go/types: simplify error messages for untyped value assignability
CL 242083 corrected an inaccurate error message related to the
assignability of untyped constant values. Previously the error message
was of the form "cannot convert ... to ...", which is misleading when
there is no explicit conversion in the syntax. The new error message
corrected this to "cannot use ... as ... in ...", but also appended an
inner error message that can be quite verbose. For example:
cannot use "123" (untyped string constant) as int value in assignment:
cannot convert "123" (untyped string constant) to int"
This might be more accurate, but is a regression in readability. Correct
this by only including the inner error message in the rare cases where
it is helpful: if the constant value overflows or is truncated.
For golang/go#22070
Change-Id: I8b8ee6ef713f64facc319894be09398b0b5ea500
Reviewed-on: https://go-review.googlesource.com/c/go/+/267717
Run-TryBot: Robert Findley <rfindley@google.com>
Reviewed-by: Robert Griesemer <gri@golang.org>
Trust: Robert Griesemer <gri@golang.org>
Trust: Robert Findley <rfindley@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
diff --git a/src/go/types/assignments.go b/src/go/types/assignments.go
index c099d11..d895c6f 100644
--- a/src/go/types/assignments.go
+++ b/src/go/types/assignments.go
@@ -45,14 +45,21 @@
target = Default(x.typ)
}
if err := check.canConvertUntyped(x, target); err != nil {
- var internalErr Error
- msg := err.Error()
+ msg := check.sprintf("cannot use %s as %s value in %s", x, target, context)
code := _IncompatibleAssign
- if errors.As(err, &internalErr) {
- msg = internalErr.Msg
- code = internalErr.go116code
+ var ierr Error
+ if errors.As(err, &ierr) {
+ // Preserve these inner errors, as they are informative.
+ switch ierr.go116code {
+ case _TruncatedFloat:
+ msg += " (truncated)"
+ code = ierr.go116code
+ case _NumericOverflow:
+ msg += " (overflows)"
+ code = ierr.go116code
+ }
}
- check.errorf(x.pos(), code, "cannot use %s as %s value in %s: %v", x, target, context, msg)
+ check.error(x.pos(), code, msg)
x.mode = invalid
return
}
diff --git a/src/go/types/errorcodes.go b/src/go/types/errorcodes.go
index ba6e2f9..e4c8311 100644
--- a/src/go/types/errorcodes.go
+++ b/src/go/types/errorcodes.go
@@ -135,8 +135,11 @@
// _InvalidConstVal occurs when a const value cannot be converted to its
// target type.
//
+ // TODO(findleyr): this error code and example are not very clear. Consider
+ // removing it.
+ //
// Example:
- // var x string = 1
+ // const _ = 1 << "hello"
_InvalidConstVal
// _InvalidConstType occurs when the underlying type in a const declaration
diff --git a/src/go/types/testdata/builtins.src b/src/go/types/testdata/builtins.src
index ecdba51..98830eb 100644
--- a/src/go/types/testdata/builtins.src
+++ b/src/go/types/testdata/builtins.src
@@ -35,9 +35,9 @@
type S []byte
type T string
var t T
- _ = append(s, "foo" /* ERROR cannot convert */ )
+ _ = append(s, "foo" /* ERROR cannot use .* in argument to append */ )
_ = append(s, "foo"...)
- _ = append(S(s), "foo" /* ERROR cannot convert */ )
+ _ = append(S(s), "foo" /* ERROR cannot use .* in argument to append */ )
_ = append(S(s), "foo"...)
_ = append(s, t /* ERROR cannot use t */ )
_ = append(s, t...)
diff --git a/src/go/types/testdata/decls1.src b/src/go/types/testdata/decls1.src
index e6beb78..f4d2eab 100644
--- a/src/go/types/testdata/decls1.src
+++ b/src/go/types/testdata/decls1.src
@@ -96,6 +96,8 @@
v11 = xx/yy*yy - xx
v12 = true && false
v13 = nil /* ERROR "use of untyped nil" */
+ v14 string = 257 // ERROR cannot use 257 .* as string value in variable declaration$
+ v15 int8 = 257 // ERROR cannot use 257 .* as int8 value in variable declaration .*overflows
)
// Multiple assignment expressions
diff --git a/src/go/types/testdata/decls2b.src b/src/go/types/testdata/decls2b.src
index 8e82c6d..5c55750 100644
--- a/src/go/types/testdata/decls2b.src
+++ b/src/go/types/testdata/decls2b.src
@@ -40,17 +40,17 @@
// Verify by checking that errors are reported.
