Utils: Continue Environment/EnvironmentChange consolidation

Make Environment a stack of changes that gets "expanded" to
a full environment before things are actively accessed.

Later this expansion should be done lazily if possible.

Task-number: QTCREATORBUG-28357
Change-Id: If1c7bfdb9f58b81e71c51ed87ee75d6964a47019
Reviewed-by: Marcus Tillmanns <marcus.tillmanns@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>

16 files changed, 263 insertions, 208 deletions

diff --git a/share/qtcreator/debugger/creatortypes.py b/share/qtcreator/debugger/creatortypes.py
index af79054460..a11377b0db 100644
--- a/share/qtcreator/debugger/creatortypes.py
+++ b/share/qtcreator/debugger/creatortypes.py
@@ -235,7 +235,7 @@ def qdump__Utils__Port(d, value):
 
 
 
-def qdump__Utils__Environment(d, value):
+def x_qdump__Utils__Environment(d, value):
     qdump__Utils__NameValueDictionary(d, value)
 
 
@@ -243,7 +243,7 @@ def qdump__Utils__DictKey(d, value):
     d.putStringValue(value["name"])
 
 
-def qdump__Utils__NameValueDictionary(d, value):
+def x_qdump__Utils__NameValueDictionary(d, value):
     dptr = d.extractPointer(value)
     if d.qtVersion() >= 0x60000:
         if dptr == 0:
diff --git a/src/libs/utils/aspects.cpp b/src/libs/utils/aspects.cpp
index 51be951a8f..aed8c851d1 100644
--- a/src/libs/utils/aspects.cpp
+++ b/src/libs/utils/aspects.cpp
@@ -632,7 +632,7 @@ public:
     QString m_placeHolderText;
     QString m_historyCompleterKey;
     PathChooser::Kind m_expectedKind = PathChooser::File;
-    EnvironmentChange m_environmentChange;
+    Environment m_environment;
     QPointer<ElidingLabel> m_labelDisplay;
     QPointer<FancyLineEdit> m_lineEditDisplay;
     QPointer<PathChooser> m_pathChooserDisplay;
@@ -975,16 +975,11 @@ void StringAspect::setExpectedKind(const PathChooser::Kind expectedKind)
         d->m_pathChooserDisplay->setExpectedKind(expectedKind);
 }
 
-void StringAspect::setEnvironmentChange(const EnvironmentChange &change)
-{
-    d->m_environmentChange = change;
-    if (d->m_pathChooserDisplay)
-        d->m_pathChooserDisplay->setEnvironmentChange(change);
-}
-
 void StringAspect::setEnvironment(const Environment &env)
 {
-    setEnvironmentChange(EnvironmentChange::fromDictionary(env.toDictionary()));
+    d->m_environment = env;
+    if (d->m_pathChooserDisplay)
+        d->m_pathChooserDisplay->setEnvironment(env);
 }
 
 void StringAspect::setBaseFileName(const FilePath &baseFileName)
@@ -1082,7 +1077,7 @@ void StringAspect::addToLayout(Layouting::LayoutBuilder &builder)
             d->m_pathChooserDisplay->setHistoryCompleter(d->m_historyCompleterKey);
         if (d->m_validator)
             d->m_pathChooserDisplay->setValidationFunction(d->m_validator);
-        d->m_pathChooserDisplay->setEnvironmentChange(d->m_environmentChange);
+        d->m_pathChooserDisplay->setEnvironment(d->m_environment);
         d->m_pathChooserDisplay->setBaseDirectory(d->m_baseFileName);
         d->m_pathChooserDisplay->setOpenTerminalHandler(d->m_openTerminal);
         if (defaultValue() == value())
diff --git a/src/libs/utils/aspects.h b/src/libs/utils/aspects.h
index 1aaaca3f29..0b9a560659 100644
--- a/src/libs/utils/aspects.h
+++ b/src/libs/utils/aspects.h
@@ -383,7 +383,6 @@ public:
     void setPlaceHolderText(const QString &placeHolderText);
     void setHistoryCompleter(const QString &historyCompleterKey);
     void setExpectedKind(const PathChooser::Kind expectedKind);
-    void setEnvironmentChange(const EnvironmentChange &change);
     void setEnvironment(const Environment &env);
     void setBaseFileName(const FilePath &baseFileName);
     void setUndoRedoEnabled(bool readOnly);
diff --git a/src/libs/utils/environment.cpp b/src/libs/utils/environment.cpp
index 462eeab31d..e64db0e2a3 100644
--- a/src/libs/utils/environment.cpp
+++ b/src/libs/utils/environment.cpp
@@ -19,84 +19,137 @@ Q_GLOBAL_STATIC_WITH_ARGS(Environment, staticSystemEnvironment,
                           (QProcessEnvironment::systemEnvironment().toStringList()))
 Q_GLOBAL_STATIC(QVector<EnvironmentProvider>, environmentProviders)
 
