cmd/compile/internal/types2: more detailed error messages for generic conversions
- slightly refactor convertibleTo and convertibleToImpl
- provide ability to return a conversion failure cause
- add detailed cause for generic conversions
For #47150.
Change-Id: Ie97d89be0234414ef4df22a6920e18acc944a102
Reviewed-on: https://go-review.googlesource.com/c/go/+/357249
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>
diff --git a/src/cmd/compile/internal/types2/api.go b/src/cmd/compile/internal/types2/api.go
index e6d28af..f13fa95 100644
--- a/src/cmd/compile/internal/types2/api.go
+++ b/src/cmd/compile/internal/types2/api.go
@@ -438,7 +438,7 @@
// ConvertibleTo reports whether a value of type V is convertible to a value of type T.
func ConvertibleTo(V, T Type) bool {
x := operand{mode: value, typ: V}
- return x.convertibleTo(nil, T) // check not needed for non-constant x
+ return x.convertibleTo(nil, T, nil) // check not needed for non-constant x; if check == nil, cause can be nil
}
// Implements reports whether type V implements interface T.
diff --git a/src/cmd/compile/internal/types2/conversions.go b/src/cmd/compile/internal/types2/conversions.go
index 112d728..a4fba28 100644
--- a/src/cmd/compile/internal/types2/conversions.go
+++ b/src/cmd/compile/internal/types2/conversions.go
@@ -17,6 +17,7 @@
constArg := x.mode == constant_
var ok bool
+ var cause string
switch {
case constArg && isConstType(T):
// constant conversion
@@ -31,17 +32,20 @@
x.val = constant.MakeString(string(codepoint))
ok = true
}
- case x.convertibleTo(check, T):
+ case x.convertibleTo(check, T, &cause):
// non-constant conversion
x.mode = value
ok = true
}
if !ok {
- if x.mode != invalid {
- check.errorf(x, "cannot convert %s to %s", x, T)
- x.mode = invalid
+ var err error_
+ err.errorf(x, "cannot convert %s to %s", x, T)
+ if cause != "" {
+ err.errorf(nopos, cause)
}
+ check.report(&err)
+ x.mode = invalid
return
}
@@ -80,57 +84,74 @@
// is tricky because we'd have to run updateExprType on the argument first.
// (Issue #21982.)
-// convertibleTo reports whether T(x) is valid.
+// convertibleTo reports whether T(x) is valid. In the failure case, *cause
+// may be set to the cause for the failure.
// The check parameter may be nil if convertibleTo is invoked through an
// exported API call, i.e., when all methods have been type-checked.
-func (x *operand) convertibleTo(check *Checker, T Type) bool {
+func (x *operand) convertibleTo(check *Checker, T Type, cause *string) bool {
// "x is assignable to T"
- if ok, _ := x.assignableTo(check, T, nil); ok {
+ if ok, _ := x.assignableTo(check, T, cause); ok {
return true
}
- // TODO(gri) consider passing under(x.typ), under(T) into convertibleToImpl (optimization)
Vp, _ := under(x.typ).(*TypeParam)
Tp, _ := under(T).(*TypeParam)
+ errorf := func(format string, args ...interface{}) {
+ if check != nil && cause != nil {
+ msg := check.sprintf(format, args...)
+ if *cause != "" {
+ msg += "\n\t" + *cause
+ }
+ *cause = msg
+ }
+ }
+
// generic cases
// (generic operands cannot be constants, so we can ignore x.val)
switch {
case Vp != nil && Tp != nil:
- x := *x // don't modify outer x
return Vp.is(func(V *term) bool {
- x.typ = V.typ
return Tp.is(func(T *term) bool {
- return x.convertibleToImpl(check, T.typ)
+ if !convertibleToImpl(check, V.typ, T.typ, cause) {
+ errorf("cannot convert %s (in %s) to %s (in %s)", V.typ, Vp, T.typ, Tp)
+ return false
+ }
+ return true
})
})
case Vp != nil:
- x := *x // don't modify outer x
return Vp.is(func(V *term) bool {
- x.typ = V.typ
- return x.convertibleToImpl(check, T)
+ if !convertibleToImpl(check, V.typ, T, cause) {
+ errorf("cannot convert %s (in %s) to %s", V.typ, Vp, T)
+ return false
+ }
+ return true
})
case Tp != nil:
return Tp.is(func(T *term) bool {
- return x.convertibleToImpl(check, T.typ)
+ if !convertibleToImpl(check, x.typ, T.typ, cause) {
+ errorf("cannot convert %s to %s (in %s)", x.typ, T.typ, Tp)
+ return false
+ }
+ return true
})
}
// non-generic case
- return x.convertibleToImpl(check, T)
+ return convertibleToImpl(check, x.typ, T, cause)
}
// convertibleToImpl should only be called by convertibleTo
-func (x *operand) convertibleToImpl(check *Checker, T Type) bool {
- // "x's type and T have identical underlying types if tags are ignored"
- V := x.typ
+func convertibleToImpl(check *Checker, V, T Type, cause *string) bool {
+ // "V and T have identical underlying types if tags are ignored"
Vu := under(V)
Tu := under(T)
if IdenticalIgnoreTags(Vu, Tu) {
return true
}
- // "x's type and T are unnamed pointer types and their pointer base types
+ // "V and T are unnamed pointer types and their pointer base types
// have identical underlying types if tags are ignored"
if V, ok := V.(*Pointer); ok {
if T, ok := T.(*Pointer); ok {
@@ -140,22 +161,22 @@
}
}
- // "x's type and T are both integer or floating point types"
+ // "V and T are both integer or floating point types"
if isIntegerOrFloat(V) && isIntegerOrFloat(T) {
return true
}
- // "x's type and T are both complex types"
+ // "V and T are both complex types"
if isComplex(V) && isComplex(T) {
return true
}
- // "x is an integer or a slice of bytes or runes and T is a string type"
+ // "V an integer or a slice of bytes or runes and T is a string type"
if (isInteger(V) || isBytesOrRunes(Vu)) && isString(T) {
return true
}
- // "x is a string and T is a slice of bytes or runes"
+ // "V a string and T is a slice of bytes or runes"
if isString(V) && isBytesOrRunes(Tu) {
return true
}
@@ -170,7 +191,7 @@
return true
}
- // "x is a slice, T is a pointer-to-array type,
+ // "V a slice, T is a pointer-to-array type,
// and the slice and array types have identical element types."
