Make parsing given definitions more robust

Fixes #12348

Author: odersky

compiler/src/dotty/tools/dotc/parsing/Parsers.scala

@@ -3573,7 +3573,7 @@ object Parsers {
             ValDef(name, parents.head, subExpr())
           else
             DefDef(name, joinParams(tparams, vparamss), parents.head, subExpr())
-        else if in.token != WITH && parentsIsType then
+        else if (isStatSep || isStatSeqEnd) && parentsIsType then
           if name.isEmpty then
             syntaxError(em"anonymous given cannot be abstract")
           DefDef(name, joinParams(tparams, vparamss), parents.head, EmptyTree)
@@ -3583,8 +3583,8 @@ object Parsers {
             vparam.withMods(vparam.mods &~ Param | ParamAccessor | Protected)))
           val constr = makeConstructor(tparams1, vparamss1)
           val templ =
-            if in.token == WITH then withTemplate(constr, parents)
-            else Template(constr, parents, Nil, EmptyValDef, Nil)
+            if isStatSep || isStatSeqEnd then Template(constr, parents, Nil, EmptyValDef, Nil)
+            else withTemplate(constr, parents)
           if noParams then ModuleDef(name, templ)
           else TypeDef(name.toTypeName, templ)
       end gdef

tests/neg/i12348.check

@@ -0,0 +1,8 @@
+-- [E040] Syntax Error: tests/neg/i12348.scala:2:15 --------------------------------------------------------------------
+2 |  given inline x: Int = 0 // error
+  |               ^
+  |               'with' expected, but identifier found
+-- [E040] Syntax Error: tests/neg/i12348.scala:3:10 --------------------------------------------------------------------
+3 |} // error
+  |          ^
+  |          '}' expected, but eof found

tests/neg/i12348.scala

@@ -0,0 +1,3 @@
+object A {
+  given inline x: Int = 0 // error
+} // error