[glib/ebassi/compile-resource-split: 1/2] Do not generate C resources for all possible toolchains

[Philip Withnall <pwithnall src gnome org>]

commit 158a64f744554f6c1f1f902fab7c02e219300d84
Author: Emmanuele Bassi <ebassi gnome org>
Date:   Sat Sep 18 13:45:57 2021 +0100

    Do not generate C resources for all possible toolchains
    
    The resources data is generated for both GCC and MSVC toolchains, even
    though we know beforehand which toolchain we're going to compile it for.
    By dropping the data duplication we make the generated resources file
    faster to compile, especially when dealing with large embedded data,
    instead of relying on the C pre-processor to walk the whole file and
    discard the branch we're not using.

 docs/reference/gio/glib-compile-resources.xml |  10 ++
 gio/glib-compile-resources.c                  | 144 ++++++++++++++++++++------
 2 files changed, 125 insertions(+), 29 deletions(-)
---
diff --git a/docs/reference/gio/glib-compile-resources.xml b/docs/reference/gio/glib-compile-resources.xml
index a85f6003c..7ab36f5a9 100644
--- a/docs/reference/gio/glib-compile-resources.xml
+++ b/docs/reference/gio/glib-compile-resources.xml
@@ -200,6 +200,16 @@ be used with <literal>make</literal>.
 </para></listitem>
 </varlistentry>
 
+<varlistentry>
+<term><option>--compiler=<replaceable>NAME</replaceable></option></term>
+<listitem><para>
+Generate code that is going to target the given compiler <replaceable>NAME</replaceable>.
+The current two compiler modes are "gcc", for all GCC-compatible toolchains; and "msvc",
+for the Microsoft Visual C Compiler. If this option isn't set, then the default will be
+taken from the <envar>CC</envar> environment variable.
+</para></listitem>
+</varlistentry>
+
 </variablelist>
 </refsect1>
 
diff --git a/gio/glib-compile-resources.c b/gio/glib-compile-resources.c
index ac95801f4..306809a18 100644
--- a/gio/glib-compile-resources.c
+++ b/gio/glib-compile-resources.c
@@ -710,6 +710,86 @@ escape_makefile_string (const char *string)
   return g_string_free (str, FALSE);
 }
 
+typedef enum {
+  COMPILER_GCC,
+  COMPILER_CLANG,
+  COMPILER_MSVC,
+  COMPILER_UNKNOWN
+} CompilerType;
+
+/* Get the compiler id from the platform, environment, or command line
+ *
+ * Keep compiler IDs consistent with https://mesonbuild.com/Reference-tables.html#compiler-ids
+ * for simplicity
+ */
+static CompilerType
+get_compiler_id (const char *compiler)
+{
+  char *base, *ext_p;
+  CompilerType compiler_type;
+
+  if (compiler == NULL)
+    {
+#ifdef G_OS_UNIX
+      const char *compiler_env = g_getenv ("CC");
+
+# ifdef __APPLE__
+      if (compiler_env == NULL || *compiler_env == '\0')
+        compiler = "clang";
+      else
+        compiler = compiler_env;
+# elif __linux__
+      if (compiler_env == NULL || *compiler_env == '\0')
+        compiler = "gcc";
+      else
+        compiler = compiler_env;
+# else
+      if (compiler_env == NULL || *compiler_env == '\0')
+        compiler = "unknown";
+      else
+        compiler = compiler_env;
+# endif
+#endif
+
+#ifdef G_OS_WIN32
+      if (g_getenv ("MSYSTEM") != NULL)
+        {
+          const char *compiler_env = g_getenv ("CC");
+
+          if (compiler_env == NULL || *compiler_env == '\0')
+            compiler = "gcc";
+          else
+            compiler = compiler_env;
+        }
+      else
+        compiler = "msvc";
+#endif
+    }
+
+  base = g_path_get_basename (compiler);
+  ext_p = strrchr (base, '.');
+  if (ext_p != NULL)
+    {
+      gsize offset = ext_p - base;
+      base[offset] = '\0';
+    }
+
+  compiler = base;
+
+  if (g_strcmp0 (compiler, "gcc") == 0)
+    compiler_type = COMPILER_GCC;
+  else if (g_strcmp0 (compiler, "clang") == 0)
+    compiler_type = COMPILER_CLANG;
+  else if (g_strcmp0 (compiler, "msvc") == 0)
+    compiler_type = COMPILER_MSVC;
+  else
+    compiler_type = COMPILER_UNKNOWN;
+
+  g_free (base);
+
+  return compiler_type;
+}
+
 int
 main (int argc, char **argv)
 {
@@ -732,6 +812,8 @@ main (int argc, char **argv)
   char *c_name = NULL;
   char *c_name_no_underscores;
   const char *linkage = "extern";
+  const char *compiler = NULL;
+  CompilerType compiler_type = COMPILER_GCC;
   GOptionContext *context;
   GOptionEntry entries[] = {
     { "version", 0, 0, G_OPTION_ARG_NONE, &show_version_and_exit, N_("Show program version and exit"), NULL 
},
@@ -747,6 +829,7 @@ main (int argc, char **argv)
     { "internal", 0, 0, G_OPTION_ARG_NONE, &internal, N_("Don’t export functions; declare them 
G_GNUC_INTERNAL"), NULL },
     { "external-data", 0, 0, G_OPTION_ARG_NONE, &external_data, N_("Don’t embed resource data in the C file; 
assume it's linked externally instead"), NULL },
     { "c-name", 0, 0, G_OPTION_ARG_STRING, &c_name, N_("C identifier name used for the generated source 
code"), NULL },
+    { "compiler", 'C', 0, G_OPTION_ARG_STRING, &compiler, N_("The target C compiler (default: the CC 
environment variable)"), NULL },
     G_OPTION_ENTRY_NULL
   };
 
