go.tools/go/types: provide TypeAndValue predicates

LGTM=adonovan
R=adonovan, pcc
CC=golang-codereviews
https://golang.org/cl/110880043

go/types/api.go

@@ -121,24 +121,23 @@ type Config struct {
 // in a client of go/types will initialize DefaultImport to gcimporter.Import.
 var DefaultImport Importer
 
-type TypeAndValue struct {
-	Type  Type
-	Value exact.Value
-}
-
 // Info holds result type information for a type-checked package.
 // Only the information for which a map is provided is collected.
 // If the package has type errors, the collected information may
 // be incomplete.
 type Info struct {
 	// Types maps expressions to their types, and for constant
-	// expressions, their values.
-	// Identifiers are collected in Defs and Uses, not Types.
+	// expressions, their values. Invalid expressions are omitted.
 	//
-	// For an expression denoting a predeclared built-in function
-	// the recorded signature is call-site specific. If the call
-	// result is not a constant, the recorded type is an argument-
-	// specific signature. Otherwise, the recorded type is invalid.
+	// For (possibly parenthesized) identifiers denoting built-in
+	// functions, the recorded signatures are call-site specific:
+	// if the call result is not a constant, the recorded type is
+	// an argument-specific signature. Otherwise, the recorded type
+	// is invalid.
+	//
+	// Identifiers on the lhs of declarations (i.e., the identifiers
+	// which are being declared) are collected in the Defs map.
+	// Identifiers denoting packages are collected in the Uses maps.
 	Types map[ast.Expr]TypeAndValue
 
 	// Defs maps identifiers to the objects they define (including
@@ -207,6 +206,69 @@ type Info struct {
 	InitOrder []*Initializer
 }
 
+// TypeAndValue reports the type and value (for constants)
+// of the corresponding expression.
+type TypeAndValue struct {
+	mode  operandMode
+	Type  Type
+	Value exact.Value
+}
+
+// TODO(gri) Consider eliminating the IsVoid predicate. Instead, report
+// "void" values as regular values but with the empty tuple type.
+
+// IsVoid reports whether the corresponding expression
+// is a function call without results.
+func (tv TypeAndValue) IsVoid() bool {
+	return tv.mode == novalue
+}
+
+// IsType reports whether the corresponding expression specifies a type.
+func (tv TypeAndValue) IsType() bool {
+	return tv.mode == typexpr
+}
+
+// IsBuiltin reports whether the corresponding expression denotes
+// a (possibly parenthesized) built-in function.
+func (tv TypeAndValue) IsBuiltin() bool {
+	return tv.mode == builtin
+}
+
+// IsValue reports whether the corresponding expression is a value.
+// Builtins are not considered values. Constant values have a non-
+// nil Value.
+func (tv TypeAndValue) IsValue() bool {
+	switch tv.mode {
+	case constant, variable, mapindex, value, commaok:
+		return true
+	}
+	return false
+}
+
+// IsNil reports whether the corresponding expression denotes the
+// predeclared value nil.
+func (tv TypeAndValue) IsNil() bool {
+	return tv.mode == value && tv.Type == Typ[UntypedNil]
+}
+
+// Addressable reports whether the corresponding expression
+// is addressable (http://golang.org/ref/spec#Address_operators).
+func (tv TypeAndValue) Addressable() bool {
+	return tv.mode == variable
+}
+
+// Assignable reports whether the corresponding expression
+// is assignable to (provided a value of the right type).
+func (tv TypeAndValue) Assignable() bool {
+	return tv.mode == variable || tv.mode == mapindex
+}
+
+// HasOk reports whether the corresponding expression may be
+// used on the lhs of a comma-ok assignment.
+func (tv TypeAndValue) HasOk() bool {
+	return tv.mode == commaok || tv.mode == mapindex
+}
+
 // An Initializer describes a package-level variable, or a list of variables in case
 // of a multi-valued initialization expression, and the corresponding initialization
 // expression.

go/types/api_test.go

@@ -5,6 +5,7 @@
 package types_test
 
 import (
+	"bytes"
 	"fmt"
 	"go/ast"
 	"go/parser"
@@ -255,6 +256,117 @@ func TestTypesInfo(t *testing.T) {
 	}
 }
 