+Environment::Environment()
+    : m_dict(HostOsInfo::hostOs())
+{}
+
+Environment::Environment(OsType osType)
+    : m_dict(osType)
+{}
+
+Environment::Environment(const QStringList &env, OsType osType)
+    : m_dict(osType)
+{
+    m_changeItems.append(NameValueDictionary(env, osType));
+}
+
+Environment::Environment(const NameValuePairs &nameValues)
+{
+    m_changeItems.append(NameValueDictionary(nameValues));
+}
+
+Environment::Environment(const NameValueDictionary &dict)
+{
+    m_changeItems.append(dict);
+}
+
 NameValueItems Environment::diff(const Environment &other, bool checkAppendPrepend) const
 {
-    return m_dict.diff(other.m_dict, checkAppendPrepend);
+    const NameValueDictionary &dict = resolved();
+    const NameValueDictionary &otherDict = other.resolved();
+    return dict.diff(otherDict, checkAppendPrepend);
 }
 
 Environment::FindResult Environment::find(const QString &name) const
 {
-    const auto it = m_dict.constFind(name);
-    if (it == m_dict.constEnd())
+    const NameValueDictionary &dict = resolved();
+    const auto it = dict.constFind(name);
+    if (it == dict.constEnd())
         return {};
      return Entry{it.key().name, it.value().first, it.value().second};
 }
 
 void Environment::forEachEntry(const std::function<void(const QString &, const QString &, bool)> &callBack) const
 {
-    for (auto it = m_dict.m_values.constBegin(); it != m_dict.m_values.constEnd(); ++it)
+    const NameValueDictionary &dict = resolved();
+    for (auto it = dict.m_values.constBegin(); it != dict.m_values.constEnd(); ++it)
         callBack(it.key().name, it.value().first, it.value().second);
 }
 
+bool Environment::operator==(const Environment &other) const
+{
+    const NameValueDictionary &dict = resolved();
+    const NameValueDictionary &otherDict = other.resolved();
+    return dict == otherDict;
+}
+
+bool Environment::operator!=(const Environment &other) const
+{
+    const NameValueDictionary &dict = resolved();
+    const NameValueDictionary &otherDict = other.resolved();
+    return dict != otherDict;
+}
+
+QString Environment::value(const QString &key) const
+{
+    const NameValueDictionary &dict = resolved();
+    return dict.value(key);
+}
+
+QString Environment::value_or(const QString &key, const QString &defaultValue) const
+{
+    const NameValueDictionary &dict = resolved();
+    return dict.hasKey(key) ? dict.value(key) : defaultValue;
+}
+
+bool Environment::hasKey(const QString &key) const
+{
+    const NameValueDictionary &dict = resolved();
+    return dict.hasKey(key);
+}
+
 bool Environment::hasChanges() const
 {
-    return m_dict.size() != 0;
+    const NameValueDictionary &dict = resolved();
+    return dict.size() != 0;
+}
+
+OsType Environment::osType() const
+{
+    return m_dict.m_osType;
+}
+
+QStringList Environment::toStringList() const
+{
+    const NameValueDictionary &dict = resolved();
+    return dict.toStringList();
 }
 
 QProcessEnvironment Environment::toProcessEnvironment() const
 {
+    const NameValueDictionary &dict = resolved();
     QProcessEnvironment result;
-    for (auto it = m_dict.m_values.constBegin(); it != m_dict.m_values.constEnd(); ++it) {
+    for (auto it = dict.m_values.constBegin(); it != dict.m_values.constEnd(); ++it) {
         if (it.value().second)
-            result.insert(it.key().name, expandedValueForKey(m_dict.key(it)));
+            result.insert(it.key().name, expandedValueForKey(dict.key(it)));
     }
     return result;
 }
 
 void Environment::appendOrSetPath(const FilePath &value)
 {
-    QTC_CHECK(value.osType() == osType());
+    QTC_CHECK(value.osType() == m_dict.m_osType);
     if (value.isEmpty())
         return;
-    appendOrSet("PATH", value.nativePath(),
-                QString(OsSpecificAspects::pathListSeparator(osType())));
+    appendOrSet("PATH", value.nativePath(), OsSpecificAspects::pathListSeparator(osType()));
 }
 
 void Environment::prependOrSetPath(const FilePath &value)
 {
-    QTC_CHECK(value.osType() == osType());
+    QTC_CHECK(value.osType() == m_dict.m_osType);
     if (value.isEmpty())
         return;
-    prependOrSet("PATH", value.nativePath(),
-                 QString(OsSpecificAspects::pathListSeparator(osType())));
+    prependOrSet("PATH", value.nativePath(), OsSpecificAspects::pathListSeparator(osType()));
 }
 
 void Environment::appendOrSet(const QString &key, const QString &value, const QString &sep)
 {
-    QTC_ASSERT(!key.contains('='), return );
-    const auto it = m_dict.findKey(key);
-    if (it == m_dict.m_values.end()) {
-        m_dict.m_values.insert(DictKey(key, m_dict.nameCaseSensitivity()), {value, true});
-    } else {
-        // Append unless it is already there
-        const QString toAppend = sep + value;
-        if (!it.value().first.endsWith(toAppend))
-            it.value().first.append(toAppend);
-    }
+    addItem(Item{std::in_place_index_t<AppendOrSet>(), key, value, sep});
 }
 
