modfile: fix trailing empty lines in require blocks

This change ensures that trailing empty lines in `require` blocks
are ignored during parsing itself. Specifically:

- Modified the `parseLineBlock` function to detect and discard blank lines
(represented by a single empty comment) at the end of a block.
- Blank lines within a block are preserved as expected, but trailing
blank lines immediately before the closing parenthesis are now skipped.

For golang/go#70632

Change-Id: Ica76b3edb3bf7fdc327c7cdc9e401dcf19c523b0
GitHub-Last-Rev: 1477d7c
GitHub-Pull-Request: #22
Reviewed-on: https://go-review.googlesource.com/c/mod/+/634875
Reviewed-by: Michael Matloob <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Cherry Mui <[email protected]>

Author: Agent-Hellboy

modfile/read.go

@@ -877,6 +877,11 @@ func (in *input) parseLineBlock(start Position, token []string, lparen token) *L
 			in.Error(fmt.Sprintf("syntax error (unterminated block started at %s:%d:%d)", in.filename, x.Start.Line, x.Start.LineRune))
 		case ')':
 			rparen := in.lex()
+			// Don't preserve blank lines (denoted by a single empty comment, added above)
+			// at the end of the block.
+			if len(comments) == 1 && comments[0] == (Comment{}) {
+				comments = nil
+			}
 			x.RParen.Before = comments
 			x.RParen.Pos = rparen.pos
 			if !in.peek().isEOL() {

modfile/testdata/issue70632.golden

@@ -0,0 +1,7 @@
+module tidy
+
+go 1.23.0
+
+require (
+	golang.org/x/time v0.8.0
+)

modfile/testdata/issue70632.in

@@ -0,0 +1,12 @@
+module tidy
+
+go 1.23.0
+
+require (
+
+    "golang.org/x/time" v0.8.0
+
+
+
+
+)