func (T /* ERROR "undeclared" */ ) _() {}
func (T1) _(undeclared /* ERROR "undeclared" */ ) {}
-func (T1) _() int { return "foo" /* ERROR "cannot convert" */ }
+func (T1) _() int { return "foo" /* ERROR "cannot use .* in return statement" */ }
// Methods with undeclared receiver type can still be checked.
// Verify by checking that errors are reported.
func (Foo /* ERROR "undeclared" */ ) m() {}
func (Foo /* ERROR "undeclared" */ ) m(undeclared /* ERROR "undeclared" */ ) {}
-func (Foo /* ERROR "undeclared" */ ) m() int { return "foo" /* ERROR "cannot convert" */ }
+func (Foo /* ERROR "undeclared" */ ) m() int { return "foo" /* ERROR "cannot use .* in return statement" */ }
func (Foo /* ERROR "undeclared" */ ) _() {}
func (Foo /* ERROR "undeclared" */ ) _(undeclared /* ERROR "undeclared" */ ) {}
-func (Foo /* ERROR "undeclared" */ ) _() int { return "foo" /* ERROR "cannot convert" */ }
+func (Foo /* ERROR "undeclared" */ ) _() int { return "foo" /* ERROR "cannot use .* in return statement" */ }
// Receiver declarations are regular parameter lists;
// receiver types may use parentheses, and the list
@@ -72,4 +72,4 @@
_ = (*T7).m4
_ = (*T7).m5
_ = (*T7).m6
-)
\ No newline at end of file
+)
diff --git a/src/go/types/testdata/expr3.src b/src/go/types/testdata/expr3.src
index 4ecb198..6f2201c 100644
--- a/src/go/types/testdata/expr3.src
+++ b/src/go/types/testdata/expr3.src
@@ -94,7 +94,7 @@
_ = &s /* ERROR "cannot take address" */ [:10]
var m map[string]int
- _ = m[0 /* ERROR "cannot convert" */ ]
+ _ = m[0 /* ERROR "cannot use .* in map index" */ ]
_ = m /* ERROR "cannot slice" */ ["foo" : "bar"]
_ = m["foo"]
// ok is of type bool
@@ -184,7 +184,7 @@
_ = T1{aa /* ERROR "unknown field" */ : 0}
_ = T1{1 /* ERROR "invalid field name" */ : 0}
_ = T1{a: 0, s: "foo", u: 0, a /* ERROR "duplicate field" */: 10}
- _ = T1{a: "foo" /* ERROR "cannot convert" */ }
+ _ = T1{a: "foo" /* ERROR "cannot use .* in struct literal" */ }
_ = T1{c /* ERROR "unknown field" */ : 0}
_ = T1{T0: { /* ERROR "missing type" */ }} // struct literal element type may not be elided
_ = T1{T0: T0{}}
@@ -195,7 +195,7 @@
_ = T0{1, b /* ERROR "mixture" */ : 2, 3}
_ = T0{1, 2} /* ERROR "too few values" */
_ = T0{1, 2, 3, 4 /* ERROR "too many values" */ }
- _ = T0{1, "foo" /* ERROR "cannot convert" */, 3.4 /* ERROR "truncated" */}
+ _ = T0{1, "foo" /* ERROR "cannot use .* in struct literal" */, 3.4 /* ERROR "cannot use .*\(truncated\)" */}
// invalid type
type P *struct{
@@ -235,7 +235,7 @@
_ = A1{5: 5, 6, 7, 4: 4, 1 /* ERROR "overflows" */ <<100: 4}
_ = A1{2.0}
_ = A1{2.1 /* ERROR "truncated" */ }
- _ = A1{"foo" /* ERROR "cannot convert" */ }
+ _ = A1{"foo" /* ERROR "cannot use .* in array or slice literal" */ }
// indices must be integer constants
i := 1
@@ -301,7 +301,7 @@
_ = S0{5: 5, 6, 7, 4: 4, 1 /* ERROR "overflows" */ <<100: 4}
_ = S0{2.0}
_ = S0{2.1 /* ERROR "truncated" */ }
- _ = S0{"foo" /* ERROR "cannot convert" */ }
+ _ = S0{"foo" /* ERROR "cannot use .* in array or slice literal" */ }
