go/types, types2: qualify named types in error messages with type kind

Change the description of an operand x that has a named type of sorts
by providing a description of the type structure (array, struct, slice,
pointer, etc).

For instance, given a (variable) operand x of a struct type T, the
operand is mentioned as (new):

        x (variable of struct type T)

instead of (old):

        x (variable of type T)

This approach is also used when a basic type is renamed, for instance
as in:

        x (value of uint type big.Word)

which makes it clear that big.Word is a uint.

This change is expected to produce more informative error messages.

Fixes #69955.

Change-Id: I544b0698f753a522c3b6e1800a492a94974fbab7
Reviewed-on: https://go-review.googlesource.com/c/go/+/621458
Reviewed-by: Alan Donovan <adonovan@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

src/cmd/compile/internal/types2/issues_test.go

@@ -729,7 +729,7 @@ var _ I0 = b.S{}
 type S struct{}
 func (S) M0(struct{ f string }) {}
 `,
-			`6:12: cannot use b[.]S{} [(]value of type b[.]S[)] as I0 value in variable declaration: b[.]S does not implement I0 [(]wrong type for method M0[)]
+			`6:12: cannot use b[.]S{} [(]value of struct type b[.]S[)] as I0 value in variable declaration: b[.]S does not implement I0 [(]wrong type for method M0[)]
 .*have M0[(]struct{f string /[*] package b [*]/ }[)]
 .*want M0[(]struct{f string /[*] package main [*]/ }[)]`},
 
@@ -745,7 +745,7 @@ var _ I1 = b.S{}
 type S struct{}
 func (S) M1(struct{ string }) {}
 `,
-			`6:12: cannot use b[.]S{} [(]value of type b[.]S[)] as I1 value in variable declaration: b[.]S does not implement I1 [(]wrong type for method M1[)]
+			`6:12: cannot use b[.]S{} [(]value of struct type b[.]S[)] as I1 value in variable declaration: b[.]S does not implement I1 [(]wrong type for method M1[)]
 .*have M1[(]struct{string /[*] package b [*]/ }[)]
 .*want M1[(]struct{string /[*] package main [*]/ }[)]`},
 
@@ -761,7 +761,7 @@ var _ I2 = b.S{}
 type S struct{}
 func (S) M2(struct{ f struct{ f string } }) {}
 `,
-			`6:12: cannot use b[.]S{} [(]value of type b[.]S[)] as I2 value in variable declaration: b[.]S does not implement I2 [(]wrong type for method M2[)]
+			`6:12: cannot use b[.]S{} [(]value of struct type b[.]S[)] as I2 value in variable declaration: b[.]S does not implement I2 [(]wrong type for method M2[)]
 .*have M2[(]struct{f struct{f string} /[*] package b [*]/ }[)]
 .*want M2[(]struct{f struct{f string} /[*] package main [*]/ }[)]`},
 
@@ -777,7 +777,7 @@ var _ I3 = b.S{}
 type S struct{}
 func (S) M3(struct{ F struct{ f string } }) {}
 `,
-			`6:12: cannot use b[.]S{} [(]value of type b[.]S[)] as I3 value in variable declaration: b[.]S does not implement I3 [(]wrong type for method M3[)]
+			`6:12: cannot use b[.]S{} [(]value of struct type b[.]S[)] as I3 value in variable declaration: b[.]S does not implement I3 [(]wrong type for method M3[)]
 .*have M3[(]struct{F struct{f string /[*] package b [*]/ }}[)]
 .*want M3[(]struct{F struct{f string /[*] package main [*]/ }}[)]`},
 
@@ -793,7 +793,7 @@ var _ I4 = b.S{}
 type S struct{}
 func (S) M4(struct { *string }) {}
 `,
-			`6:12: cannot use b[.]S{} [(]value of type b[.]S[)] as I4 value in variable declaration: b[.]S does not implement I4 [(]wrong type for method M4[)]
+			`6:12: cannot use b[.]S{} [(]value of struct type b[.]S[)] as I4 value in variable declaration: b[.]S does not implement I4 [(]wrong type for method M4[)]
 .*have M4[(]struct{[*]string /[*] package b [*]/ }[)]
 .*want M4[(]struct{[*]string /[*] package main [*]/ }[)]`},
 
