A production can now be marked both %inline and %prec,

provided it appears in tail position in its caller and
its caller does not itself have a %prec annotation.

bench/bad/no-prec-and-inline.expected

-File "no-prec-and-inline.mly", line 7, characters 17-20:
-Error: use of %prec is forbidden in an %inlined nonterminal definition.

bench/bad/no-prec-and-inline.mly

-%start<int> a
-%left foo
-%%
-
-a: {}
-
-%inline b: %prec foo {} 

bench/bad/prec-inline-non-tail.expected

+File "prec-inline-non-tail.mly", line 35, characters 23-29:
+File "prec-inline-non-tail.mly", line 19, characters 2-18:
+Error: this production carries a %prec annotation,
+and the nonterminal symbol raw_expr is marked %inline.
+For this reason, raw_expr can be used only in tail position.

bench/bad/prec-inline-non-tail.mly

+%token <int> INT
+%token PLUS MINUS TIMES DIV
+%token LPAREN RPAREN
+%token EOL
+
+%left PLUS MINUS        /* lowest precedence */
+%left TIMES DIV         /* medium precedence */
+%nonassoc UMINUS        /* highest precedence */
+
+%start <int> main
+
+%%
+
+main:
+| e = expr EOL
+    { e }
+
+expr:
+  e = raw_expr INT
+    { e }
+
+%inline raw_expr:
+| i = INT
+    { i }
+| LPAREN e = expr RPAREN
+    { e }
+| e1 = expr PLUS e2 = expr
+    { e1 + e2 }
+| e1 = expr MINUS e2 = expr
+    { e1 - e2 }
+| e1 = expr TIMES e2 = expr
+    { e1 * e2 }
+| e1 = expr DIV e2 = expr
+    { e1 / e2 }
+| MINUS e = expr %prec UMINUS
+    { - e }
+

bench/bad/prec-inline-prec.expected

+File "prec-inline-prec.mly", line 35, characters 23-29:
+File "prec-inline-prec.mly", line 19, characters 21-27:
+Error: this production carries a %prec annotation,
+and the nonterminal symbol raw_expr is marked %inline.
+For this reason, raw_expr cannot be used in a production
+which itself carries a %prec annotation.

bench/bad/prec-inline-prec.mly

+%token <int> INT
+%token PLUS MINUS TIMES DIV
+%token LPAREN RPAREN
+%token EOL
+
+%left PLUS MINUS        /* lowest precedence */
+%left TIMES DIV         /* medium precedence */
+%nonassoc UMINUS        /* highest precedence */
+
+%start <int> main
+
+%%
+
+main:
+| e = expr EOL
+    { e }
+
+expr:
+  e = raw_expr %prec UMINUS
+    { e }
+
+%inline raw_expr:
+| i = INT
+    { i }
+| LPAREN e = expr RPAREN
+    { e }
+| e1 = expr PLUS e2 = expr
+    { e1 + e2 }
+| e1 = expr MINUS e2 = expr
+    { e1 - e2 }
+| e1 = expr TIMES e2 = expr
+    { e1 * e2 }
+| e1 = expr DIV e2 = expr
+    { e1 / e2 }
+| MINUS e = expr %prec UMINUS
+    { - e }
+

bench/good/dario.mly

+// Example inspired by Dario Teixeira's question.
+%token A B
+%start<unit> main
+%nonassoc block_is_finished
+%nonassoc A
+%%
+main:  block* B   {}
+block: items      {}
+items: item       {} %prec block_is_finished
+     | item items {}
+item:  A          {}

bench/good/dario.opp.exp

+%start main
+%token B
+%token A
+%nonassoc block_is_finished 
+%nonassoc A 
+%type <unit> main
+%%
+
+main:
+| _1 = list_block_ _2 = B
+    {                  ()}
+
+block:
+| _1 = items
+    {                  ()}
+
+items:
+| _1 = item %prec block_is_finished
+    {                  ()}
+| _1 = item _2 = items
+    {                  ()}
+
+item:
+| _1 = A
+    {                  ()}
+
+list_block_:
+| 
+    {    ( [] )}
+| x = block xs = list_block_
+    {    ( x :: xs )}
+
+%%
+
+
+

bench/good/prec_inline.exp

+Warning: you are using the standard library and/or the %inline keyword. We
+recommend switching on --infer in order to avoid obscure type error messages.

bench/good/prec_inline.mly

+%token <int> INT
+%token PLUS MINUS TIMES DIV
+%token LPAREN RPAREN
+%token EOL
+
+%left PLUS MINUS        /* lowest precedence */
+%left TIMES DIV         /* medium precedence */
+%nonassoc UMINUS        /* highest precedence */
+
+%start <int> main
+
+%%
+
+main:
+| e = expr EOL
+    { e }
+
+(* [raw_expr] is inlined into [expr], and some of its productions
+   carry %prec annotations. This is OK under the new rules of
+   2015/11/18. *)
+expr:
+  e = raw_expr
+    { e }
+
+%inline raw_expr:
+| i = INT
+    { i }
+| LPAREN e = expr RPAREN
+    { e }
+| e1 = expr PLUS e2 = expr
+    { e1 + e2 }
+| e1 = expr MINUS e2 = expr
+    { e1 - e2 }
+| e1 = expr TIMES e2 = expr
+    { e1 * e2 }
+| e1 = expr DIV e2 = expr
+    { e1 / e2 }
+| MINUS e = expr %prec UMINUS
+    { - e }
+

