From 6c1a739687f706cf6630c55f8d53c92aacaf6e3d Mon Sep 17 00:00:00 2001
From: Nadrieril
Date: Sun, 24 Mar 2019 14:05:16 +0100
Subject: Disallow builtins as bound variables

---
 dhall/tests/parser.rs       |  2 +-
 dhall_core/src/parser.rs    | 16 ++++++++++++----
 dhall_parser/src/dhall.abnf | 12 +++++++-----
 3 files changed, 20 insertions(+), 10 deletions(-)

diff --git a/dhall/tests/parser.rs b/dhall/tests/parser.rs
index fcc2fa9..5f57068 100644
--- a/dhall/tests/parser.rs
+++ b/dhall/tests/parser.rs
@@ -62,7 +62,7 @@ parser_success!(spec_parser_success_whitespace, "whitespace");
 parser_success!(spec_parser_success_whitespaceBuffet, "whitespaceBuffet");
 
 parser_failure!(spec_parser_failure_annotation, "annotation");
-// parser_failure!(spec_parser_failure_builtins, "builtins");
+parser_failure!(spec_parser_failure_builtins, "builtins");
 parser_failure!(spec_parser_failure_doubleBoundsNeg, "doubleBoundsNeg");
 parser_failure!(spec_parser_failure_doubleBoundsPos, "doubleBoundsPos");
 parser_failure!(spec_parser_failure_importAccess, "importAccess");
diff --git a/dhall_core/src/parser.rs b/dhall_core/src/parser.rs
index 3f53c49..4f26b0f 100644
--- a/dhall_core/src/parser.rs
+++ b/dhall_core/src/parser.rs
@@ -266,6 +266,14 @@ make_parser! {
         [simple_label(l)] => l,
         [quoted_label(l)] => l,
     ));
+    rule!(unreserved_label<Label>; children!(
+        [label(l)] => {
+            if Builtin::parse(&String::from(&l)).is_some() {
+                Err(format!("Builtin names are not allowed as bound variables"))?
+            }
+            l
+        },
+    ));
 
     rule!(double_quote_literal<ParsedText>; children!(
         [double_quote_chunk(chunks..)] => {
@@ -493,7 +501,7 @@ make_parser! {
     ));
 
     rule!(lambda_expression<ParsedExpr> as expression; children!(
-        [label(l), expression(typ), expression(body)] => {
+        [unreserved_label(l), expression(typ), expression(body)] => {
             bx(Expr::Lam(l, typ, body))
         }
     ));
@@ -511,12 +519,12 @@ make_parser! {
     ));
 
     rule!(let_binding<(Label, Option<ParsedExpr>, ParsedExpr)>; children!(
-        [label(name), expression(annot), expression(expr)] => (name, Some(annot), expr),
-        [label(name), expression(expr)] => (name, None, expr),
+        [unreserved_label(name), expression(annot), expression(expr)] => (name, Some(annot), expr),
+        [unreserved_label(name), expression(expr)] => (name, None, expr),
     ));
 
     rule!(forall_expression<ParsedExpr> as expression; children!(
-        [label(l), expression(typ), expression(body)] => {
+        [unreserved_label(l), expression(typ), expression(body)] => {
             bx(Expr::Pi(l, typ, body))
         }
     ));
diff --git a/dhall_parser/src/dhall.abnf b/dhall_parser/src/dhall.abnf
index d27554c..02edc84 100644
--- a/dhall_parser/src/dhall.abnf
+++ b/dhall_parser/src/dhall.abnf
@@ -168,11 +168,13 @@ quoted-label = 1*quoted-label-char
 
 ; NOTE: Dhall does not support Unicode labels, mainly to minimize the potential
 ; for code obfuscation
-; A label cannot not be any of the reserved identifiers for builtins (unless quoted).
+label = ("`" quoted-label "`" / simple-label)
+
+; An unreserved-label cannot not be any of the reserved identifiers for builtins (unless quoted).
 ; Their list can be found in semantics.md. This is not enforced by the grammar but
 ; should be checked by implementations. The only place where this restriction applies
 ; is bound variables.
-label = ("`" quoted-label "`" / simple-label)
+unreserved-label = label
 
 ; An any-label is allowed to be one of the reserved identifiers.
 any-label = label
@@ -541,7 +543,7 @@ expression =
     / annotated-expression
 
 ; "\(x : a) -> b"
-lambda-expression = lambda whitespace "(" whitespace label whitespace ":" nonempty-whitespace expression ")" whitespace arrow whitespace expression
+lambda-expression = lambda whitespace "(" whitespace unreserved-label whitespace ":" nonempty-whitespace expression ")" whitespace arrow whitespace expression
 
 ; "if a then b else c"
 ifthenelse-expression = if nonempty-whitespace expression then nonempty-whitespace expression else nonempty-whitespace expression
@@ -550,10 +552,10 @@ ifthenelse-expression = if nonempty-whitespace expression then nonempty-whitespa
 ; "let x     = e1 in e2"
 ; "let x = e1 let y = e2 in e3"
 let-expression = 1*let-binding in nonempty-whitespace expression
-let-binding = let nonempty-whitespace label whitespace [ ":" nonempty-whitespace expression ] "=" whitespace expression
+let-binding = let nonempty-whitespace unreserved-label whitespace [ ":" nonempty-whitespace expression ] "=" whitespace expression
 
 ; "forall (x : a) -> b"
-forall-expression = forall whitespace "(" whitespace label whitespace ":" nonempty-whitespace expression ")" whitespace arrow whitespace expression
+forall-expression = forall whitespace "(" whitespace unreserved-label whitespace ":" nonempty-whitespace expression ")" whitespace arrow whitespace expression
 
 ; "a -> b"
 arrow-expression = operator-expression arrow whitespace expression
-- 
cgit v1.2.3