@@ -811,7 +811,7 @@ type S struct{}
 type t struct{ A int }
 func (S) M5(struct {S;t}) {}
 `,
-			`7:12: cannot use b[.]S{} [(]value of type b[.]S[)] as I5 value in variable declaration: b[.]S does not implement I5 [(]wrong type for method M5[)]
+			`7:12: cannot use b[.]S{} [(]value of struct type b[.]S[)] as I5 value in variable declaration: b[.]S does not implement I5 [(]wrong type for method M5[)]
 .*have M5[(]struct{b[.]S; b[.]t}[)]
 .*want M5[(]struct{b[.]S; t}[)]`},
 	}

src/cmd/compile/internal/types2/operand.go

@@ -178,15 +178,33 @@ func operandString(x *operand, qf Qualifier) string {
 	// <typ>
 	if hasType {
 		if isValid(x.typ) {
-			var intro string
+			var desc string
 			if isGeneric(x.typ) {
-				intro = " of generic type "
-			} else {
-				intro = " of type "
+				desc = "generic "
 			}
-			buf.WriteString(intro)
+
+			// Describe the type structure if it is an *Alias or *Named type.
+			// If the type is a renamed basic type, describe the basic type,
+			// as in "int32 type MyInt" for a *Named type MyInt.
+			// If it is a type parameter, describe the constraint instead.
+			tpar, _ := Unalias(x.typ).(*TypeParam)
+			if tpar == nil {
+				switch x.typ.(type) {
+				case *Alias, *Named:
+					what := compositeKind(x.typ)
+					if what == "" {
+						// x.typ must be basic type
+						what = under(x.typ).(*Basic).name
+					}
+					desc += what + " "
+				}
+			}
+			// desc is "" or has a trailing space at the end
+
+			buf.WriteString(" of " + desc + "type ")
 			WriteType(&buf, x.typ, qf)
-			if tpar, _ := Unalias(x.typ).(*TypeParam); tpar != nil {
+
+			if tpar != nil {
 				buf.WriteString(" constrained by ")
 				WriteType(&buf, tpar.bound, qf) // do not compute interface type sets here
 				// If we have the type set and it's empty, say so for better error messages.

src/go/types/issues_test.go

@@ -737,7 +737,7 @@ var _ I0 = b.S{}
 type S struct{}
 func (S) M0(struct{ f string }) {}
 `,
-			`6:12: cannot use b[.]S{} [(]value of type b[.]S[)] as I0 value in variable declaration: b[.]S does not implement I0 [(]wrong type for method M0[)]
+			`6:12: cannot use b[.]S{} [(]value of struct type b[.]S[)] as I0 value in variable declaration: b[.]S does not implement I0 [(]wrong type for method M0[)]
 .*have M0[(]struct{f string /[*] package b [*]/ }[)]
 .*want M0[(]struct{f string /[*] package main [*]/ }[)]`},
 
@@ -753,7 +753,7 @@ var _ I1 = b.S{}
 type S struct{}
 func (S) M1(struct{ string }) {}
 `,
-			`6:12: cannot use b[.]S{} [(]value of type b[.]S[)] as I1 value in variable declaration: b[.]S does not implement I1 [(]wrong type for method M1[)]
+			`6:12: cannot use b[.]S{} [(]value of struct type b[.]S[)] as I1 value in variable declaration: b[.]S does not implement I1 [(]wrong type for method M1[)]
 .*have M1[(]struct{string /[*] package b [*]/ }[)]
 .*want M1[(]struct{string /[*] package main [*]/ }[)]`},
 
@@ -769,7 +769,7 @@ var _ I2 = b.S{}
 type S struct{}
 func (S) M2(struct{ f struct{ f string } }) {}
 `,
-			`6:12: cannot use b[.]S{} [(]value of type b[.]S[)] as I2 value in variable declaration: b[.]S does not implement I2 [(]wrong type for method M2[)]
+			`6:12: cannot use b[.]S{} [(]value of struct type b[.]S[)] as I2 value in variable declaration: b[.]S does not implement I2 [(]wrong type for method M2[)]
 .*have M2[(]struct{f struct{f string} /[*] package b [*]/ }[)]
 .*want M2[(]struct{f struct{f string} /[*] package main [*]/ }[)]`},
 
