From c4acac64432aa6026ae24422abfee7c3014576e3 Mon Sep 17 00:00:00 2001
From: Nika Layzell <nika@thelayzells.com>
Date: Sat, 9 Jul 2022 11:34:06 -0400
Subject: [PATCH] proc_macro: Move subspan to be a method on Span in the bridge

This method is still only used for Literal::subspan, however the
implementation only depends on the Span component, so it is simpler and
more efficient for now to pass down only the information that is needed.
In the future, if more information about the Literal is required in the
implementation (e.g. to validate that spans line up as expected with
source text), that extra information can be added back with extra
arguments.
---
 .../rustc_expand/src/proc_macro_server.rs     | 73 +++++++++----------
 library/proc_macro/src/bridge/mod.rs          |  2 +-
 library/proc_macro/src/lib.rs                 |  7 +-
 3 files changed, 38 insertions(+), 44 deletions(-)

diff --git a/compiler/rustc_expand/src/proc_macro_server.rs b/compiler/rustc_expand/src/proc_macro_server.rs
index 0618c9aa084d6..176c77ca6edc6 100644
--- a/compiler/rustc_expand/src/proc_macro_server.rs
+++ b/compiler/rustc_expand/src/proc_macro_server.rs
@@ -436,43 +436,6 @@ impl server::FreeFunctions for Rustc<'_, '_> {
             span: self.call_site,
         })
     }
-
-    fn literal_subspan(
-        &mut self,
-        literal: Literal<Self::Span, Self::Symbol>,
-        start: Bound<usize>,
-        end: Bound<usize>,
-    ) -> Option<Self::Span> {
-        let span = literal.span;
-        let length = span.hi().to_usize() - span.lo().to_usize();
-
-        let start = match start {
-            Bound::Included(lo) => lo,
-            Bound::Excluded(lo) => lo.checked_add(1)?,
-            Bound::Unbounded => 0,
-        };
-
-        let end = match end {
-            Bound::Included(hi) => hi.checked_add(1)?,
-            Bound::Excluded(hi) => hi,
-            Bound::Unbounded => length,
-        };
-
-        // Bounds check the values, preventing addition overflow and OOB spans.
-        if start > u32::MAX as usize
-            || end > u32::MAX as usize
-            || (u32::MAX - start as u32) < span.lo().to_u32()
-            || (u32::MAX - end as u32) < span.lo().to_u32()
-            || start >= end
-            || end > length
-        {
-            return None;
-        }
-
-        let new_lo = span.lo() + BytePos::from_usize(start);
-        let new_hi = span.lo() + BytePos::from_usize(end);
-        Some(span.with_lo(new_lo).with_hi(new_hi))
-    }
 }
 
 impl server::TokenStream for Rustc<'_, '_> {
@@ -697,6 +660,42 @@ impl server::Span for Rustc<'_, '_> {
         Some(first.to(second))
     }
 
+    fn subspan(
+        &mut self,
+        span: Self::Span,
+        start: Bound<usize>,
+        end: Bound<usize>,
+    ) -> Option<Self::Span> {
+        let length = span.hi().to_usize() - span.lo().to_usize();
+
+        let start = match start {
+            Bound::Included(lo) => lo,
+            Bound::Excluded(lo) => lo.checked_add(1)?,
+            Bound::Unbounded => 0,
+        };
+
+        let end = match end {
+            Bound::Included(hi) => hi.checked_add(1)?,
+            Bound::Excluded(hi) => hi,
+            Bound::Unbounded => length,
+        };
+
+        // Bounds check the values, preventing addition overflow and OOB spans.
+        if start > u32::MAX as usize
+            || end > u32::MAX as usize
+            || (u32::MAX - start as u32) < span.lo().to_u32()
+            || (u32::MAX - end as u32) < span.lo().to_u32()
+            || start >= end
+            || end > length
+        {
+            return None;
+        }
+
+        let new_lo = span.lo() + BytePos::from_usize(start);
+        let new_hi = span.lo() + BytePos::from_usize(end);
+        Some(span.with_lo(new_lo).with_hi(new_hi))
+    }
+
     fn resolved_at(&mut self, span: Self::Span, at: Self::Span) -> Self::Span {
         span.with_ctxt(at.ctxt())
     }
diff --git a/library/proc_macro/src/bridge/mod.rs b/library/proc_macro/src/bridge/mod.rs
index 712b8c637973e..5cde966bf173d 100644
--- a/library/proc_macro/src/bridge/mod.rs
+++ b/library/proc_macro/src/bridge/mod.rs
@@ -57,7 +57,6 @@ macro_rules! with_api {
                 fn track_env_var(var: &str, value: Option<&str>);
                 fn track_path(path: &str);
                 fn literal_from_str(s: &str) -> Result<Literal<$S::Span, $S::Symbol>, ()>;
-                fn literal_subspan(lit: Literal<$S::Span, $S::Symbol>, start: Bound<usize>, end: Bound<usize>) -> Option<$S::Span>;
             },
             TokenStream {
                 fn drop($self: $S::TokenStream);
@@ -114,6 +113,7 @@ macro_rules! with_api {
                 fn before($self: $S::Span) -> $S::Span;
                 fn after($self: $S::Span) -> $S::Span;
                 fn join($self: $S::Span, other: $S::Span) -> Option<$S::Span>;
+                fn subspan($self: $S::Span, start: Bound<usize>, end: Bound<usize>) -> Option<$S::Span>;
                 fn resolved_at($self: $S::Span, at: $S::Span) -> $S::Span;
                 fn source_text($self: $S::Span) -> Option<String>;
                 fn save_span($self: $S::Span) -> usize;
diff --git a/library/proc_macro/src/lib.rs b/library/proc_macro/src/lib.rs
index 372bd3ac2141e..5cf16bdd08cdd 100644
--- a/library/proc_macro/src/lib.rs
+++ b/library/proc_macro/src/lib.rs
@@ -1379,12 +1379,7 @@ impl Literal {
     // was 'c' or whether it was '\u{63}'.
     #[unstable(feature = "proc_macro_span", issue = "54725")]
     pub fn subspan<R: RangeBounds<usize>>(&self, range: R) -> Option<Span> {
-        bridge::client::FreeFunctions::literal_subspan(
-            self.0.clone(),
-            range.start_bound().cloned(),
-            range.end_bound().cloned(),
-        )
-        .map(Span)
+        self.0.span.subspan(range.start_bound().cloned(), range.end_bound().cloned()).map(Span)
     }
 
     fn with_symbol_and_suffix<R>(&self, f: impl FnOnce(&str, &str) -> R) -> R {