Fixed the Studio view test comparing goldens at the wrong offset (#184)

compare_file() locates the line where comparison should start, so that the
banner GUIX Studio writes into every generated file -- which carries a revision
string and a generation timestamp -- is skipped rather than compared. It looked
that line up correctly in the first file and then looked it up in the first file
again for the second:

    for line in list_2:
        if compare_start_string in line:
            start_row_2 = list_1.index(line)

So the golden was sliced at the *generated* file's offset. While both files
happened to reach "#include" on the same line the mistake was invisible, which
is why it survived since the tests were added in #84.

The offsets diverged when 6ba13db added a ten-line MIT licence header to all
111 golden .c and .h files. GUIX Studio does not emit that header, so every
golden now reaches its first #include ten lines later than the file it is
compared against. The golden was therefore sliced ten lines early and compared
banner text against source.

That made every one of the 107 .c and .h comparisons in the suite fail -- all 29
reported test failures -- while the .csv, .xliff and .xml comparisons passed.
Those use skip_line instead of compare_start_string and never reach this code,
which is exactly the split the failure log shows.

The reported mismatch is the same in all 29: a generated "#include" line against
a golden banner comment. Confirmed arithmetically -- in every case the golden
line reported sits exactly ten lines before that golden's own first #include:

    generic_16bpp_resources.c        reported idx 13, #include at 23, delta 10
    generic_16bpp_resources.h        reported idx 16, #include at 26, delta 10
    generic_16bpp_specifications.c   reported idx 14, #include at 24, delta 10
    generic_16bpp_specifications.h   reported idx 16, #include at 26, delta 10

compare_output_file() is the only caller that passes compare_start_string, so
the change cannot affect the xliff, xml or plain-file comparisons.

Verified by running the suite locally against a Studio built from this tree.
Seven suites that fail in CI now pass with no mismatches at all, each gaining
exactly the tests it had been failing:

                              CI (broken)   local (fixed)
    Font                       9 / 1         10 / 0
    Multi-Themes              18 / 1         19 / 0
    Project Import            10 / 2         12 / 0
    Trigger Edit               6 / 1          7 / 0
    Trigger Target Rename      1 / 1          2 / 0
    Bidi Text                  3 / 1          4 / 0
    Widget Name                3 / 1          4 / 0

Project Import compares a generated specifications file, so this also shows that
the screen flow prototype block added by #173 does not disturb these goldens:
that block is only emitted for projects that use Screen Flow, and these do not.

No golden file is regenerated. The goldens still carry "GUIX Studio Revision
6.1.12.0" and a 2022 timestamp in their banners, and still name Azure RTOS
rather than Eclipse ThreadX, but the banner is what the comparison is supposed
to skip -- so none of that needs to be touched to make the suite correct.

This workflow had never actually executed before 2026-08-27. Every earlier run
was cancelled after queueing 24 hours for the retired windows-2019 image, or
sat awaiting approval on a fork pull request, including the run for the v6.5.1
release itself. #174 gave it a runner again; this is the first result it has
ever produced, and the defect it found is in the test harness rather than in
GUIX or in Studio.

Note that studio_view_test.yml triggers only on pull requests targeting master,
so this change is not exercised by its own pull request into dev. It is
validated by the release pull request that carries dev to master.

Assisted-by: Claude Code (Opus 5)

Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: fdesbiens

test/guix_studio_test/test_view/test_utils.py

@@ -7,6 +7,7 @@
 # https://opensource.org/licenses/MIT.
 #
 # SPDX-License-Identifier: MIT
+# Some portions generated by Claude Code (Opus 5).
 
 import os
 import sys
@@ -217,15 +218,19 @@ def compare_file(pathname_1, pathname_2, encoding = "", compare_start_string = "
     start_row_2 = 0
 
     if compare_start_string != "":
-        # find the line where comparing starts 
+        # Find the line where comparing starts, independently in each file. The
+        # two files may reach that line at different offsets -- a generated file
+        # carries the Studio banner, while the golden checked in beside it also
+        # carries a licence header -- so each start row must be looked up in its
+        # own list.
         for line in list_1:
             if compare_start_string in line:
                 start_row_1 = list_1.index(line)
                 break;
 
         for line in list_2:
             if compare_start_string in line:
-                start_row_2 = list_1.index(line)
+                start_row_2 = list_2.index(line)
                 break;
 
     # compare from the start line