cmd/compile: new absdiff.go test, fix problem with g.curDecl

Added a new absdiff2.go test case, which works fully without using a
typeparam on the right-hand-side of a type declaration (which is
disallowed). Fixed an issue that the test revealed, which is that we
need to set g.curDecl properly for the "later" functions which are
deferred until after all declarations are initially processed. Also,
g.curDecl may be non-nil in typeDecl for local type declaration. So, we
adjust the associate assertion, and save/restore g.curDecl
appropriately.

Fixes #50790

Change-Id: Ieed76a7ad0a83bccb99cbad4bf98a7bfafbcbbd3
Reviewed-on: https://go-review.googlesource.com/c/go/+/380594
Reviewed-by: Keith Randall <khr@golang.org>
Trust: Dan Scales <danscales@google.com>

6 files changed, 235 insertions, 6 deletions

diff --git a/src/cmd/compile/internal/noder/decl.go b/src/cmd/compile/internal/noder/decl.go
index df1ca1c505..a9522d09af 100644
--- a/src/cmd/compile/internal/noder/decl.go
+++ b/src/cmd/compile/internal/noder/decl.go
@@ -133,12 +133,20 @@ func (g *irgen) funcDecl(out *ir.Nodes, decl *syntax.FuncDecl) {
 		g.target.Inits = append(g.target.Inits, fn)
 	}
 
-	haveEmbed := g.haveEmbed
+	saveHaveEmbed := g.haveEmbed
+	saveCurDecl := g.curDecl
 	g.curDecl = ""
 	g.later(func() {
-		defer func(b bool) { g.haveEmbed = b }(g.haveEmbed)
-
-		g.haveEmbed = haveEmbed
+		defer func(b bool, s string) {
+			// Revert haveEmbed and curDecl back to what they were before
+			// the "later" function.
+			g.haveEmbed = b
+			g.curDecl = s
+		}(g.haveEmbed, g.curDecl)
+
+		// Set haveEmbed and curDecl to what they were for this funcDecl.
+		g.haveEmbed = saveHaveEmbed
+		g.curDecl = saveCurDecl
 		if fn.Type().HasTParam() {
 			g.topFuncIsGeneric = true
 		}
@@ -162,9 +170,10 @@ func (g *irgen) funcDecl(out *ir.Nodes, decl *syntax.FuncDecl) {
 func (g *irgen) typeDecl(out *ir.Nodes, decl *syntax.TypeDecl) {
 	// Set the position for any error messages we might print (e.g. too large types).
 	base.Pos = g.pos(decl)
-	assert(g.curDecl == "")
+	assert(ir.CurFunc != nil || g.curDecl == "")
 	// Set g.curDecl to the type name, as context for the type params declared
 	// during types2-to-types1 translation if this is a generic type.
+	saveCurDecl := g.curDecl
 	g.curDecl = decl.Name.Value
 	if decl.Alias {
 		name, _ := g.def(decl.Name)
@@ -225,7 +234,7 @@ func (g *irgen) typeDecl(out *ir.Nodes, decl *syntax.TypeDecl) {
 	}
 	types.ResumeCheckSize()
 
-	g.curDecl = ""
+	g.curDecl = saveCurDecl
 	if otyp, ok := otyp.(*types2.Named); ok && otyp.NumMethods() != 0 {
 		methods := make([]*types.Field, otyp.NumMethods())
 		for i := range methods {
diff --git a/test/run.go b/test/run.go
index 2a7f080f9d..0e35ed2c0f 100644
--- a/test/run.go
+++ b/test/run.go
@@ -2180,6 +2180,8 @@ var unifiedFailures = setOf(
 	"typeparam/typeswitch4.go", // duplicate case failure due to stenciling
 	"typeparam/issue50417b.go", // Need to handle field access on a type param
 	"typeparam/issue50552.go",  // gives missing method for instantiated type
+	"typeparam/absdiff2.go",    // wrong assertion about closure variables
+	"typeparam/absdiffimp2.go", // wrong assertion about closure variables
 )
 