 void Environment::prependOrSet(const QString &key, const QString &value, const QString &sep)
 {
-    QTC_ASSERT(!key.contains('='), return );
-    const auto it = m_dict.findKey(key);
-    if (it == m_dict.m_values.end()) {
-        m_dict.m_values.insert(DictKey(key, m_dict.nameCaseSensitivity()), {value, true});
-    } else {
-        // Prepend unless it is already there
-        const QString toPrepend = value + sep;
-        if (!it.value().first.startsWith(toPrepend))
-            it.value().first.prepend(toPrepend);
-    }
+    addItem(Item{std::in_place_index_t<PrependOrSet>(), key, value, sep});
 }
 
 void Environment::prependOrSetLibrarySearchPath(const FilePath &value)
@@ -105,11 +158,11 @@ void Environment::prependOrSetLibrarySearchPath(const FilePath &value)
     switch (osType()) {
     case OsTypeWindows: {
         const QChar sep = ';';
-        prependOrSet("PATH", value.nativePath(), QString(sep));
+        prependOrSet("PATH", value.nativePath(), sep);
         break;
     }
     case OsTypeMac: {
-        const QString sep =  ":";
+        const QChar sep =  ':';
         const QString nativeValue = value.nativePath();
         prependOrSet("DYLD_LIBRARY_PATH", nativeValue, sep);
         prependOrSet("DYLD_FRAMEWORK_PATH", nativeValue, sep);
@@ -118,7 +171,7 @@ void Environment::prependOrSetLibrarySearchPath(const FilePath &value)
     case OsTypeLinux:
     case OsTypeOtherUnix: {
         const QChar sep = ':';
-        prependOrSet("LD_LIBRARY_PATH", value.nativePath(), QString(sep));
+        prependOrSet("LD_LIBRARY_PATH", value.nativePath(), sep);
         break;
     }
     default:
@@ -141,8 +194,7 @@ Environment Environment::systemEnvironment()
 
 void Environment::setupEnglishOutput()
 {
-    m_dict.set("LC_MESSAGES", "en_US.utf8");
-    m_dict.set("LANGUAGE", "en_US:en");
+    addItem(Item{std::in_place_index_t<SetupEnglishOutput>()});
 }
 
 using SearchResultCallback = std::function<IterationPolicy(const FilePath &)>;
@@ -190,7 +242,8 @@ static FilePaths appendExeExtensions(const Environment &env, const FilePath &exe
 
 QString Environment::expandedValueForKey(const QString &key) const
 {
-    return expandVariables(m_dict.value(key));
+    const NameValueDictionary &dict = resolved();
+    return expandVariables(dict.value(key));
 }
 
 static void searchInDirectoriesHelper(const SearchResultCallback &resultCallback,
@@ -324,14 +377,16 @@ void Environment::setSystemEnvironment(const Environment &environment)
  */
 QString Environment::expandVariables(const QString &input) const
 {
+    const NameValueDictionary &dict = resolved();
+
     QString result = input;
 
     if (osType() == OsTypeWindows) {
         for (int vStart = -1, i = 0; i < result.length(); ) {
             if (result.at(i++) == '%') {
                 if (vStart > 0) {
-                    const auto it = m_dict.findKey(result.mid(vStart, i - vStart - 1));
-                    if (it != m_dict.m_values.constEnd()) {
+                    const auto it = dict.findKey(result.mid(vStart, i - vStart - 1));
+                    if (it != dict.m_values.constEnd()) {
                         result.replace(vStart - 1, i - vStart + 1, it->first);
                         i = vStart - 1 + it->first.length();
                         vStart = -1;
@@ -403,6 +458,12 @@ QStringList Environment::expandVariables(const QStringList &variables) const
     return transform(variables, [this](const QString &i) { return expandVariables(i); });
 }
 
+NameValueDictionary Environment::toDictionary() const
+{
+    const NameValueDictionary &dict = resolved();
+    return dict;
+}
+
 void EnvironmentProvider::addProvider(EnvironmentProvider &&provider)
 {
     environmentProviders->append(std::move(provider));
@@ -421,63 +482,125 @@ std::optional<EnvironmentProvider> EnvironmentProvider::provider(const QByteArra
     return std::nullopt;
 }
 
-void EnvironmentChange::addSetValue(const QString &key, const QString &value)
+void Environment::addItem(const Item &item)
+{
+    m_dict.clear();
+    m_changeItems.append(item);
+}
+
+void Environment::set(const QString &key, const QString &value, bool enabled)
 {
-    m_changeItems.append(Item{std::in_place_index_t<SetValue>(), QPair<QString, QString>{key, value}});
+    addItem(Item{std::in_place_index_t<SetValue>(),
+                 std::tuple<QString, QString, bool>{key, value, enabled}});
 }
 
-void EnvironmentChange::addUnsetValue(const QString &key)
+void Environment::unset(const QString &key)
 {
-    m_changeItems.append(Item{std::in_place_index_t<UnsetValue>(), key});
+    addItem(Item{std::in_place_index_t<UnsetValue>(), key});
 }
 
