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Rollup merge of #76699 - lcnr:const-infer-err, r=varkor

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improve const infer error

cc #72328

reduces it from
```
error[E0282]: type annotations needed
  --> src/main.rs:17:5
   |
17 |     Foo.bar().bar().bar().bar().baz();
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: unable to infer the value of a const parameter
```
to
```
error[E0282]: type annotations needed
  --> $DIR/method-chain.rs:21:33
   |
LL |     Foo.bar().bar().bar().bar().baz();
   |                                 ^^^
   |
   = note: cannot infer the value of the const parameter `N`
```

r? @varkor
This commit is contained in:
Dylan DPC 2020-09-16 12:34:21 +02:00 • committed by GitHub
commit 3f9e7fc049
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11 changed files with 74 additions and 16 deletions
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29
compiler/rustc_infer/src/infer/error_reporting/need_type_info.rs
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@ -6,9 +6,10 @@ use rustc_hir::def::{DefKind, Namespace};
use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
use rustc_hir::{Body, Expr, ExprKind, FnRetTy, HirId, Local, Pat};
use rustc_middle::hir::map::Map;
use rustc_middle::infer::unify_key::ConstVariableOriginKind;
use rustc_middle::ty::print::Print;
use rustc_middle::ty::subst::{GenericArg, GenericArgKind};
use rustc_middle::ty::{self, DefIdTree, Ty};
use rustc_middle::ty::{self, DefIdTree, InferConst, Ty};
use rustc_span::source_map::DesugaringKind;
use rustc_span::symbol::kw;
use rustc_span::Span;
@ -569,14 +570,26 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
local_visitor.visit_expr(expr);
}
let error_code = error_code.into();
let mut err = self.tcx.sess.struct_span_err_with_code(
local_visitor.target_span,
"type annotations needed",
error_code,
);
let mut param_name = None;
let span = if let ty::ConstKind::Infer(InferConst::Var(vid)) = ct.val {
let origin = self.inner.borrow_mut().const_unification_table().probe_value(vid).origin;
if let ConstVariableOriginKind::ConstParameterDefinition(param) = origin.kind {
param_name = Some(param);
}
origin.span
} else {
local_visitor.target_span
};
err.note("unable to infer the value of a const parameter");
let error_code = error_code.into();
let mut err =
self.tcx.sess.struct_span_err_with_code(span, "type annotations needed", error_code);
if let Some(param_name) = param_name {
err.note(&format!("cannot infer the value of the const parameter `{}`", param_name));
} else {
err.note("unable to infer the value of a const parameter");
}
err
}