+func predString(tv TypeAndValue) string {
+	var buf bytes.Buffer
+	pred := func(b bool, s string) {
+		if b {
+			if buf.Len() > 0 {
+				buf.WriteString(", ")
+			}
+			buf.WriteString(s)
+		}
+	}
+
+	pred(tv.IsVoid(), "void")
+	pred(tv.IsType(), "type")
+	pred(tv.IsBuiltin(), "builtin")
+	pred(tv.IsValue() && tv.Value != nil, "const")
+	pred(tv.IsValue() && tv.Value == nil, "value")
+	pred(tv.IsNil(), "nil")
+	pred(tv.Addressable(), "addressable")
+	pred(tv.Assignable(), "assignable")
+	pred(tv.HasOk(), "hasOk")
+
+	if buf.Len() == 0 {
+		return "invalid"
+	}
+	return buf.String()
+}
+
+func TestPredicatesInfo(t *testing.T) {
+	var tests = []struct {
+		src  string
+		expr string
+		pred string
+	}{
+		// void
+		{`package n0; func f() { f() }`, `f()`, `void`},
+
+		// types
+		{`package t0; type _ int`, `int`, `type`},
+		{`package t1; type _ []int`, `[]int`, `type`},
+		{`package t2; type _ func()`, `func()`, `type`},
+
+		// built-ins
+		{`package b0; var _ = len("")`, `len`, `builtin`},
+		{`package b1; var _ = (len)("")`, `(len)`, `builtin`},
+
+		// constants
+		{`package c0; var _ = 42`, `42`, `const`},
+		{`package c1; var _ = "foo" + "bar"`, `"foo" + "bar"`, `const`},
+		{`package c2; const (i = 1i; _ = i)`, `i`, `const`},
+
+		// values
+		{`package v0; var (a, b int; _ = a + b)`, `a + b`, `value`},
+		{`package v1; var _ = &[]int{1}`, `([]int literal)`, `value`},
+		{`package v2; var _ = func(){}`, `(func() literal)`, `value`},
+		{`package v4; func f() { _ = f }`, `f`, `value`},
+		{`package v3; var _ *int = nil`, `nil`, `value, nil`},
+		{`package v3; var _ *int = (nil)`, `(nil)`, `value, nil`},
+
+		// addressable (and thus assignable) operands
+		{`package a0; var (x int; _ = x)`, `x`, `value, addressable, assignable`},
+		{`package a1; var (p *int; _ = *p)`, `*p`, `value, addressable, assignable`},
+		{`package a2; var (s []int; _ = s[0])`, `s[0]`, `value, addressable, assignable`},
+		{`package a3; var (s struct{f int}; _ = s.f)`, `s.f`, `value, addressable, assignable`},
+		{`package a4; var (a [10]int; _ = a[0])`, `a[0]`, `value, addressable, assignable`},
+		{`package a5; func _(x int) { _ = x }`, `x`, `value, addressable, assignable`},
+		{`package a6; func _()(x int) { _ = x; return }`, `x`, `value, addressable, assignable`},
+		{`package a7; type T int; func (x T) _() { _ = x }`, `x`, `value, addressable, assignable`},
+		// composite literals are not addressable
+
+		// assignable but not addressable values
+		{`package s0; var (m map[int]int; _ = m[0])`, `m[0]`, `value, assignable, hasOk`},
+		{`package s1; var (m map[int]int; _, _ = m[0])`, `m[0]`, `value, assignable, hasOk`},
+
+		// hasOk expressions
+		{`package k0; var (ch chan int; _ = <-ch)`, `<-ch`, `value, hasOk`},
+		{`package k1; var (ch chan int; _, _ = <-ch)`, `<-ch`, `value, hasOk`},
+
+		// missing entries
+		// - package names are collected in the Uses map
+		// - identifiers being declared are collected in the Defs map
+		{`package m0; import "os"; func _() { _ = os.Stdout }`, `os`, `<missing>`},
+		{`package m1; import p "os"; func _() { _ = p.Stdout }`, `p`, `<missing>`},
+		{`package m2; const c = 0`, `c`, `<missing>`},
+		{`package m3; type T int`, `T`, `<missing>`},
+		{`package m4; var v int`, `v`, `<missing>`},
+		{`package m5; func f() {}`, `f`, `<missing>`},
+		{`package m6; func _(x int) {}`, `x`, `<missing>`},
+		{`package m6; func _()(x int) { return }`, `x`, `<missing>`},
+		{`package m6; type T int; func (x T) _() {}`, `x`, `<missing>`},
+	}
+
+	for _, test := range tests {
+		info := Info{Types: make(map[ast.Expr]TypeAndValue)}
+		name := mustTypecheck(t, "PredicatesInfo", test.src, &info)
+
+		// look for expression predicates
+		got := "<missing>"
+		for e, tv := range info.Types {
+			//println(name, ExprString(e))
+			if ExprString(e) == test.expr {
+				got = predString(tv)
+				break
+			}
+		}
+
+		if got != test.pred {
+			t.Errorf("package %s: got %s; want %s", name, got, test.pred)
+		}
+	}
+}
+
 func TestScopesInfo(t *testing.T) {
 	var tests = []struct {
 		src    string

go/types/check.go

@@ -20,9 +20,10 @@ const (
 	trace = false // turn on for detailed type resolution traces
 )
 
-// exprInfo stores type and constant value for an untyped expression.
+// exprInfo stores information about an untyped expression.
 type exprInfo struct {
 	isLhs bool // expression is lhs operand of a shift with delayed type-check
+	mode  operandMode
 	typ   *Basic
 	val   exact.Value // constant value; or nil (if not a constant)
 }
@@ -98,13 +99,13 @@ func (check *Checker) assocMethod(tname string, meth *Func) {
 	m[tname] = append(m[tname], meth)
 }
 
