[gi-docgen/msvc] utils.py: Improve .gir search on Windows

[Chun-wei Fan <fanchunwei src gnome org>]

commit be9df05db1488ab081e20933e153e47d50f8214b
Author: Chun-wei Fan <fanchunwei src gnome org>
Date:   Wed May 5 10:46:13 2021 +0800

    utils.py: Improve .gir search on Windows
    
    On Windows, we tend to look for .gir files in the $(prefix) directory
    indicated by $(prefix)/bin/g-ir-scanner when running g-ir-scanner, so:
    
    *  We add a special case for find_program() to look for g-ir-scanner on
       Windows without any executable extensions, since that is how
       g-ir-scanner is being deployed as a Python script.
    
    *  Update default_search_paths() to first look for the presence of
       g-ir-scanner, and use its "installation prefix" to construct the
       default path where g-ir-scanner looks for the .gir files.
    
    This way, we can make gi-docgen work better on Visual Studio builds
    where Python (i.e. the official binary installers from www.python.org)
    is generally installed seperately from the $(prefix) of our GNOME stack,
    meaning that we can reduce the need to copy the dependent .gir files
    from under our $(prefix).

 gidocgen/utils.py | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)
---
diff --git a/gidocgen/utils.py b/gidocgen/utils.py
index 655ea7a..d781900 100644
--- a/gidocgen/utils.py
+++ b/gidocgen/utils.py
@@ -794,7 +794,10 @@ def find_program(bin_name, path=None):
         search_paths.insert(0, '')
 
     for ext in bin_extensions:
-        executable = bin_name + ext
+        if bin_name == 'g-ir-scanner':
+            executable = bin_name
+        else:
+            executable = bin_name + ext
 
         for p in search_paths:
             full_path = os.path.join(p, executable)
@@ -818,9 +821,15 @@ def default_search_paths():
 
     paths = []
     paths.append(os.getcwd())
-    # Add sys.base_prefix when using MSYS2
-    if sys.platform == 'win32' and 'GCC' in sys.version:
-        paths.append(os.path.join(sys.base_prefix, 'share', 'gir-1.0'))
+    if sys.platform == 'win32':
+        # Use the prefix directory of g-ir-scanner on Windows
+        g_ir_scanner = find_program('g-ir-scanner')
+        if g_ir_scanner is not None:
+            g_ir_scanner_prefix = os.path.dirname(os.path.dirname(g_ir_scanner))
+            paths.append(os.path.join(g_ir_scanner_prefix, 'share', 'gir-1.0'))
+        # Add sys.base_prefix when using MSYS2
+        if 'GCC' in sys.version:
+            paths.append(os.path.join(sys.base_prefix, 'share', 'gir-1.0'))
     if xdg_data_home is not None:
         paths.append(os.path.join(xdg_data_home, "gir-1.0"))
     if xdg_data_dirs is not None: