go/types, types2: better error message for invalid array length

If an invalid array length is just an identifier, mention
"array length" so that it's clear this is an invalid array
declaration and not a (invalid) generic type declaration.

Fixes #51145.

Change-Id: I8878cbb6c7b1277fc0a9a014712ec8d55499c5c7
Reviewed-on: https://go-review.googlesource.com/c/go/+/385255
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

diff --git a/src/cmd/compile/internal/types2/testdata/fixedbugs/issue43527.go2 b/src/cmd/compile/internal/types2/testdata/fixedbugs/issue43527.go2
index e4bcee51fe5f90420af7c385a53e748f485a4edc..2955c261f954ee33e647b83b6ddadbe651e57ca7 100644 (file)
--- a/src/cmd/compile/internal/types2/testdata/fixedbugs/issue43527.go2
+++ b/src/cmd/compile/internal/types2/testdata/fixedbugs/issue43527.go2
@@ -9,7 +9,7 @@ const L = 10
 type (
        _        [L]struct{}
        _        [A /* ERROR undeclared name A for array length */ ]struct{}
-       _        [B /* ERROR not an expression */ ]struct{}
+       _        [B /* ERROR invalid array length B */ ]struct{}
        _[A any] struct{}
 
        B int

diff --git a/src/cmd/compile/internal/types2/testdata/fixedbugs/issue51145.go b/src/cmd/compile/internal/types2/testdata/fixedbugs/issue51145.go
new file mode 100644 (file)
index 0000000..b84391d
--- /dev/null
+++ b/src/cmd/compile/internal/types2/testdata/fixedbugs/issue51145.go
@@ -0,0 +1,18 @@
+// Copyright 2022 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
+
+import "fmt"
+
+type (
+       _ [fmt /* ERROR invalid array length fmt */ ]int
+       _ [float64 /* ERROR invalid array length float64 */ ]int
+       _ [f /* ERROR invalid array length f */ ]int
+       _ [nil /* ERROR invalid array length nil */ ]int
+)
+
+func f()
+
+var _ fmt.Stringer // use fmt

diff --git a/src/cmd/compile/internal/types2/typexpr.go b/src/cmd/compile/internal/types2/typexpr.go
index de778fb010bf549b81503057079fc86746cacaa8..149bd5b0b3dfccc42448aa003e19fa7c7eec6887 100644 (file)
--- a/src/cmd/compile/internal/types2/typexpr.go
+++ b/src/cmd/compile/internal/types2/typexpr.go
@@ -502,12 +502,20 @@ func (check *Checker) instantiatedType(x syntax.Expr, xlist []syntax.Expr, def *
 // and returns the constant length >= 0, or a value < 0
 // to indicate an error (and thus an unknown length).
 func (check *Checker) arrayLength(e syntax.Expr) int64 {
-       // If e is an undeclared identifier, the array declaration might be an
-       // attempt at a parameterized type declaration with missing constraint.
-       // Provide a better error message than just "undeclared name: X".
-       if name, _ := e.(*syntax.Name); name != nil && check.lookup(name.Value) == nil {
-               check.errorf(name, "undeclared name %s for array length", name.Value)
-               return -1
+       // If e is an identifier, the array declaration might be an
+       // attempt at a parameterized type declaration with missing
+       // constraint. Provide an error message that mentions array
+       // length.
+       if name, _ := e.(*syntax.Name); name != nil {
+               obj := check.lookup(name.Value)
+               if obj == nil {
+                       check.errorf(name, "undeclared name %s for array length", name.Value)
+                       return -1
+               }
+               if _, ok := obj.(*Const); !ok {
+                       check.errorf(name, "invalid array length %s", name.Value)
+                       return -1
+               }
        }
 
        var x operand

diff --git a/src/go/types/errorcodes.go b/src/go/types/errorcodes.go
index 51f091a9cbe857c5f83ad57f9c2c71f89cdb1268..a7514b317a0ce11ff3953cf634df1419511edcf1 100644 (file)
--- a/src/go/types/errorcodes.go
+++ b/src/go/types/errorcodes.go
@@ -98,13 +98,10 @@ const (
        // _InvalidDeclCycle occurs when a declaration cycle is not valid.
        //
        // Example:
-       //  import "unsafe"
-       //
-       //  type T struct {
-       //      a [n]int
+       //  type S struct {
+       //      S
        //  }
        //
-       //  var n = unsafe.Sizeof(T{})
        _InvalidDeclCycle
 
