go/types, types2: disallow real, imag, complex on type parameters

We can type-check these fine but the API implications are unclear.

Fixes #50912.
For #50937.

Change-Id: If29bbb4a257ff6a85e3bfcd4755fd8f90c80fb87
Reviewed-on: https://go-review.googlesource.com/c/go/+/382116
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>

3 files changed, 54 insertions, 6 deletions

diff --git a/test/typeparam/absdiff2.go b/test/typeparam/absdiff2.go
index 2d82c4721c..36de8ff2c9 100644
--- a/test/typeparam/absdiff2.go
+++ b/test/typeparam/absdiff2.go
@@ -66,9 +66,25 @@ type complexAbs[T Complex] struct {
 	Value T
 }
 
+func realimag(x any) (re, im float64) {
+	switch z := x.(type) {
+	case complex64:
+		re = float64(real(z))
+		im = float64(imag(z))
+	case complex128:
+		re = real(z)
+		im = imag(z)
+	default:
+		panic("unknown complex type")
+	}
+	return
+}
+
 func (a complexAbs[T]) Abs() T {
-	r := float64(real(a.Value))
-	i := float64(imag(a.Value))
+	// TODO use direct conversion instead of realimag once #50937 is fixed
+	r, i := realimag(a.Value)
+	// r := float64(real(a.Value))
+	// i := float64(imag(a.Value))
 	d := math.Sqrt(r*r + i*i)
 	return T(complex(d, 0))
 }
diff --git a/test/typeparam/absdiff3.go b/test/typeparam/absdiff3.go
index 3ca03fe26f..99fa6f11ab 100644
--- a/test/typeparam/absdiff3.go
+++ b/test/typeparam/absdiff3.go
@@ -43,9 +43,25 @@ type Complex interface {
 	~complex64 | ~complex128
 }
 
+func realimag(x any) (re, im float64) {
+	switch z := x.(type) {
+	case complex64:
+		re = float64(real(z))
+		im = float64(imag(z))
+	case complex128:
+		re = real(z)
+		im = imag(z)
+	default:
+		panic("unknown complex type")
+	}
+	return
+}
+
 func ComplexAbs[T Complex](a T) T {
-	r := float64(real(a))
-	i := float64(imag(a))
+	// TODO use direct conversion instead of realimag once #50937 is fixed
+	r, i := realimag(a)
+	// r := float64(real(a))
+	// i := float64(imag(a))
 	d := math.Sqrt(r*r + i*i)
 	return T(complex(d, 0))
 }
diff --git a/test/typeparam/absdiffimp2.dir/a.go b/test/typeparam/absdiffimp2.dir/a.go
index 302b69b976..43493e1430 100644
--- a/test/typeparam/absdiffimp2.dir/a.go
+++ b/test/typeparam/absdiffimp2.dir/a.go
@@ -60,9 +60,25 @@ type complexAbs[T Complex] struct {
 	Value T
 }
 
+func realimag(x any) (re, im float64) {
+	switch z := x.(type) {
+	case complex64:
+		re = float64(real(z))
+		im = float64(imag(z))
+	case complex128:
+		re = real(z)
+		im = imag(z)
+	default:
+		panic("unknown complex type")
+	}
+	return
+}
+
 func (a complexAbs[T]) Abs() T {
-	r := float64(real(a.Value))
-	i := float64(imag(a.Value))
+	// TODO use direct conversion instead of realimag once #50937 is fixed
+	r, i := realimag(a.Value)
+	// r := float64(real(a.Value))
+	// i := float64(imag(a.Value))
 	d := math.Sqrt(r*r + i*i)
 	return T(complex(d, 0))
 }