std.zig.render: Fix multiple fmt invocations needed for array initializers with switch expressions

Author: jgautheron

lib/std/zig/render.zig

@@ -2076,8 +2076,9 @@ fn renderArrayInit(
 
     const contains_comment = hasComment(tree, array_init.ast.lbrace, rbrace);
     const contains_multiline_string = hasMultilineString(tree, array_init.ast.lbrace, rbrace);
+    const contains_switch = containsSwitch(tree, array_init.ast.elements);
 
-    if (!trailing_comma and !contains_comment and !contains_multiline_string) {
+    if (!trailing_comma and !contains_comment and !contains_multiline_string and !contains_switch) {
         // Render all on one line, no trailing comma.
         if (array_init.ast.elements.len == 1) {
             // If there is only one element, we don't use spaces
@@ -2260,6 +2261,27 @@ fn renderArrayInit(
     return renderToken(r, rbrace, space); // rbrace
 }
 
+/// Returns true if any array element is or contains a switch expression
+fn containsSwitch(tree: Ast, elements: []const Ast.Node.Index) bool {
+    const tags = tree.nodes.items(.tag);
+
+    for (elements) |elem| {
+        const tag = tags[@intFromEnum(elem)];
+
+        if (tag == .switch_case or
+            tag == .switch_case_inline or
+            tag == .switch_case_one or
+            tag == .switch_case_inline_one or
+            tag == .@"switch" or
+            tag == .switch_comma)
+        {
+            return true;
+        }
+    }
+
+    return false;
+}
+
 fn renderContainerDecl(
     r: *Render,
     container_decl_node: Ast.Node.Index,

test/tests.zig

@@ -1299,6 +1299,50 @@ pub fn addCliTests(b: *std.Build) *Step {
         });
         check6.step.dependOn(&run6.step);
 
+        // Test `zig fmt` handling switch expressions in array initializers
+        const switch_in_array_code =
+            \\const bar = .{ .{ switch ({}) {
+            \\        else => {},
+            \\    } }, .{}, .{}, .{},
+            \\};
+            \\
+        ;
+
+        const fmt7_path = b.pathJoin(&.{ tmp_path, "fmt7.zig" });
+        const write7 = b.addUpdateSourceFiles();
+        write7.addBytesToSource(switch_in_array_code, fmt7_path);
+        write7.step.dependOn(&check6.step);
+
+        // Test `zig fmt` handling switch expressions in array initializers
+        const run7 = b.addSystemCommand(&.{ b.graph.zig_exe, "fmt", "fmt7.zig" });
+        run7.setName("run zig fmt on array with switch");
+        run7.setCwd(.{ .cwd_relative = tmp_path });
+        run7.has_side_effects = true;
+        run7.expectStdOutEqual("fmt7.zig\n");
+        run7.step.dependOn(&write7.step);
+
+        // Check that the file is formatted correctly after a single fmt invocation
+        const check7 = b.addCheckFile(.{ .cwd_relative = fmt7_path }, .{
+            .expected_matches = &.{
+                "const bar = .{",
+                "    .{switch ({}) {",
+                "        else => {},",
+                "    }},",
+                "    .{},",
+                "    .{},",
+                "    .{},",
+                "};",
+            },
+        });
+        check7.step.dependOn(&run7.step);
+
+        // Run fmt again to verify that no further changes are made (idempotence)
+        const run8 = b.addSystemCommand(&.{ b.graph.zig_exe, "fmt", "fmt7.zig" });
+        run8.setName("run zig fmt again on array with switch");
+        run8.setCwd(.{ .cwd_relative = tmp_path });
+        run8.has_side_effects = true;
+        run8.step.dependOn(&check7.step);
+
         const cleanup = b.addRemoveDirTree(.{ .cwd_relative = tmp_path });
         cleanup.step.dependOn(&check6.step);