Add support for declarations in switch expressions (#505)

Co-authored-by: Jan Jurzitza <gh@webfreak.org>

Author: Mai-Lapyst

src/dparse/ast.d

@@ -3147,11 +3147,18 @@ final class SwitchStatement : BaseNode
 {
     override void accept(ASTVisitor visitor) const
     {
-        mixin (visitIfNotNull!(expression, statement));
+        mixin (visitIfNotNull!(condition, statement));
     }
-    /** */ Expression expression;
+    /** */ IfCondition condition;
     /** */ Statement statement;
     mixin OpEquals;
+
+    deprecated("use condition.expression") inout(Expression) expression() inout @property @safe nothrow @nogc pure
+    {
+        if (!condition)
+            return null;
+        return condition.expression;
+    }
 }
 
 ///

src/dparse/formatter.d

@@ -2958,15 +2958,15 @@ class Formatter(Sink)
         debug(verbose) writeln("SwitchStatement");
 
         /**
-        Expression expression;
+        IfCondition condition;
         Statement statement;
         **/
 
         with(switchStatement)
         {
             newThing(What.other);
             isFinal ? put(" final switch(") : put("switch(");
-            format(expression);
+            format(condition);
             put(")");
 
             bool needBlock = statement.statementNoCaseNoDefault &&

src/dparse/parser.d

@@ -6755,17 +6755,13 @@ class Parser
         // DCD #453
         // with just `switch(stuff` returns a non null node,
         // which allows DCD to gives completion on `stuff`.
-        if (auto e = parseExpression())
+        mixin(parseNodeQ!(`node.condition`, `IfCondition`));
+        if (currentIs(tok!")"))
         {
-            node.expression = e;
-            if (currentIs(tok!")"))
-            {
-                advance();
-                // returns null only from here.
-                mixin(parseNodeQ!(`node.statement`, `Statement`));
-            }
+            advance();
+            // returns null only from here.
+            mixin(parseNodeQ!(`node.statement`, `Statement`));
         }
-        else error("Expression expected after `switch(`", false);
         node.tokens = tokens[startIndex .. index];
         return node;
     }

test/ast_checks/switch_condition.d

@@ -0,0 +1,35 @@
+void a()
+{
+	switch (auto line = readln)
+	{
+		default:
+			line.strip;
+	}
+}
+
+void b()
+{
+	switch (scope line = readln)
+	{
+		default:
+			line.strip;
+	}
+}
+
+void c()
+{
+	switch (const line = readln)
+	{
+		default:
+			line.strip;
+	}
+}
+
+void d()
+{
+	switch (const inout string line = readln)
+	{
+		default:
+			line.strip;
+	}
+}

test/ast_checks/switch_condition.txt

@@ -0,0 +1,28 @@
+//functionDeclaration[name = 'a']//functionBody//switchStatement/condition/auto
+not(//functionDeclaration[name = 'a']//functionBody//switchStatement/condition/scope)
+//functionDeclaration[name = 'a']//functionBody//switchStatement/condition/identifier[text()='line']
+//functionDeclaration[name = 'a']//functionBody//switchStatement/condition/unaryExpression//identifier[text()='readln']
+//functionDeclaration[name = 'a']//functionBody//switchStatement/statement//defaultStatement//identifier[text()='line']
+//functionDeclaration[name = 'a']//functionBody//switchStatement/statement//defaultStatement//identifier[text()='strip']
+not(//functionDeclaration[name = 'b']//functionBody//switchStatement/condition/auto)
+//functionDeclaration[name = 'b']//functionBody//switchStatement/condition/scope
+//functionDeclaration[name = 'b']//functionBody//switchStatement/condition/identifier[text()='line']
+//functionDeclaration[name = 'b']//functionBody//switchStatement/condition/unaryExpression//identifier[text()='readln']
+//functionDeclaration[name = 'b']//functionBody//switchStatement/statement//defaultStatement//identifier[text()='line']
+//functionDeclaration[name = 'b']//functionBody//switchStatement/statement//defaultStatement//identifier[text()='strip']
+not(//functionDeclaration[name = 'c']//functionBody//switchStatement/condition/auto)
+not(//functionDeclaration[name = 'c']//functionBody//switchStatement/condition/scope)
+//functionDeclaration[name = 'c']//functionBody//switchStatement/condition/typeConstructor[text()='const']
+//functionDeclaration[name = 'c']//functionBody//switchStatement/condition/identifier[text()='line']
+//functionDeclaration[name = 'c']//functionBody//switchStatement/condition/unaryExpression//identifier[text()='readln']
+//functionDeclaration[name = 'c']//functionBody//switchStatement/statement//defaultStatement//identifier[text()='line']
+//functionDeclaration[name = 'c']//functionBody//switchStatement/statement//defaultStatement//identifier[text()='strip']
+not(//functionDeclaration[name = 'd']//functionBody//switchStatement/condition/auto)
+not(//functionDeclaration[name = 'd']//functionBody//switchStatement/condition/scope)
+//functionDeclaration[name = 'd']//functionBody//switchStatement/condition/typeConstructor[text()='const']
+//functionDeclaration[name = 'd']//functionBody//switchStatement/condition/typeConstructor[text()='inout']
+//functionDeclaration[name = 'd']//functionBody//switchStatement/condition/type[@pretty='string']
+//functionDeclaration[name = 'd']//functionBody//switchStatement/condition/identifier[text()='line']
+//functionDeclaration[name = 'd']//functionBody//switchStatement/condition/unaryExpression//identifier[text()='readln']
+//functionDeclaration[name = 'd']//functionBody//switchStatement/statement//defaultStatement//identifier[text()='line']
+//functionDeclaration[name = 'd']//functionBody//switchStatement/statement//defaultStatement//identifier[text()='strip']

test/pass_files/switch_condition_assignment.d

@@ -0,0 +1,14 @@
+import std : writeln, format;
+
+int get()
+{
+    return 1;
+}
+
+void main()
+{
+    switch (auto x = get()) {
+        default:
+            writeln("inside switch: ", x);
+    }
+}