@@ -802,6 +885,8 @@ main (int argc, char **argv)
   if (internal)
     linkage = "G_GNUC_INTERNAL";
 
+  compiler_type = get_compiler_id (compiler);
+
   srcfile = argv[1];
 
   xmllint = g_strdup (g_getenv ("XMLLINT"));
@@ -1105,40 +1190,41 @@ main (int argc, char **argv)
         }
       else
         {
-          /* For Visual Studio builds: Avoid surpassing the 65535-character limit for a string, GitLab issue 
#1580 */
-          g_fprintf (file, "#ifdef _MSC_VER\n");
-          g_fprintf (file,
-                     "static const SECTION union { const guint8 data[%"G_GSIZE_FORMAT"]; const double 
alignment; void * const ptr;}  %s_resource_data = { {\n",
-                     data_size + 1 /* nul terminator */, c_name);
-
-          for (i = 0; i < data_size; i++)
+          if (compiler_type == COMPILER_MSVC || compiler_type == COMPILER_UNKNOWN)
             {
-              if (i % 16 == 0)
-                g_fprintf (file, "  ");
-              g_fprintf (file, "0%3.3o", (int)data[i]);
-              if (i != data_size - 1)
-                g_fprintf (file, ", ");
-              if (i % 16 == 15 || i == data_size - 1)
-                g_fprintf (file, "\n");
-            }
+              /* For Visual Studio builds: Avoid surpassing the 65535-character limit for a string, GitLab 
issue #1580 */
+              g_fprintf (file,
+                         "static const SECTION union { const guint8 data[%"G_GSIZE_FORMAT"]; const double 
alignment; void * const ptr;}  %s_resource_data = { {\n",
+                         data_size + 1 /* nul terminator */, c_name);
 
-          g_fprintf (file, "} };\n");
-
-          /* For other compilers, use the long string approach */
-          g_fprintf (file, "#else /* _MSC_VER */\n");
-          g_fprintf (file,
-                     "static const SECTION union { const guint8 data[%"G_GSIZE_FORMAT"]; const double 
alignment; void * const ptr;}  %s_resource_data = {\n  \"",
-                     data_size + 1 /* nul terminator */, c_name);
+              for (i = 0; i < data_size; i++)
+                {
+                  if (i % 16 == 0)
+                    g_fprintf (file, "  ");
+                  g_fprintf (file, "0%3.3o", (int)data[i]);
+                  if (i != data_size - 1)
+                    g_fprintf (file, ", ");
+                  if (i % 16 == 15 || i == data_size - 1)
+                     g_fprintf (file, "\n");
+                }
 
-          for (i = 0; i < data_size; i++)
-            {
-              g_fprintf (file, "\\%3.3o", (int)data[i]);
-              if (i % 16 == 15)
-                g_fprintf (file, "\"\n  \"");
+              g_fprintf (file, "} };\n");
             }
+          else
+            {
+              g_fprintf (file,
+                         "static const SECTION union { const guint8 data[%"G_GSIZE_FORMAT"]; const double 
alignment; void * const ptr;}  %s_resource_data = {\n  \"",
+                         data_size + 1 /* nul terminator */, c_name);
 
-          g_fprintf (file, "\" };\n");
-          g_fprintf (file, "#endif /* !_MSC_VER */\n");
+              for (i = 0; i < data_size; i++)
+                {
+                  g_fprintf (file, "\\%3.3o", (int)data[i]);
+                  if (i % 16 == 15)
+                    g_fprintf (file, "\"\n  \"");
+                }
+
+              g_fprintf (file, "\" };\n");
+            }
         }
 
       g_fprintf (file,