// indices must be resolved correctly
const index1 = 1
@@ -354,8 +354,8 @@
_ = M0{}
_ = M0{1 /* ERROR "missing key" */ }
- _ = M0{1 /* ERROR "cannot convert" */ : 2}
- _ = M0{"foo": "bar" /* ERROR "cannot convert" */ }
+ _ = M0{1 /* ERROR "cannot use .* in map literal" */ : 2}
+ _ = M0{"foo": "bar" /* ERROR "cannot use .* in map literal" */ }
_ = M0{"foo": 1, "bar": 2, "foo" /* ERROR "duplicate key" */ : 3 }
_ = map[interface{}]int{2: 1, 2 /* ERROR "duplicate key" */ : 1}
diff --git a/src/go/types/testdata/issues.src b/src/go/types/testdata/issues.src
index 4944f6f..e0c5d7a 100644
--- a/src/go/types/testdata/issues.src
+++ b/src/go/types/testdata/issues.src
@@ -354,10 +354,10 @@
func issue35895() {
// T is defined in this package, don't qualify its name with the package name.
- var _ T = 0 // ERROR cannot convert 0 \(untyped int constant\) to T
+ var _ T = 0 // ERROR cannot use 0 \(untyped int constant\) as T
// There is only one package with name syntax imported, only use the (global) package name in error messages.
- var _ *syn.File = 0 // ERROR cannot convert 0 \(untyped int constant\) to \*syntax.File
+ var _ *syn.File = 0 // ERROR cannot use 0 \(untyped int constant\) as \*syntax.File
// Because both t1 and t2 have the same global package name (template),
// qualify packages with full path name in this case.
diff --git a/src/go/types/testdata/stmt0.src b/src/go/types/testdata/stmt0.src
index 446997a..1377729 100644
--- a/src/go/types/testdata/stmt0.src
+++ b/src/go/types/testdata/stmt0.src
@@ -182,7 +182,7 @@
var x int
x <- /* ERROR "cannot send" */ x
rch <- /* ERROR "cannot send" */ x
- ch <- "foo" /* ERROR "cannot convert" */
+ ch <- "foo" /* ERROR "cannot use .* in send" */
ch <- x
}
@@ -381,13 +381,13 @@
func returns1(x float64) (int, *float64) {
return 0, &x
return /* ERROR wrong number of return values */
- return "foo" /* ERROR "cannot convert" */, x /* ERROR "cannot use .* in return statement" */
+ return "foo" /* ERROR "cannot .* in return statement" */, x /* ERROR "cannot use .* in return statement" */
return /* ERROR wrong number of return values */ 0, &x, 1
}
func returns2() (a, b int) {
return
- return 1, "foo" /* ERROR cannot convert */
+ return 1, "foo" /* ERROR cannot use .* in return statement */
return /* ERROR wrong number of return values */ 1, 2, 3
{
type a int
@@ -609,7 +609,7 @@
// untyped constants are converted to default types
switch 1<<63-1 {
}
- switch 1 /* ERROR "overflows int" */ << 63 {
+ switch 1 /* ERROR "cannot use .* as int value.*\(overflows\)" */ << 63 {
}
var x int
switch 1.0 {
@@ -631,9 +631,9 @@
}
func issue11667() {
- switch 9223372036854775808 /* ERROR "overflows int" */ {
+ switch 9223372036854775808 /* ERROR "cannot use .* as int value.*\(overflows\)" */ {
}
- switch 9223372036854775808 /* ERROR "overflows int" */ {
+ switch 9223372036854775808 /* ERROR "cannot use .* as int value.*\(overflows\)" */ {
case 9223372036854775808:
}
var x int
