[rustdoc] Don't try to print the value of a non-primitive const

src/librustdoc/clean/utils.rs

@@ -371,6 +371,9 @@ pub(crate) fn print_evaluated_const(
 ) -> Option<String> {
     tcx.const_eval_poly(def_id).ok().and_then(|val| {
         let ty = tcx.type_of(def_id).instantiate_identity();
+        if !ty.is_primitive() {
+            return None;
+        }
         match (val, ty.kind()) {
             (_, &ty::Ref(..)) => None,
             (mir::ConstValue::Scalar(_), &ty::Adt(_, _)) => None,
@@ -439,19 +442,16 @@ fn print_const_with_custom_print_scalar<'tcx>(
 }
 
 pub(crate) fn is_literal_expr(tcx: TyCtxt<'_>, hir_id: hir::HirId) -> bool {
-    if let hir::Node::Expr(expr) = tcx.hir_node(hir_id) {
-        if let hir::ExprKind::Lit(_) = &expr.kind {
-            return true;
-        }
-
-        if let hir::ExprKind::Unary(hir::UnOp::Neg, expr) = &expr.kind
-            && let hir::ExprKind::Lit(_) = &expr.kind
-        {
-            return true;
-        }
-    }
-
-    false
+    use ExprKind::{Lit, Path, Unary};
+    use hir::{Expr, ExprKind, Node, UnOp};
+
+    matches!(
+        tcx.hir_node(hir_id),
+        Node::Expr(Expr {
+            kind: Lit(_) | Path(_) | Unary(UnOp::Neg, Expr { kind: Lit(_) | Path(_), .. }),
+            ..
+        })
+    )
 }
 
 /// Given a type Path, resolve it to a Type using the TyCtxt

src/librustdoc/html/render/print_item.rs

@@ -1920,9 +1920,19 @@ fn item_constant(
             let tcx = cx.tcx();
             render_attributes_in_code(w, it, "", cx)?;
 
+            let val = fmt::from_fn(|f| {
+                let is_literal = c.is_literal(tcx);
+                let expr = c.expr(tcx);
+                if is_literal {
+                    write!(f, " = {expr}", expr = Escape(&expr))
+                } else {
+                    f.write_str(" = _")
+                }
+            });
+
             write!(
                 w,
-                "{vis}const {name}{generics}: {typ}{where_clause}",
+                "{vis}const {name}{generics}: {typ}{val}{where_clause};",
                 vis = visibility_print_with_space(it, cx),
                 name = it.name.unwrap(),
                 generics = print_generics(generics, cx),
@@ -1931,34 +1941,6 @@ fn item_constant(
                     print_where_clause(generics, cx, 0, Ending::NoNewline).maybe_display(),
             )?;
 
-            // FIXME: The code below now prints
-            //            ` = _; // 100i32`
-            //        if the expression is
-            //            `50 + 50`
-            //        which looks just wrong.
-            //        Should we print
-            //            ` = 100i32;`
-            //        instead?
-
-            let value = c.value(tcx);
-            let is_literal = c.is_literal(tcx);
-            let expr = c.expr(tcx);
-            if value.is_some() || is_literal {
-                write!(w, " = {expr};", expr = Escape(&expr))?;
-            } else {
-                w.write_str(";")?;
-            }
-
-            if !is_literal && let Some(value) = &value {
-                let value_lowercase = value.to_lowercase();
-                let expr_lowercase = expr.to_lowercase();
-
-                if value_lowercase != expr_lowercase
-                    && value_lowercase.trim_end_matches("i32") != expr_lowercase
-                {
-                    write!(w, " // {value}", value = Escape(value))?;
-                }
-            }
             Ok::<(), fmt::Error>(())
         })?;
 

tests/rustdoc-ui/const-evalutation-ice.rs

@@ -1,3 +1,4 @@
+//@ check-pass
 // Just check we don't get an ICE for `N`.
 
 use std::cell::Cell;
@@ -8,4 +9,3 @@ pub struct S {
 }
 
 pub const N: usize = 0 - (mem::size_of::<S>() != 400) as usize;
-//~^ ERROR overflow

tests/rustdoc-ui/issues/issue-79494.rs

@@ -1,6 +1,6 @@
+//@ check-pass
 //@ only-64bit
 
 #![feature(const_transmute)]
 
 pub const ZST: &[u8] = unsafe { std::mem::transmute(1usize) };
-//~^ ERROR transmuting from 8-byte type to 16-byte type

tests/rustdoc-ui/track-diagnostics.rs

@@ -1,13 +1,7 @@
+//@ check-pass
 //@ compile-flags: -Z track-diagnostics
 
-// Normalize the emitted location so this doesn't need
-// updating everytime someone adds or removes a line.
-//@ normalize-stderr: ".rs:\d+:\d+" -> ".rs:LL:CC"
-
 struct A;
 struct B;
 
 pub const S: A = B;
-//~^ ERROR mismatched types
-//~| NOTE created at
-//~| NOTE expected `A`, found `B`

tests/rustdoc/constant/const-value-display.rs

@@ -1,9 +1,9 @@
 #![crate_name = "foo"]
 
