From df96cba432d9e869765385d6474b505494533435 Mon Sep 17 00:00:00 2001
From: Zalathar <Zalathar@users.noreply.github.com>
Date: Mon, 3 Jun 2024 17:00:10 +1000
Subject: [PATCH] Add `Span::trim_end`

This is the counterpart of `Span::trim_start`.
---
 compiler/rustc_span/src/lib.rs   |  7 +++++++
 compiler/rustc_span/src/tests.rs | 19 +++++++++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/compiler/rustc_span/src/lib.rs b/compiler/rustc_span/src/lib.rs
index b2ca01fe3b9..82179a4a058 100644
--- a/compiler/rustc_span/src/lib.rs
+++ b/compiler/rustc_span/src/lib.rs
@@ -682,6 +682,13 @@ impl Span {
         if span.hi > other.hi { Some(span.with_lo(cmp::max(span.lo, other.hi))) } else { None }
     }
 
+    /// Returns `Some(span)`, where the end is trimmed by the start of `other`.
+    pub fn trim_end(self, other: Span) -> Option<Span> {
+        let span = self.data();
+        let other = other.data();
+        if span.lo < other.lo { Some(span.with_hi(cmp::min(span.hi, other.lo))) } else { None }
+    }
+
     /// Returns the source span -- this is either the supplied span, or the span for
     /// the macro callsite that expanded to it.
     pub fn source_callsite(self) -> Span {
diff --git a/compiler/rustc_span/src/tests.rs b/compiler/rustc_span/src/tests.rs
index 5c9dcc2a80f..48fa786fb1c 100644
--- a/compiler/rustc_span/src/tests.rs
+++ b/compiler/rustc_span/src/tests.rs
@@ -61,6 +61,25 @@ fn test_trim() {
     // The resulting span's context should be that of `self`, not `other`.
     let other = span(start, end).with_ctxt(SyntaxContext::from_u32(999));
 
+    // Test cases for `trim_end`.
+
+    assert_eq!(span(well_before, before).trim_end(other), Some(span(well_before, before)));
+    assert_eq!(span(well_before, start).trim_end(other), Some(span(well_before, start)));
+    assert_eq!(span(well_before, mid).trim_end(other), Some(span(well_before, start)));
+    assert_eq!(span(well_before, end).trim_end(other), Some(span(well_before, start)));
+    assert_eq!(span(well_before, after).trim_end(other), Some(span(well_before, start)));
+
+    assert_eq!(span(start, mid).trim_end(other), None);
+    assert_eq!(span(start, end).trim_end(other), None);
+    assert_eq!(span(start, after).trim_end(other), None);
+
+    assert_eq!(span(mid, end).trim_end(other), None);
+    assert_eq!(span(mid, after).trim_end(other), None);
+
+    assert_eq!(span(end, after).trim_end(other), None);
+
+    assert_eq!(span(after, well_after).trim_end(other), None);
+
     // Test cases for `trim_start`.
 
     assert_eq!(span(after, well_after).trim_start(other), Some(span(after, well_after)));