zig fmt: fix comments ending with EOF after decls

Achieve this by reducing the amount of special casing to handle EOF so
that the already correct logic for normal comments does not need to be
duplicated.

lib/std/zig/parser_test.zig

@@ -93,6 +93,17 @@ test "zig fmt: file ends in comment" {
     );
 }
 
+test "zig fmt: file ends in comment after var decl" {
+    try testTransform(
+        \\const x = 42;
+        \\     //foobar
+    ,
+        \\const x = 42;
+        \\//foobar
+        \\
+    );
+}
+
 test "zig fmt: doc comments on test" {
     try testCanonical(
         \\/// hello

lib/std/zig/render.zig

@@ -26,10 +26,7 @@ pub fn renderTree(buffer: *std.ArrayList(u8), tree: ast.Tree) Error!void {
     const ais = &auto_indenting_stream;
 
     // Render all the line comments at the beginning of the file.
-    const comment_end_loc = if (tree.tokens.items(.tag)[0] == .eof)
-        tree.source.len
-    else
-        tree.tokens.items(.start)[0];
+    const comment_end_loc = tree.tokens.items(.start)[0];
     _ = try renderComments(ais, tree, 0, comment_end_loc);
 
     try renderMembers(ais, tree, tree.rootDecls());
@@ -1609,15 +1606,18 @@ fn renderArrayInit(
     } else {
         try renderExpression(ais, tree, array_init.ast.type_expr, .none); // T
     }
+
     if (array_init.ast.elements.len == 0) {
         ais.pushIndentNextLine();
         try renderToken(ais, tree, array_init.ast.lbrace, .none); // lbrace
         ais.popIndent();
         return renderToken(ais, tree, array_init.ast.lbrace + 1, space); // rbrace
     }
+
     const last_elem = array_init.ast.elements[array_init.ast.elements.len - 1];
     const last_elem_token = tree.lastToken(last_elem);
-    if (token_tags[last_elem_token + 1] == .comma) {
+    const trailing_comma = token_tags[last_elem_token + 1] == .comma;
+    if (trailing_comma) {
         // Render one element per line.
         ais.pushIndentNextLine();
         try renderToken(ais, tree, array_init.ast.lbrace, .newline);
@@ -2001,18 +2001,12 @@ fn renderComments(ais: *Ais, tree: ast.Tree, start: usize, end: usize) Error!boo
     var rendered_empty_comments = false;
     while (mem.indexOf(u8, tree.source[index..end], "//")) |offset| {
         const comment_start = index + offset;
-        const newline_index = mem.indexOfScalar(u8, tree.source[comment_start..end], '\n') orelse {
-            // comment ends in EOF.
-            const untrimmed_comment = tree.source[comment_start..];
-            const trimmed_comment = mem.trimRight(u8, untrimmed_comment, &std.ascii.spaces);
-            if (trimmed_comment.len != 2) {
-                try ais.writer().print("{s}\n", .{trimmed_comment});
-                index = end;
-            }
-            return index != start;
-        };
-        const newline = comment_start + newline_index;
-        const untrimmed_comment = tree.source[comment_start..newline];
+
+        // If there is no newline, the comment ends with EOF
+        const newline_index = mem.indexOfScalar(u8, tree.source[comment_start..end], '\n');
+        const newline = if (newline_index) |i| comment_start + i else null;
+
+        const untrimmed_comment = tree.source[comment_start .. newline orelse tree.source.len];
         const trimmed_comment = mem.trimRight(u8, untrimmed_comment, &std.ascii.spaces);
 
         // Don't leave any whitespace at the start of the file
@@ -2041,7 +2035,7 @@ fn renderComments(ais: *Ais, tree: ast.Tree, start: usize, end: usize) Error!boo
             try ais.writer().print("{s}\n", .{trimmed_comment});
             rendered_empty_comments = false;
         }
-        index = newline + 1;
+        index = 1 + (newline orelse return true);
 
         if (ais.disabled_offset) |disabled_offset| {
             if (mem.eql(u8, trimmed_comment, "// zig fmt: on")) {

lib/std/zig/tokenizer.zig

@@ -1444,6 +1444,7 @@ pub const Tokenizer = struct {
                 self.pending_invalid_token = null;
                 return token;
             }
+            result.loc.start = self.index;
         }
 
         result.loc.end = self.index;
@@ -2055,4 +2056,5 @@ fn testTokenize(source: []const u8, expected_tokens: []const Token.Tag) void {
     }
     const last_token = tokenizer.next();
     std.testing.expect(last_token.tag == .eof);
+    std.testing.expect(last_token.loc.start == source.len);
 }