compiler: honor //line directives in DWARF variable file/line attrs

During DWARF debug generation, the DW_AT_decl_line / DW_AT_decl_file
attributes for variable DIEs were being computed without taking into
account the possibility of "//line" directives. Fix things up to use
the correct src.Pos methods to pick up this info.

Fixes #23704.

Change-Id: I88c21a0e0a9602392be229252d856a6d665868e2
Reviewed-on: https://go-review.googlesource.com/92255
Run-TryBot: Than McIntosh <thanm@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Heschi Kreinick <heschi@google.com>

src/cmd/compile/internal/gc/pgen.go

@@ -424,8 +424,8 @@ func createSimpleVars(automDecls []*Node) ([]*Node, []*dwarf.Var, map[*Node]bool
 			Abbrev:        abbrev,
 			StackOffset:   int32(offs),
 			Type:          Ctxt.Lookup(typename),
-			DeclFile:      declpos.Base().SymFilename(),
-			DeclLine:      declpos.Line(),
+			DeclFile:      declpos.RelFilename(),
+			DeclLine:      declpos.RelLine(),
 			DeclCol:       declpos.Col(),
 			InlIndex:      int32(inlIndex),
 			ChildIndex:    -1,
@@ -519,8 +519,8 @@ func createDwarfVars(fnsym *obj.LSym, fn *Func, automDecls []*Node) ([]*Node, []
 			Abbrev:        abbrev,
 			StackOffset:   int32(n.Xoffset),
 			Type:          Ctxt.Lookup(typename),
-			DeclFile:      declpos.Base().SymFilename(),
-			DeclLine:      declpos.Line(),
+			DeclFile:      declpos.RelFilename(),
+			DeclLine:      declpos.RelLine(),
 			DeclCol:       declpos.Col(),
 			InlIndex:      int32(inlIndex),
 			ChildIndex:    -1,
@@ -651,8 +651,8 @@ func createComplexVar(fn *Func, varID ssa.VarID) *dwarf.Var {
 		// This won't work well if the first slot hasn't been assigned a stack
 		// location, but it's not obvious how to do better.
 		StackOffset: stackOffset(*debug.Slots[debug.VarSlots[varID][0]]),
-		DeclFile:    declpos.Base().SymFilename(),
-		DeclLine:    declpos.Line(),
+		DeclFile:    declpos.RelFilename(),
+		DeclLine:    declpos.RelLine(),
 		DeclCol:     declpos.Col(),
 		InlIndex:    int32(inlIndex),
 		ChildIndex:  -1,

src/cmd/link/internal/ld/dwarf_test.go

@@ -308,22 +308,11 @@ func main() {
 	}
 }
 
-func TestVarDeclCoordsAndSubrogramDeclFile(t *testing.T) {
-	testenv.MustHaveGoBuild(t)
+func varDeclCoordsAndSubrogramDeclFile(t *testing.T, testpoint string, expectFile int, expectLine int, directive string) {
 
-	if runtime.GOOS == "plan9" {
-		t.Skip("skipping on plan9; no DWARF symbol table in executables")
-	}
-
-	const prog = `
-package main
+	prog := fmt.Sprintf("package main\n\nfunc main() {\n%s\nvar i int\ni = i\n}\n", directive)
 
-func main() {
-	var i int
-	i = i
-}
-`
-	dir, err := ioutil.TempDir("", "TestVarDeclCoords")
+	dir, err := ioutil.TempDir("", testpoint)
 	if err != nil {
 		t.Fatalf("could not create directory: %v", err)
 	}
@@ -373,14 +362,35 @@ func main() {
 
 	// Verify line/file attributes.
 	line := iEntry.Val(dwarf.AttrDeclLine)
-	if line == nil || line.(int64) != 5 {
-		t.Errorf("DW_AT_decl_line for i is %v, want 5", line)
+	if line == nil || line.(int64) != int64(expectLine) {
+		t.Errorf("DW_AT_decl_line for i is %v, want %d", line, expectLine)
 	}
 
 	file := maindie.Val(dwarf.AttrDeclFile)
 	if file == nil || file.(int64) != 1 {
-		t.Errorf("DW_AT_decl_file for main is %v, want 1", file)
+		t.Errorf("DW_AT_decl_file for main is %v, want %d", file, expectFile)
+	}
+}
+
+func TestVarDeclCoordsAndSubrogramDeclFile(t *testing.T) {
+	testenv.MustHaveGoBuild(t)
+
+	if runtime.GOOS == "plan9" {
+		t.Skip("skipping on plan9; no DWARF symbol table in executables")
+	}
+
+	varDeclCoordsAndSubrogramDeclFile(t, "TestVarDeclCoords", 1, 5, "")
+}
+
+func TestVarDeclCoordsWithLineDirective(t *testing.T) {
+	testenv.MustHaveGoBuild(t)
+
+	if runtime.GOOS == "plan9" {
+		t.Skip("skipping on plan9; no DWARF symbol table in executables")
 	}
+
+	varDeclCoordsAndSubrogramDeclFile(t, "TestVarDeclCoordsWithLineDirective",
+		2, 200, "//line /foobar.go:200")
 }
 
 // Helper class for supporting queries on DIEs within a DWARF .debug_info