Revert "cmd/compile: improve errors for invalid conversions of consts"

This reverts commit 2da9c3e0.

Reason for revert: while the new error messages are more informative,
they're not strictly correct. This CL also conflicts with CL 187657.

Change-Id: I1c36cf7e86c2f35ee83a4f98918ee38aa1f59965
Reviewed-on: https://go-review.googlesource.com/c/go/+/193977
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

src/cmd/compile/internal/gc/const.go

@@ -413,20 +413,16 @@ func convlit1(n *Node, t *types.Type, explicit bool, reuse canReuseNode) *Node {
 	return n
 
 bad:
-	reportErr := false
 	if !n.Diag() {
-		reportErr = !t.Broke()
+		if !t.Broke() {
+			yyerror("cannot convert %L to type %v", n, t)
+		}
 		n.SetDiag(true)
 	}
 
 	if n.Type.IsUntyped() {
 		n = defaultlitreuse(n, nil, reuse)
 	}
-
-	if reportErr {
-		yyerror("cannot convert %L to type %v", n, t)
-	}
-
 	return n
 }
 

test/fixedbugs/issue21979.go

-// errorcheck
-
-// Copyright 2019 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-package p
-
-func f() {
-	// old error: "(type untyped string)"
-	_ = bool("") // ERROR "cannot convert .. \(type string\) to type bool"
-
-	// old error: "(type untyped number)"
-	_ = bool(1) // ERROR "cannot convert 1 \(type int\) to type bool"
-
-	// old error: "(type untyped number)"
-	_ = bool(1.0) // ERROR "cannot convert 1 \(type float64\) to type bool"
-
-	// old error: "(type untyped number)"
-	_ = bool(-4 + 2i) // ERROR "cannot convert -4 \+ 2i \(type complex128\) to type bool"
-
-	// old error: "(type untyped bool)"
-	_ = string(true) // ERROR "cannot convert true \(type bool\) to type string"
-
-	_ = string(-1)
-
-	// old error: "(type untyped number)"
-	_ = string(1.0) // ERROR "cannot convert 1 \(type float64\) to type string"
-
-	// old error: "(type untyped number)"
-	_ = string(-4 + 2i) // ERROR "cannot convert -4 \+ 2i \(type complex128\) to type string"
-
-	// old error: "(type untyped string)"
-	_ = int("") // ERROR "cannot convert .. \(type string\) to type int"
-
-	// old error: "(type untyped bool)"
-	_ = int(true) // ERROR "cannot convert true \(type bool\) to type int"
-
-	_ = int(-1)
-	_ = int(1)
-	_ = int(1.0)
-	_ = int(-4 + 2i) // ERROR "truncated to integer"
-
-	// old error: "(type untyped string)"
-	_ = uint("") // ERROR "cannot convert .. \(type string\) to type uint"
-
-	// old error: "(type untyped bool)"
-	_ = uint(true) // ERROR "cannot convert true \(type bool\) to type uint"
-
-	_ = uint(-1) // ERROR "constant -1 overflows uint"
-	_ = uint(1)
-	_ = uint(1.0)
-	_ = uint(-4 + 2i) // ERROR "constant -4 overflows uint" "truncated to integer"
-
-	// old error: "(type untyped string)"
-	_ = float64("") // ERROR "cannot convert .. \(type string\) to type float64"
-
-	// old error: "(type untyped bool)"
-	_ = float64(true) // ERROR "cannot convert true \(type bool\) to type float64"
-
-	_ = float64(-1)
-	_ = float64(1)
-	_ = float64(1.0)
-	_ = float64(-4 + 2i) // ERROR "truncated to real"
-
-	// old error: "(type untyped string)"
-	_ = complex128("") // ERROR "cannot convert .. \(type string\) to type complex128"
-
-	// old error: "(type untyped bool)"
-	_ = complex128(true) // ERROR "cannot convert true \(type bool\) to type complex128"
-
-	_ = complex128(-1)
-	_ = complex128(1)
-	_ = complex128(1.0)
-}