From 7a392b07166c089979e69d4c8a68da3298964c28 Mon Sep 17 00:00:00 2001
From: Nadrieril
Date: Mon, 7 Dec 2020 17:48:20 +0000
Subject: Defer name errors to typechecking

We aren't supposed to inspect anything before alternatives are chosen
---
 dhall/src/semantics/nze/normalize.rs   | 1 +
 dhall/src/semantics/resolve/hir.rs     | 3 +++
 dhall/src/semantics/resolve/resolve.rs | 9 ++++-----
 dhall/src/semantics/tck/typecheck.rs   | 5 +++++
 4 files changed, 13 insertions(+), 5 deletions(-)

(limited to 'dhall/src')

diff --git a/dhall/src/semantics/nze/normalize.rs b/dhall/src/semantics/nze/normalize.rs
index d545750..0a09a80 100644
--- a/dhall/src/semantics/nze/normalize.rs
+++ b/dhall/src/semantics/nze/normalize.rs
@@ -154,6 +154,7 @@ pub fn normalize_one_layer<'cx>(expr: ExprKind<Nir<'cx>>) -> NirKind<'cx> {
 /// Normalize Hir into WHNF
 pub fn normalize_hir<'cx>(env: &NzEnv<'cx>, hir: &Hir<'cx>) -> NirKind<'cx> {
     match hir.kind() {
+        HirKind::MissingVar(..) => unreachable!("ruled out by typechecking"),
         HirKind::Var(var) => env.lookup_val(*var),
         HirKind::Import(import) => {
             let typed = env.cx()[import].unwrap_result();
diff --git a/dhall/src/semantics/resolve/hir.rs b/dhall/src/semantics/resolve/hir.rs
index 3e282b4..05a8550 100644
--- a/dhall/src/semantics/resolve/hir.rs
+++ b/dhall/src/semantics/resolve/hir.rs
@@ -13,6 +13,8 @@ pub struct AlphaVar {
 pub enum HirKind<'cx> {
     /// A resolved variable (i.e. a DeBruijn index)
     Var(AlphaVar),
+    /// A variable that couldn't be resolved. Detected during resolution, but causes an error during typeck.
+    MissingVar(V),
     /// An import. It must have been resolved by the time we get to typechecking/normalization.
     Import(ImportId<'cx>),
     // Forbidden ExprKind variants: Var, Import, Completion
@@ -104,6 +106,7 @@ fn hir_to_expr<'cx>(
     let kind = match hir.kind() {
         HirKind::Var(v) if opts.alpha => ExprKind::Var(V("_".into(), v.idx())),
         HirKind::Var(v) => ExprKind::Var(env.label_var(*v)),
+        HirKind::MissingVar(v) => ExprKind::Var(v.clone()),
         HirKind::Import(import) => {
             let typed = cx[import].unwrap_result();
             return hir_to_expr(cx, &typed.hir, opts, &mut NameEnv::new());
diff --git a/dhall/src/semantics/resolve/resolve.rs b/dhall/src/semantics/resolve/resolve.rs
index 7450825..c4cd518 100644
--- a/dhall/src/semantics/resolve/resolve.rs
+++ b/dhall/src/semantics/resolve/resolve.rs
@@ -377,11 +377,7 @@ fn traverse_resolve_expr<'cx>(
     Ok(match expr.kind() {
         ExprKind::Var(var) => match name_env.unlabel_var(&var) {
             Some(v) => Hir::new(HirKind::Var(v), expr.span()),
-            None => mkerr(
-                ErrorBuilder::new(format!("unbound variable `{}`", var))
-                    .span_err(expr.span(), "not found in this scope")
-                    .format(),
-            )?,
+            None => Hir::new(HirKind::MissingVar(var.clone()), expr.span()),
         },
         ExprKind::Op(OpKind::BinOp(BinOp::ImportAlt, l, r)) => {
             match traverse_resolve_expr(name_env, l, f) {
@@ -492,6 +488,8 @@ fn resolve_with_env<'cx>(
     Ok(Resolved(resolved))
 }
 
+/// Resolves all imports and names. Returns errors if importing failed. Name errors are deferred to
+/// typechecking.
 pub fn resolve<'cx>(
     cx: Ctxt<'cx>,
     parsed: Parsed,
@@ -499,6 +497,7 @@ pub fn resolve<'cx>(
     resolve_with_env(&mut ImportEnv::new(cx), parsed)
 }
 
+/// Resolves names and errors if we find any imports.
 pub fn skip_resolve<'cx>(
     cx: Ctxt<'cx>,
     parsed: Parsed,
diff --git a/dhall/src/semantics/tck/typecheck.rs b/dhall/src/semantics/tck/typecheck.rs
index 5a44c9c..e14bcc6 100644
--- a/dhall/src/semantics/tck/typecheck.rs
+++ b/dhall/src/semantics/tck/typecheck.rs
@@ -184,6 +184,11 @@ pub fn type_with<'cx, 'hir>(
 ) -> Result<Tir<'cx, 'hir>, TypeError> {
     let tir = match hir.kind() {
         HirKind::Var(var) => Tir::from_hir(hir, env.lookup(*var)),
+        HirKind::MissingVar(var) => mkerr(
+            ErrorBuilder::new(format!("unbound variable `{}`", var))
+                .span_err(hir.span(), "not found in this scope")
+                .format(),
+        )?,
         HirKind::Import(import) => {
             let typed = env.cx()[import].unwrap_result();
             Tir::from_hir(hir, typed.ty.clone())
-- 
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