fix #20645 - implement C++ style init-statement for if

compiler/src/dmd/cparse.d

@@ -514,7 +514,7 @@ final class CParser(AST) : Parser!AST
             else
                 elsebody = null;
             if (condition && ifbody)
-                s = new AST.IfStatement(loc, null, condition, ifbody, elsebody, token.loc);
+                s = new AST.IfStatement(loc, null, condition, null, ifbody, elsebody, token.loc);
             else
                 s = null; // don't propagate parsing errors
             break;

compiler/src/dmd/dsymbolsem.d

@@ -2700,7 +2700,7 @@ private extern(C++) final class DsymbolSemanticVisitor : Visitor
             }
             IntegerExp cmp = isDestructor ? IntegerExp.literal!0 : IntegerExp.literal!1;
             e = new EqualExp(EXP.notEqual, Loc.initial, e, cmp);
-            s = new IfStatement(Loc.initial, null, e, new ReturnStatement(Loc.initial, null), null, Loc.initial);
+            s = new IfStatement(Loc.initial, null, e, null, new ReturnStatement(Loc.initial, null), null, Loc.initial);
 
             sa.push(s);
             if (sd.fbody)

compiler/src/dmd/inline.d

@@ -325,7 +325,7 @@ public:
 
         static if (asStatements)
         {
-            result = new IfStatement(s.loc, s.param, econd, ifbody, elsebody, s.endloc);
+            result = new IfStatement(s.loc, s.param, econd, s._init, ifbody, elsebody, s.endloc);
         }
         else
         {
@@ -1034,7 +1034,7 @@ public:
                     return null;
                 auto ifbody   = !s1 ? new ExpStatement(e.e1.loc, e.e1) : s1;
                 auto elsebody = !s2 ? new ExpStatement(e.e2.loc, e.e2) : s2;
-                return new IfStatement(exp.loc, null, e.econd, ifbody, elsebody, exp.loc);
+                return new IfStatement(exp.loc, null, e.econd, null, ifbody, elsebody, exp.loc);
             }
             if (auto e = exp.isCommaExp())
             {

compiler/src/dmd/parse.d

@@ -6246,10 +6246,20 @@
             }
         case TOK.if_:
             {
+                AST.Statement _init;
                 nextToken();
                 check(TOK.leftParenthesis);
                 auto param = parseAssignCondition();
-                auto condition = parseExpression();
+                // if ( _init ; condition )
+                if (token.value == TOK.semicolon)
+                {
+                    const lookingForElseSave = lookingForElse;
+                    lookingForElse = Loc.initial;
+                    _init = parseStatement(0);
+                    lookingForElse = lookingForElseSave;
+                    nextToken();
+                }
+                AST.Expression condition = parseExpression();
                 closeCondition("if", param, condition);
 
                 {
@@ -6268,7 +6278,7 @@
                 else
                     elsebody = null;
                 if (condition && ifbody)
-                    s = new AST.IfStatement(loc, param, condition, ifbody, elsebody, token.loc);
+                    s = new AST.IfStatement(loc, param, condition, _init, ifbody, elsebody, token.loc);
                 else
                     s = null; // don't propagate parsing errors
                 break;

compiler/src/dmd/statement.d

@@ -937,16 +937,18 @@ extern (C++) final class IfStatement : Statement
 {
     Parameter param;
     Expression condition;
+    Statement _init;     // if ( init ; condition )
     Statement ifbody;
     Statement elsebody;
     VarDeclaration match;   // for MatchExpression results
     Loc endloc;                 // location of closing curly bracket
 
-    extern (D) this(const ref Loc loc, Parameter param, Expression condition, Statement ifbody, Statement elsebody, Loc endloc) @safe
+    extern (D) this(const ref Loc loc, Parameter param, Expression condition, Statement _init, Statement ifbody, Statement elsebody, Loc endloc) @safe
     {
         super(loc, STMT.If);
         this.param = param;
         this.condition = condition;
+        this._init = _init;
         this.ifbody = ifbody;
         this.elsebody = elsebody;
         this.endloc = endloc;
@@ -957,6 +959,7 @@ extern (C++) final class IfStatement : Statement
         return new IfStatement(loc,
             param ? param.syntaxCopy() : null,
             condition.syntaxCopy(),
+            _init ? _init.syntaxCopy() : null,
             ifbody ? ifbody.syntaxCopy() : null,
             elsebody ? elsebody.syntaxCopy() : null,
             endloc);

