go/ast/astutil: handle documentation of imports in DeleteNamedImport.

If the parens of an ast.GenDecl are dropped, move the documentation
of the ImportSpec above the import statement, otherwise the the
code is invalid.

Fixes golang/go#15432.

Change-Id: I715750b8f528380b96a6bc8b5f216043937976c2
Reviewed-on: https://go-review.googlesource.com/22415
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

go/ast/astutil/imports.go

@@ -180,6 +180,7 @@ func DeleteImport(fset *token.FileSet, f *ast.File, path string) (deleted bool)
 // DeleteNamedImport deletes the import with the given name and path from the file f, if present.
 func DeleteNamedImport(fset *token.FileSet, f *ast.File, name, path string) (deleted bool) {
 	var delspecs []*ast.ImportSpec
+	var delcomments []*ast.CommentGroup
 
 	// Find the import nodes that import path, if any.
 	for i := 0; i < len(f.Decls); i++ {
@@ -216,7 +217,35 @@ func DeleteNamedImport(fset *token.FileSet, f *ast.File, name, path string) (del
 				i--
 				break
 			} else if len(gen.Specs) == 1 {
+				if impspec.Doc != nil {
+					delcomments = append(delcomments, impspec.Doc)
+				}
+				if impspec.Comment != nil {
+					delcomments = append(delcomments, impspec.Comment)
+				}
+				for _, cg := range f.Comments {
+					// Found comment on the same line as the import spec.
+					if cg.End() < impspec.Pos() && fset.Position(cg.End()).Line == fset.Position(impspec.Pos()).Line {
+						delcomments = append(delcomments, cg)
+						break
+					}
+				}
+
 				gen.Lparen = token.NoPos // drop parens
+				spec := gen.Specs[0].(*ast.ImportSpec)
+				if spec.Doc != nil {
+					// Move the documentation above the import statement.
+					gen.TokPos = spec.Doc.End() + 1
+				}
+
+				for _, cg := range f.Comments {
+					if cg.End() < spec.Pos() && fset.Position(cg.End()).Line == fset.Position(spec.Pos()).Line {
+						for fset.Position(gen.TokPos).Line != fset.Position(spec.Pos()).Line {
+							fset.File(gen.TokPos).MergeLine(fset.Position(gen.TokPos).Line)
+						}
+						break
+					}
+				}
 			}
 			if j > 0 {
 				lastImpspec := gen.Specs[j-1].(*ast.ImportSpec)
@@ -238,7 +267,7 @@ func DeleteNamedImport(fset *token.FileSet, f *ast.File, name, path string) (del
 		}
 	}
 
-	// Delete them from f.Imports.
+	// Delete imports from f.Imports.
 	for i := 0; i < len(f.Imports); i++ {
 		imp := f.Imports[i]
 		for j, del := range delspecs {
@@ -253,6 +282,21 @@ func DeleteNamedImport(fset *token.FileSet, f *ast.File, name, path string) (del
 		}
 	}
 
+	// Delete comments from f.Comments.
+	for i := 0; i < len(f.Comments); i++ {
+		cg := f.Comments[i]
+		for j, del := range delcomments {
+			if cg == del {
+				copy(f.Comments[i:], f.Comments[i+1:])
+				f.Comments = f.Comments[:len(f.Comments)-1]
+				copy(delcomments[j:], delcomments[j+1:])
+				delcomments = delcomments[:len(delcomments)-1]
+				i--
+				break
+			}
+		}
+	}
+
 	if len(delspecs) > 0 {
 		panic(fmt.Sprintf("deleted specs from Decls but not Imports: %v", delspecs))
 	}

