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-rw-r--r--dhall/src/syntax/ast/span.rs12
1 files changed, 7 insertions, 5 deletions
diff --git a/dhall/src/syntax/ast/span.rs b/dhall/src/syntax/ast/span.rs
index 79bcc52..2e09863 100644
--- a/dhall/src/syntax/ast/span.rs
+++ b/dhall/src/syntax/ast/span.rs
@@ -75,13 +75,15 @@ impl Span {
}
/// Convert a byte idx into a string into a char idx for consumption by annotate_snippets.
+/// The byte idx must be at a char boundary.
fn char_idx_from_byte_idx(input: &str, idx: usize) -> usize {
+ use std::iter::once;
input
.char_indices()
+ .map(|(byte_i, _)| byte_i) // We don't care about the char
+ .chain(once(input.len())) // In case the idx points to the end of the string
.enumerate()
- .find(|(_, (i, _))| *i == idx)
- .map(|(i, (_, _))| i)
- // We should be able to unwrap() here, but somehow it panics on an example from
- // serde_dhall/lib.rs...
- .unwrap_or(0)
+ .find(|(_, byte_i)| *byte_i == idx)
+ .map(|(char_i, _)| char_i)
+ .unwrap()
}