-void EnvironmentChange::addPrependToPath(const FilePaths &values)
+void Environment::modify(const NameValueItems &items)
 {
+    addItem(Item{std::in_place_index_t<Modify>(), items});
+}
+
+void Environment::prependToPath(const FilePaths &values)
+{
+    m_dict.clear();
     for (int i = values.size(); --i >= 0; ) {
         const FilePath value = values.at(i);
-        m_changeItems.append(Item{std::in_place_index_t<PrependToPath>(), value});
+        m_changeItems.append(Item{
+            std::in_place_index_t<PrependOrSet>(),
+            QString("PATH"),
+            value.nativePath(),
+            value.pathListSeparator()
+        });
     }
 }
 
-void EnvironmentChange::addAppendToPath(const FilePaths &values)
+void Environment::appendToPath(const FilePaths &values)
 {
-    for (const FilePath &value : values)
-        m_changeItems.append(Item{std::in_place_index_t<AppendToPath>(), value});
+    m_dict.clear();
+    for (const FilePath &value : values) {
+        m_changeItems.append(Item{
+            std::in_place_index_t<AppendOrSet>(),
+            QString("PATH"),
+            value.nativePath(),
+            value.pathListSeparator()
+        });
+    }
 }
 
-EnvironmentChange EnvironmentChange::fromDictionary(const NameValueDictionary &dict)
+const NameValueDictionary &Environment::resolved() const
 {
-    EnvironmentChange change;
-    change.m_changeItems.append(Item{std::in_place_index_t<SetFixedDictionary>(), dict});
-    return change;
-}
+    if (m_dict.size() != 0)
+        return m_dict;
 
-void EnvironmentChange::applyToEnvironment(Environment &env) const
-{
     for (const Item &item : m_changeItems) {
         switch (item.index()) {
         case SetSystemEnvironment:
-            env = Environment::systemEnvironment();
+            m_dict = Environment::systemEnvironment().toDictionary();
             break;
         case SetFixedDictionary:
-            env = Environment(std::get<SetFixedDictionary>(item));
+            m_dict = std::get<SetFixedDictionary>(item);
             break;
         case SetValue: {
-            const QPair<QString, QString> data = std::get<SetValue>(item);
-            env.set(data.first, data.second);
+            auto [key, value, enabled] = std::get<SetValue>(item);
+            m_dict.set(key, value, enabled);
             break;
         }
         case UnsetValue:
-            env.unset(std::get<UnsetValue>(item));
+            m_dict.unset(std::get<UnsetValue>(item));
             break;
-        case PrependToPath:
-            env.prependOrSetPath(std::get<PrependToPath>(item));
+        case PrependOrSet: {
+            auto [key, value, sep] = std::get<PrependOrSet>(item);
+            QTC_ASSERT(!key.contains('='), return m_dict);
+            const auto it = m_dict.findKey(key);
+            if (it == m_dict.m_values.end()) {
+                m_dict.m_values.insert(DictKey(key, m_dict.nameCaseSensitivity()), {value, true});
+            } else {
+                // Prepend unless it is already there
+                const QString toPrepend = value + sep;
+                if (!it.value().first.startsWith(toPrepend))
+                    it.value().first.prepend(toPrepend);
+            }
             break;
-        case AppendToPath:
-            env.appendOrSetPath(std::get<AppendToPath>(item));
+        }
+        case AppendOrSet: {
+            auto [key, value, sep] = std::get<AppendOrSet>(item);
+            QTC_ASSERT(!key.contains('='), return m_dict);
+            const auto it = m_dict.findKey(key);
+            if (it == m_dict.m_values.end()) {
+                m_dict.m_values.insert(DictKey(key, m_dict.nameCaseSensitivity()), {value, true});
+            } else {
+                // Prepend unless it is already there
+                const QString toAppend = sep + value;
+                if (!it.value().first.endsWith(toAppend))
+                    it.value().first.append(toAppend);
+            }
+            break;
+        }
+        case Modify: {
+            NameValueItems items = std::get<Modify>(item);
+            m_dict.modify(items);
+            break;
+        }
+        case SetupEnglishOutput:
+            m_dict.set("LC_MESSAGES", "en_US.utf8");
+            m_dict.set("LANGUAGE", "en_US:en");
             break;
         }
     }
+
+    return m_dict;
+}
+
+Environment Environment::appliedToEnvironment(const Environment &base) const
+{
+    Environment res = base;
+    res.m_dict.clear();
+    res.m_changeItems.append(m_changeItems);
+    return res;
 }
 
