From: Robert Griesemer <gri@golang.org>
Date: Thu, 25 Aug 2022 21:50:27 +0000 (-0700)
Subject: go/types: provide a better error message for [...] array types
X-Git-Tag: go1.20rc1~1404
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=2eba2ff8a1572d7fcba65a5f9d54f73e307a0054;p=gostls13.git

go/types: provide a better error message for [...] array types

This matches types2 behavior.

For #54511.

Change-Id: Iea906e9fec7e334b7aa7f481de87373fa93d1c7c
Reviewed-on: https://go-review.googlesource.com/c/go/+/425715
Reviewed-by: Robert Griesemer <gri@google.com>
Run-TryBot: Robert Griesemer <gri@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
Reviewed-by: Alan Donovan <adonovan@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
---

diff --git a/src/go/types/testdata/check/decls0.go b/src/go/types/testdata/check/decls0.go
index d8fcef0824..7ba90c0504 100644
--- a/src/go/types/testdata/check/decls0.go
+++ b/src/go/types/testdata/check/decls0.go
@@ -51,7 +51,7 @@ func _() { var init int; _ = init }
 
 // invalid array types
 type (
-	iA0 [... /* ERROR "invalid use of '...'" */ ]byte
+	iA0 [... /* ERROR "invalid use of \[...\] array" */ ]byte
 	// The error message below could be better. At the moment
 	// we believe an integer that is too large is not an integer.
 	// But at least we get an error.
diff --git a/src/go/types/typexpr.go b/src/go/types/typexpr.go
index 13adb9f2a9..ff6bb36255 100644
--- a/src/go/types/typexpr.go
+++ b/src/go/types/typexpr.go
@@ -292,11 +292,19 @@ func (check *Checker) typInternal(e0 ast.Expr, def *Named) (T Type) {
 
 		typ := new(Array)
 		def.setUnderlying(typ)
-		typ.len = check.arrayLength(e.Len)
+		// Provide a more specific error when encountering a [...] array
+		// rather than leaving it to the handling of the ... expression.
+		if _, ok := e.Len.(*ast.Ellipsis); ok {
+			check.error(e.Len, _BadDotDotDotSyntax, "invalid use of [...] array (outside a composite literal)")
+			typ.len = -1
+		} else {
+			typ.len = check.arrayLength(e.Len)
+		}
 		typ.elem = check.varType(e.Elt)
 		if typ.len >= 0 {
 			return typ
 		}
+		// report error if we encountered [...]
 
 	case *ast.Ellipsis:
 		// dots are handled explicitly where they are legal