[dev.typeparams] cmd/compile: fix crawling of embeddable types

In reflectdata, we have a hack to only apply inlining for (*T).M
wrappers generated around T.M. This was a hack because I didn't
understand at the time why other cases were failing.

But I understand now: during export, we generally skip exporting the
inline bodies for unexported methods (unless they're reachable through
some other exported method). But it doesn't take into account that
embedding a type requires generating wrappers for promoted methods,
including imported, unexported methods.

For example:

	package a
	type T struct{}
	func (T) m() {} // previously omitted by exported

	package b
	import "./a"
	type U struct { a.T } // needs U.m -> T.m wrapper

This CL adds extra logic to the crawler to recognize that T is an
exported type directly reachable by the user, so *all* of its methods
need to be re-exported.

This finally allows simplifying reflectdata.methodWrapper to always
call inline.InlineCalls.

Change-Id: I25031d41fd6b6cd69d31c6a864b5329cdb5780e2
Reviewed-on: https://go-review.googlesource.com/c/go/+/327872
Trust: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>

src/cmd/compile/internal/reflectdata/reflect.go

@@ -1795,20 +1795,24 @@ func methodWrapper(rcvr *types.Type, method *types.Field, forItab bool) *obj.LSy
 		return lsym
 	}
 
-	// Only generate (*T).M wrappers for T.M in T's own package, except for
-	// instantiated methods.
-	if rcvr.IsPtr() && rcvr.Elem() == method.Type.Recv().Type &&
-		rcvr.Elem().Sym() != nil && rcvr.Elem().Sym().Pkg != types.LocalPkg &&
-		!rcvr.Elem().IsFullyInstantiated() {
-		return lsym
+	// imported reports whether typ is a defined type that was declared
+	// in an imported package, and therefore must have been compiled in
+	// that package.
+	importedType := func(typ *types.Type) bool {
+		return typ.Sym() != nil && typ.Sym().Pkg != types.LocalPkg &&
+
+			// Exception: need wrapper for error.Error (#29304).
+			// TODO(mdempsky): Put this in package runtime, like we do for
+			// the type descriptors for predeclared types.
+			typ != types.ErrorType &&
+
+			// Exception: parameterized types may have been instantiated
+			// with new type arguments, so we don't assume they've been
+			// compiled before.
+			!typ.IsFullyInstantiated()
 	}
 
-	// Only generate I.M wrappers for I in I's own package
-	// but keep doing it for error.Error (was issue #29304)
-	// and methods of instantiated interfaces.
-	if rcvr.IsInterface() && rcvr != types.ErrorType &&
-		rcvr.Sym() != nil && rcvr.Sym().Pkg != types.LocalPkg &&
-		!rcvr.IsFullyInstantiated() {
+	if importedType(rcvr) || rcvr.IsPtr() && importedType(rcvr.Elem()) {
 		return lsym
 	}
 
@@ -1922,9 +1926,16 @@ func methodWrapper(rcvr *types.Type, method *types.Field, forItab bool) *obj.LSy
 	ir.CurFunc = fn
 	typecheck.Stmts(fn.Body)
 
-	// Inline calls within (*T).M wrappers. This is safe because we only
-	// generate those wrappers within the same compilation unit as (T).M.
-	// TODO(mdempsky): Investigate why we can't enable this more generally.
+	// TODO(mdempsky): Make this unconditional. The exporter now
+	// includes all of the inline bodies we need, and the "importedType"
+	// logic above now correctly suppresses compiling out-of-package
+	// types that we might not have inline bodies for. The only problem
+	// now is that the extra inlining can now introduce further new
+	// itabs, and gc.dumpdata's ad hoc compile loop doesn't handle this.
+	//
+	// CL 327871 will address this by writing itabs and generating
+	// wrappers as part of the loop, so we won't have to worry about
+	// "itabs changed after compile functions loop" errors anymore.
 	if rcvr.IsPtr() && rcvr.Elem() == method.Type.Recv().Type && rcvr.Elem().Sym() != nil {
 		inline.InlineCalls(fn)
 	}

src/cmd/compile/internal/typecheck/crawler.go

@@ -15,14 +15,18 @@ import (
 // callable by importers are marked with ExportInline so that
 // iexport.go knows to re-export their inline body.
 func crawlExports(exports []*ir.Name) {
-	p := crawler{marked: make(map[*types.Type]bool)}
+	p := crawler{
+		marked:   make(map[*types.Type]bool),
+		embedded: make(map[*types.Type]bool),
+	}
 	for _, n := range exports {
 		p.markObject(n)
 	}
 }
 
 type crawler struct {
-	marked map[*types.Type]bool // types already seen by markType
+	marked   map[*types.Type]bool // types already seen by markType
+	embedded map[*types.Type]bool // types already seen by markEmbed
 }
 
 // markObject visits a reachable object.
@@ -31,6 +35,12 @@ func (p *crawler) markObject(n *ir.Name) {
 		p.markInlBody(n)
 	}
 
+	// If a declared type name is reachable, users can embed it in their
+	// own types, which makes even its unexported methods reachable.
+	if n.Op() == ir.OTYPE {
+		p.markEmbed(n.Type())
+	}
+
 	p.markType(n.Type())
 }
 
@@ -46,7 +56,7 @@ func (p *crawler) markType(t *types.Type) {
 	}
 	p.marked[t] = true
 
-	// If this is a named type, mark all of its associated
+	// If this is a defined type, mark all of its associated
 	// methods. Skip interface types because t.Methods contains
 	// only their unexpanded method set (i.e., exclusive of
 	// interface embeddings), and the switch statement below
@@ -107,6 +117,48 @@ func (p *crawler) markType(t *types.Type) {
 	}
 }
 
+// markEmbed is similar to markType, but handles finding methods that
+// need to be re-exported because t can be embedded in user code
+// (possibly transitively).
+func (p *crawler) markEmbed(t *types.Type) {
+	if t.IsPtr() {
+		// Defined pointer type; not allowed to embed anyway.
+		if t.Sym() != nil {
+			return
+		}
+		t = t.Elem()
+	}
+
+	if t.IsInstantiatedGeneric() {
+		// Re-instantiated types don't add anything new, so don't follow them.
+		return
+	}
+
+	if p.embedded[t] {
+		return
+	}
+	p.embedded[t] = true
+
+	// If t is a defined type, then re-export all of its methods. Unlike
+	// in markType, we include even unexported methods here, because we
+	// still need to generate wrappers for them, even if the user can't
+	// refer to them directly.
+	if t.Sym() != nil && t.Kind() != types.TINTER {
+		for _, m := range t.Methods().Slice() {
+			p.markObject(m.Nname.(*ir.Name))
+		}
+	}
+
+	// If t is a struct, recursively visit its embedded fields.
+	if t.IsStruct() {
+		for _, f := range t.FieldSlice() {
+			if f.Embedded != 0 {
+				p.markEmbed(f.Type)
+			}
+		}
+	}
+}
+
 // markInlBody marks n's inline body for export and recursively
 // ensures all called functions are marked too.
 func (p *crawler) markInlBody(n *ir.Name) {