 /*!
diff --git a/src/libs/utils/environment.h b/src/libs/utils/environment.h
index 541a730965..8424eb1d24 100644
--- a/src/libs/utils/environment.h
+++ b/src/libs/utils/environment.h
@@ -22,27 +22,24 @@ namespace Utils {
 class QTCREATOR_UTILS_EXPORT Environment final
 {
 public:
-    Environment() : m_dict(HostOsInfo::hostOs()) {}
-    explicit Environment(OsType osType) : m_dict(osType) {}
-    explicit Environment(const QStringList &env, OsType osType = HostOsInfo::hostOs())
-        : m_dict(env, osType) {}
-    explicit Environment(const NameValuePairs &nameValues) : m_dict(nameValues) {}
-    explicit Environment(const NameValueDictionary &dict) : m_dict(dict) {}
-
-    QString value(const QString &key) const { return m_dict.value(key); }
-    QString value_or(const QString &key, const QString &defaultValue) const
-    {
-        return m_dict.hasKey(key) ? m_dict.value(key) : defaultValue;
-    }
-    bool hasKey(const QString &key) const { return m_dict.hasKey(key); }
-
-    void set(const QString &key, const QString &value, bool enabled = true) { m_dict.set(key, value, enabled); }
-    void unset(const QString &key) { m_dict.unset(key); }
-    void modify(const NameValueItems &items) { m_dict.modify(items); }
+    Environment();
+    explicit Environment(OsType osType);
+    explicit Environment(const QStringList &env, OsType osType = HostOsInfo::hostOs());
+    explicit Environment(const NameValuePairs &nameValues);
+    explicit Environment(const NameValueDictionary &dict);
+
+    QString value(const QString &key) const;
+    QString value_or(const QString &key, const QString &defaultValue) const;
+    bool hasKey(const QString &key) const;
+
+    void set(const QString &key, const QString &value, bool enabled = true);
+    void unset(const QString &key);
+    void modify(const NameValueItems &items);
 
     bool hasChanges() const;
 
-    QStringList toStringList() const { return m_dict.toStringList(); }
+    OsType osType() const;
+    QStringList toStringList() const;
     QProcessEnvironment toProcessEnvironment() const;
 
     void appendOrSet(const QString &key, const QString &value, const QString &sep = QString());
@@ -54,6 +51,9 @@ public:
     void prependOrSetLibrarySearchPath(const FilePath &value);
     void prependOrSetLibrarySearchPaths(const FilePaths &values);
 
+    void prependToPath(const FilePaths &values);
+    void appendToPath(const FilePaths &values);
+
     void setupEnglishOutput();
 
     FilePath searchInPath(const QString &executable,
@@ -74,76 +74,58 @@ public:
     FilePath expandVariables(const FilePath &input) const;
     QStringList expandVariables(const QStringList &input) const;
 
-    OsType osType() const { return m_dict.osType(); }
-
-    NameValueDictionary toDictionary() const { return m_dict; } // FIXME: avoid
+    NameValueDictionary toDictionary() const; // FIXME: avoid
     NameValueItems diff(const Environment &other, bool checkAppendPrepend = false) const; // FIXME: avoid
 
-    void setCombineWithDeviceEnvironment(bool combine) { m_combineWithDeviceEnvironment = combine; }
-    bool combineWithDeviceEnvironment() const { return m_combineWithDeviceEnvironment; }
-
     struct Entry { QString key; QString value; bool enabled; };
     using FindResult = std::optional<Entry>;
     FindResult find(const QString &name) const; // Note res->key may differ in case from name.
 
     void forEachEntry(const std::function<void (const QString &, const QString &, bool)> &callBack) const;
 
-    friend bool operator!=(const Environment &first, const Environment &second)
-    {
-        return first.m_dict != second.m_dict;
-    }
-
-    friend bool operator==(const Environment &first, const Environment &second)
-    {
-        return first.m_dict == second.m_dict;
-    }
+    bool operator!=(const Environment &other) const;
+    bool operator==(const Environment &other) const;
 
     static Environment systemEnvironment();
 
     static void modifySystemEnvironment(const EnvironmentItems &list); // use with care!!!
     static void setSystemEnvironment(const Environment &environment);  // don't use at all!!!
 
-private:
-    NameValueDictionary m_dict;
-    bool m_combineWithDeviceEnvironment = true;
-};
-
-class QTCREATOR_UTILS_EXPORT EnvironmentChange final
-{
-public:
-    EnvironmentChange() = default;
-
     enum Type {
         SetSystemEnvironment,
         SetFixedDictionary,
         SetValue,
         UnsetValue,
-        PrependToPath,
-        AppendToPath,
+        PrependOrSet,
+        AppendOrSet,
+        Modify,
+        SetupEnglishOutput,
     };
 
     using Item = std::variant<
-        std::monostate,          // SetSystemEnvironment dummy
-        NameValueDictionary,     // SetFixedDictionary
-        QPair<QString, QString>, // SetValue
-        QString,                 // UnsetValue
-        FilePath,                // PrependToPath
-        FilePath                 // AppendToPath
+        std::monostate,                          // SetSystemEnvironment dummy
+        NameValueDictionary,                     // SetFixedDictionary
+        std::tuple<QString, QString, bool>,      // SetValue (key, value, enabled)
+        QString,                                 // UnsetValue (key)
+        std::tuple<QString, QString, QString>,   // PrependOrSet (key, value, separator)
+        std::tuple<QString, QString, QString>,   // AppendOrSet (key, value, separator)
+        NameValueItems,                          // Modify
+        std::monostate                           // SetupEnglishOutput
     >;
 
-    static EnvironmentChange fromDictionary(const NameValueDictionary &dict);
+    void addItem(const Item &item);
 
-    void applyToEnvironment(Environment &) const;
+    Environment appliedToEnvironment(const Environment &base) const;
 