@@ -785,7 +785,7 @@ var _ I3 = b.S{}
 type S struct{}
 func (S) M3(struct{ F struct{ f string } }) {}
 `,
-			`6:12: cannot use b[.]S{} [(]value of type b[.]S[)] as I3 value in variable declaration: b[.]S does not implement I3 [(]wrong type for method M3[)]
+			`6:12: cannot use b[.]S{} [(]value of struct type b[.]S[)] as I3 value in variable declaration: b[.]S does not implement I3 [(]wrong type for method M3[)]
 .*have M3[(]struct{F struct{f string /[*] package b [*]/ }}[)]
 .*want M3[(]struct{F struct{f string /[*] package main [*]/ }}[)]`},
 
@@ -801,7 +801,7 @@ var _ I4 = b.S{}
 type S struct{}
 func (S) M4(struct { *string }) {}
 `,
-			`6:12: cannot use b[.]S{} [(]value of type b[.]S[)] as I4 value in variable declaration: b[.]S does not implement I4 [(]wrong type for method M4[)]
+			`6:12: cannot use b[.]S{} [(]value of struct type b[.]S[)] as I4 value in variable declaration: b[.]S does not implement I4 [(]wrong type for method M4[)]
 .*have M4[(]struct{[*]string /[*] package b [*]/ }[)]
 .*want M4[(]struct{[*]string /[*] package main [*]/ }[)]`},
 
@@ -819,7 +819,7 @@ type S struct{}
 type t struct{ A int }
 func (S) M5(struct {S;t}) {}
 `,
-			`7:12: cannot use b[.]S{} [(]value of type b[.]S[)] as I5 value in variable declaration: b[.]S does not implement I5 [(]wrong type for method M5[)]
+			`7:12: cannot use b[.]S{} [(]value of struct type b[.]S[)] as I5 value in variable declaration: b[.]S does not implement I5 [(]wrong type for method M5[)]
 .*have M5[(]struct{b[.]S; b[.]t}[)]
 .*want M5[(]struct{b[.]S; t}[)]`},
 	}

src/go/types/operand.go

@@ -182,15 +182,33 @@ func operandString(x *operand, qf Qualifier) string {
 	// <typ>
 	if hasType {
 		if isValid(x.typ) {
-			var intro string
+			var desc string
 			if isGeneric(x.typ) {
-				intro = " of generic type "
-			} else {
-				intro = " of type "
+				desc = "generic "
 			}
-			buf.WriteString(intro)
+
+			// Describe the type structure if it is an *Alias or *Named type.
+			// If the type is a renamed basic type, describe the basic type,
+			// as in "int32 type MyInt" for a *Named type MyInt.
+			// If it is a type parameter, describe the constraint instead.
+			tpar, _ := Unalias(x.typ).(*TypeParam)
+			if tpar == nil {
+				switch x.typ.(type) {
+				case *Alias, *Named:
+					what := compositeKind(x.typ)
+					if what == "" {
+						// x.typ must be basic type
+						what = under(x.typ).(*Basic).name
+					}
+					desc += what + " "
+				}
+			}
+			// desc is "" or has a trailing space at the end
+
+			buf.WriteString(" of " + desc + "type ")
 			WriteType(&buf, x.typ, qf)
-			if tpar, _ := Unalias(x.typ).(*TypeParam); tpar != nil {
+
+			if tpar != nil {
 				buf.WriteString(" constrained by ")
 				WriteType(&buf, tpar.bound, qf) // do not compute interface type sets here
 				// If we have the type set and it's empty, say so for better error messages.

src/internal/types/testdata/check/builtins0.go

@@ -515,7 +515,7 @@ func max1() {
 	_ = max(s)
 	_ = max(x, x)
 	_ = max(x, x, x, x, x)
-	var _ int = max /* ERROR "cannot use max(m) (value of type myint) as int value" */ (m)
+	var _ int = max /* ERROR "cannot use max(m) (value of int type myint) as int value" */ (m)
 	_ = max(x, m /* ERROR "invalid argument: mismatched types int (previous argument) and myint (type of m)" */ , x)
 