        // _InvalidTypeCycle occurs when a cycle in type definitions results in a

diff --git a/src/go/types/testdata/fixedbugs/issue43527.go2 b/src/go/types/testdata/fixedbugs/issue43527.go2
index e4bcee51fe5f90420af7c385a53e748f485a4edc..2955c261f954ee33e647b83b6ddadbe651e57ca7 100644 (file)
--- a/src/go/types/testdata/fixedbugs/issue43527.go2
+++ b/src/go/types/testdata/fixedbugs/issue43527.go2
@@ -9,7 +9,7 @@ const L = 10
 type (
        _        [L]struct{}
        _        [A /* ERROR undeclared name A for array length */ ]struct{}
-       _        [B /* ERROR not an expression */ ]struct{}
+       _        [B /* ERROR invalid array length B */ ]struct{}
        _[A any] struct{}
 
        B int

diff --git a/src/go/types/testdata/fixedbugs/issue51145.go b/src/go/types/testdata/fixedbugs/issue51145.go
new file mode 100644 (file)
index 0000000..b84391d
--- /dev/null
+++ b/src/go/types/testdata/fixedbugs/issue51145.go
@@ -0,0 +1,18 @@
+// Copyright 2022 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
+
+import "fmt"
+
+type (
+       _ [fmt /* ERROR invalid array length fmt */ ]int
+       _ [float64 /* ERROR invalid array length float64 */ ]int
+       _ [f /* ERROR invalid array length f */ ]int
+       _ [nil /* ERROR invalid array length nil */ ]int
+)
+
+func f()
+
+var _ fmt.Stringer // use fmt

diff --git a/src/go/types/typexpr.go b/src/go/types/typexpr.go
index 00c250b5b6378714aa730eaaf615b45a044c26a1..db6a904aaa50e73bf82fc65d2eec926d4d735216 100644 (file)
--- a/src/go/types/typexpr.go
+++ b/src/go/types/typexpr.go
@@ -487,12 +487,20 @@ func (check *Checker) instantiatedType(ix *typeparams.IndexExpr, def *Named) (re
 // and returns the constant length >= 0, or a value < 0
 // to indicate an error (and thus an unknown length).
 func (check *Checker) arrayLength(e ast.Expr) int64 {
-       // If e is an undeclared identifier, the array declaration might be an
-       // attempt at a parameterized type declaration with missing constraint.
-       // Provide a better error message than just "undeclared name: X".
-       if name, _ := e.(*ast.Ident); name != nil && check.lookup(name.Name) == nil {
-               check.errorf(name, _InvalidArrayLen, "undeclared name %s for array length", name.Name)
-               return -1
+       // If e is an identifier, the array declaration might be an
+       // attempt at a parameterized type declaration with missing
+       // constraint. Provide an error message that mentions array
+       // length.
+       if name, _ := e.(*ast.Ident); name != nil {
+               obj := check.lookup(name.Name)
+               if obj == nil {
+                       check.errorf(name, _InvalidArrayLen, "undeclared name %s for array length", name.Name)
+                       return -1
+               }
+               if _, ok := obj.(*Const); !ok {
+                       check.errorf(name, _InvalidArrayLen, "invalid array length %s", name.Name)
+                       return -1
+               }
        }
 
        var x operand

diff --git a/test/fixedbugs/bug255.go b/test/fixedbugs/bug255.go
index 38df7813c9d5a1dbee651fd3d421d1f5ddfb7a0d..184ff2d378b58d722711a78859437d757694ba72 100644 (file)
--- a/test/fixedbugs/bug255.go
+++ b/test/fixedbugs/bug255.go
@@ -6,12 +6,13 @@
 
 package main
 
-var a [10]int      // ok
-var b [1e1]int     // ok
-var c [1.5]int     // ERROR "truncated|must be integer"
-var d ["abc"]int   // ERROR "invalid array bound|not numeric|must be integer"
-var e [nil]int     // ERROR "use of untyped nil|invalid array bound|not numeric|must be constant"
-var f [e]int       // ok: error already reported for e
+var a [10]int    // ok
+var b [1e1]int   // ok
+var c [1.5]int   // ERROR "truncated|must be integer"
+var d ["abc"]int // ERROR "invalid array bound|not numeric|must be integer"
+var e [nil]int   // ERROR "use of untyped nil|invalid array (bound|length)|not numeric|must be constant"
+// var f [e]int  // ok with Go 1.17 because an error was reported for e; leads to an error for Go 1.18
+var f [ee]int      // ERROR "undefined|undeclared"
 var g [1 << 65]int // ERROR "array bound is too large|overflows|must be integer"
 var h [len(a)]int  // ok