Don't show a computed value in the docs of a literal const

Author: ohadravid

src/libcore/num/f32.rs

@@ -30,7 +30,7 @@ pub const DIGITS: u32 = 6;
 ///
 /// [Machine epsilon]: https://en.wikipedia.org/wiki/Machine_epsilon
 #[stable(feature = "rust1", since = "1.0.0")]
-pub const EPSILON: f32 = 1.19209290e-07_f32;
+pub const EPSILON: f32 = 1.1920929e-07_f32;
 
 /// Smallest finite `f32` value.
 #[stable(feature = "rust1", since = "1.0.0")]

src/librustdoc/clean/inline.rs

@@ -467,6 +467,9 @@ fn build_const(cx: &DocContext<'_>, did: DefId) -> clean::Constant {
         type_: cx.tcx.type_of(did).clean(cx),
         expr: print_inlined_const(cx, did),
         value: clean::print_evaluated_const(cx, did),
+        is_literal: cx.tcx.hir().as_local_hir_id(did).map(
+            |hir_id| clean::is_literal_expr(cx, hir_id)
+        ).unwrap_or(false),
     }
 }
 

src/librustdoc/clean/mod.rs

@@ -1301,6 +1301,7 @@ impl Clean<Constant> for hir::ConstArg {
             type_: cx.tcx.type_of(cx.tcx.hir().body_owner_def_id(self.value.body)).clean(cx),
             expr: print_const_expr(cx, self.value.body),
             value: None,
+            is_literal: is_literal_expr(cx, self.value.body.hir_id),
         }
     }
 }
@@ -3276,6 +3277,7 @@ impl<'tcx> Clean<Constant> for ty::Const<'tcx> {
             type_: self.ty.clean(cx),
             expr: format!("{}", self),
             value: None,
+            is_literal: false,
         }
     }
 }
@@ -3834,11 +3836,13 @@ pub struct Constant {
     pub type_: Type,
     pub expr: String,
     pub value: Option<String>,
+    pub is_literal: bool,
 }
 
 impl Clean<Item> for doctree::Constant<'_> {
     fn clean(&self, cx: &DocContext<'_>) -> Item {
         let def_id = cx.tcx.hir().local_def_id(self.id);
+
         Item {
             name: Some(self.name.clean(cx)),
             attrs: self.attrs.clean(cx),
@@ -3851,6 +3855,7 @@ impl Clean<Item> for doctree::Constant<'_> {
                 type_: self.type_.clean(cx),
                 expr: print_const_expr(cx, self.expr),
                 value: print_evaluated_const(cx, def_id),
+                is_literal: is_literal_expr( cx, self.expr.hir_id),
             }),
         }
     }
@@ -4248,6 +4253,7 @@ pub fn print_evaluated_const(cx: &DocContext<'_>, def_id: DefId) -> Option<Strin
     let value = cx.tcx.const_eval(param_env.and(cid)).ok().and_then(|value| {
         match (value.val, &value.ty.kind) {
             (_, ty::Ref(..)) => None,
+            (ty::ConstKind::Value(ConstValue::Scalar(_)), ty::Adt(_, _)) => None,
             (ty::ConstKind::Value(ConstValue::Scalar(_)), _) =>
                 Some(print_const_with_custom_print_scalar(cx, value)),
             _ => None,
@@ -4310,6 +4316,22 @@ fn print_const_expr(cx: &DocContext<'_>, body: hir::BodyId) -> String {
     cx.tcx.hir().hir_to_pretty_string(body.hir_id)
 }
 
+fn is_literal_expr(cx: &DocContext<'_>, hir_id: hir::HirId) -> bool {
+    if let hir::Node::Expr(expr) = cx.tcx.hir().get(hir_id) {
+        if let hir::ExprKind::Lit(_) = &expr.kind {
+            return true;
+        }
+
+        if let hir::ExprKind::Unary(hir::UnOp::UnNeg, expr) = &expr.kind {
+            if let hir::ExprKind::Lit(_) = &expr.kind {
+                return true;
+            }
+        }
+    }
+
+    false
+}
+
 /// Given a type Path, resolve it to a Type using the TyCtxt
 fn resolve_type(cx: &DocContext<'_>,
                 path: Path,

src/librustdoc/html/render.rs

@@ -2297,7 +2297,7 @@ fn item_constant(w: &mut Buffer, cx: &Context, it: &clean::Item, c: &clean::Cons
     );
 
     if let Some(value) = &c.value {
-        if value != &c.expr {
+        if value.to_lowercase() != c.expr.to_lowercase() && !c.is_literal {
             write!(w, " /* {value} */", value = value);
         }
     }

src/test/rustdoc/show-const-contents.rs

@@ -4,9 +4,14 @@
 // @has show_const_contents/constant.CONST_S.html 'show this'
 pub const CONST_S: &'static str = "show this";
 
-// @has show_const_contents/constant.CONST_I32.html '= 42; /* 42i32 */'
+// @has show_const_contents/constant.CONST_I32.html '= 42;'
+// @!has show_const_contents/constant.CONST_I32.html '; /*'
 pub const CONST_I32: i32 = 42;
 
+// @has show_const_contents/constant.CONST_NEG_I32.html '= -42;'
+// @!has show_const_contents/constant.CONST_NEG_I32.html '; /*'
+pub const CONST_NEG_I32: i32 = -42;
+
 // @has show_const_contents/constant.CONST_EQ_TO_VALUE_I32.html '= 42i32;'
 // @!has show_const_contents/constant.CONST_EQ_TO_VALUE_I32.html '/* 42i32 */'
 pub const CONST_EQ_TO_VALUE_I32: i32 = 42i32;
@@ -26,4 +31,11 @@ pub const UNIT: () = ();
 pub struct MyType(i32);
 
 // @has show_const_contents/constant.MY_TYPE.html '= MyType(42);'
+// @!has show_const_contents/constant.MY_TYPE.html '; /*'
 pub const MY_TYPE: MyType = MyType(42);
+
+pub struct MyTypeWithStr(&'static str);
+
+// @has show_const_contents/constant.MY_TYPE_WITH_STR.html '= MyTypeWithStr("show this");'
+// @!has show_const_contents/constant.MY_TYPE_WITH_STR.html '; /*'
+pub const MY_TYPE_WITH_STR: MyTypeWithStr = MyTypeWithStr("show this");