go/ast/astutil/imports_test.go

@@ -923,6 +923,270 @@ import y "fmt"
 		out: `package main
 
 import y "fmt"
+`,
+	},
+	// Issue #15432
+	{
+		name: "import.19",
+		pkg:  "fmt",
+		in: `package main
+
+import (
+	"fmt"
+
+	// Some comment.
+	"io"
+)`,
+		out: `package main
+
+// Some comment.
+import "io"
+`,
+	},
+	{
+		name: "import.20",
+		pkg:  "fmt",
+		in: `package main
+
+import (
+	"fmt"
+
+	// Some
+	// comment.
+	"io"
+)`,
+		out: `package main
+
+// Some
+// comment.
+import "io"
+`,
+	},
+	{
+		name: "import.21",
+		pkg:  "fmt",
+		in: `package main
+
+import (
+	"fmt"
+
+	/*
+		Some
+		comment.
+	*/
+	"io"
+)`,
+		out: `package main
+
+/*
+	Some
+	comment.
+*/
+import "io"
+`,
+	},
+	{
+		name: "import.22",
+		pkg:  "fmt",
+		in: `package main
+
+import (
+	/* Some */
+	// comment.
+	"io"
+	"fmt"
+)`,
+		out: `package main
+
+/* Some */
+// comment.
+import "io"
+`,
+	},
+	{
+		name: "import.23",
+		pkg:  "fmt",
+		in: `package main
+
+import (
+	// comment 1
+	"fmt"
+	// comment 2
+	"io"
+)`,
+		out: `package main
+
+// comment 2
+import "io"
+`,
+	},
+	{
+		name: "import.24",
+		pkg:  "fmt",
+		in: `package main
+
+import (
+	"fmt" // comment 1
+	"io" // comment 2
+)`,
+		out: `package main
+
+import "io" // comment 2
+`,
+	},
+	{
+		name: "import.25",
+		pkg:  "fmt",
+		in: `package main
+
+import (
+	"fmt"
+	/* comment */ "io"
+)`,
+		out: `package main
+
+import /* comment */ "io"
+`,
+	},
+	{
+		name: "import.26",
+		pkg:  "fmt",
+		in: `package main
+
+import (
+	"fmt"
+	"io" /* comment */
+)`,
+		out: `package main
+
+import "io" /* comment */
+`,
+	},
+	{
+		name: "import.27",
+		pkg:  "fmt",
+		in: `package main
+
+import (
+	"fmt" /* comment */
+	"io"
+)`,
+		out: `package main
+
+import "io"
+`,
+	},
+	{
+		name: "import.28",
+		pkg:  "fmt",
+		in: `package main
+
+import (
+	/* comment */  "fmt"
+	"io"
+)`,
+		out: `package main
+
+import "io"
+`,
+	},
+	{
+		name: "import.29",
+		pkg:  "fmt",
+		in: `package main
+
+// comment 1
+import (
+	"fmt"
+	"io" // comment 2
+)`,
+		out: `package main
+
+// comment 1
+import "io" // comment 2
+`,
+	},
+	{
+		name: "import.30",
+		pkg:  "fmt",
+		in: `package main
+
+// comment 1
+import (
+	"fmt" // comment 2
+	"io"
+)`,
+		out: `package main
+
+// comment 1
+import "io"
+`,
+	},
+	{
+		name: "import.31",
+		pkg:  "fmt",
+		in: `package main
+
+// comment 1
+import (
+	"fmt"
+	/* comment 2 */ "io"
+)`,
+		out: `package main
+
+// comment 1
+import /* comment 2 */ "io"
+`,
+	},
+	{
+		name:       "import.32",
+		pkg:        "fmt",
+		renamedPkg: "f",
+		in: `package main
+
+// comment 1
+import (
+	f "fmt"
+	/* comment 2 */ i "io"
+)`,
+		out: `package main
+
+// comment 1
+import /* comment 2 */ i "io"
+`,
+	},
+	{
+		name:       "import.33",
+		pkg:        "fmt",
+		renamedPkg: "f",
+		in: `package main
+
+// comment 1
+import (
+	/* comment 2 */ f "fmt"
+	i "io"
+)`,
+		out: `package main
+
+// comment 1
+import i "io"
+`,
+	},
+	{
+		name:       "import.34",
+		pkg:        "fmt",
+		renamedPkg: "f",
+		in: `package main
+
+// comment 1
+import (
+	f "fmt" /* comment 2 */
+	i "io"
+)`,
+		out: `package main
+
+// comment 1
+import i "io"
 `,
 	},
 }