 	_ = max(1, x)
@@ -569,7 +569,7 @@ func min1() {
 	_ = min(s)
 	_ = min(x, x)
 	_ = min(x, x, x, x, x)
-	var _ int = min /* ERROR "cannot use min(m) (value of type myint) as int value" */ (m)
+	var _ int = min /* ERROR "cannot use min(m) (value of int type myint) as int value" */ (m)
 	_ = min(x, m /* ERROR "invalid argument: mismatched types int (previous argument) and myint (type of m)" */ , x)
 
 	_ = min(1, x)

src/internal/types/testdata/check/errors.go

@@ -58,7 +58,7 @@ func _() {
 
 // Use unqualified names for package-local objects.
 type T struct{}
-var _ int = T /* ERROR "value of type T" */ {} // use T in error message rather than errors.T
+var _ int = T /* ERROR "value of struct type T" */ {} // use T in error message rather than errors.T
 
 // Don't report errors containing "invalid type" (issue #24182).
 func _(x *missing /* ERROR "undefined: missing" */ ) {

src/internal/types/testdata/check/issues0.go

@@ -363,7 +363,7 @@ func issue35895() {
 
 	// Because both t1 and t2 have the same global package name (template),
 	// qualify packages with full path name in this case.
-	var _ t1.Template = t2 /* ERRORx `cannot use .* \(value of type .html/template.\.Template\) as .text/template.\.Template` */ .Template{}
+	var _ t1.Template = t2 /* ERRORx `cannot use .* \(value of struct type .html/template.\.Template\) as .text/template.\.Template` */ .Template{}
 }
 
 func issue42989(s uint) {

src/internal/types/testdata/fixedbugs/issue49005.go

@@ -26,6 +26,6 @@ type X2 struct{}
 
 func _() {
 	switch F2().(type) {
-	case * /* ERROR "impossible type switch case: *X2\n\tF2() (value of type T2) cannot have dynamic type *X2 (missing method M)" */ X2:
+	case * /* ERROR "impossible type switch case: *X2\n\tF2() (value of interface type T2) cannot have dynamic type *X2 (missing method M)" */ X2:
 	}
 }

src/internal/types/testdata/fixedbugs/issue60377.go

@@ -57,7 +57,7 @@ func _() {
 	var x S[int]
 	g4(x)      // we can infer int for P
 	g4[int](x) // int is the correct type argument
-	g4[string](x /* ERROR "cannot use x (variable of type S[int]) as S[string] value in argument to g4[string]" */)
+	g4[string](x /* ERROR "cannot use x (variable of struct type S[int]) as S[string] value in argument to g4[string]" */)
 }
 
 // This is similar to the first example but here T1 is a component

src/internal/types/testdata/fixedbugs/issue62157.go

@@ -90,7 +90,7 @@ func _() {
 	B = f(B, b, a)
 
 	// verify type error
-	A = f /* ERROR "cannot use f(B, b, a) (value of type namedB) as namedA value in assignment" */ (B, b, a)
+	A = f /* ERROR "cannot use f(B, b, a) (value of chan type namedB) as namedA value in assignment" */ (B, b, a)
 }
 
 // Test case 4: some more combinations

src/internal/types/testdata/fixedbugs/issue69955.go

@@ -0,0 +1,42 @@
+// -gotypesalias=1
+
+// Copyright 2024 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 "math/big"
+
+type (
+	S struct{}
+	N int
+
+	A = S
+	B = int
+	C = N
+)
+
+var (
+	i int
+	s S
+	n N
+	a A
+	b B
+	c C
+	w big.Word
+)
+
+const (
+	_ = i // ERROR "i (variable of type int) is not constant"
+	_ = s // ERROR "s (variable of struct type S) is not constant"
+	_ = struct /* ERROR "struct{}{} (value of type struct{}) is not constant" */ {}{}
+	_ = n // ERROR "n (variable of int type N) is not constant"
+
+	_ = a // ERROR "a (variable of struct type A) is not constant"
+	_ = b // ERROR "b (variable of int type B) is not constant"
+	_ = c // ERROR "c (variable of int type C) is not constant"
+	_ = w // ERROR "w (variable of uint type big.Word) is not constant"
+)
+
+var _ int = w /* ERROR "cannot use w + 1 (value of uint type big.Word) as int value in variable declaration" */ + 1

