#464 Improve error message when program is missing arm of branching statement

CHANGELOG.md

@@ -26,6 +26,7 @@ and this project does not currently adhere to a particular versioning scheme.
 ### Changed
 
 - Change tuple syntax to not require parentheses in some cases. ([#554][gh-554])
+- Improve error messages in branching statements. ([#464][gh-464])
 
 ## [0.2.36] - 2024-07-04
 
@@ -369,6 +370,7 @@ and this project does not currently adhere to a particular versioning scheme.
 [gh-444]: https://github.com/HigherOrderCO/Bend/issues/444
 [gh-451]: https://github.com/HigherOrderCO/Bend/issues/451
 [gh-463]: https://github.com/HigherOrderCO/Bend/issues/463
+[gh-464]: https://github.com/HigherOrderCO/Bend/issues/464
 [gh-465]: https://github.com/HigherOrderCO/Bend/issues/465
 [gh-466]: https://github.com/HigherOrderCO/Bend/issues/466
 [gh-467]: https://github.com/HigherOrderCO/Bend/issues/467

src/fun/transform/float_combinators.rs

@@ -131,6 +131,7 @@ impl Term {
   /// - An application or numeric operation where all arguments are safe.
   /// - A safe Lambda, e.g. a nullary constructor or a lambda with safe body.
   /// - A Reference with a safe body.
+  ///
   /// A reference to a recursive definition (or mutually recursive) is not safe.
   fn is_safe(&self, ctx: &mut FloatCombinatorsCtx) -> bool {
     maybe_grow(|| match self {

src/imp/parser.rs

@@ -575,7 +575,9 @@ impl<'a> PyParser<'a> {
     indent.exit_level();
 
     if nxt_indent != *indent {
-      return self.expected_indent(*indent, nxt_indent);
+      return self
+        .expected_indent(*indent, nxt_indent)
+        .or(self.expected_spanned("'else' or 'elif'", self.index..self.index + 1));
     }
     let mut elifs = Vec::new();
     while self.try_parse_keyword("elif") {
@@ -588,7 +590,9 @@ impl<'a> PyParser<'a> {
       indent.exit_level();
 
       if nxt_indent != *indent {
-        return self.expected_indent(*indent, nxt_indent);
+        return self
+          .expected_indent(*indent, nxt_indent)
+          .or(self.expected_spanned("'else' or 'elif'", self.index..self.index + 1));
       }
       elifs.push((cond, then));
     }
@@ -630,7 +634,7 @@ impl<'a> PyParser<'a> {
     self.consume_new_line()?;
     indent.enter_level();
 
-    self.consume_indent_exactly(*indent)?;
+    self.consume_indent_exactly(*indent).or(self.expected_spanned("'case'", self.index..self.index + 1))?;
     let (case, mut nxt_indent) = self.parse_match_case(indent)?;
     let mut arms = vec![case];
     while nxt_indent == *indent {
@@ -728,7 +732,9 @@ impl<'a> PyParser<'a> {
     let mut expected_num = 1;
     while should_continue {
       if nxt_indent != *indent {
-        return self.expected_indent(*indent, nxt_indent);
+        return self
+          .expected_indent(*indent, nxt_indent)
+          .or(self.expected_spanned("'case'", self.index..self.index + 1));
       }
       let (case, stmt, nxt_indent_) = self.parse_switch_case(indent)?;
       nxt_indent = nxt_indent_;
@@ -793,7 +799,7 @@ impl<'a> PyParser<'a> {
     self.consume_new_line()?;
     indent.enter_level();
 
-    self.consume_indent_exactly(*indent)?;
+    self.consume_indent_exactly(*indent).or(self.expected_spanned("'case'", self.index..self.index + 1))?;
     let (case, mut nxt_indent) = self.parse_match_case(indent)?;
     let mut arms = vec![case];
     while nxt_indent == *indent {
@@ -824,7 +830,7 @@ impl<'a> PyParser<'a> {
     self.consume_new_line()?;
     indent.enter_level();
 
