cmd/compile/internal/types2: systematic detection of missing instantiation

When type-checking expressions, detection of uninstantiated generic
functions and types was somewhat ad-hoc.

Add an extra parameter "allowGenerics" to rawExpr. If not set, the
result operand cannot be generic.

The only place where rawExpr is called with allowGenerics != false
is from exprOrType, which passes an allowGenerics parameter through.

The only place where exprOrType is called with allowGenerics == true
is when handling index expressions and calls. Make sure that we only
accept generic operands where expected, and check the other branches.

As a result, a recently added varType call (CL 345970) can be removed
again.

This also fixes a bug where an error for a conversion to generic
type was reported after the conversion (i.e., with the converted
value, rather than the generic type). Added a test case for that.

For #48048.

Change-Id: I8576326f5fcfb58d78b3ce8572068aa32e66c568
Reviewed-on: https://go-review.googlesource.com/c/go/+/346471
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>

diff --git a/src/cmd/compile/internal/types2/builtins.go b/src/cmd/compile/internal/types2/builtins.go
index 87295fe0e709bc9580c74942348432fb4332ed84..e3844d5163e168313143e038e568052eb5474ba3 100644 (file)
--- a/src/cmd/compile/internal/types2/builtins.go
+++ b/src/cmd/compile/internal/types2/builtins.go
@@ -763,7 +763,7 @@ func (check *Checker) builtin(x *operand, call *syntax.CallExpr, id builtinId) (
                var t operand
                x1 := x
                for _, arg := range call.ArgList {
-                       check.rawExpr(x1, arg, nil) // permit trace for types, e.g.: new(trace(T))
+                       check.rawExpr(x1, arg, nil, false) // permit trace for types, e.g.: new(trace(T))
                        check.dump("%v: %s", posFor(x1), x1)
                        x1 = &t // use incoming x only for first argument
                }

diff --git a/src/cmd/compile/internal/types2/call.go b/src/cmd/compile/internal/types2/call.go
index 954aa1de207bce3faba662047e43676c35276623..5bf17876c15bda2491a1e3850b966a5107cd7025 100644 (file)
--- a/src/cmd/compile/internal/types2/call.go
+++ b/src/cmd/compile/internal/types2/call.go
@@ -83,8 +83,9 @@ func (check *Checker) callExpr(x *operand, call *syntax.CallExpr) exprKind {
                x.expr = iexpr
                check.record(x)
        } else {
-               check.exprOrType(x, call.Fun)
+               check.exprOrType(x, call.Fun, true)
        }
+       // x.typ may be generic
 
        switch x.mode {
        case invalid:
@@ -94,6 +95,10 @@ func (check *Checker) callExpr(x *operand, call *syntax.CallExpr) exprKind {
 
        case typexpr:
                // conversion
+               check.nonGeneric(x)
+               if x.mode == invalid {
+                       return conversion
+               }
                T := x.typ
                x.mode = invalid
                switch n := len(call.ArgList); n {
@@ -122,6 +127,7 @@ func (check *Checker) callExpr(x *operand, call *syntax.CallExpr) exprKind {
                return conversion
 
        case builtin:
+               // no need to check for non-genericity here
                id := x.id
                if !check.builtin(x, call, id) {
                        x.mode = invalid
@@ -135,6 +141,7 @@ func (check *Checker) callExpr(x *operand, call *syntax.CallExpr) exprKind {
        }
 
        // ordinary function/method call
+       // signature may be generic
        cgocall := x.mode == cgofunc
 
        sig := asSignature(x.typ)
@@ -474,15 +481,11 @@ func (check *Checker) selector(x *operand, e *syntax.SelectorExpr) {
                }
        }
 
-       check.exprOrType(x, e.X)
+       check.exprOrType(x, e.X, false)
        if x.mode == invalid {
                goto Error
        }
 
-       if x.mode == typexpr {
-               x.typ = check.varType(e.X)
-       }
-
        obj, index, indirect = LookupFieldOrMethod(x.typ, x.mode == variable, check.pkg, sel)
        if obj == nil {
                switch {
@@ -683,7 +686,7 @@ func (check *Checker) use(arg ...syntax.Expr) {
                        check.use(l.ElemList...)
                        continue
                }
-               check.rawExpr(&x, e, nil)
+               check.rawExpr(&x, e, nil, false)
        }
 }
 
