pkg/compiler: prohibit not DirIn resources inside fmt

The problem mentioned in the previous commit is actually not only
ANY-specific, it's only by a happy coincidence that all our descriptions
already avoided such situations.

Enforce this rule at the compilation stage.

3 files changed, 17 insertions, 5 deletions

diff --git a/pkg/compiler/check.go b/pkg/compiler/check.go
index 5f7bb7108..44c354606 100644
--- a/pkg/compiler/check.go
+++ b/pkg/compiler/check.go
@@ -672,10 +672,10 @@ func (comp *compiler) checkConstructors() {
 		switch n := decl.(type) {
 		case *ast.Call:
 			for _, arg := range n.Args {
-				comp.checkTypeCtors(arg.Type, prog.DirIn, true, true, ctors, inputs, checked)
+				comp.checkTypeCtors(arg.Type, prog.DirIn, true, true, ctors, inputs, checked, nil)
 			}
 			if n.Ret != nil {
-				comp.checkTypeCtors(n.Ret, prog.DirOut, true, true, ctors, inputs, checked)
+				comp.checkTypeCtors(n.Ret, prog.DirOut, true, true, ctors, inputs, checked, nil)
 			}
 		}
 	}
@@ -699,17 +699,23 @@ func (comp *compiler) checkConstructors() {
 }
 
 func (comp *compiler) checkTypeCtors(t *ast.Type, dir prog.Dir, isArg, canCreate bool,
-	ctors, inputs map[string]bool, checked map[structDir]bool) {
+	ctors, inputs map[string]bool, checked map[structDir]bool, neverOutAt *ast.Pos) {
 	desc, args, base := comp.getArgsBase(t, isArg)
 	if base.IsOptional {
 		canCreate = false
 	}
+	if desc.CantHaveOut {
+		neverOutAt = &t.Pos
+	}
 	if desc == typeResource {
 		// TODO(dvyukov): consider changing this to "dir == prog.DirOut".
 		// We have few questionable cases where resources can be created
 		// only by inout struct fields. These structs should be split
 		// into two different structs: one is in and second is out.
 		// But that will require attaching dir to individual fields.
+		if dir != prog.DirIn && neverOutAt != nil {
+			comp.error(*neverOutAt, "resource %s cannot be created in fmt", t.Ident)
+		}
 		if canCreate && dir != prog.DirIn {
 			r := comp.resources[t.Ident]
 			for r != nil && !ctors[r.Name.Name] {
@@ -742,7 +748,7 @@ func (comp *compiler) checkTypeCtors(t *ast.Type, dir prog.Dir, isArg, canCreate
 			if !fldHasDir {
 				fldDir = dir
 			}
-			comp.checkTypeCtors(fld.Type, fldDir, false, canCreate, ctors, inputs, checked)
+			comp.checkTypeCtors(fld.Type, fldDir, false, canCreate, ctors, inputs, checked, neverOutAt)
 		}
 		return
 	}
@@ -751,7 +757,7 @@ func (comp *compiler) checkTypeCtors(t *ast.Type, dir prog.Dir, isArg, canCreate
 	}
 	for i, arg := range args {
 		if desc.Args[i].Type == typeArgType {
-			comp.checkTypeCtors(arg, dir, desc.Args[i].IsArg, canCreate, ctors, inputs, checked)
+			comp.checkTypeCtors(arg, dir, desc.Args[i].IsArg, canCreate, ctors, inputs, checked, neverOutAt)
 		}
 	}
 }
diff --git a/pkg/compiler/testdata/errors2.txt b/pkg/compiler/testdata/errors2.txt
index 3cd63ebd2..e99610c58 100644
--- a/pkg/compiler/testdata/errors2.txt
+++ b/pkg/compiler/testdata/errors2.txt
@@ -421,3 +421,7 @@ foo$non_generatable(a compressed_image) (no_minimize)	### call foo$non_generatab
 foo$non_minimizable(a compressed_image) (no_generate)	### call foo$non_minimizable refers to type compressed_image and so must be marked no_minimize
 foo$non_generatable_via_struct(a ptr[in, struct_non_generatable])	(no_minimize)	### call foo$non_generatable_via_struct refers to type compressed_image and so must be marked no_generate
 foo$non_minimizable_via_union(a ptr[in, union_non_minimizable])	(no_generate)	### call foo$non_minimizable_via_union refers to type compressed_image and so must be marked no_minimize
+
+resource for_fmt[int32]
+foo$fmt_copyin(a ptr[in, fmt[dec, for_fmt]])
+foo$fmt_copyout(a ptr[out, fmt[dec, for_fmt]])	### resource for_fmt cannot be created in fmt
diff --git a/pkg/compiler/types.go b/pkg/compiler/types.go
index 099ab0009..a55a6c50d 100644
--- a/pkg/compiler/types.go
+++ b/pkg/compiler/types.go
@@ -20,6 +20,7 @@ type typeDesc struct {
 	CanBeTypedef      bool            // can be type alias target?
 	CantBeOpt         bool            // can't be marked as opt?
 	CantBeOut         bool            // can't be used as an explicitly output argument?
+	CantHaveOut       bool            // everything inside can only be in
 	NeedBase          bool            // needs base type when used as field?
 	MaxColon          int             // max number of colons (int8:2) on fields
 	OptArgs           int             // number of optional arguments in Args array
@@ -764,6 +765,7 @@ var typeFmt = &typeDesc{
 	CanBeTypedef: true,
 	CantBeOpt:    true,
 	CantBeOut:    true,
+	CantHaveOut:  true,
 	Args: []namedArg{
 		{Name: "format", Type: typeFmtFormat},
 		{Name: "value", Type: typeArgType, IsArg: true},