if s := asSlice(V); s != nil {
if p := asPointer(T); p != nil {
@@ -180,12 +201,15 @@
return true
}
// check != nil
- if check.conf.CompilerErrorMessages {
- check.error(x, "conversion of slices to array pointers only supported as of -lang=go1.17")
- } else {
- check.error(x, "conversion of slices to array pointers requires go1.17 or later")
+ if cause != nil {
+ if check.conf.CompilerErrorMessages {
+ // compiler error message assumes a -lang flag
+ *cause = "conversion of slices to array pointers only supported as of -lang=go1.17"
+ } else {
+ *cause = "conversion of slices to array pointers requires go1.17 or later"
+ }
}
- x.mode = invalid // avoid follow-up error
+ return false
}
}
}
diff --git a/src/cmd/compile/internal/types2/operand.go b/src/cmd/compile/internal/types2/operand.go
index a5b2729..5c8654d 100644
--- a/src/cmd/compile/internal/types2/operand.go
+++ b/src/cmd/compile/internal/types2/operand.go
@@ -296,6 +296,7 @@
if Ti, ok := Tu.(*Interface); ok {
if m, wrongType := check.missingMethod(V, Ti, true); m != nil /* Implements(V, Ti) */ {
if reason != nil {
+ // TODO(gri) the error messages here should follow the style in Checker.typeAssertion (factor!)
if wrongType != nil {
if Identical(m.typ, wrongType.typ) {
*reason = fmt.Sprintf("missing method %s (%s has pointer receiver)", m.name, m.name)
diff --git a/src/cmd/compile/internal/types2/testdata/examples/conversions.go2 b/src/cmd/compile/internal/types2/testdata/examples/conversions.go2
index 5c1b30a..0acd276 100644
--- a/src/cmd/compile/internal/types2/testdata/examples/conversions.go2
+++ b/src/cmd/compile/internal/types2/testdata/examples/conversions.go2
@@ -21,7 +21,7 @@
func _[X Foo, T Bar](x X) T { return T(x) }
func _[X Foo|Bar, T Bar](x X) T { return T(x) }
func _[X Foo, T Foo|Bar](x X) T { return T(x) }
-func _[X Foo, T Far](x X) T { return T(x /* ERROR cannot convert */ ) }
+func _[X Foo, T Far](x X) T { return T(x /* ERROR cannot convert x \(variable of type X constrained by Foo\) to T\n\tcannot convert Foo \(in X\) to Far \(in T\) */ ) }
// "x's type and T are unnamed pointer types and their pointer base types
// have identical underlying types if tags are ignored"
@@ -29,7 +29,7 @@
func _[X ~*Foo, T ~*Bar](x X) T { return T(x) }
func _[X ~*Foo|~*Bar, T ~*Bar](x X) T { return T(x) }
func _[X ~*Foo, T ~*Foo|~*Bar](x X) T { return T(x) }
-func _[X ~*Foo, T ~*Far](x X) T { return T(x /* ERROR cannot convert */ ) }
+func _[X ~*Foo, T ~*Far](x X) T { return T(x /* ERROR cannot convert x \(variable of type X constrained by ~\*Foo\) to T\n\tcannot convert \*Foo \(in X\) to \*Far \(in T\) */ ) }
// Verify that the defined types in constraints are considered for the rule above.
