diff --git a/lib/std/Build.zig b/lib/std/Build.zig
index bb642b5e66..bf0c74bd64 100644
--- a/lib/std/Build.zig
+++ b/lib/std/Build.zig
@@ -759,7 +759,7 @@ pub fn dupePath(self: *Build, bytes: []const u8) []u8 {
 
 pub fn addWriteFile(self: *Build, file_path: []const u8, data: []const u8) *Step.WriteFile {
     const write_file_step = self.addWriteFiles();
-    write_file_step.add(file_path, data);
+    _ = write_file_step.add(file_path, data);
     return write_file_step;
 }
 
diff --git a/lib/std/Build/Step/WriteFile.zig b/lib/std/Build/Step/WriteFile.zig
index 0d817e7430..0448aa8d2a 100644
--- a/lib/std/Build/Step/WriteFile.zig
+++ b/lib/std/Build/Step/WriteFile.zig
@@ -27,6 +27,10 @@ pub const File = struct {
     generated_file: std.Build.GeneratedFile,
     sub_path: []const u8,
     contents: Contents,
+
+    pub fn getFileSource(self: *File) std.Build.FileSource {
+        return .{ .generated = &self.generated_file };
+    }
 };
 
 pub const OutputSourceFile = struct {
@@ -55,7 +59,7 @@ pub fn create(owner: *std.Build) *WriteFile {
     return wf;
 }
 
-pub fn add(wf: *WriteFile, sub_path: []const u8, bytes: []const u8) void {
+pub fn add(wf: *WriteFile, sub_path: []const u8, bytes: []const u8) std.Build.FileSource {
     const b = wf.step.owner;
     const gpa = b.allocator;
     const file = gpa.create(File) catch @panic("OOM");
@@ -65,8 +69,8 @@ pub fn add(wf: *WriteFile, sub_path: []const u8, bytes: []const u8) void {
         .contents = .{ .bytes = b.dupe(bytes) },
     };
     wf.files.append(gpa, file) catch @panic("OOM");
-
     wf.maybeUpdateName();
+    return file.getFileSource();
 }
 
 /// Place the file into the generated directory within the local cache,
@@ -76,7 +80,7 @@ pub fn add(wf: *WriteFile, sub_path: []const u8, bytes: []const u8) void {
 /// include sub-directories, in which case this step will ensure the
 /// required sub-path exists.
 /// This is the option expected to be used most commonly with `addCopyFile`.
-pub fn addCopyFile(wf: *WriteFile, source: std.Build.FileSource, sub_path: []const u8) void {
+pub fn addCopyFile(wf: *WriteFile, source: std.Build.FileSource, sub_path: []const u8) std.Build.FileSource {
     const b = wf.step.owner;
     const gpa = b.allocator;
     const file = gpa.create(File) catch @panic("OOM");
@@ -89,6 +93,7 @@ pub fn addCopyFile(wf: *WriteFile, source: std.Build.FileSource, sub_path: []con
 
     wf.maybeUpdateName();
     source.addStepDependencies(&wf.step);
+    return file.getFileSource();
 }
 
 /// A path relative to the package root.
@@ -96,7 +101,6 @@ pub fn addCopyFile(wf: *WriteFile, source: std.Build.FileSource, sub_path: []con
 /// used as part of the normal build process, but as a utility occasionally
 /// run by a developer with intent to modify source files and then commit
 /// those changes to version control.
-/// A file added this way is not available with `getFileSource`.
 pub fn addCopyFileToSource(wf: *WriteFile, source: std.Build.FileSource, sub_path: []const u8) void {
     const b = wf.step.owner;
     wf.output_source_files.append(b.allocator, .{
@@ -111,7 +115,6 @@ pub fn addCopyFileToSource(wf: *WriteFile, source: std.Build.FileSource, sub_pat
 /// used as part of the normal build process, but as a utility occasionally
 /// run by a developer with intent to modify source files and then commit
 /// those changes to version control.
-/// A file added this way is not available with `getFileSource`.
 pub fn addBytesToSource(wf: *WriteFile, bytes: []const u8, sub_path: []const u8) void {
     const b = wf.step.owner;
     wf.output_source_files.append(b.allocator, .{
@@ -120,15 +123,7 @@ pub fn addBytesToSource(wf: *WriteFile, bytes: []const u8, sub_path: []const u8)
     }) catch @panic("OOM");
 }
 
-/// Gets a file source for the given sub_path. If the file does not exist, returns `null`.
-pub fn getFileSource(wf: *WriteFile, sub_path: []const u8) ?std.Build.FileSource {
-    for (wf.files.items) |file| {
-        if (std.mem.eql(u8, file.sub_path, sub_path)) {
-            return .{ .generated = &file.generated_file };
-        }
-    }
-    return null;
-}
+pub const getFileSource = @compileError("Deprecated; use the return value from add()/addCopyFile(), or use files[i].getFileSource()");
 
