct:][:space:]]\|_\)*\|\d\+\)}\|\%([^}]\=[<>=^]\)\=[ +-]\=#\=0\=\d*,\=\%(\.\d\+\)\=[bcdeEfFgGnosxX%]\=\)\=\)\=}' contained containedin=pythonString,pythonRawString
+    syn match pythonStrFormat "{{\|}}" contained containedin=pythonString,pythonRawString,pythonFString
+    syn match pythonStrFormat "{\%(\%([^[:cntrl:][:space:][:punct:][:digit:]]\|_\)\%([^[:cntrl:][:punct:][:space:]]\|_\)*\|\d\+\)\=\%(\.\%([^[:cntrl:][:space:][:punct:][:digit:]]\|_\)\%([^[:cntrl:][:punct:][:space:]]\|_\)*\|\[\%(\d\+\|[^!:\}]\+\)\]\)*\%(![rsa]\)\=\%(:\%({\%(\%([^[:cntrl:][:space:][:punct:][:digit:]]\|_\)\%([^[:cntrl:][:punct:][:space:]]\|_\)*\|\d\+\)}\|\%([^}]\=[<>=^]\)\=[ +-]\=#\=0\=\d*,\=\%(\.\d\+\)\=[bcdeEfFgGnosxX%]\=\)\=\)\=}" contained containedin=pythonString,pythonRawString
+    syn region pythonStrInterpRegion start="{"he=e+1,rs=e+1 end="\%(![rsa]\)\=\%(:\%({\%(\%([^[:cntrl:][:space:][:punct:][:digit:]]\|_\)\%([^[:cntrl:][:punct:][:space:]]\|_\)*\|\d\+\)}\|\%([^}]\=[<>=^]\)\=[ +-]\=#\=0\=\d*,\=\%(\.\d\+\)\=[bcdeEfFgGnosxX%]\=\)\=\)\=}"hs=s-1,re=s-1 extend contained containedin=pythonFString contains=pythonStrInterpRegion,@pythonExpression
   endif
 endif
 
@@ -474,6 +481,8 @@ if v:version >= 508 || !exists('did_python_syn_inits')
     HiLink pythonBytesError         Error
     HiLink pythonBytesEscape        Special
     HiLink pythonBytesEscapeError   Error
+    HiLink pythonFString            String
+    HiLink pythonStrInterpRegion    Special
   endif
 
   HiLink pythonStrFormatting    Special