-    void addSetValue(const QString &key, const QString &value);
-    void addUnsetValue(const QString &key);
-    void addPrependToPath(const FilePaths &values);
-    void addAppendToPath(const FilePaths &values);
+    const NameValueDictionary &resolved() const;
 
 private:
-    QList<Item> m_changeItems;
+    mutable QList<Item> m_changeItems;
+    mutable NameValueDictionary m_dict; // Latest resolved.
 };
 
+using EnviromentChange = Environment;
+
 class QTCREATOR_UTILS_EXPORT EnvironmentProvider
 {
 public:
diff --git a/src/libs/utils/filepath.h b/src/libs/utils/filepath.h
index 0ecdc09dab..220c6de5da 100644
--- a/src/libs/utils/filepath.h
+++ b/src/libs/utils/filepath.h
@@ -32,7 +32,6 @@ namespace Utils {
 
 class DeviceFileAccess;
 class Environment;
-class EnvironmentChange;
 enum class FileStreamHandle;
 
 template <class ...Args> using Continuation = std::function<void(Args...)>;
diff --git a/src/libs/utils/launchersocket.cpp b/src/libs/utils/launchersocket.cpp
index f4feda595a..ccf2ee7b2f 100644
--- a/src/libs/utils/launchersocket.cpp
+++ b/src/libs/utils/launchersocket.cpp
@@ -246,6 +246,8 @@ void CallerHandle::start(const QString &program, const QStringList &arguments)
     p.command = m_command;
     p.arguments = m_arguments;
     p.env = m_setup->m_environment.toStringList();
+    if (p.env.isEmpty())
+        p.env = Environment::systemEnvironment().toStringList();
     p.workingDir = m_setup->m_workingDirectory.path();
     p.processMode = m_setup->m_processMode;
     p.writeData = m_setup->m_writeData;
diff --git a/src/libs/utils/pathchooser.cpp b/src/libs/utils/pathchooser.cpp
index 53825931b9..0f0737f54c 100644
--- a/src/libs/utils/pathchooser.cpp
+++ b/src/libs/utils/pathchooser.cpp
@@ -171,7 +171,7 @@ public:
     FilePath m_initialBrowsePathOverride;
     QString m_defaultValue;
     FilePath m_baseDirectory;
-    EnvironmentChange m_environmentChange;
+    Environment m_environment;
     BinaryVersionToolTipEventFilter *m_binaryVersionToolTipEventFilter = nullptr;
     QList<QAbstractButton *> m_buttons;
     const MacroExpander *m_macroExpander = globalMacroExpander();
@@ -196,8 +196,7 @@ FilePath PathChooserPrivate::expandedPath(const FilePath &input) const
 
     FilePath path = input;
 
-    Environment env = path.deviceEnvironment();
-    m_environmentChange.applyToEnvironment(env);
+    Environment env = m_environment.appliedToEnvironment(path.deviceEnvironment());
     path = env.expandVariables(path);
 
     if (m_macroExpander)
@@ -324,20 +323,15 @@ void PathChooser::setBaseDirectory(const FilePath &base)
     triggerChanged();
 }
 
-void PathChooser::setEnvironment(const Environment &env)
-{
-    setEnvironmentChange(EnvironmentChange::fromDictionary(env.toDictionary()));
-}
-
 FilePath PathChooser::baseDirectory() const
 {
     return d->m_baseDirectory;
 }
 
-void PathChooser::setEnvironmentChange(const EnvironmentChange &env)
+void PathChooser::setEnvironment(const Environment &env)
 {
     QString oldExpand = filePath().toString();
-    d->m_environmentChange = env;
+    d->m_environment = env;
     if (filePath().toString() != oldExpand) {
         triggerChanged();
         emit rawPathChanged();
diff --git a/src/libs/utils/pathchooser.h b/src/libs/utils/pathchooser.h
index 92b5973b2d..62a370185d 100644
--- a/src/libs/utils/pathchooser.h
+++ b/src/libs/utils/pathchooser.h
@@ -20,7 +20,6 @@ namespace Utils {
 class CommandLine;
 class MacroExpander;
 class Environment;
-class EnvironmentChange;
 class PathChooserPrivate;
 
 class QTCREATOR_UTILS_EXPORT PathChooser : public QWidget
@@ -77,7 +76,6 @@ public:
     void setBaseDirectory(const FilePath &base);
 
     void setEnvironment(const Environment &env);
-    void setEnvironmentChange(const EnvironmentChange &change);
 
     /** Returns the suggested label title when used in a form layout. */
     static QString label();
diff --git a/src/libs/utils/qtcprocess.cpp b/src/libs/utils/qtcprocess.cpp
index 04276a610b..5220e8b5d5 100644
--- a/src/libs/utils/qtcprocess.cpp
+++ b/src/libs/utils/qtcprocess.cpp
@@ -353,13 +353,18 @@ public:
             return;
         }
 