 func setOf(keys ...string) map[string]bool {
diff --git a/test/typeparam/absdiff2.go b/test/typeparam/absdiff2.go
new file mode 100644
index 0000000000..8f13bad2b6
--- /dev/null
+++ b/test/typeparam/absdiff2.go
@@ -0,0 +1,102 @@
+// run -gcflags=-G=3
+
+// 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 main
+
+import (
+	"fmt"
+	"math"
+)
+
+type Numeric interface {
+	~int | ~int8 | ~int16 | ~int32 | ~int64 |
+		~uint | ~uint8 | ~uint16 | ~uint32 | ~uint64 | ~uintptr |
+		~float32 | ~float64 |
+		~complex64 | ~complex128
+}
+
+// numericAbs matches a struct containing a numeric type that has an Abs method.
+type numericAbs[T Numeric] interface {
+	~struct{ Value T }
+	Abs() T
+}
+
+// AbsDifference computes the absolute value of the difference of
+// a and b, where the absolute value is determined by the Abs method.
+func absDifference[T Numeric, U numericAbs[T]](a, b U) T {
+	d := a.Value - b.Value
+	dt := U{Value: d}
+	return dt.Abs()
+}
+
+// orderedNumeric matches numeric types that support the < operator.
+type orderedNumeric interface {
+	~int | ~int8 | ~int16 | ~int32 | ~int64 |
+		~uint | ~uint8 | ~uint16 | ~uint32 | ~uint64 | ~uintptr |
+		~float32 | ~float64
+}
+
+// Complex matches the two complex types, which do not have a < operator.
+type Complex interface {
+	~complex64 | ~complex128
+}
+
+// orderedAbs is a helper type that defines an Abs method for
+// a struct containing an ordered numeric type.
+type orderedAbs[T orderedNumeric] struct {
+	Value T
+}
+
+func (a orderedAbs[T]) Abs() T {
+	if a.Value < 0 {
+		return -a.Value
+	}
+	return a.Value
+}
+
+// complexAbs is a helper type that defines an Abs method for
+// a struct containing a complex type.
+type complexAbs[T Complex] struct {
+	Value T
+}
+
+func (a complexAbs[T]) Abs() T {
+	r := float64(real(a.Value))
+	i := float64(imag(a.Value))
+	d := math.Sqrt(r*r + i*i)
+	return T(complex(d, 0))
+}
+
+// OrderedAbsDifference returns the absolute value of the difference
+// between a and b, where a and b are of an ordered type.
+func OrderedAbsDifference[T orderedNumeric](a, b T) T {
+	return absDifference(orderedAbs[T]{a}, orderedAbs[T]{b})
+}
+
+// ComplexAbsDifference returns the absolute value of the difference
+// between a and b, where a and b are of a complex type.
+func ComplexAbsDifference[T Complex](a, b T) T {
+	return absDifference(complexAbs[T]{a}, complexAbs[T]{b})
+}
+
+func main() {
+	if got, want := OrderedAbsDifference(1.0, -2.0), 3.0; got != want {
+		panic(fmt.Sprintf("got = %v, want = %v", got, want))
+	}
+	if got, want := OrderedAbsDifference(-1.0, 2.0), 3.0; got != want {
+		panic(fmt.Sprintf("got = %v, want = %v", got, want))
+	}
+	if got, want := OrderedAbsDifference(-20, 15), 35; got != want {
+		panic(fmt.Sprintf("got = %v, want = %v", got, want))
+	}
+
+	if got, want := ComplexAbsDifference(5.0+2.0i, 2.0-2.0i), 5+0i; got != want {
+		panic(fmt.Sprintf("got = %v, want = %v", got, want))
+	}
+	if got, want := ComplexAbsDifference(2.0-2.0i, 5.0+2.0i), 5+0i; got != want {
+		panic(fmt.Sprintf("got = %v, want = %v", got, want))
+	}
+}
diff --git a/test/typeparam/absdiffimp2.dir/a.go b/test/typeparam/absdiffimp2.dir/a.go
new file mode 100644
index 0000000000..782e000da9
--- /dev/null
+++ b/test/typeparam/absdiffimp2.dir/a.go
@@ -0,0 +1,80 @@
+// 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 a
+
+import (
