From 9d6750935e6440a5f3ade988703b1b4f5c244fb6 Mon Sep 17 00:00:00 2001
From: Jan200101 <sentrycraft123@gmail.com>
Date: Sun, 1 Jun 2025 20:48:44 +0200
Subject: [PATCH] std.Build.Step.ConfigHeader: handle empty keys more
 permissively

${} is never used in a cmake config header but still needs to be
substituted
instead of erroring because of an empty key simply omit the value
---
 lib/std/Build/Step/ConfigHeader.zig           | 14 ++++++++------
 test/standalone/cmakedefine/config.h.in       |  3 +++
 test/standalone/cmakedefine/expected_config.h |  3 +++
 3 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/lib/std/Build/Step/ConfigHeader.zig b/lib/std/Build/Step/ConfigHeader.zig
index 6bfda7667bac..f1cbd463d3f8 100644
--- a/lib/std/Build/Step/ConfigHeader.zig
+++ b/lib/std/Build/Step/ConfigHeader.zig
@@ -748,10 +748,12 @@ fn expand_variables_cmake(
 
                 const key_start = open_pos.target + open_var.len;
                 const key = result.items[key_start..];
-                if (key.len == 0) {
-                    return error.MissingKey;
-                }
-                const value = values.get(key) orelse return error.MissingValue;
+                const value = values.get(key) orelse
+                    if (key.len == 0)
+                        .undef
+                    else
+                        return error.MissingValue;
+
                 result.shrinkRetainingCapacity(result.items.len - key.len - open_var.len);
                 switch (value) {
                     .undef, .defined => {},
@@ -952,8 +954,8 @@ test "expand_variables_cmake simple cases" {
     // line with misc content is preserved
     try testReplaceVariablesCMake(allocator, "no substitution", "no substitution", values);
 
-    // empty ${} wrapper leads to an error
-    try std.testing.expectError(error.MissingKey, testReplaceVariablesCMake(allocator, "${}", "", values));
+    // empty ${} wrapper is removed
+    try testReplaceVariablesCMake(allocator, "${}", "", values);
 
     // empty @ sigils are preserved
     try testReplaceVariablesCMake(allocator, "@", "@", values);
diff --git a/test/standalone/cmakedefine/config.h.in b/test/standalone/cmakedefine/config.h.in
index f6f973d004fd..7a1981130a69 100644
--- a/test/standalone/cmakedefine/config.h.in
+++ b/test/standalone/cmakedefine/config.h.in
@@ -94,6 +94,9 @@
 // test10
 // @noval@@stringval@@trueval@@zeroval@
 
+// empty key, removed
+// ${}
+
 // no substition
 // ${noval}
 
diff --git a/test/standalone/cmakedefine/expected_config.h b/test/standalone/cmakedefine/expected_config.h
index b991727ffff1..c783552a18a7 100644
--- a/test/standalone/cmakedefine/expected_config.h
+++ b/test/standalone/cmakedefine/expected_config.h
@@ -94,6 +94,9 @@
 // test10
 // test10
 
+// empty key, removed
+// 
+
 // no substition
 //