Utils: use system case for environment variables on windows

Match case of user changed environment variables to the
already defined variables.

Change-Id: Ic012d35faa0822df3523ab642491c9f19051853c
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@qt.io>
Reviewed-by: hjk <hjk@qt.io>

src/libs/utils/environment.cpp

@@ -500,7 +500,7 @@ Environment::const_iterator Environment::constEnd() const
 
 Environment::const_iterator Environment::constFind(const QString &name) const
 {
-    return m_values.constFind(name);
+    return findKey(m_values, m_osType, name);
 }
 
 int Environment::size() const
@@ -567,6 +567,11 @@ bool Environment::hasKey(const QString &key) const
     return m_values.contains(key);
 }
 
+OsType Environment::osType() const
+{
+    return m_osType;
+}
+
 QString Environment::userName() const
 {
     return value(QString::fromLatin1(m_osType == OsTypeWindows ? "USERNAME" : "USER"));

src/libs/utils/environment.h

@@ -91,6 +91,7 @@ public:
     /// Return the Environment changes necessary to modify this into the other environment.
     QList<EnvironmentItem> diff(const Environment &other, bool checkAppendPrepend = false) const;
     bool hasKey(const QString &key) const;
+    OsType osType() const;
 
     QString userName() const;
 

src/libs/utils/environmentmodel.cpp

@@ -364,6 +364,13 @@ void EnvironmentModel::setUserChanges(QList<EnvironmentItem> list)
         name = name.trimmed();
         if (name.startsWith(QLatin1String("export ")))
             name = name.mid(7).trimmed();
+        if (d->m_baseEnvironment.osType() == OsTypeWindows) {
+            // Environment variable names are case-insensitive under windows, but we still
+            // want to preserve the case of pre-existing variables.
+            auto it = d->m_baseEnvironment.constFind(name);
+            if (it != d->m_baseEnvironment.constEnd())
+                name = d->m_baseEnvironment.key(it);
+        }
     }
 
     d->updateResultEnvironment();