bench/good/prec_inline.opp.exp

+Warning: you are using the standard library and/or the %inline keyword. We
+recommend switching on --infer in order to avoid obscure type error messages.
+%start main
+%token RPAREN
+%token LPAREN
+%token <int> INT
+%token EOL
+%token PLUS
+%token MINUS
+%token TIMES
+%token DIV
+%left PLUS MINUS 
+%left TIMES DIV 
+%nonassoc UMINUS 
+%type <int> main
+%%
+
+main:
+| e = expr _2 = EOL
+    {    ( e )}
+
+expr:
+| i0 = INT
+    {let e =
+  let i = i0 in
+      ( i )
+in
+    ( e )}
+| _10 = LPAREN e0 = expr _30 = RPAREN
+    {let e =
+  let _3 = _30 in
+  let e = e0 in
+  let _1 = _10 in
+      ( e )
+in
+    ( e )}
+| e10 = expr _20 = PLUS e20 = expr
+    {let e =
+  let e2 = e20 in
+  let _2 = _20 in
+  let e1 = e10 in
+      ( e1 + e2 )
+in
+    ( e )}
+| e10 = expr _20 = MINUS e20 = expr
+    {let e =
+  let e2 = e20 in
+  let _2 = _20 in
+  let e1 = e10 in
+      ( e1 - e2 )
+in
+    ( e )}
+| e10 = expr _20 = TIMES e20 = expr
+    {let e =
+  let e2 = e20 in
+  let _2 = _20 in
+  let e1 = e10 in
+      ( e1 * e2 )
+in
+    ( e )}
+| e10 = expr _20 = DIV e20 = expr
+    {let e =
+  let e2 = e20 in
+  let _2 = _20 in
+  let e1 = e10 in
+      ( e1 / e2 )
+in
+    ( e )}
+| _10 = MINUS e0 = expr %prec UMINUS
+    {let e =
+  let e = e0 in
+  let _1 = _10 in
+      ( - e )
+in
+    ( e )}
+
+%%
+
+
+

src/nonTerminalDefinitionInlining.ml

@@ -148,11 +148,37 @@ let inline grammar =
   and expand_branch (b : branch) : branch ListMonad.m =
     try
       (* [c] is the identifier under which the callee is known. *)
-      let prefix, p, _nt, c, suffix = find_inline_producer b in
+      let prefix, p, nt, c, suffix = find_inline_producer b in
       use_inline := true;
       (* Inline a branch of [nt] at position [prefix] ... [suffix] in
 	 the branch [b]. *)
       let inline_branch pb =
+
+        (* 2015/11/18. The interaction of %prec and %inline is not documented.
+           It used to be the case that we would disallow marking a production
+           both %inline and %prec. Now, we allow it, but we check that (1) it
+           is inlined at the last position of the host production and (2) the
+           host production does not already have a %prec annotation. *)
+        pb.branch_prec_annotation |> Option.iter (fun callee_prec ->
+          (* The callee has a %prec annotation. *)
+          (* Check condition 1. *)
+          if List.length suffix > 0 then
+            Error.error [ Positions.position callee_prec; b.branch_position ]
+              "this production carries a %%prec annotation,\n\
+               and the nonterminal symbol %s is marked %%inline.\n\
+               For this reason, %s can be used only in tail position."
+              nt nt;
+          (* Check condition 2. *)
+          b.branch_prec_annotation |> Option.iter (fun caller_prec ->
+            Error.error [ Positions.position callee_prec; Positions.position caller_prec ]
+              "this production carries a %%prec annotation,\n\
+               and the nonterminal symbol %s is marked %%inline.\n\
+               For this reason, %s cannot be used in a production\n\
+               which itself carries a %%prec annotation."
+              nt nt
+          )
+        );
+
 	(* Rename the producers of this branch is they conflict with
 	   the name of the host's producers. *)
 	let phi, inlined_producers = rename_if_necessary b pb.producers in
@@ -232,9 +258,23 @@ let inline grammar =
 	  Action.rename (rename_sw_inner beforeendp) phi pb.action
 	in
 
+        (* 2015/11/18. If the callee has a %prec annotation (which implies
+           the caller does not have one, and the callee appears in tail
+           position in the caller) then the annotation is inherited. This
+           seems reasonable, but remains undocumented. *)
+        let branch_prec_annotation =
+          match pb.branch_prec_annotation with
+          | (Some _) as annotation ->
+              assert (b.branch_prec_annotation = None);
+              annotation
+          | None ->
+              b.branch_prec_annotation
+        in
+
 	{ b with
-	  producers = producers;
-	  action = Action.compose c action' outer_action
+	  producers;
+	  action = Action.compose c action' outer_action;
+          branch_prec_annotation;
 	}
       in
       List.map inline_branch p.branches >>= expand_branch

src/partialGrammar.ml

@@ -680,11 +680,6 @@ let check_parameterized_grammar_is_well_defined grammar =
 		  check_identifier_reference grammar prule 
 		    terminal.value terminal.position;
 
-		  (* It is forbidden to use the %prec directive with %inline. *)
-		  if prule.pr_inline_flag then
-		    Error.errorp terminal
-		      "use of %%prec is forbidden in an %%inlined nonterminal definition.";
-
 		  (* Furthermore, the symbol following %prec must be a valid
 		     token identifier. *)  
                   if not (StringMap.mem terminal.value grammar.p_tokens) then