+	"math"
+)
+
+type Numeric interface {
+	~int | ~int8 | ~int16 | ~int32 | ~int64 |
+		~uint | ~uint8 | ~uint16 | ~uint32 | ~uint64 | ~uintptr |
+		~float32 | ~float64 |
+		~complex64 | ~complex128
+}
+
+// numericAbs matches a struct containing a numeric type that has an Abs method.
+type numericAbs[T Numeric] interface {
+	~struct{ Value T }
+	Abs() T
+}
+
+// AbsDifference computes the absolute value of the difference of
+// a and b, where the absolute value is determined by the Abs method.
+func absDifference[T Numeric, U numericAbs[T]](a, b U) T {
+	d := a.Value - b.Value
+	dt := U{Value: d}
+	return dt.Abs()
+}
+
+// orderedNumeric matches numeric types that support the < operator.
+type orderedNumeric interface {
+	~int | ~int8 | ~int16 | ~int32 | ~int64 |
+		~uint | ~uint8 | ~uint16 | ~uint32 | ~uint64 | ~uintptr |
+		~float32 | ~float64
+}
+
+// Complex matches the two complex types, which do not have a < operator.
+type Complex interface {
+	~complex64 | ~complex128
+}
+
+// orderedAbs is a helper type that defines an Abs method for
+// a struct containing an ordered numeric type.
+type orderedAbs[T orderedNumeric] struct {
+	Value T
+}
+
+func (a orderedAbs[T]) Abs() T {
+	if a.Value < 0 {
+		return -a.Value
+	}
+	return a.Value
+}
+
+// complexAbs is a helper type that defines an Abs method for
+// a struct containing a complex type.
+type complexAbs[T Complex] struct {
+	Value T
+}
+
+func (a complexAbs[T]) Abs() T {
+	r := float64(real(a.Value))
+	i := float64(imag(a.Value))
+	d := math.Sqrt(r*r + i*i)
+	return T(complex(d, 0))
+}
+
+// OrderedAbsDifference returns the absolute value of the difference
+// between a and b, where a and b are of an ordered type.
+func OrderedAbsDifference[T orderedNumeric](a, b T) T {
+	return absDifference(orderedAbs[T]{a}, orderedAbs[T]{b})
+}
+
+// ComplexAbsDifference returns the absolute value of the difference
+// between a and b, where a and b are of a complex type.
+func ComplexAbsDifference[T Complex](a, b T) T {
+	return absDifference(complexAbs[T]{a}, complexAbs[T]{b})
+}
diff --git a/test/typeparam/absdiffimp2.dir/main.go b/test/typeparam/absdiffimp2.dir/main.go
new file mode 100644
index 0000000000..8eefdbdf38
--- /dev/null
+++ b/test/typeparam/absdiffimp2.dir/main.go
@@ -0,0 +1,29 @@
+// Copyright 2021 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 main
+
+import (
+	"a"
+	"fmt"
+)
+
+func main() {
+	if got, want := a.OrderedAbsDifference(1.0, -2.0), 3.0; got != want {
+		panic(fmt.Sprintf("got = %v, want = %v", got, want))
+	}
+	if got, want := a.OrderedAbsDifference(-1.0, 2.0), 3.0; got != want {
+		panic(fmt.Sprintf("got = %v, want = %v", got, want))
+	}
+	if got, want := a.OrderedAbsDifference(-20, 15), 35; got != want {
+		panic(fmt.Sprintf("got = %v, want = %v", got, want))
+	}
+
+	if got, want := a.ComplexAbsDifference(5.0+2.0i, 2.0-2.0i), 5+0i; got != want {
+		panic(fmt.Sprintf("got = %v, want = %v", got, want))
+	}
+	if got, want := a.ComplexAbsDifference(2.0-2.0i, 5.0+2.0i), 5+0i; got != want {
+		panic(fmt.Sprintf("got = %v, want = %v", got, want))
+	}
+}
diff --git a/test/typeparam/absdiffimp2.go b/test/typeparam/absdiffimp2.go
new file mode 100644
index 0000000000..76930e5e4f
--- /dev/null
+++ b/test/typeparam/absdiffimp2.go
@@ -0,0 +1,7 @@
+// rundir -G=3
+
+// Copyright 2021 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 ignored