@@ -60,12 +60,12 @@
func _[X Float, T Float](x X) T { return T(x) }
func _[X, T Integer|Unsigned|Float](x X) T { return T(x) }
-func _[X, T Integer|~string](x X) T { return T(x /* ERROR cannot convert */ ) }
+func _[X, T Integer|~string](x X) T { return T(x /* ERROR cannot convert x \(variable of type X constrained by Integer\|~string\) to T\n\tcannot convert string \(in X\) to int \(in T\) */ ) }
// "x's type and T are both complex types"
func _[X, T Complex](x X) T { return T(x) }
-func _[X, T Float|Complex](x X) T { return T(x /* ERROR cannot convert */ ) }
+func _[X, T Float|Complex](x X) T { return T(x /* ERROR cannot convert x \(variable of type X constrained by Float\|Complex\) to T\n\tcannot convert float32 \(in X\) to complex64 \(in T\) */ ) }
// "x is an integer or a slice of bytes or runes and T is a string type"
@@ -76,25 +76,25 @@
func _[T ~string](x myInt) T { return T(x) }
func _[X Integer](x X) string { return string(x) }
func _[X Integer](x X) myString { return myString(x) }
-func _[X Integer](x X) *string { return (*string)(x /* ERROR cannot convert */ ) }
+func _[X Integer](x X) *string { return (*string)(x /* ERROR cannot convert x \(variable of type X constrained by Integer\) to \*string\n\tcannot convert int \(in X\) to \*string */ ) }
func _[T ~string](x []byte) T { return T(x) }
func _[T ~string](x []rune) T { return T(x) }
func _[X ~[]byte, T ~string](x X) T { return T(x) }
func _[X ~[]rune, T ~string](x X) T { return T(x) }
func _[X Integer|~[]byte|~[]rune, T ~string](x X) T { return T(x) }
-func _[X Integer|~[]byte|~[]rune, T ~*string](x X) T { return T(x /* ERROR cannot convert */ ) }
+func _[X Integer|~[]byte|~[]rune, T ~*string](x X) T { return T(x /* ERROR cannot convert x \(variable of type X constrained by Integer\|~\[\]byte\|~\[\]rune\) to T\n\tcannot convert int \(in X\) to \*string \(in T\) */ ) }
// "x is a string and T is a slice of bytes or runes"
func _[T ~[]byte](x string) T { return T(x) }
func _[T ~[]rune](x string) T { return T(x) }
-func _[T ~[]rune](x *string) T { return T(x /* ERROR cannot convert */ ) }
+func _[T ~[]rune](x *string) T { return T(x /* ERROR cannot convert x \(variable of type \*string\) to T\n\tcannot convert \*string to \[\]rune \(in T\) */ ) }
func _[X ~string, T ~[]byte](x X) T { return T(x) }
func _[X ~string, T ~[]rune](x X) T { return T(x) }
func _[X ~string, T ~[]byte|~[]rune](x X) T { return T(x) }
-func _[X ~*string, T ~[]byte|~[]rune](x X) T { return T(x /* ERROR cannot convert */ ) }
+func _[X ~*string, T ~[]byte|~[]rune](x X) T { return T(x /* ERROR cannot convert x \(variable of type X constrained by ~\*string\) to T\n\tcannot convert \*string \(in X\) to \[\]byte \(in T\) */ ) }
// package unsafe:
// "any pointer or value of underlying type uintptr can be converted into a unsafe.Pointer"
@@ -103,20 +103,20 @@
func _[X ~uintptr](x X) unsafe.Pointer { return unsafe.Pointer(x) }
func _[T unsafe.Pointer](x myUintptr) T { return T(x) }
-func _[T unsafe.Pointer](x int64) T { return T(x /* ERROR cannot convert */ ) }
+func _[T unsafe.Pointer](x int64) T { return T(x /* ERROR cannot convert x \(variable of type int64\) to T\n\tcannot convert int64 to unsafe\.Pointer \(in T\) */ ) }
// "and vice versa"
func _[T ~uintptr](x unsafe.Pointer) T { return T(x) }
func _[X unsafe.Pointer](x X) uintptr { return uintptr(x) }
func _[X unsafe.Pointer](x X) myUintptr { return myUintptr(x) }
-func _[X unsafe.Pointer](x X) int64 { return int64(x /* ERROR cannot convert */ ) }
+func _[X unsafe.Pointer](x X) int64 { return int64(x /* ERROR cannot convert x \(variable of type X constrained by unsafe\.Pointer\) to int64\n\tcannot convert unsafe\.Pointer \(in X\) to int64 */ ) }
// "x is a slice, T is a pointer-to-array type,
// and the slice and array types have identical element types."
func _[X ~[]E, T ~*[10]E, E any](x X) T { return T(x) }
-func _[X ~[]E, T ~[10]E, E any](x X) T { return T(x /* ERROR cannot convert */ ) }
+func _[X ~[]E, T ~[10]E, E any](x X) T { return T(x /* ERROR cannot convert x \(variable of type X constrained by ~\[\]E\) to T\n\tcannot convert \[\]E \(in X\) to \[10\]E \(in T\) */ ) }
// ----------------------------------------------------------------------------
// The following declarations can be replaced by the exported types of the
