cmd/cgo: annotate named return struct members in comments

If an exported function has named return variables, then show the names
as comments in the return struct we create in the header file.

Example here:

 https://groups.google.com/forum/#!topic/golang-nuts/r393ne4zIfY

Change-Id: I21fb4ca2673f6977bec35ccab0cef7d42b311f96
Reviewed-on: https://go-review.googlesource.com/13061Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/cmd/cgo/out.go

@@ -693,7 +693,7 @@ func (p *Package) writeExports(fgo2, fm, fgcc, fgcch io.Writer) {
 		}
 		fntype := fn.Type
 		forFieldList(fntype.Params,
-			func(i int, atype ast.Expr) {
+			func(i int, aname string, atype ast.Expr) {
 				t := p.cgoType(atype)
 				if off%t.Align != 0 {
 					pad := t.Align - off%t.Align
@@ -711,7 +711,7 @@ func (p *Package) writeExports(fgo2, fm, fgcc, fgcch io.Writer) {
 			npad++
 		}
 		forFieldList(fntype.Results,
-			func(i int, atype ast.Expr) {
+			func(i int, aname string, atype ast.Expr) {
 				t := p.cgoType(atype)
 				if off%t.Align != 0 {
 					pad := t.Align - off%t.Align
@@ -744,8 +744,12 @@ func (p *Package) writeExports(fgo2, fm, fgcc, fgcch io.Writer) {
 			fmt.Fprintf(fgcch, "\n/* Return type for %s */\n", exp.ExpName)
 			fmt.Fprintf(fgcch, "struct %s_return {\n", exp.ExpName)
 			forFieldList(fntype.Results,
-				func(i int, atype ast.Expr) {
-					fmt.Fprintf(fgcch, "\t%s r%d;\n", p.cgoType(atype).C, i)
+				func(i int, aname string, atype ast.Expr) {
+					fmt.Fprintf(fgcch, "\t%s r%d;", p.cgoType(atype).C, i)
+					if len(aname) > 0 {
+						fmt.Fprintf(fgcch, " /* %s */", aname)
+					}
+					fmt.Fprint(fgcch, "\n")
 				})
 			fmt.Fprintf(fgcch, "};\n")
 			gccResult = "struct " + exp.ExpName + "_return"
@@ -758,7 +762,7 @@ func (p *Package) writeExports(fgo2, fm, fgcc, fgcch io.Writer) {
 			s += " recv"
 		}
 		forFieldList(fntype.Params,
-			func(i int, atype ast.Expr) {
+			func(i int, aname string, atype ast.Expr) {
 				if i > 0 || fn.Recv != nil {
 					s += ", "
 				}
@@ -783,7 +787,7 @@ func (p *Package) writeExports(fgo2, fm, fgcc, fgcch io.Writer) {
 			fmt.Fprintf(fgcc, "\ta.recv = recv;\n")
 		}
 		forFieldList(fntype.Params,
-			func(i int, atype ast.Expr) {
+			func(i int, aname string, atype ast.Expr) {
 				fmt.Fprintf(fgcc, "\ta.p%d = p%d;\n", i, i)
 			})
 		fmt.Fprintf(fgcc, "\tcrosscall2(_cgoexp%s_%s, &a, %d);\n", cPrefix, exp.ExpName, off)
@@ -792,7 +796,7 @@ func (p *Package) writeExports(fgo2, fm, fgcc, fgcch io.Writer) {
 				fmt.Fprintf(fgcc, "\treturn a.r0;\n")
 			} else {
 				forFieldList(fntype.Results,
-					func(i int, atype ast.Expr) {
+					func(i int, aname string, atype ast.Expr) {
 						fmt.Fprintf(fgcc, "\tr.r%d = a.r%d;\n", i, i)
 					})
 				fmt.Fprintf(fgcc, "\treturn r;\n")
@@ -824,7 +828,7 @@ func (p *Package) writeExports(fgo2, fm, fgcc, fgcch io.Writer) {
 			fmt.Fprintf(fgo2, "func %s(recv ", goname)
 			conf.Fprint(fgo2, fset, fn.Recv.List[0].Type)
 			forFieldList(fntype.Params,
-				func(i int, atype ast.Expr) {
+				func(i int, aname string, atype ast.Expr) {
 					fmt.Fprintf(fgo2, ", p%d ", i)
 					conf.Fprint(fgo2, fset, atype)
 				})
@@ -832,7 +836,7 @@ func (p *Package) writeExports(fgo2, fm, fgcc, fgcch io.Writer) {
 			if gccResult != "void" {
 				fmt.Fprint(fgo2, " (")
 				forFieldList(fntype.Results,
-					func(i int, atype ast.Expr) {
+					func(i int, aname string, atype ast.Expr) {
 						if i > 0 {
 							fmt.Fprint(fgo2, ", ")
 						}
@@ -847,7 +851,7 @@ func (p *Package) writeExports(fgo2, fm, fgcc, fgcch io.Writer) {
 			}
 			fmt.Fprintf(fgo2, "recv.%s(", exp.Func.Name)
