From 9fd63daff2f6b98c2c7ae3a2668d2fa6cd92589c Mon Sep 17 00:00:00 2001
From: Jan200101 <sentrycraft123@gmail.com>
Date: Thu, 12 Mar 2026 21:23:28 +0100
Subject: [PATCH] std.Build.Step.ConfigHeader: handle leading whitespace for
 cmake

---
 lib/std/Build/Step/ConfigHeader.zig           | 14 ++++++++++++--
 test/standalone/cmakedefine/config.h.in       |  4 ++++
 test/standalone/cmakedefine/expected_config.h |  4 ++++
 3 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/lib/std/Build/Step/ConfigHeader.zig b/lib/std/Build/Step/ConfigHeader.zig
index 34d24f26d0..f9d792a268 100644
--- a/lib/std/Build/Step/ConfigHeader.zig
+++ b/lib/std/Build/Step/ConfigHeader.zig
@@ -420,12 +420,21 @@ fn render_cmake(
         };
         defer allocator.free(line);
 
-        if (!std.mem.startsWith(u8, line, "#")) {
+        const line_start = std.mem.findNone(u8, line, " \t\r") orelse {
+            try bw.writeAll(line);
+            if (!last_line) try bw.writeByte('\n');
+            continue;
+        };
+        const whitespace_prefix = line[0..line_start];
+        const trimmed_line = line[line_start..];
+
+        if (!std.mem.startsWith(u8, trimmed_line, "#")) {
             try bw.writeAll(line);
             if (!last_line) try bw.writeByte('\n');
             continue;
         }
-        var it = std.mem.tokenizeAny(u8, line[1..], " \t\r");
+
+        var it = std.mem.tokenizeAny(u8, trimmed_line[1..], " \t\r");
         const cmakedefine = it.next().?;
         if (!std.mem.eql(u8, cmakedefine, "cmakedefine") and
             !std.mem.eql(u8, cmakedefine, "cmakedefine01"))
@@ -502,6 +511,7 @@ fn render_cmake(
             value = Value{ .ident = it.rest() };
         }
 
+        try bw.writeAll(whitespace_prefix);
         try renderValueC(bw, name, value);
     }
 
diff --git a/test/standalone/cmakedefine/config.h.in b/test/standalone/cmakedefine/config.h.in
index f6f973d004..3f9c60c752 100644
--- a/test/standalone/cmakedefine/config.h.in
+++ b/test/standalone/cmakedefine/config.h.in
@@ -20,6 +20,10 @@
 // 1
 #cmakedefine stringval 1
 
+// whitespace test
+    #cmakedefine stringval 1
+	#cmakedefine stringval 1
+
 
 // cmakedefine01
 // 0
diff --git a/test/standalone/cmakedefine/expected_config.h b/test/standalone/cmakedefine/expected_config.h
index b991727fff..9ebe80956e 100644
--- a/test/standalone/cmakedefine/expected_config.h
+++ b/test/standalone/cmakedefine/expected_config.h
@@ -20,6 +20,10 @@
 // 1
 #define stringval 1
 
+// whitespace test
+    #define stringval 1
+	#define stringval 1
+
 
 // cmakedefine01
 // 0