+        QProcessEnvironment penv = m_setup.m_environment.toProcessEnvironment();
+        if (penv.isEmpty())
+            penv = Environment::systemEnvironment().toProcessEnvironment();
+        const QStringList senv = penv.toStringList();
+
         bool startResult
             = m_ptyProcess->startProcess(program,
                                          HostOsInfo::isWindowsHost()
                                              ? QStringList{m_setup.m_nativeArguments} << arguments
                                              : arguments,
                                          m_setup.m_workingDirectory.nativePath(),
-                                         m_setup.m_environment.toProcessEnvironment().toStringList(),
+                                         senv,
                                          m_setup.m_ptyData->size().width(),
                                          m_setup.m_ptyData->size().height());
 
@@ -458,7 +463,9 @@ private:
         handler->setWindowsSpecificStartupFlags(m_setup.m_belowNormalPriority,
                                                 m_setup.m_createConsoleOnWindows);
 
-        m_process->setProcessEnvironment(m_setup.m_environment.toProcessEnvironment());
+        const QProcessEnvironment penv = m_setup.m_environment.toProcessEnvironment();
+        if (!penv.isEmpty())
+            m_process->setProcessEnvironment(penv);
         m_process->setWorkingDirectory(m_setup.m_workingDirectory.path());
         m_process->setStandardInputFile(m_setup.m_standardInputFile);
         m_process->setProcessChannelMode(m_setup.m_processChannelMode);
@@ -715,7 +722,6 @@ public:
         , q(parent)
         , m_killTimer(this)
     {
-        m_setup.m_controlEnvironment = Environment::systemEnvironment();
         m_killTimer.setSingleShot(true);
         connect(&m_killTimer, &QTimer::timeout, this, [this] {
             m_killTimer.stop();
@@ -769,22 +775,6 @@ public:
         return rootCommand;
     }
 
-    Environment fullEnvironment() const
-    {
-        Environment env = m_setup.m_environment;
-        if (!env.hasChanges() && env.combineWithDeviceEnvironment()) {
-            // FIXME: Either switch to using EnvironmentChange instead of full Environments, or
-            // feed the full environment into the QtcProcess instead of fixing it up here.
-            //            qWarning("QtcProcess::start: Empty environment set when running '%s'.",
-            //                 qPrintable(m_setup.m_commandLine.executable().toString()));
-            env = m_setup.m_commandLine.executable().deviceEnvironment();
-        }
-        // TODO: needs SshSettings
-        //        if (m_runAsRoot)
-        //            RunControl::provideAskPassEntry(env);
-        return env;
-    }
-
     QtcProcess *q;
     std::unique_ptr<ProcessBlockingInterface> m_blockingInterface;
     std::unique_ptr<ProcessInterface> m_process;
@@ -1227,7 +1217,6 @@ void QtcProcess::start()
     d->m_state = QProcess::Starting;
     d->m_process->m_setup = d->m_setup;
     d->m_process->m_setup.m_commandLine = d->fullCommandLine();
-    d->m_process->m_setup.m_environment = d->fullEnvironment();
     d->emitGuardedSignal(&QtcProcess::starting);
     d->m_process->start();
 }
diff --git a/src/plugins/cmakeprojectmanager/presetsparser.cpp b/src/plugins/cmakeprojectmanager/presetsparser.cpp
index ceb67a50be..06c12de840 100644
--- a/src/plugins/cmakeprojectmanager/presetsparser.cpp
+++ b/src/plugins/cmakeprojectmanager/presetsparser.cpp
@@ -482,16 +482,6 @@ static QHash<QString, QString> merge(const QHash<QString, QString> &first,
     return result;
 }
 
-static Utils::Environment merge(const Utils::Environment &first, const Utils::Environment &second)
-{
-    Utils::Environment result = first;
-    second.forEachEntry([&](const QString &key, const QString &value, bool) {
-        result.set(key, value);
-    });
-
-    return result;
-}
-
 static CMakeConfig merge(const CMakeConfig &first, const CMakeConfig &second)
 {
     return Utils::setUnionMerge<CMakeConfig>(
@@ -549,7 +539,7 @@ void PresetsDetails::ConfigurePreset::inheritFrom(const ConfigurePreset &other)
     if (!environment && other.environment)
         environment = other.environment;
     else if (environment && other.environment)
-        environment = merge(other.environment.value(), environment.value());
+        environment = environment.value().appliedToEnvironment(other.environment.value());
 
     if (!warnings && other.warnings)
         warnings = other.warnings;
@@ -575,7 +565,7 @@ void PresetsDetails::BuildPreset::inheritFrom(const BuildPreset &other)
     if (!environment && other.environment)
         environment = other.environment;
     else if (environment && other.environment)
-        environment = merge(other.environment.value(), environment.value());
+        environment = environment.value().appliedToEnvironment(other.environment.value());
 
     if (!configurePreset && other.configurePreset)
         configurePreset = other.configurePreset;
diff --git a/src/plugins/coreplugin/systemsettings.cpp b/src/plugins/coreplugin/systemsettings.cpp
index f34e7fb5b7..a65f7fee8b 100644
--- a/src/plugins/coreplugin/systemsettings.cpp
+++ b/src/plugins/coreplugin/systemsettings.cpp
@@ -438,9 +438,9 @@ void SystemSettingsWidget::resetFileBrowser()
 