 			forFieldList(fntype.Params,
-				func(i int, atype ast.Expr) {
+				func(i int, aname string, atype ast.Expr) {
 					if i > 0 {
 						fmt.Fprint(fgo2, ", ")
 					}
@@ -879,13 +883,13 @@ func (p *Package) writeGccgoExports(fgo2, fm, fgcc, fgcch io.Writer) {
 		cdeclBuf := new(bytes.Buffer)
 		resultCount := 0
 		forFieldList(fntype.Results,
-			func(i int, atype ast.Expr) { resultCount++ })
+			func(i int, aname string, atype ast.Expr) { resultCount++ })
 		switch resultCount {
 		case 0:
 			fmt.Fprintf(cdeclBuf, "void")
 		case 1:
 			forFieldList(fntype.Results,
-				func(i int, atype ast.Expr) {
+				func(i int, aname string, atype ast.Expr) {
 					t := p.cgoType(atype)
 					fmt.Fprintf(cdeclBuf, "%s", t.C)
 				})
@@ -894,9 +898,13 @@ func (p *Package) writeGccgoExports(fgo2, fm, fgcc, fgcch io.Writer) {
 			fmt.Fprintf(fgcch, "\n/* Return type for %s */\n", exp.ExpName)
 			fmt.Fprintf(fgcch, "struct %s_result {\n", exp.ExpName)
 			forFieldList(fntype.Results,
-				func(i int, atype ast.Expr) {
+				func(i int, aname string, atype ast.Expr) {
 					t := p.cgoType(atype)
-					fmt.Fprintf(fgcch, "\t%s r%d;\n", t.C, i)
+					fmt.Fprintf(fgcch, "\t%s r%d;", t.C, i)
+					if len(aname) > 0 {
+						fmt.Fprintf(fgcch, " /* %s */", aname)
+					}
+					fmt.Fprint(fgcch, "\n")
 				})
 			fmt.Fprintf(fgcch, "};\n")
 			fmt.Fprintf(cdeclBuf, "struct %s_result", exp.ExpName)
@@ -911,7 +919,7 @@ func (p *Package) writeGccgoExports(fgo2, fm, fgcc, fgcch io.Writer) {
 		}
 		// Function parameters.
 		forFieldList(fntype.Params,
-			func(i int, atype ast.Expr) {
+			func(i int, aname string, atype ast.Expr) {
 				if i > 0 || fn.Recv != nil {
 					fmt.Fprintf(cdeclBuf, ", ")
 				}
@@ -956,7 +964,7 @@ func (p *Package) writeGccgoExports(fgo2, fm, fgcc, fgcch io.Writer) {
 			fmt.Fprint(fgcc, "recv")
 		}
 		forFieldList(fntype.Params,
-			func(i int, atype ast.Expr) {
+			func(i int, aname string, atype ast.Expr) {
 				if i > 0 || fn.Recv != nil {
 					fmt.Fprintf(fgcc, ", ")
 				}
@@ -982,7 +990,7 @@ func (p *Package) writeGccgoExports(fgo2, fm, fgcc, fgcch io.Writer) {
 			printer.Fprint(fgo2, fset, fn.Recv.List[0].Type)
 		}
 		forFieldList(fntype.Params,
-			func(i int, atype ast.Expr) {
+			func(i int, aname string, atype ast.Expr) {
 				if i > 0 || fn.Recv != nil {
 					fmt.Fprintf(fgo2, ", ")
 				}
@@ -993,7 +1001,7 @@ func (p *Package) writeGccgoExports(fgo2, fm, fgcc, fgcch io.Writer) {
 		if resultCount > 0 {
 			fmt.Fprintf(fgo2, " (")
 			forFieldList(fntype.Results,
-				func(i int, atype ast.Expr) {
+				func(i int, aname string, atype ast.Expr) {
 					if i > 0 {
 						fmt.Fprint(fgo2, ", ")
 					}
@@ -1013,7 +1021,7 @@ func (p *Package) writeGccgoExports(fgo2, fm, fgcc, fgcch io.Writer) {
 		}
 		fmt.Fprintf(fgo2, "%s(", exp.Func.Name)
 		forFieldList(fntype.Params,
-			func(i int, atype ast.Expr) {
+			func(i int, aname string, atype ast.Expr) {
 				if i > 0 {
 					fmt.Fprint(fgo2, ", ")
 				}
@@ -1071,19 +1079,19 @@ func (p *Package) gccgoSymbolPrefix() string {
 }
 
 // Call a function for each entry in an ast.FieldList, passing the
-// index into the list and the type.
-func forFieldList(fl *ast.FieldList, fn func(int, ast.Expr)) {
+// index into the list, the name if any, and the type.
+func forFieldList(fl *ast.FieldList, fn func(int, string, ast.Expr)) {
 	if fl == nil {
 		return
 	}
 	i := 0
 	for _, r := range fl.List {
 		if r.Names == nil {
-			fn(i, r.Type)
+			fn(i, "", r.Type)
 			i++
 		} else {
-			for range r.Names {
-				fn(i, r.Type)
+			for _, n := range r.Names {
+				fn(i, n.Name, r.Type)
 				i++
 			}
 		}