From 3ac33cd6c3f4519336d5266418948b69a4be5657 Mon Sep 17 00:00:00 2001
From: Christian Kandeler <christian.kandeler@qt.io>
Date: Fri, 19 Jan 2024 15:45:55 +0100
Subject: Loader: Deprecate the fallback provider

The fallback provider creates modules for all named dependencies that
were not found and only later checks during validation whether such a
pkg-config module exists. This breaks assumptions all over the place.
Since we have a superior replacement in qbspkgconfig, we now deprecate
the fallback provider.

Change-Id: I3694515865d63e7308cfab7778068aa2e480fe23
Reviewed-by: Ivan Komissarov <ABBAPOH@gmail.com>
---
 doc/howtos.qdoc                                  | 10 ++++++----
 doc/qbs.qdoc                                     |  6 ------
 doc/reference/items/language/depends.qdoc        |  9 ---------
 src/lib/corelib/language/builtindeclarations.cpp | 10 ++++++++--
 4 files changed, 14 insertions(+), 21 deletions(-)

diff --git a/doc/howtos.qdoc b/doc/howtos.qdoc
index 268bee7c0..b3b385feb 100644
--- a/doc/howtos.qdoc
+++ b/doc/howtos.qdoc
@@ -467,15 +467,17 @@
 
     \section1 How do I build against libraries that provide pkg-config files?
 
-    Just add a \l Depends item that matches the name of the pkg-config module, and \QBS
-    will automatically employ \l{https://www.freedesktop.org/wiki/Software/pkg-config}{pkg-config}
+    Just add a \l Depends item that matches the name of the pkg-config module,
+    set the \l Product::qbsModuleProviders property to \c "qbspkgconfig",
+    and \QBS will employ
+    \l{https://www.freedesktop.org/wiki/Software/pkg-config}{pkg-config}
     to find the headers and libraries if no matching \QBS module can be found. For instance,
     to build against the OpenSSL library, you would write this:
     \code
+    qbsModuleProviders: "qbspkgconfig"
     Depends { name: "openssl" }
     \endcode
-    That's it. The pkg-config behavior can be fine-tuned via the \l pkgconfig module,
-    but normally you will not need to pull it in explicitly.
+    That's it. The pkg-config behavior can be fine-tuned via the \l qbspkgconfig provider.
 
     Internally, this functionality is implemented via \l {Module Providers}
 
diff --git a/doc/qbs.qdoc b/doc/qbs.qdoc
index 76bbf2a61..b37095854 100644
--- a/doc/qbs.qdoc
+++ b/doc/qbs.qdoc
@@ -1922,12 +1922,6 @@
             a second attempt will be made to locate the dependency using the new paths.
             The search for a matching module provider ends as soon as one was found, regardless
             of whether it created any modules or not.
-        \li If no matching module provider was found in any of the search paths, \QBS will fall back
-            to a generic module provider, which creates a module that attempts to locate the
-            dependency via \c pkg-config.
-            This fallback mechanism can be disabled in the respective
-            \l{Depends::enableFallback}{Depends} item or globally via the
-            \l{no-fallback-module-provider}{--no-fallback-module-provider} option.
     \endlist
 
     \section1 Selecting Module Providers
diff --git a/doc/reference/items/language/depends.qdoc b/doc/reference/items/language/depends.qdoc
index 7cc270483..937828b8c 100644
--- a/doc/reference/items/language/depends.qdoc
+++ b/doc/reference/items/language/depends.qdoc
@@ -197,12 +197,3 @@
 
     \nodefaultvalue
 */
-
-/*!
-    \qmlproperty bool Depends::enableFallback
-
-    Whether to fall back to a pkg-config based \l{Module Providers}{module provider}
-    if the dependency is not found.
-
-    \defaultvalue \c true
-*/
diff --git a/src/lib/corelib/language/builtindeclarations.cpp b/src/lib/corelib/language/builtindeclarations.cpp
index 2ad0e3ef4..4a83279a8 100644
--- a/src/lib/corelib/language/builtindeclarations.cpp
+++ b/src/lib/corelib/language/builtindeclarations.cpp
@@ -247,8 +247,14 @@ void BuiltinDeclarations::addDependsItem()
     item << PropertyDeclaration(StringConstants::multiplexConfigurationIdsProperty(),
                                 PropertyDeclaration::StringList, QString(),
                                 PropertyDeclaration::ReadOnlyFlag);
-    item << PropertyDeclaration(StringConstants::enableFallbackProperty(),
-                                PropertyDeclaration::Boolean, StringConstants::trueValue());
+    PropertyDeclaration fallbackProp(
+        StringConstants::enableFallbackProperty(),
+        PropertyDeclaration::Boolean,
+        StringConstants::falseValue());
+    fallbackProp.setDeprecationInfo(DeprecationInfo(
+        Version(2, 4),
+        Tr::tr("The fallback provider has been deprecated. Use qbspkgconfig instead.")));
+    item << fallbackProp;
     insert(item);
 }
 
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