From eb8201afde98d9ba35d0c8488d418b1b0bef4f35 Mon Sep 17 00:00:00 2001
From: Andrew Kelley <andrew@ziglang.org>
Date: Sun, 16 Jun 2024 19:30:14 -0700
Subject: [PATCH] std.Build.Step.Fmt: display non-conforming files

When in --check mode, and files are found to not conform, emit them
explicitly as step errors. Previously this stdout data was being
ignored.
---
 lib/std/Build/Step/Fmt.zig | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/lib/std/Build/Step/Fmt.zig b/lib/std/Build/Step/Fmt.zig
index f346c6cc39..1d3850a7ec 100644
--- a/lib/std/Build/Step/Fmt.zig
+++ b/lib/std/Build/Step/Fmt.zig
@@ -37,9 +37,6 @@ pub fn create(owner: *std.Build, options: Options) *Fmt {
 }
 
 fn make(step: *Step, prog_node: std.Progress.Node) !void {
-    // zig fmt is fast enough that no progress is needed.
-    _ = prog_node;
-
     // TODO: if check=false, this means we are modifying source files in place, which
     // is an operation that could race against other operations also modifying source files
     // in place. In this case, this step should obtain a write lock while making those
@@ -68,5 +65,15 @@ fn make(step: *Step, prog_node: std.Progress.Node) !void {
         argv.appendAssumeCapacity(b.pathFromRoot(p));
     }
 
-    return step.evalChildProcess(argv.items);
+    const run_result = try step.captureChildProcess(prog_node, argv.items);
+    if (fmt.check) switch (run_result.term) {
+        .Exited => |code| if (code != 0 and run_result.stdout.len != 0) {
+            var it = std.mem.tokenizeScalar(u8, run_result.stdout, '\n');
+            while (it.next()) |bad_file_name| {
+                try step.addError("{s}: non-conforming formatting", .{bad_file_name});
+            }
+        },
+        else => {},
+    };
+    try step.handleChildProcessTerm(run_result.term, null, argv.items);
 }