 //@ has 'foo/constant.HOUR_IN_SECONDS.html'
-//@ has - '//*[@class="rust item-decl"]//code' 'pub const HOUR_IN_SECONDS: u64 = _; // 3_600u64'
+//@ has - '//*[@class="rust item-decl"]//code' 'pub const HOUR_IN_SECONDS: u64 = _;'
 pub const HOUR_IN_SECONDS: u64 = 60 * 60;
 
 //@ has 'foo/constant.NEGATIVE.html'
-//@ has - '//*[@class="rust item-decl"]//code' 'pub const NEGATIVE: i64 = _; // -3_600i64'
+//@ has - '//*[@class="rust item-decl"]//code' 'pub const NEGATIVE: i64 = _;'
 pub const NEGATIVE: i64 = -60 * 60;

tests/rustdoc/constant/generic-const-items.rs

@@ -3,7 +3,7 @@
 
 //@ has 'generic_const_items/constant.K.html'
 //@ has - '//*[@class="rust item-decl"]//code' \
-// "pub const K<'a, T: 'a + Copy, const N: usize>: Option<[T; N]> \
+// "pub const K<'a, T: 'a + Copy, const N: usize>: Option<[T; N]> = None \
 // where \
 //     String: From<T>;"
 pub const K<'a, T: 'a + Copy, const N: usize>: Option<[T; N]> = None

tests/rustdoc/constant/show-const-contents.rs

@@ -21,14 +21,14 @@ pub const CONST_NEG_I32: i32 = -42;
 //@ !hasraw show_const_contents/constant.CONST_EQ_TO_VALUE_I32.html '// 42i32'
 pub const CONST_EQ_TO_VALUE_I32: i32 = 42i32;
 
-//@ hasraw show_const_contents/constant.CONST_CALC_I32.html '= _; // 43i32'
+//@ hasraw show_const_contents/constant.CONST_CALC_I32.html '= _;'
 pub const CONST_CALC_I32: i32 = 42 + 1;
 
 //@ !hasraw show_const_contents/constant.CONST_REF_I32.html '= &42;'
 //@ !hasraw show_const_contents/constant.CONST_REF_I32.html '; //'
 pub const CONST_REF_I32: &'static i32 = &42;
 
-//@ hasraw show_const_contents/constant.CONST_I32_MAX.html '= i32::MAX; // 2_147_483_647i32'
+//@ hasraw show_const_contents/constant.CONST_I32_MAX.html '= i32::MAX;'
 pub const CONST_I32_MAX: i32 = i32::MAX;
 
 //@ !hasraw show_const_contents/constant.UNIT.html '= ();'
@@ -47,21 +47,19 @@ pub struct MyTypeWithStr(&'static str);
 //@ !hasraw show_const_contents/constant.MY_TYPE_WITH_STR.html '; //'
 pub const MY_TYPE_WITH_STR: MyTypeWithStr = MyTypeWithStr("show this");
 
-//@ hasraw show_const_contents/constant.PI.html '= 3.14159265358979323846264338327950288_f32;'
-//@ hasraw show_const_contents/constant.PI.html '; // 3.14159274f32'
+//@ hasraw show_const_contents/constant.PI.html '= _;'
 pub use std::f32::consts::PI;
-
-//@ hasraw show_const_contents/constant.MAX.html '= i32::MAX; // 2_147_483_647i32'
+//@ hasraw show_const_contents/constant.MAX.html '= i32::MAX;'
 #[allow(deprecated, deprecated_in_future)]
 pub use std::i32::MAX;
 
 macro_rules! int_module {
-    ($T:ident) => (
+    ($T:ident) => {
         pub const MIN: $T = $T::MIN;
-    )
+    };
 }
 
-//@ hasraw show_const_contents/constant.MIN.html '= i16::MIN; // -32_768i16'
+//@ hasraw show_const_contents/constant.MIN.html '= i16::MIN;'
 int_module!(i16);
 
 //@ has show_const_contents/constant.ESCAPE.html //pre '= r#"<script>alert("ESCAPE");</script>"#;'

tests/rustdoc/inline_cross/generic-const-items.rs

@@ -5,7 +5,7 @@
 
 //@ has 'user/constant.K.html'
 //@ has - '//*[@class="rust item-decl"]//code' \
-// "pub const K<'a, T: 'a + Copy, const N: usize>: Option<[T; N]> \
+// "pub const K<'a, T: 'a + Copy, const N: usize>: Option<[T; N]> = _ \
 // where \
 //     String: From<T>;"
 pub use generic_const_items::K;

tests/rustdoc/non-primitive-assoc-const-150312.rs

@@ -0,0 +1,18 @@
+#![crate_name = "foo"]
+
+pub trait Foo {
+    type AssocType;
+
+    const THE_CONST: Self::AssocType;
+}
+
+pub struct Bar;
+
+impl Foo for Bar {
+    type AssocType = (u32,);
+
+    //@ has foo/struct.Bar.html
+    //@ matches - '//section[@id="associatedconstant.THE_CONST"]/h4[@class="code-header"]' '^const THE_CONST: Self::AssocType'
+    //@ !matches - '//section[@id="associatedconstant.THE_CONST"]//*[last()]' '{transmute'
+    const THE_CONST: Self::AssocType = (1u32,);
+}