go/ast: fix SortImports to handle block comments

The current algorithm only assumed line comments which always
appear at the end of an import spec. This caused block comments
which can appear before a spec to be attached to the previous spec.

So while mapping a comment to an import spec, we maintain additional
information on whether the comment is supposed to appear on the left
or right of the spec.

And we also take into account the possibility of "//line" comments
in the source. So we use unadjusted line numbers.

While at it, added some more testcases from tools/go/ast/astutil/imports_test.go

Fixes #18929

Change-Id: If920426641702a8a93904b2ec1d3455749169f69
Reviewed-on: https://go-review.googlesource.com/c/go/+/162337
Run-TryBot: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

2 files changed, 122 insertions, 0 deletions

diff --git a/src/cmd/gofmt/testdata/import.golden b/src/cmd/gofmt/testdata/import.golden
index 51d7be79df..f7d742e3e8 100644
--- a/src/cmd/gofmt/testdata/import.golden
+++ b/src/cmd/gofmt/testdata/import.golden
@@ -1,3 +1,4 @@
+// package comment
 package main
 
 import (
@@ -20,6 +21,10 @@ import (
 	"io"
 )
 
+// We reset the line numbering to test that
+// the formatting works independent of line directives
+//line :19
+
 import (
 	"errors"
 	"fmt"
@@ -124,3 +129,58 @@ import (
 
 	"dedup_by_group"
 )
+
+import (
+	"fmt" // for Printf
+	/* comment */ io1 "io"
+	/* comment */ io2 "io"
+	/* comment */ "log"
+)
+
+import (
+	"fmt"
+	/* comment */ io1 "io"
+	/* comment */ io2 "io" // hello
+	"math"                 /* right side */
+	// end
+)
+
+import (
+	"errors" // for New
+	"fmt"
+	/* comment */ io1 "io" /* before */ // after
+	io2 "io"               // another
+	// end
+)
+
+import (
+	"errors" // for New
+	/* left */ "fmt" /* right */
+	"log"            // for Fatal
+	/* left */ "math" /* right */
+)
+
+import /* why */ /* comment here? */ (
+	/* comment */ "fmt"
+	"math"
+)
+
+// Reset it again
+//line :100
+
+// Dedup with different import styles
+import (
+	"path"
+	. "path"
+	_ "path"
+	pathpkg "path"
+)
+
+/* comment */
+import (
+	"fmt"
+	"math" // for Abs
+	// This is a new run
+	"errors"
+	"fmt"
+)
diff --git a/src/cmd/gofmt/testdata/import.input b/src/cmd/gofmt/testdata/import.input
index 9a4b09dbf9..6e3a3a3bed 100644
--- a/src/cmd/gofmt/testdata/import.input
+++ b/src/cmd/gofmt/testdata/import.input
@@ -1,3 +1,4 @@
+// package comment
 package main
 
 import (
@@ -20,6 +21,10 @@ import (
 	"io"
 )
 
+// We reset the line numbering to test that
+// the formatting works independent of line directives
+//line :19
+
 import (
 	"fmt"
 	"math"
@@ -129,3 +134,60 @@ import (
 
 	"dedup_by_group"
 )
+
+import (
+	/* comment */ io1 "io"
+	"fmt" // for Printf
+	/* comment */ "log"
+	/* comment */ io2 "io"
+)
+
+import (
+	/* comment */ io2 "io" // hello
+	/* comment */ io1 "io"
+	"math" /* right side */
+	"fmt"
+	// end
+)
+
+import (
+	/* comment */ io1 "io" /* before */ // after
+	"fmt"
+	"errors" // for New
+	io2 "io" // another
+	// end
+)
+
+import (
+	/* left */ "fmt" /* right */
+	"errors" // for New
+	/* left */ "math" /* right */
+	"log" // for Fatal
+)
+
+import /* why */ /* comment here? */ (
+	/* comment */ "fmt"
+	"math"
+)
+
+// Reset it again
+//line :100
+
+// Dedup with different import styles
+import (
+	"path"
+	. "path"
+	_ "path"
+	"path"
+	pathpkg "path"
+)
+
+/* comment */
+import (
+	"math" // for Abs
+	"fmt"
+	// This is a new run
+	"errors"
+	"fmt"
+	"errors"
+)