compiler/src/dmd/statement.h

@@ -366,6 +366,7 @@ class IfStatement final : public Statement
 public:
     Parameter *param;
     Expression *condition;
+    Statement* _init;
     Statement *ifbody;
     Statement *elsebody;
     VarDeclaration *match;      // for MatchExpression results

compiler/src/dmd/statementsem.d

@@ -547,7 +547,7 @@
              *     else
              *     { break; }
              */
-            _body = new IfStatement(ws.loc, ws.param, ws.condition, ws._body, new BreakStatement(ws.loc, null), ws.endloc);
+            _body = new IfStatement(ws.loc, ws.param, ws.condition, null, ws._body, new BreakStatement(ws.loc, null), ws.endloc);
             cond = IntegerExp.createBool(true);
         }
         Statement s = new ForStatement(ws.loc, null, cond, null, _body, ws.endloc);
@@ -591,6 +591,30 @@
         result = ds;
     }
 
+    /* Rewrites:
+     * controlflow (auto v1 = i1, v2 = i2; condition [; increment]) { ... }
+     * to:
+     *  { auto v1 = i1, v2 = i2; controlflow ([;] condition [; increment]) { ... } }
+     * then lowered to:
+     *  auto v1 = i1;
+     *  try {
+     *    auto v2 = i2;
+     *    try {
+     *      controlflow ([;] condition [; increment]) { ... }
+     *    } finally { v2.~this(); }
+     *  } finally { v1.~this(); }
+     *  where controlflow = `for` or `if`
+     */
+    Statement expandInit(S)(S cfs)
+    {
+        auto ainit = new Statements();
+        ainit.push(cfs._init);
+        cfs._init = null;
+        ainit.push(cfs);
+        Statement s = new CompoundStatement(cfs.loc, ainit);
+        s = new ScopeStatement(cfs.loc, s, cfs.endloc);
+        return s.statementSemantic(sc);
+    }
     void visitFor(ForStatement fs)
     {
         /* https://dlang.org/spec/statement.html#for-statement
@@ -599,26 +623,7 @@
 
         if (fs._init)
         {
-            /* Rewrite:
-             *  for (auto v1 = i1, v2 = i2; condition; increment) { ... }
-             * to:
-             *  { auto v1 = i1, v2 = i2; for (; condition; increment) { ... } }
-             * then lowered to:
-             *  auto v1 = i1;
-             *  try {
-             *    auto v2 = i2;
-             *    try {
-             *      for (; condition; increment) { ... }
-             *    } finally { v2.~this(); }
-             *  } finally { v1.~this(); }
-             */
-            auto ainit = new Statements();
-            ainit.push(fs._init);
-            fs._init = null;
-            ainit.push(fs);
-            Statement s = new CompoundStatement(fs.loc, ainit);
-            s = new ScopeStatement(fs.loc, s, fs.endloc);
-            s = s.statementSemantic(sc);
+            Statement s = expandInit(fs);
             if (!s.isErrorStatement())
             {
                 if (LabelStatement ls = checkLabeledLoop(sc, fs))
@@ -1637,6 +1642,11 @@
         /* https://dlang.org/spec/statement.html#IfStatement
          */
 
+        if (ifs._init)
+        {
+            result = expandInit(ifs);
+            return;
+        }
         // check in syntax level
         ifs.condition = checkAssignmentAsCondition(ifs.condition, sc);
 
@@ -4161,7 +4171,7 @@
 
             Expression ec = new IdentifierExp(loc, Id.ctfe);
             ec = new NotExp(loc, ec);
-            Statement s = new IfStatement(loc, null, ec, new ExpStatement(loc, e), null, loc);
+            Statement s = new IfStatement(loc, null, ec, null, new ExpStatement(loc, e), null, loc);
             c.handler = new TryFinallyStatement(loc, c.handler, s);
         }
 
@@ -4266,7 +4276,7 @@
 
                 e = new VarExp(Loc.initial, v);
                 e = new NotExp(Loc.initial, e);
-                sfinally = new IfStatement(Loc.initial, null, e, s, null, Loc.initial);
+                sfinally = new IfStatement(Loc.initial, null, e, null, s, null, Loc.initial);
 
                 break;
             }

compiler/test/runnable/controlflow_init.d

@@ -0,0 +1,12 @@
+
+
+int main()
+{
+    if (int a = 4; a)
+    {
+
+    }
+    else
+        assert(0);
+    return 0;
+}