From 0d2e9906f3d31a2b3ce94afc433c38a17849424b Mon Sep 17 00:00:00 2001
From: David Aguilar <davvid@gmail.com>
Date: Thu, 12 Oct 2023 14:37:52 -0700
Subject: [PATCH] feat(idiff): allow users to specify a directory as the 2nd
 argument (#4015)

Teach `idiff` to accept a directory as the 2nd argument.

Fixes #4009

## Tests

Functional tests for `idiff` don't currently exist. Manual testing
verifies it works as advertised.

---------

Signed-off-by: David Aguilar <davvid@gmail.com>
---
 src/doc/idiff.rst   |  5 ++++-
 src/idiff/idiff.cpp | 24 ++++++++++++++++++++++--
 2 files changed, 26 insertions(+), 3 deletions(-)

diff --git a/src/doc/idiff.rst b/src/doc/idiff.rst
index bebb068850..92cc15a131 100644
--- a/src/doc/idiff.rst
+++ b/src/doc/idiff.rst
@@ -26,12 +26,15 @@ Using `idiff`
 
 The `idiff` utility is invoked as follows:
 
-    `idiff` [*options*] *image1* *image2*
+    `idiff` [*options*] *input1* *input2|directory*
 
 Where *input1* and *input2* are the names of two image files that should be
 compared.  They may be of any format recognized by OpenImageIO (i.e., for
 which image-reading plugins are available).
 
+When a *directory* is specified instead of *input2* then `idiff` will use
+the same-named file as *input1* in the specified directory.
+
 If the two input images are not the same resolutions, or do not have the
 same number of channels, the comparison will return FAILURE immediately and
 will not attempt to compare the pixels of the two images.  If they are the
diff --git a/src/idiff/idiff.cpp b/src/idiff/idiff.cpp
index c892b9d60c..8b0346389e 100644
--- a/src/idiff/idiff.cpp
+++ b/src/idiff/idiff.cpp
@@ -43,7 +43,7 @@ getargs(int argc, char* argv[])
     ArgParse ap;
     ap.intro("idiff -- compare two images\n"
              OIIO_INTRO_STRING)
-      .usage("idiff [options] image1 image2")
+      .usage("idiff [options] <image1> <image2 | directory>")
       .add_version(OIIO_VERSION_STRING)
       .print_defaults(true);
 
@@ -169,6 +169,24 @@ print_subimage(ImageBuf& img0, int subimage, int miplevel)
 }
 
 
+// Append the filename from "first" when "second" is a directory.
+// "second" is an output variable and modified in-place.
+inline void
+add_filename_to_directory(const std::string& first, std::string& second)
+{
+    if (Filesystem::is_directory(second)) {
+        char last_byte = second.at(second.size() - 1);
+        if (last_byte != '/' && last_byte != '\\') {
+#if defined(_MSC_VER)
+            second += '\\';
+#else
+            second += '/';
+#endif
+        }
+        second += Filesystem::filename(first);
+    }
+}
+
 
 int
 main(int argc, char* argv[])
@@ -181,7 +199,9 @@ main(int argc, char* argv[])
     ArgParse ap = getargs(argc, argv);
 
     std::vector<std::string> filenames = ap["filename"].as_vec<std::string>();
-    if (filenames.size() != 2) {
+    if (filenames.size() == 2) {
+        add_filename_to_directory(filenames[0], filenames[1]);
+    } else {
         print(stderr, "idiff: Must have two input filenames.\n");
         print(stderr, "> {}\n", Strutil::join(filenames, ", "));
         ap.usage();