 /// Returns a `FileSource` representing the base directory that contains all the
 /// files from this `WriteFile`.
diff --git a/test/src/Cases.zig b/test/src/Cases.zig
index 08568d0dd6..e4f3d532ce 100644
--- a/test/src/Cases.zig
+++ b/test/src/Cases.zig
@@ -494,10 +494,12 @@ pub fn lowerToBuildSteps(
         }
 
         const writefiles = b.addWriteFiles();
+        var file_sources = std.StringHashMap(std.Build.FileSource).init(b.allocator);
+        defer file_sources.deinit();
         for (update.files.items) |file| {
-            writefiles.add(file.path, file.src);
+            file_sources.put(file.path, writefiles.add(file.path, file.src)) catch @panic("OOM");
         }
-        const root_source_file = writefiles.getFileSource(update.files.items[0].path).?;
+        const root_source_file = writefiles.files.items[0].getFileSource();
 
         const artifact = if (case.is_test) b.addTest(.{
             .root_source_file = root_source_file,
@@ -540,7 +542,7 @@ pub fn lowerToBuildSteps(
 
         for (case.deps.items) |dep| {
             artifact.addAnonymousModule(dep.name, .{
-                .source_file = writefiles.getFileSource(dep.path).?,
+                .source_file = file_sources.get(dep.path).?,
             });
         }
 
diff --git a/test/src/CompareOutput.zig b/test/src/CompareOutput.zig
index fb89082def..d2f7a23089 100644
--- a/test/src/CompareOutput.zig
+++ b/test/src/CompareOutput.zig
@@ -82,7 +82,7 @@ pub fn addCase(self: *CompareOutput, case: TestCase) void {
 
     const write_src = b.addWriteFiles();
     for (case.sources.items) |src_file| {
-        write_src.add(src_file.filename, src_file.source);
+        _ = write_src.add(src_file.filename, src_file.source);
     }
 
     switch (case.special) {
@@ -99,7 +99,7 @@ pub fn addCase(self: *CompareOutput, case: TestCase) void {
                 .target = .{},
                 .optimize = .Debug,
             });
-            exe.addAssemblyFileSource(write_src.getFileSource(case.sources.items[0].filename).?);
+            exe.addAssemblyFileSource(write_src.files.items[0].getFileSource());
 
             const run = b.addRunArtifact(exe);
             run.setName(annotated_case_name);
@@ -117,10 +117,9 @@ pub fn addCase(self: *CompareOutput, case: TestCase) void {
                     if (mem.indexOf(u8, annotated_case_name, filter) == null) continue;
                 }
 
-                const basename = case.sources.items[0].filename;
                 const exe = b.addExecutable(.{
                     .name = "test",
-                    .root_source_file = write_src.getFileSource(basename).?,
+                    .root_source_file = write_src.files.items[0].getFileSource(),
                     .optimize = optimize,
                     .target = .{},
                 });
@@ -144,10 +143,9 @@ pub fn addCase(self: *CompareOutput, case: TestCase) void {
                 if (mem.indexOf(u8, annotated_case_name, filter) == null) return;
             }
 
-            const basename = case.sources.items[0].filename;
             const exe = b.addExecutable(.{
                 .name = "test",
-                .root_source_file = write_src.getFileSource(basename).?,
+                .root_source_file = write_src.files.items[0].getFileSource(),
                 .target = .{},
                 .optimize = .Debug,
             });
diff --git a/test/src/StackTrace.zig b/test/src/StackTrace.zig
index 0d0b7155e6..0552b419c0 100644
--- a/test/src/StackTrace.zig
+++ b/test/src/StackTrace.zig
@@ -72,11 +72,10 @@ fn addExpect(
         if (mem.indexOf(u8, annotated_case_name, filter) == null) return;
     }
 
-    const src_basename = "source.zig";
-    const write_src = b.addWriteFile(src_basename, source);
+    const write_src = b.addWriteFile("source.zig", source);
     const exe = b.addExecutable(.{
         .name = "test",
-        .root_source_file = write_src.getFileSource(src_basename).?,
+        .root_source_file = write_src.files.items[0].getFileSource(),
         .optimize = optimize_mode,
         .target = .{},
     });
diff --git a/test/src/run_translated_c.zig b/test/src/run_translated_c.zig
index 946e56f512..42db8b19c5 100644
--- a/test/src/run_translated_c.zig
+++ b/test/src/run_translated_c.zig
@@ -82,10 +82,10 @@ pub const RunTranslatedCContext = struct {
 
         const write_src = b.addWriteFiles();
         for (case.sources.items) |src_file| {
-            write_src.add(src_file.filename, src_file.source);
+            _ = write_src.add(src_file.filename, src_file.source);
         }
         const translate_c = b.addTranslateC(.{
-            .source_file = write_src.getFileSource(case.sources.items[0].filename).?,
+            .source_file = write_src.files.items[0].getFileSource(),
             .target = .{},
             .optimize = .Debug,
         });
diff --git a/test/src/translate_c.zig b/test/src/translate_c.zig
index e275ee57ee..a1f312d623 100644
--- a/test/src/translate_c.zig
+++ b/test/src/translate_c.zig
@@ -104,11 +104,11 @@ pub const TranslateCContext = struct {
 
         const write_src = b.addWriteFiles();
         for (case.sources.items) |src_file| {
-            write_src.add(src_file.filename, src_file.source);
+            _ = write_src.add(src_file.filename, src_file.source);
         }
 
         const translate_c = b.addTranslateC(.{
-            .source_file = write_src.getFileSource(case.sources.items[0].filename).?,
+            .source_file = write_src.files.items[0].getFileSource(),
             .target = case.target,
             .optimize = .Debug,
         });
diff --git a/test/tests.zig b/test/tests.zig
index 641914aabe..5912ceb907 100644
--- a/test/tests.zig
+++ b/test/tests.zig
@@ -759,7 +759,7 @@ pub fn addCliTests(b: *std.Build) *Step {
             "-fno-emit-bin", "-fno-emit-h",
             "-fstrip",       "-OReleaseFast",
         });
-        run.addFileSourceArg(writefile.getFileSource("example.zig").?);
+        run.addFileSourceArg(writefile.files.items[0].getFileSource());
         const example_s = run.addPrefixedOutputFileArg("-femit-asm=", "example.s");
 
         const checkfile = b.addCheckFile(example_s, .{