@@ -714,7 +717,7 @@ func (check *Checker) useLHS(arg ...syntax.Expr) {
                                }
                        }
                }
-               check.rawExpr(&x, e, nil)
+               check.rawExpr(&x, e, nil, false)
                if v != nil {
                        v.used = v_used // restore v.used
                }

diff --git a/src/cmd/compile/internal/types2/expr.go b/src/cmd/compile/internal/types2/expr.go
index 799874624d1696f7200ed5636e9e7e4b61cc95ac..99204762bc8ddac3296341f2d812e55f87ab9326 100644 (file)
--- a/src/cmd/compile/internal/types2/expr.go
+++ b/src/cmd/compile/internal/types2/expr.go
@@ -1085,8 +1085,10 @@ const (
 // rawExpr typechecks expression e and initializes x with the expression
 // value or type. If an error occurred, x.mode is set to invalid.
 // If hint != nil, it is the type of a composite literal element.
+// If allowGeneric is set, the operand type may be an uninstantiated
+// parameterized type or function value.
 //
-func (check *Checker) rawExpr(x *operand, e syntax.Expr, hint Type) exprKind {
+func (check *Checker) rawExpr(x *operand, e syntax.Expr, hint Type, allowGeneric bool) exprKind {
        if check.conf.Trace {
                check.trace(e.Pos(), "expr %s", e)
                check.indent++
@@ -1097,11 +1099,40 @@ func (check *Checker) rawExpr(x *operand, e syntax.Expr, hint Type) exprKind {
        }
 
        kind := check.exprInternal(x, e, hint)
+
+       if !allowGeneric {
+               check.nonGeneric(x)
+       }
+
        check.record(x)
 
        return kind
 }
 
+// If x is a generic function or type, nonGeneric reports an error and invalidates x.mode and x.typ.
+// Otherwise it leaves x alone.
+func (check *Checker) nonGeneric(x *operand) {
+       if x.mode == invalid || x.mode == novalue {
+               return
+       }
+       var what string
+       switch t := x.typ.(type) {
+       case *Named:
+               if isGeneric(t) {
+                       what = "type"
+               }
+       case *Signature:
+               if t.tparams != nil {
+                       what = "function"
+               }
+       }
+       if what != "" {
+               check.errorf(x.expr, "cannot use generic %s %s without instantiation", what, x.expr)
+               x.mode = invalid
+               x.typ = Typ[Invalid]
+       }
+}
+
 // exprInternal contains the core of type checking of expressions.
 // Must only be called by rawExpr.
 //
@@ -1386,7 +1417,7 @@ func (check *Checker) exprInternal(x *operand, e syntax.Expr, hint Type) exprKin
                x.typ = typ
 
        case *syntax.ParenExpr:
-               kind := check.rawExpr(x, e.X, nil)
+               kind := check.rawExpr(x, e.X, nil, false)
                x.expr = e
                return kind
 
@@ -1468,7 +1499,7 @@ func (check *Checker) exprInternal(x *operand, e syntax.Expr, hint Type) exprKin
                        // unary expression
                        if e.Op == syntax.Mul {
                                // pointer indirection
-                               check.exprOrType(x, e.X)
+                               check.exprOrType(x, e.X, false)
                                switch x.mode {
                                case invalid:
                                        goto Error
@@ -1595,14 +1626,14 @@ func (check *Checker) typeAssertion(pos syntax.Pos, x *operand, xtyp *Interface,
 // If an error occurred, x.mode is set to invalid.
 //
 func (check *Checker) expr(x *operand, e syntax.Expr) {
-       check.rawExpr(x, e, nil)
+       check.rawExpr(x, e, nil, false)
        check.exclude(x, 1<<novalue|1<<builtin|1<<typexpr)
        check.singleValue(x)
 }
 
 // multiExpr is like expr but the result may also be a multi-value.
 func (check *Checker) multiExpr(x *operand, e syntax.Expr) {
-       check.rawExpr(x, e, nil)
+       check.rawExpr(x, e, nil, false)
        check.exclude(x, 1<<novalue|1<<builtin|1<<typexpr)
 }
 
@@ -1612,16 +1643,18 @@ func (check *Checker) multiExpr(x *operand, e syntax.Expr) {
 //
 func (check *Checker) exprWithHint(x *operand, e syntax.Expr, hint Type) {
        assert(hint != nil)
-       check.rawExpr(x, e, hint)
+       check.rawExpr(x, e, hint, false)
        check.exclude(x, 1<<novalue|1<<builtin|1<<typexpr)
        check.singleValue(x)
 }
 
