From 138099ae96332d2a5a63888c96001286d7273907 Mon Sep 17 00:00:00 2001
From: Simon Whitehead <chemnova@gmail.com>
Date: Tue, 1 Jul 2014 09:32:03 -0700
Subject: [PATCH] gofmt/main: Added removal of empty declaration groups.

Fixes #7631.

LGTM=gri
R=golang-codereviews, bradfitz, gri
CC=golang-codereviews
https://golang.org/cl/101410046
---
 src/cmd/gofmt/gofmt_test.go             |  5 +++--
 src/cmd/gofmt/simplify.go               | 29 +++++++++++++++++++++++++
 src/cmd/gofmt/testdata/emptydecl.golden | 10 +++++++++
 src/cmd/gofmt/testdata/emptydecl.input  | 12 ++++++++++
 4 files changed, 54 insertions(+), 2 deletions(-)
 create mode 100644 src/cmd/gofmt/testdata/emptydecl.golden
 create mode 100644 src/cmd/gofmt/testdata/emptydecl.input

diff --git a/src/cmd/gofmt/gofmt_test.go b/src/cmd/gofmt/gofmt_test.go
index b9335b8f3d..b767a6bf55 100644
--- a/src/cmd/gofmt/gofmt_test.go
+++ b/src/cmd/gofmt/gofmt_test.go
@@ -87,8 +87,9 @@ var tests = []struct {
 	{"testdata/stdin*.input", "-stdin"},
 	{"testdata/comments.input", ""},
 	{"testdata/import.input", ""},
-	{"testdata/crlf.input", ""},       // test case for issue 3961; see also TestCRLF
-	{"testdata/typeswitch.input", ""}, // test case for issue 4470
+	{"testdata/crlf.input", ""},        // test case for issue 3961; see also TestCRLF
+	{"testdata/typeswitch.input", ""},  // test case for issue 4470
+	{"testdata/emptydecl.input", "-s"}, // test case for issue 7631
 }
 
 func TestRewrite(t *testing.T) {
diff --git a/src/cmd/gofmt/simplify.go b/src/cmd/gofmt/simplify.go
index 45d000d675..b1556be74e 100644
--- a/src/cmd/gofmt/simplify.go
+++ b/src/cmd/gofmt/simplify.go
@@ -117,5 +117,34 @@ func simplify(f *ast.File) {
 		}
 	}
 
+	// remove empty declarations such as "const ()", etc
+	removeEmptyDeclGroups(f)
+
 	ast.Walk(&s, f)
 }
+
+func removeEmptyDeclGroups(f *ast.File) {
+	i := 0
+	for _, d := range f.Decls {
+		if g, ok := d.(*ast.GenDecl); !ok || !isEmpty(f, g) {
+			f.Decls[i] = d
+			i++
+		}
+	}
+	f.Decls = f.Decls[:i]
+}
+
+func isEmpty(f *ast.File, g *ast.GenDecl) bool {
+	if g.Doc != nil || g.Specs != nil {
+		return false
+	}
+
+	for _, c := range f.Comments {
+		// if there is a comment in the declaration, it is not considered empty
+		if g.Pos() <= c.Pos() && c.End() <= g.End() {
+			return false
+		}
+	}
+
+	return true
+}
diff --git a/src/cmd/gofmt/testdata/emptydecl.golden b/src/cmd/gofmt/testdata/emptydecl.golden
new file mode 100644
index 0000000000..9fe62c9738
--- /dev/null
+++ b/src/cmd/gofmt/testdata/emptydecl.golden
@@ -0,0 +1,10 @@
+package main
+
+// Keep this declaration
+var ()
+
+const (
+// Keep this declaration
+)
+
+func main() {}
diff --git a/src/cmd/gofmt/testdata/emptydecl.input b/src/cmd/gofmt/testdata/emptydecl.input
new file mode 100644
index 0000000000..d1cab00ef7
--- /dev/null
+++ b/src/cmd/gofmt/testdata/emptydecl.input
@@ -0,0 +1,12 @@
+package main
+
+// Keep this declaration
+var ()
+
+const (
+// Keep this declaration
+)
+
+type ()
+
+func main() {}
\ No newline at end of file
-- 
2.50.0