-func (check *Checker) rememberUntyped(e ast.Expr, lhs bool, typ *Basic, val exact.Value) {
+func (check *Checker) rememberUntyped(e ast.Expr, lhs bool, mode operandMode, typ *Basic, val exact.Value) {
 	m := check.untyped
 	if m == nil {
 		m = make(map[ast.Expr]exprInfo)
 		check.untyped = m
 	}
-	m[e] = exprInfo{lhs, typ, val}
+	m[e] = exprInfo{lhs, mode, typ, val}
 }
 
 func (check *Checker) later(name string, decl *declInfo, sig *Signature, body *ast.BlockStmt) {
@@ -239,17 +240,23 @@ func (check *Checker) recordUntyped() {
 			check.dump("%s: %s (type %s) is typed", x.Pos(), x, info.typ)
 			unreachable()
 		}
-		check.recordTypeAndValue(x, info.typ, info.val)
+		check.recordTypeAndValue(x, info.mode, info.typ, info.val)
 	}
 }
 
-func (check *Checker) recordTypeAndValue(x ast.Expr, typ Type, val exact.Value) {
-	assert(x != nil && typ != nil)
-	if val != nil {
+func (check *Checker) recordTypeAndValue(x ast.Expr, mode operandMode, typ Type, val exact.Value) {
+	assert(x != nil)
+	assert(typ != nil)
+	if mode == invalid {
+		return // omit
+	}
+	assert(typ != nil)
+	if mode == constant {
+		assert(val != nil)
 		assert(isConstType(typ))
 	}
 	if m := check.Types; m != nil {
-		m[x] = TypeAndValue{typ, val}
+		m[x] = TypeAndValue{mode, typ, val}
 	}
 }
 
@@ -259,7 +266,7 @@ func (check *Checker) recordBuiltinType(f ast.Expr, sig *Signature) {
 	// we don't record their signatures, so we don't see qualified idents
 	// here): record the signature for f and possible children.
 	for {
-		check.recordTypeAndValue(f, sig, nil)
+		check.recordTypeAndValue(f, builtin, sig, nil)
 		switch p := f.(type) {
 		case *ast.Ident:
 			return // we're done
@@ -313,7 +320,8 @@ func (check *Checker) recordUse(id *ast.Ident, obj Object) {
 }
 
 func (check *Checker) recordImplicit(node ast.Node, obj Object) {
-	assert(node != nil && obj != nil)
+	assert(node != nil)
+	assert(obj != nil)
 	if m := check.Implicits; m != nil {
 		m[node] = obj
 	}
@@ -329,7 +337,8 @@ func (check *Checker) recordSelection(x *ast.SelectorExpr, kind SelectionKind, r
 }
 
 func (check *Checker) recordScope(node ast.Node, scope *Scope) {
-	assert(node != nil && scope != nil)
+	assert(node != nil)
+	assert(scope != nil)
 	if m := check.Scopes; m != nil {
 		m[node] = scope
 	}

go/types/expr.go

@@ -451,7 +451,7 @@ func (check *Checker) updateExprType(x ast.Expr, typ Type, final bool) {
 	}
 
 	// Everything's fine, record final type and value for x.
-	check.recordTypeAndValue(x, typ, old.val)
+	check.recordTypeAndValue(x, old.mode, typ, old.val)
 }
 
 // updateExprVal updates the value of x to val.
@@ -908,6 +908,7 @@ func (check *Checker) rawExpr(x *operand, e ast.Expr, hint Type) exprKind {
 	kind := check.exprInternal(x, e, hint)
 
 	// convert x into a user-friendly set of values
+	// TODO(gri) this code can be simplified
 	var typ Type
 	var val exact.Value
 	switch x.mode {
@@ -926,9 +927,9 @@ func (check *Checker) rawExpr(x *operand, e ast.Expr, hint Type) exprKind {
 	if isUntyped(typ) {
 		// delay type and value recording until we know the type
 		// or until the end of type checking
-		check.rememberUntyped(x.expr, false, typ.(*Basic), val)
+		check.rememberUntyped(x.expr, false, x.mode, typ.(*Basic), val)
 	} else {
-		check.recordTypeAndValue(e, typ, val)
+		check.recordTypeAndValue(e, x.mode, typ, val)
 	}
 
 	return kind

go/types/operand.go

@@ -15,7 +15,7 @@ import (
 )
 
 // An operandMode specifies the (addressing) mode of an operand.
-type operandMode int
+type operandMode byte
 
 const (
 	invalid  operandMode = iota // operand is invalid

go/types/typexpr.go

@@ -129,7 +129,7 @@ func (check *Checker) typExpr(e ast.Expr, def *Named, path []*TypeName) (T Type)
 
 	T = check.typExprInternal(e, def, path)
 	assert(isTyped(T))
-	check.recordTypeAndValue(e, T, nil)
+	check.recordTypeAndValue(e, typexpr, T, nil)
 
 	return
 }