src/internal/types/testdata/spec/range.go

@@ -102,11 +102,11 @@ func test() {
 	for mi, ms := range f8 {
 		_, _ = mi, ms
 	}
-	for i /* ERROR "cannot use i (value of type MyInt) as int value in assignment" */, s /* ERROR "cannot use s (value of type MyString) as string value in assignment" */ = range f8 {
+	for i /* ERROR "cannot use i (value of int32 type MyInt) as int value in assignment" */, s /* ERROR "cannot use s (value of string type MyString) as string value in assignment" */ = range f8 {
 		_, _ = mi, ms
 	}
 	for mi, ms := range f8 {
-		i, s = mi /* ERROR "cannot use mi (variable of type MyInt) as int value in assignment" */, ms /* ERROR "cannot use ms (variable of type MyString) as string value in assignment" */
+		i, s = mi /* ERROR "cannot use mi (variable of int32 type MyInt) as int value in assignment" */, ms /* ERROR "cannot use ms (variable of string type MyString) as string value in assignment" */
 	}
 	for mi, ms = range f8 {
 		_, _ = mi, ms

src/internal/types/testdata/spec/range_int.go

@@ -44,7 +44,7 @@ func _() {
 	for i, j /* ERROR "range over 10 (untyped int constant) permits only one iteration variable" */ := range 10 {
 		_, _ = i, j
 	}
-	for i = range MyInt /* ERROR "cannot use MyInt(10) (constant 10 of type MyInt) as int value in range clause" */ (10) {
+	for i = range MyInt /* ERROR "cannot use MyInt(10) (constant 10 of int32 type MyInt) as int value in range clause" */ (10) {
 		_ = i
 	}
 	for mi := range MyInt(10) {

test/alias2.go

@@ -46,8 +46,8 @@ var _ A0 = T0{}
 var _ T0 = A0{}
 
 // But aliases and original types cannot be used with new types based on them.
-var _ N0 = T0{} // ERROR "cannot use T0{} \(value of type T0\) as N0 value in variable declaration"
-var _ N0 = A0{} // ERROR "cannot use A0{} \(value of type A0\) as N0 value in variable declaration"
+var _ N0 = T0{} // ERROR "cannot use T0{} \(value of struct type T0\) as N0 value in variable declaration"
+var _ N0 = A0{} // ERROR "cannot use A0{} \(value of struct type A0\) as N0 value in variable declaration"
 
 var _ A5 = Value{}
 
@@ -82,10 +82,10 @@ func _() {
 	var _ A0 = T0{}
 	var _ T0 = A0{}
 
-	var _ N0 = T0{} // ERROR "cannot use T0{} \(value of type T0\) as N0 value in variable declaration"
-	var _ N0 = A0{} // ERROR "cannot use A0{} \(value of type A0\) as N0 value in variable declaration"
+	var _ N0 = T0{} // ERROR "cannot use T0{} \(value of struct type T0\) as N0 value in variable declaration"
+	var _ N0 = A0{} // ERROR "cannot use A0{} \(value of struct type A0\) as N0 value in variable declaration"
 
-	var _ A5 = Value{} // ERROR "cannot use Value{} \(value of type reflect\.Value\) as A5 value in variable declaration"
+	var _ A5 = Value{} // ERROR "cannot use Value{} \(value of struct type reflect\.Value\) as A5 value in variable declaration"
 }
 
 // Invalid type alias declarations.

test/fixedbugs/issue48471.go

@@ -51,6 +51,6 @@ func g() {
 	_ = i.(T6)  // ERROR "impossible type assertion: i.\(T6\)\n\tT6 does not implement I \(missing method M\)\n\t\thave m\(int\) string\n\t\twant M\(int\)"
 
 	var t *T4
-	t = i // ERROR "cannot use i \(variable of type I\) as \*T4 value in assignment: need type assertion"
+	t = i // ERROR "cannot use i \(variable of interface type I\) as \*T4 value in assignment: need type assertion"
 	_ = t
 }