patch: provide real file transformation workflows

Formula/patch.rb

@@ -0,0 +1,119 @@
+require (Tap.fetch("automattic", "kandelo-homebrew").path/"Kandelo/formula_support/kandelo_formula_support").to_s
+
+class Patch < Formula
+  include KandeloFormulaSupport
+
+  desc "GNU utility for applying differences to files in Kandelo"
+  homepage "https://savannah.gnu.org/projects/patch/"
+  url "https://ftpmirror.gnu.org/gnu/patch/patch-2.8.tar.xz"
+  mirror "https://ftp.gnu.org/gnu/patch/patch-2.8.tar.xz"
+  sha256 "f87cee69eec2b4fcbf60a396b030ad6aa3415f192aa5f7ee84cad5e11f7f5ae3"
+  license "GPL-3.0-or-later"
+
+  depends_on "binaryen" => :build
+  depends_on "wabt" => :build
+  depends_on "automattic/kandelo-homebrew/dash"
+  depends_on "automattic/kandelo-homebrew/ed"
+
+  skip_clean "bin/patch"
+
+  def install
+    kandelo_require_arch!("wasm32")
+
+    kandelo_wasm_build do
+      # Resolve the external editor from the guest PATH, not the build host.
+      ENV["ac_cv_path_ED"] = "ed"
+
+      system kandelo_configure, *kandelo_std_configure_args,
+        "--disable-xattr",
+        "--disable-dependency-tracking"
+      system "make", "-j#{ENV.make_jobs}"
+      kandelo_validate_wasm_artifact(buildpath/"src/patch", fork: :forbidden)
+    end
+
+    kandelo_install_bin(buildpath/"src", "patch", "patch")
+    man1.install buildpath/"patch.man" => "patch.1"
+  end
+
+  test do
+    assert_match(/patch(?:\.wasm)? 2\.8$/, kandelo_run_wasm(bin/"patch", ["--version"]))
+
+    workspace = testpath/"workspace"
+    project = workspace/"project"
+    project.mkpath
+    (project/"notes.txt").write("alpha\nbeta\ngamma\n")
+    (project/"remove.txt").write("remove me\n")
+    env = { "KERNEL_CWD" => workspace }
+    diff = <<~DIFF
+      --- a/project/notes.txt
+      +++ b/project/notes.txt
+      @@ -1,3 +1,4 @@
+       alpha
+      -beta
+      +beta revised
+       gamma
+      +delta
+      --- /dev/null
+      +++ b/project/new.txt
+      @@ -0,0 +1,2 @@
+      +created
+      +file
+      --- a/project/remove.txt
+      +++ /dev/null
+      @@ -1 +0,0 @@
+      -remove me
+    DIFF
+
+    kandelo_run_wasm(bin/"patch", ["--batch", "-p1"], env: env, stdin: diff)
+    assert_equal "alpha\nbeta revised\ngamma\ndelta\n", (project/"notes.txt").read
+    assert_equal "created\nfile\n", (project/"new.txt").read
+    refute_path_exists project/"remove.txt"
+
+    kandelo_run_wasm(bin/"patch", ["--batch", "--dry-run", "-R", "-p1"], env: env, stdin: diff)
+    assert_equal "alpha\nbeta revised\ngamma\ndelta\n", (project/"notes.txt").read
+    assert_path_exists project/"new.txt"
+
+    kandelo_run_wasm(bin/"patch", ["--batch", "-R", "-p1"], env: env, stdin: diff)
+    assert_equal "alpha\nbeta\ngamma\n", (project/"notes.txt").read
+    refute_path_exists project/"new.txt"
+    assert_equal "remove me\n", (project/"remove.txt").read
+
+    rejected = <<~DIFF
+      --- a/project/notes.txt
+      +++ b/project/notes.txt
+      @@ -1,3 +1,3 @@
+      -missing
+      +replacement
+       beta
+       gamma
+    DIFF
+    failure = kandelo_run_wasm(
+      bin/"patch",
+      ["--batch", "--reject-file=failed.rej", "-p1"],
+      env:             env,
+      stdin:           rejected,
+      merge_stderr:    true,
+      expected_status: 1,
+    )
+    assert_match(/1 out of 1 hunk FAILED/, failure)
+    assert_match(/missing/, (workspace/"failed.rej").read)
+    assert_equal "alpha\nbeta\ngamma\n", (project/"notes.txt").read
+
+    (workspace/"ed-target.txt").write("one\nremove\nthree\n")
+    guest_work = "/work"
+    guest_ed = "/home/linuxbrew/.linuxbrew/opt/ed/bin/ed"
+    kandelo_run_wasm(
+      bin/"patch",
+      ["--batch", "--silent", "-e", "ed-target.txt"],
+      env:                       { "KERNEL_CWD" => guest_work, "PATH" => "#{File.dirname(guest_ed)}:/bin" },
+      stdin:                     "3a\nfour\n.\n1,2c\nONE\n.\n",
+      exec_programs:             {
+        "/bin/sh" => formula_opt_bin("automattic/kandelo-homebrew/dash")/"dash",
+        guest_ed  => formula_opt_bin("automattic/kandelo-homebrew/ed")/"ed",
+      },
+      writable_host_directories: { guest_work => workspace },
+      expected_fork_descendants: 1,
+    )
+    assert_equal "ONE\nthree\nfour\n", (workspace/"ed-target.txt").read
+  end
+end

README.md

@@ -43,6 +43,7 @@ Current migration controls and pilots include:
 - `dash`, the dependency-free POSIX shell with instrumented subprocess support;
 - `make`, GNU dependency-driven build automation using the tap's POSIX shell;
 - `ed`, the conforming line editor and restricted editor required by patch workflows;
+- `patch`, GNU's real multi-format file transformation utility replacing the compact metadata scanner;
 - `asa`, FreeBSD's POSIX carriage-control translator for FORTRAN output;
 - `m4`, the GNU macro processor with process-executing builtins backed by the tap's Dash shell;
 - `gawk`, GNU's pattern scanning and text-processing language;