 void SystemSettingsWidget::updatePath()
 {
-    EnvironmentChange change;
-    change.addAppendToPath(VcsManager::additionalToolsPath());
-    m_patchChooser->setEnvironmentChange(change);
+    Environment env;
+    env.appendToPath(VcsManager::additionalToolsPath());
+    m_patchChooser->setEnvironment(env);
 }
 
 void SystemSettingsWidget::updateEnvironmentChangesLabel()
diff --git a/src/plugins/projectexplorer/runconfigurationaspects.cpp b/src/plugins/projectexplorer/runconfigurationaspects.cpp
index 9ba24c0467..7e278d353e 100644
--- a/src/plugins/projectexplorer/runconfigurationaspects.cpp
+++ b/src/plugins/projectexplorer/runconfigurationaspects.cpp
@@ -570,19 +570,12 @@ void ExecutableAspect::setExpectedKind(const PathChooser::Kind expectedKind)
    Sets the environment in which paths will be searched when the expected kind
    of paths is chosen as PathChooser::Command or PathChooser::ExistingCommand
    to \a env.
-
-   \sa Utils::StringAspect::setEnvironmentChange()
 */
-void ExecutableAspect::setEnvironmentChange(const EnvironmentChange &change)
-{
-    m_executable.setEnvironmentChange(change);
-    if (m_alternativeExecutable)
-        m_alternativeExecutable->setEnvironmentChange(change);
-}
-
 void ExecutableAspect::setEnvironment(const Environment &env)
 {
-    setEnvironmentChange(EnvironmentChange::fromDictionary(env.toDictionary()));
+    m_executable.setEnvironment(env);
+    if (m_alternativeExecutable)
+        m_alternativeExecutable->setEnvironment(env);
 }
 
 /*!
diff --git a/src/plugins/projectexplorer/runconfigurationaspects.h b/src/plugins/projectexplorer/runconfigurationaspects.h
index 9e948bc6ec..9656c2f5bd 100644
--- a/src/plugins/projectexplorer/runconfigurationaspects.h
+++ b/src/plugins/projectexplorer/runconfigurationaspects.h
@@ -168,7 +168,6 @@ public:
     void setPlaceHolderText(const QString &placeHolderText);
     void setHistoryCompleter(const QString &historyCompleterKey);
     void setExpectedKind(const Utils::PathChooser::Kind expectedKind);
-    void setEnvironmentChange(const Utils::EnvironmentChange &change);
     void setEnvironment(const Utils::Environment &env);
     void setDisplayStyle(Utils::StringAspect::DisplayStyle style);
 
diff --git a/src/plugins/remotelinux/linuxdevice.cpp b/src/plugins/remotelinux/linuxdevice.cpp
index 191ee9d5d3..aa5889516c 100644
--- a/src/plugins/remotelinux/linuxdevice.cpp
+++ b/src/plugins/remotelinux/linuxdevice.cpp
@@ -338,9 +338,6 @@ Environment LinuxDevicePrivate::getEnvironment()
 
     QtcProcess getEnvProc;
     getEnvProc.setCommand({FilePath("env").onDevice(q->rootPath()), {}});
-    Environment inEnv;
-    inEnv.setCombineWithDeviceEnvironment(false);
-    getEnvProc.setEnvironment(inEnv);
     getEnvProc.runBlocking();
 
     const QString remoteOutput = getEnvProc.cleanedStdOut();
@@ -919,16 +916,11 @@ LinuxDevice::LinuxDevice()
             d->m_terminals.removeOne(proc);
         });
 
-        // We recreate the same way that QtcProcess uses to create the actual environment.
-        const Environment finalEnv = (!env.hasChanges() && env.combineWithDeviceEnvironment())
-                                         ? d->getEnvironment()
-                                         : env;
         // If we will not set any environment variables, we can leave out the shell executable
         // as the "ssh ..." call will automatically launch the default shell if there are
         // no arguments. But if we will set environment variables, we need to explicitly
         // specify the shell executable.
-        const QString shell = finalEnv.hasChanges() ? finalEnv.value_or("SHELL", "/bin/sh")
-                                                    : QString();
+        const QString shell = env.hasChanges() ? env.value_or("SHELL", "/bin/sh") : QString();
 
         proc->setCommand({filePath(shell), {}});
         proc->setTerminalMode(TerminalMode::On);
diff --git a/src/plugins/vcsbase/commonvcssettings.cpp b/src/plugins/vcsbase/commonvcssettings.cpp
index 160095d38d..2f970ccbb8 100644
--- a/src/plugins/vcsbase/commonvcssettings.cpp
+++ b/src/plugins/vcsbase/commonvcssettings.cpp
@@ -135,9 +135,9 @@ CommonSettingsWidget::CommonSettingsWidget(CommonOptionsPage *page)
 
 void CommonSettingsWidget::updatePath()
 {
-    EnvironmentChange change;
-    change.addAppendToPath(Core::VcsManager::additionalToolsPath());
-    m_page->settings().sshPasswordPrompt.setEnvironmentChange(change);
+    Environment env;
+    env.appendToPath(Core::VcsManager::additionalToolsPath());
+    m_page->settings().sshPasswordPrompt.setEnvironment(env);
 }
 
 void CommonSettingsWidget::apply()