cmd/internal/obj: add Func type to replace "curfn any"

This adds a modicum of type safety to these APIs, which are otherwise
quite confusing to follow.

Change-Id: I268a9a1a99a47dcfef6dc1e9e5be13673af3fb85
Reviewed-on: https://go-review.googlesource.com/c/go/+/523396
Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Matthew Dempsky <mdempsky@google.com>

3 files changed, 16 insertions, 13 deletions

diff --git a/src/cmd/internal/obj/dwarf.go b/src/cmd/internal/obj/dwarf.go
index 482222bb74..825f0133f1 100644
--- a/src/cmd/internal/obj/dwarf.go
+++ b/src/cmd/internal/obj/dwarf.go
@@ -345,7 +345,7 @@ func (ctxt *Link) fileSymbol(fn *LSym) *LSym {
 // populateDWARF fills in the DWARF Debugging Information Entries for
 // TEXT symbol 's'. The various DWARF symbols must already have been
 // initialized in InitTextSym.
-func (ctxt *Link) populateDWARF(curfn interface{}, s *LSym) {
+func (ctxt *Link) populateDWARF(curfn Func, s *LSym) {
 	myimportpath := ctxt.Pkgpath
 	if myimportpath == "" {
 		return
@@ -358,9 +358,7 @@ func (ctxt *Link) populateDWARF(curfn interface{}, s *LSym) {
 	var scopes []dwarf.Scope
 	var inlcalls dwarf.InlCalls
 	if ctxt.DebugInfo != nil {
-		// Don't need startPos because s.Func().StartLine is populated,
-		// as s is in this package.
-		scopes, inlcalls, _ = ctxt.DebugInfo(s, info, curfn)
+		scopes, inlcalls = ctxt.DebugInfo(s, info, curfn)
 	}
 	var err error
 	dwctxt := dwCtxt{ctxt}
@@ -427,7 +425,7 @@ func (ctxt *Link) DwarfGlobal(typename string, varSym *LSym) {
 	dwarf.PutGlobal(dwCtxt{ctxt}, dieSym, typeSym, varSym, varname)
 }
 
-func (ctxt *Link) DwarfAbstractFunc(curfn interface{}, s *LSym) {
+func (ctxt *Link) DwarfAbstractFunc(curfn Func, s *LSym) {
 	absfn := ctxt.DwFixups.AbsFuncDwarfSym(s)
 	if absfn.Size != 0 {
 		ctxt.Diag("internal error: DwarfAbstractFunc double process %v", s)
@@ -435,8 +433,8 @@ func (ctxt *Link) DwarfAbstractFunc(curfn interface{}, s *LSym) {
 	if s.Func() == nil {
 		s.NewFuncInfo()
 	}
-	scopes, _, startPos := ctxt.DebugInfo(s, absfn, curfn)
-	_, startLine := ctxt.getFileSymbolAndLine(startPos)
+	scopes, _ := ctxt.DebugInfo(s, absfn, curfn)
+	_, startLine := ctxt.getFileSymbolAndLine(curfn.Pos())
 	dwctxt := dwCtxt{ctxt}
 	fnstate := dwarf.FnState{
 		Name:          s.Name,
@@ -515,8 +513,8 @@ type relFixup struct {
 }
 
 type fnState struct {
-	// precursor function (really *gc.Node)
-	precursor interface{}
+	// precursor function
+	precursor Func
 	// abstract function symbol
 	absfn *LSym
 }
@@ -529,14 +527,14 @@ func NewDwarfFixupTable(ctxt *Link) *DwarfFixupTable {
 	}
 }
 
-func (ft *DwarfFixupTable) GetPrecursorFunc(s *LSym) interface{} {
+func (ft *DwarfFixupTable) GetPrecursorFunc(s *LSym) Func {
 	if fnstate, found := ft.precursor[s]; found {
 		return fnstate.precursor
 	}
 	return nil
 }
 
-func (ft *DwarfFixupTable) SetPrecursorFunc(s *LSym, fn interface{}) {
+func (ft *DwarfFixupTable) SetPrecursorFunc(s *LSym, fn Func) {
 	if _, found := ft.precursor[s]; found {
 		ft.ctxt.Diag("internal error: DwarfFixupTable.SetPrecursorFunc double call on %v", s)
 	}
diff --git a/src/cmd/internal/obj/link.go b/src/cmd/internal/obj/link.go
index f13f9b4c70..0b7878656c 100644
--- a/src/cmd/internal/obj/link.go
+++ b/src/cmd/internal/obj/link.go
@@ -1001,6 +1001,11 @@ type RegSpill struct {
 	Spill, Unspill As
 }
 
+// A Func represents a Go function. If non-nil, it must be a *ir.Func.
+type Func interface {
+	Pos() src.XPos
+}
+
 // Link holds the context for writing object code from a compiler
 // to be linker input or for reading that input into the linker.
 type Link struct {
@@ -1030,7 +1035,7 @@ type Link struct {
 	Imports            []goobj.ImportedPkg
 	DiagFunc           func(string, ...interface{})
 	DiagFlush          func()
-	DebugInfo          func(fn *LSym, info *LSym, curfn interface{}) ([]dwarf.Scope, dwarf.InlCalls, src.XPos) // if non-nil, curfn is a *ir.Func
+	DebugInfo          func(fn *LSym, info *LSym, curfn Func) ([]dwarf.Scope, dwarf.InlCalls)
 	GenAbstractFunc    func(fn *LSym)
 	Errors             int
 
diff --git a/src/cmd/internal/obj/plist.go b/src/cmd/internal/obj/plist.go
index 6aa5888d3d..cd6e2313ad 100644
--- a/src/cmd/internal/obj/plist.go
+++ b/src/cmd/internal/obj/plist.go
@@ -14,7 +14,7 @@ import (
 
 type Plist struct {
 	Firstpc *Prog
-	Curfn   interface{} // holds a *gc.Node, if non-nil
+	Curfn   Func
 }
 
 // ProgAlloc is a function that allocates Progs.