From 806545fcc8d6b3b96a5191a00a31e9a39837189c Mon Sep 17 00:00:00 2001
From: Thiago Macieira <thiago.macieira@intel.com>
Date: Mon, 20 Sep 2021 23:07:52 -0700
Subject: QLoggingRegistry: add the ability to have environment variable
 overrides

Quite a lot of our code in Qt predating QLoggingCategory has manual
environment variable controls. For compatibility with established
documentation and tips-and-tricks out there, we should keep them working
when switching to categorized logging.

Change-Id: I3eb1bd30e0124f89a052fffd16a6c151d3e9d552
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
---
 src/corelib/io/qloggingregistry.cpp | 24 +++++++++++++++++++++++-
 src/corelib/io/qloggingregistry_p.h | 33 +++++++++++++++++++++++++++++++++
 2 files changed, 56 insertions(+), 1 deletion(-)

diff --git a/src/corelib/io/qloggingregistry.cpp b/src/corelib/io/qloggingregistry.cpp
index 08818c89d7..1c26e3d1c1 100644
--- a/src/corelib/io/qloggingregistry.cpp
+++ b/src/corelib/io/qloggingregistry.cpp
@@ -370,6 +370,20 @@ void QLoggingRegistry::unregisterCategory(QLoggingCategory *cat)
     categories.remove(cat);
 }
 
+/*!
+    \since 6.3
+    \internal
+
+    Registers the environment variable \a environment as the control variable
+    for enabling debugging by default for category \a categoryName. The
+    category name must start with "qt."
+*/
+void QLoggingRegistry::registerEnvironmentOverrideForCategory(QByteArrayView categoryName,
+                                                              QByteArrayView environment)
+{
+    qtCategoryEnvironmentOverrides.insert(categoryName, environment);
+}
+
 /*!
     \internal
     Installs logging rules as specified in \a content.
@@ -451,8 +465,16 @@ void QLoggingRegistry::defaultCategoryFilter(QLoggingCategory *cat)
     //   qt.debug=false
     if (const char *categoryName = cat->categoryName()) {
         // == "qt" or startsWith("qt.")
-        if (strcmp(categoryName, "qt") == 0 || strncmp(categoryName, "qt.", 3) == 0)
+        if (strcmp(categoryName, "qt") == 0) {
             debug = false;
+        } else if (strncmp(categoryName, "qt.", 3) == 0) {
+            // may be overridden
+            auto it = reg->qtCategoryEnvironmentOverrides.find(categoryName);
+            if (it == reg->qtCategoryEnvironmentOverrides.end())
+                debug = false;
+            else
+                debug = qEnvironmentVariableIntValue(it.value().data());
+        }
     }
 
     const auto categoryName = QLatin1String(cat->categoryName());
diff --git a/src/corelib/io/qloggingregistry_p.h b/src/corelib/io/qloggingregistry_p.h
index e8a94a030a..0009d8d2ea 100644
--- a/src/corelib/io/qloggingregistry_p.h
+++ b/src/corelib/io/qloggingregistry_p.h
@@ -63,6 +63,16 @@ class tst_QLoggingRegistry;
 
 QT_BEGIN_NAMESPACE
 
+#define Q_LOGGING_CATEGORY_WITH_ENV_OVERRIDE(name, env, categoryName) \
+    const QLoggingCategory &name() \
+    { \
+        static constexpr char cname[] = categoryName;                               \
+        static_assert(cname[0] == 'q' && cname[1] == 't' && cname[2] == '.'         \
+                      && cname[4] != '\0', "Category name must start with 'qt.'");  \
+        static const QLoggingCategoryWithEnvironmentOverride category(cname, env);  \
+        return category;                                                            \
+    }
+
 class Q_AUTOTEST_EXPORT QLoggingRule
 {
 public:
@@ -118,6 +128,11 @@ public:
     void registerCategory(QLoggingCategory *category, QtMsgType enableForLevel);
     void unregisterCategory(QLoggingCategory *category);
 
+#ifndef QT_BUILD_INTERNAL
+    Q_CORE_EXPORT   // always export from QtCore
+#endif
+    void registerEnvironmentOverrideForCategory(QByteArrayView categoryName, QByteArrayView environment);
+
     void setApiRules(const QString &content);
 
     QLoggingCategory::CategoryFilter
@@ -146,10 +161,28 @@ private:
     QList<QLoggingRule> ruleSets[NumRuleSets];
     QHash<QLoggingCategory *, QtMsgType> categories;
     QLoggingCategory::CategoryFilter categoryFilter;
+    QMap<QByteArrayView, QByteArrayView> qtCategoryEnvironmentOverrides;
 
     friend class ::tst_QLoggingRegistry;
 };
 
+class QLoggingCategoryWithEnvironmentOverride : public QLoggingCategory
+{
+public:
+    QLoggingCategoryWithEnvironmentOverride(const char *category, const char *env)
+        : QLoggingCategory(registerOverride(category, env), QtInfoMsg)
+    {}
+
+private:
+    static const char *registerOverride(QByteArrayView categoryName, QByteArrayView environment)
+    {
+        QLoggingRegistry *c = QLoggingRegistry::instance();
+        if (c)
+            c->registerEnvironmentOverrideForCategory(categoryName, environment);
+        return categoryName.data();
+    }
+};
+
 QT_END_NAMESPACE
 
 #endif // QLOGGINGREGISTRY_P_H
-- 
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