zig fmt: fix handling of comments at top of file

std/zig/parse.zig

@@ -41,6 +41,13 @@ pub fn parse(allocator: &mem.Allocator, source: []const u8) !ast.Tree {
     }
     var tok_it = tree.tokens.iterator(0);
 
+    // skip over line comments at the top of the file
+    while (true) {
+        const next_tok = tok_it.peek() ?? break;
+        if (next_tok.id != Token.Id.LineComment) break;
+        _ = tok_it.next();
+    }
+
     try stack.append(State.TopLevel);
 
     while (true) {

std/zig/parser_test.zig

@@ -1,3 +1,23 @@
+test "zig fmt: first thing in file is line comment" {
+    try testCanonical(
+        \\// Introspection and determination of system libraries needed by zig.
+        \\
+        \\// Introspection and determination of system libraries needed by zig.
+        \\
+        \\const std = @import("std");
+        \\
+    );
+}
+
+test "zig fmt: line comment after doc comment" {
+    try testCanonical(
+        \\/// doc comment
+        \\// line comment
+        \\fn foo() void {}
+        \\
+    );
+}
+
 test "zig fmt: float literal with exponent" {
     try testCanonical(
         \\test "bit field alignment" {

std/zig/render.zig

@@ -15,6 +15,20 @@ pub const Error = error{
 pub fn render(allocator: &mem.Allocator, stream: var, tree: &ast.Tree) (@typeOf(stream).Child.Error || Error)!void {
     comptime assert(@typeId(@typeOf(stream)) == builtin.TypeId.Pointer);
 
+    // render all the line comments at the beginning of the file
+    var tok_it = tree.tokens.iterator(0);
+    while (tok_it.next()) |token| {
+        if (token.id != Token.Id.LineComment) break;
+        try stream.print("{}\n", tree.tokenSlicePtr(token));
+        if (tok_it.peek()) |next_token| {
+            const loc = tree.tokenLocationPtr(token.end, next_token);
+            if (loc.line >= 2) {
+                try stream.writeByte('\n');
+            }
+        }
+    }
+
+
     var it = tree.root_node.decls.iterator(0);
     while (it.next()) |decl| {
         try renderTopLevelDecl(allocator, stream, tree, 0, decl.*);
@@ -1455,7 +1469,7 @@ fn renderDocComments(tree: &ast.Tree, stream: var, node: var, indent: usize) (@t
     const comment = node.doc_comments ?? return;
     var it = comment.lines.iterator(0);
     while (it.next()) |line_token_index| {
-        try stream.print("{}\n", tree.tokenSlice(line_token_index.*));
+        try renderToken(tree, stream, line_token_index.*, indent, Space.Newline);
         try stream.writeByteNTimes(' ', indent);
     }
 }