Rollup merge of #96581 - RalfJung:debug-size-align, r=oli-obk

make Size and Align debug-printing a bit more compact

In particular in `{:#?}`-mode, these take up a lot of space, so I think this is the better alternative (even though it is a bit longer in `{:?}` mode, I think it is still more readable).

We could make it even smaller by deviating further from what the actual code looks like, e.g. via something like `Size(4 bytes)`. Not sure what people would think about that?

Cc `````@oli-obk`````

compiler/rustc_middle/src/mir/pretty.rs

@@ -448,6 +448,12 @@ impl<'tcx> Visitor<'tcx> for ExtraComments<'tcx> {
                 self.push(&format!("+ user_ty: {:?}", user_ty));
             }
 
+            let fmt_val = |val: &ConstValue<'tcx>| match val {
+                ConstValue::Scalar(s) => format!("Scalar({:?})", s),
+                ConstValue::Slice { .. } => format!("Slice(..)"),
+                ConstValue::ByRef { .. } => format!("ByRef(..)"),
+            };
+
             let val = match literal {
                 ConstantKind::Ty(ct) => match ct.val() {
                     ty::ConstKind::Param(p) => format!("Param({})", p),
@@ -457,7 +463,7 @@ impl<'tcx> Visitor<'tcx> for ExtraComments<'tcx> {
                         uv.substs,
                         uv.promoted,
                     ),
-                    ty::ConstKind::Value(val) => format!("Value({:?})", val),
+                    ty::ConstKind::Value(val) => format!("Value({})", fmt_val(&val)),
                     ty::ConstKind::Error(_) => "Error".to_string(),
                     // These variants shouldn't exist in the MIR.
                     ty::ConstKind::Placeholder(_)
@@ -467,7 +473,7 @@ impl<'tcx> Visitor<'tcx> for ExtraComments<'tcx> {
                 // To keep the diffs small, we render this like we render `ty::Const::Value`.
                 //
                 // This changes once `ty::Const::Value` is represented using valtrees.
-                ConstantKind::Val(val, _) => format!("Value({:?})", val),
+                ConstantKind::Val(val, _) => format!("Value({})", fmt_val(&val)),
             };
 
             self.push(&format!("+ literal: Const {{ ty: {}, val: {} }}", literal.ty(), val));

compiler/rustc_target/src/abi/mod.rs

@@ -276,12 +276,19 @@ impl ToJson for Endian {
 }
 
 /// Size of a type in bytes.
-#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug, Encodable, Decodable)]
+#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Encodable, Decodable)]
 #[derive(HashStable_Generic)]
 pub struct Size {
     raw: u64,
 }
 
+// This is debug-printed a lot in larger structs, don't waste too much space there
+impl fmt::Debug for Size {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "Size({} bytes)", self.bytes())
+    }
+}
+
 impl Size {
     pub const ZERO: Size = Size { raw: 0 };
 
@@ -485,12 +492,19 @@ impl Step for Size {
 }
 
 /// Alignment of a type in bytes (always a power of two).
-#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug, Encodable, Decodable)]
+#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Encodable, Decodable)]
 #[derive(HashStable_Generic)]
 pub struct Align {
     pow2: u8,
 }
 
+// This is debug-printed a lot in larger structs, don't waste too much space there
+impl fmt::Debug for Align {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "Align({} bytes)", self.bytes())
+    }
+}
+
 impl Align {
     pub const ONE: Align = Align { pow2: 0 };