-    self.consume_indent_exactly(*indent)?;
+    self.consume_indent_exactly(*indent).or(self.expected_spanned("'when'", self.index..self.index + 1))?;
     self.parse_keyword("when")?;
     let cond = self.parse_expr(true, false)?;
     self.skip_trivia_inline()?;
@@ -837,7 +843,9 @@ impl<'a> PyParser<'a> {
     indent.exit_level();
 
     if nxt_indent != *indent {
-      return self.expected_indent(*indent, nxt_indent);
+      return self
+        .expected_indent(*indent, nxt_indent)
+        .or(self.expected_spanned("'else'", self.index..self.index + 1));
     }
     self.parse_keyword("else")?;
     self.skip_trivia_inline()?;

src/lib.rs

@@ -14,6 +14,7 @@ use diagnostics::{Diagnostics, DiagnosticsConfig, ERR_INDENT_SIZE};
 use net::hvm_to_net::hvm_to_net;
 
 pub mod diagnostics;
+#[allow(clippy::mutable_key_type)]
 pub mod fun;
 pub mod hvm;
 pub mod imp;
@@ -197,6 +198,7 @@ pub fn readback_hvm_net(
   let mut diags = Diagnostics::default();
   let net = hvm_to_net(net);
   let mut term = net_to_term(&net, book, labels, linear, &mut diags);
+  #[allow(clippy::mutable_key_type)]
   let recursive_defs = book.recursive_defs();
   term.expand_generated(book, &recursive_defs);
   term.resugar_strings(adt_encoding);

tests/golden_tests/parse_file/bend_missing_else.bend

@@ -0,0 +1,15 @@
+def is_even(n):
+  if n % 2 == 0:
+    return 1
+  else:
+    return 0
+
+def get_even_sum_under_if(this_number):
+  bend current = 0:
+    when current < this_number:
+      new_num = fork(current + is_even(current))
+
+      return new_num
+
+def main():
+  return get_even_sum_under_if(1000)

tests/golden_tests/parse_file/fold_missing_case.bend

@@ -0,0 +1,3 @@
+def main:
+  fold [] with x = 1:
+

tests/golden_tests/parse_file/if_missing_else.bend

@@ -0,0 +1,4 @@
+def main:
+  if 1 == 1:
+    return "true"
+

tests/golden_tests/parse_file/match_missing_case.bend

@@ -0,0 +1,3 @@
+def main:
+  match []:
+

tests/snapshots/compile_file__elif_no_else.bend.snap

@@ -4,5 +4,6 @@ input_file: tests/golden_tests/compile_file/elif_no_else.bend
 ---
 Errors:
 In tests/golden_tests/compile_file/elif_no_else.bend :
-Indentation error. Expected 2 spaces, got end-of-input.
+- expected: 'else' or 'elif'
+- detected: end of input
   6 |  

tests/snapshots/parse_file__bend_missing_else.bend.snap

@@ -0,0 +1,9 @@
+---
+source: tests/golden_tests.rs
+input_file: tests/golden_tests/parse_file/bend_missing_else.bend
+---
+Errors:
+In tests/golden_tests/parse_file/bend_missing_else.bend :
+- expected: 'else'
+- detected:
+  14 | def main():

tests/snapshots/parse_file__fold_missing_case.bend.snap

@@ -0,0 +1,9 @@
+---
+source: tests/golden_tests.rs
+input_file: tests/golden_tests/parse_file/fold_missing_case.bend
+---
+Errors:
+In tests/golden_tests/parse_file/fold_missing_case.bend :
+- expected: 'case'
+- detected: end of input
+  4 |  

tests/snapshots/parse_file__if_missing_else.bend.snap

@@ -0,0 +1,9 @@
+---
+source: tests/golden_tests.rs
+input_file: tests/golden_tests/parse_file/if_missing_else.bend
+---
+Errors:
+In tests/golden_tests/parse_file/if_missing_else.bend :
+- expected: 'else' or 'elif'
+- detected: end of input
+  5 |  

tests/snapshots/parse_file__match_missing_case.bend.snap

@@ -0,0 +1,9 @@
+---
+source: tests/golden_tests.rs
+input_file: tests/golden_tests/parse_file/match_missing_case.bend
+---
+Errors:
+In tests/golden_tests/parse_file/match_missing_case.bend :
+- expected: 'case'
+- detected: end of input
+  4 |