 // exprOrType typechecks expression or type e and initializes x with the expression value or type.
+// If allowGeneric is set, the operand type may be an uninstantiated parameterized type or function
+// value.
 // If an error occurred, x.mode is set to invalid.
 //
-func (check *Checker) exprOrType(x *operand, e syntax.Expr) {
-       check.rawExpr(x, e, nil)
+func (check *Checker) exprOrType(x *operand, e syntax.Expr, allowGeneric bool) {
+       check.rawExpr(x, e, nil, allowGeneric)
        check.exclude(x, 1<<novalue)
        check.singleValue(x)
 }

diff --git a/src/cmd/compile/internal/types2/index.go b/src/cmd/compile/internal/types2/index.go
index e8755a1a68ea3872d1cf5e205eb50c21ca8f9d15..febfd21ea3386124cf3185c51b90b510138895c3 100644 (file)
--- a/src/cmd/compile/internal/types2/index.go
+++ b/src/cmd/compile/internal/types2/index.go
@@ -15,7 +15,8 @@ import (
 // In that case x represents the uninstantiated function value and
 // it is the caller's responsibility to instantiate the function.
 func (check *Checker) indexExpr(x *operand, e *syntax.IndexExpr) (isFuncInst bool) {
-       check.exprOrType(x, e.X)
+       check.exprOrType(x, e.X, true)
+       // x may be generic
 
        switch x.mode {
        case invalid:
@@ -25,6 +26,7 @@ func (check *Checker) indexExpr(x *operand, e *syntax.IndexExpr) (isFuncInst boo
        case typexpr:
                // type instantiation
                x.mode = invalid
+               // TODO(gri) here we re-evaluate e.X - try to avoid this
                x.typ = check.varType(e)
                if x.typ != Typ[Invalid] {
                        x.mode = typexpr
@@ -38,6 +40,12 @@ func (check *Checker) indexExpr(x *operand, e *syntax.IndexExpr) (isFuncInst boo
                }
        }
 
+       // x should not be generic at this point, but be safe and check
+       check.nonGeneric(x)
+       if x.mode == invalid {
+               return false
+       }
+
        // ordinary index expression
        valid := false
        length := int64(-1) // valid if >= 0

diff --git a/src/cmd/compile/internal/types2/stmt.go b/src/cmd/compile/internal/types2/stmt.go
index 3231fbec93696f079b95af2e458c63cea31a3859..e138c58123034649064f1376530c7e92055aa09a 100644 (file)
--- a/src/cmd/compile/internal/types2/stmt.go
+++ b/src/cmd/compile/internal/types2/stmt.go
@@ -170,7 +170,7 @@ func (check *Checker) closeScope() {
 func (check *Checker) suspendedCall(keyword string, call *syntax.CallExpr) {
        var x operand
        var msg string
-       switch check.rawExpr(&x, call, nil) {
+       switch check.rawExpr(&x, call, nil, false) {
        case conversion:
                msg = "requires function call, not conversion"
        case expression:
@@ -386,7 +386,7 @@ func (check *Checker) stmt(ctxt stmtContext, s syntax.Stmt) {
                // function and method calls and receive operations can appear
                // in statement context. Such statements may be parenthesized."
                var x operand
-               kind := check.rawExpr(&x, s.X, nil)
+               kind := check.rawExpr(&x, s.X, nil, false)
                var msg string
                switch x.mode {
                default:

diff --git a/src/cmd/compile/internal/types2/testdata/examples/types.go2 b/src/cmd/compile/internal/types2/testdata/examples/types.go2
index 9ee014452c5500c956ea4072328aaea36109c321..97c9951ada56d0a520bff3b257b7ed568b0f72b0 100644 (file)
--- a/src/cmd/compile/internal/types2/testdata/examples/types.go2
+++ b/src/cmd/compile/internal/types2/testdata/examples/types.go2
@@ -102,6 +102,7 @@ func _() {
 
 // Generic types cannot be used without instantiation.
 var _ T // ERROR cannot use generic type T
+var _ = T /* ERROR cannot use generic type T */ (0)
 
 // In type context, generic (parameterized) types cannot be parenthesized before
 // being instantiated. See also NOTES entry from 12/4/2019.

diff --git a/src/cmd/compile/internal/types2/testdata/fixedbugs/issue39634.go2 b/src/cmd/compile/internal/types2/testdata/fixedbugs/issue39634.go2
index 8d14f8acaf825937d8d77d59533978ddd87f58d9..8e6bd974e88b414fd4fc06a1438aefdb1c4bb3bf 100644 (file)
--- a/src/cmd/compile/internal/types2/testdata/fixedbugs/issue39634.go2
+++ b/src/cmd/compile/internal/types2/testdata/fixedbugs/issue39634.go2
@@ -85,7 +85,7 @@ var x T25 /* ERROR without instantiation */ .m1
 
 // crash 26
 type T26 = interface{ F26[ /* ERROR cannot have type parameters */ Z any]() }
-func F26[Z any]() T26 { return F26 /* ERROR without instantiation */ /* ERROR missing method */ [] /* ERROR operand */ }
+func F26[Z any]() T26 { return F26 /* ERROR without instantiation */ [] /* ERROR operand */ }
 
 // crash 27
 func e27[T any]() interface{ x27 /* ERROR not a type */ } { panic(0) }