[TEST ONLY] Enable preview=in by default

compiler/src/dmd/dinterpret.d

@@ -2117,6 +2117,16 @@ public:
                     return CTFEExp.cantexp;
                 assert(e.type);
 
+                // There's a terrible hack in `dmd.dsymbolsem` that special case
+                // a struct with all zeros to an `ExpInitializer(BlitExp(IntegerExp(0)))`
+                // There's matching code for it in e2ir (toElem's visitAssignExp),
+                // so we need the same hack here.
+                // This does not trigger for global as they get a normal initializer.
+                if (auto ts = e.type.isTypeStruct())
+                    if (auto ae = e.isBlitExp())
+                        if (ae.e2.op == EXP.int64)
+                            e = ts.defaultInitLiteral(loc);
+
                 if (e.op == EXP.construct || e.op == EXP.blit)
                 {
                     AssignExp ae = cast(AssignExp)e;

compiler/src/dmd/globals.d

@@ -162,7 +162,7 @@ extern (C++) struct Param
                                  // https://digitalmars.com/d/archives/digitalmars/D/Binding_rvalues_to_ref_parameters_redux_325087.html
                                  // Implementation: https://github.com/dlang/dmd/pull/9817
     FeatureState noSharedAccess; // read/write access to shared memory objects
-    bool previewIn;              // `in` means `[ref] scope const`, accepts rvalues
+    bool previewIn = true;       // `in` means `[ref] scope const`, accepts rvalues
     bool inclusiveInContracts;   // 'in' contracts of overridden methods must be a superset of parent contract
     bool shortenedMethods = true;       // allow => in normal function declarations
     bool fixImmutableConv;       // error on unsound immutable conversion - https://github.com/dlang/dmd/pull/14070

compiler/test/compilable/test17351.d

@@ -1,3 +1,4 @@
+// PERMUTE_ARGS: -preview=in
 bool fun(S)(ref S[3] a) { assert(a == [42, 84, 169]); return true; }
 bool fun2(S)(ref S a) { return true; }
 void main()
@@ -14,4 +15,12 @@ void test2()
 {
     static immutable int[2] P = [ 0, 1 ];
     static assert(f2(P) == 1);
+    immutable BigInt a, b;
+    static assert(glob1.twice == b.twice);
+    static assert(a.twice == b.twice);
 }
+
+struct BigInt { int[64] big; }
+BigInt twice (in BigInt v) @safe pure nothrow @nogc { return v; }
+
+immutable BigInt glob1 = BigInt.init;

compiler/test/compilable/testfptr.d

@@ -107,17 +107,12 @@ void bug3797()
     static assert(!is(typeof( purefunc = nonpurefunc )));
     static assert( is(typeof( nonpurefunc = purefunc )));
 
-    // Cannot convert parameter storage classes (except const to in and in to const)
-
-    void function(const(int)) constfunc;
+    // Cannot convert parameter storage classes
     void function(in int) infunc;
     void function(out int) outfunc;
     void function(ref int) reffunc;
     void function(lazy int) lazyfunc;
 
-    static assert(is(typeof( infunc = constfunc )));
-    static assert(is(typeof( constfunc = infunc )));
-
     static assert(!is(typeof( infunc = outfunc )));
     static assert(!is(typeof( infunc = reffunc )));
     static assert(!is(typeof( infunc = lazyfunc )));
@@ -250,17 +245,12 @@ void bug3797dg()
     static assert(!is(typeof( purefunc = nonpurefunc )));
     static assert( is(typeof( nonpurefunc = purefunc )));
 
-    // Cannot convert parameter storage classes (except const to in and in to const)
-
-    void delegate(const(int)) constfunc;
+    // Cannot convert parameter storage classes
     void delegate(in int) infunc;
     void delegate(out int) outfunc;
     void delegate(ref int) reffunc;
     void delegate(lazy int) lazyfunc;
 
-    static assert(is(typeof( infunc = constfunc )));
-    static assert(is(typeof( constfunc = infunc )));
-
     static assert(!is(typeof( infunc = outfunc )));
     static assert(!is(typeof( infunc = reffunc )));
     static assert(!is(typeof( infunc = lazyfunc )));

compiler/test/fail_compilation/deprecatedinref.d

@@ -2,8 +2,8 @@
 REQUIRED_ARGS: -de
 TEST_OUTPUT:
 ---
-fail_compilation/deprecatedinref.d(9): Deprecation: using `in ref` is deprecated, use `-preview=in` and `in` instead
-fail_compilation/deprecatedinref.d(10): Deprecation: using `ref in` is deprecated, use `-preview=in` and `in` instead
+fail_compilation/deprecatedinref.d(9): Error: attribute `ref` is redundant with previously-applied `in`
+fail_compilation/deprecatedinref.d(10): Error: attribute `in` cannot be added after `ref`: remove `ref`
 ---
 */
 void foo(in ref int);

compiler/test/fail_compilation/deprecations_preview_in.d

@@ -2,7 +2,7 @@
 REQUIRED_ARGS: -de
 TEST_OUTPUT:
 ---
-fail_compilation/deprecations_preview_in.d(1): Deprecation: using `in` parameters with `extern(C)` functions is deprecated
+fail_compilation/deprecations_preview_in.d(1): Error: cannot use `in` parameters with `extern(C)` functions
 fail_compilation/deprecations_preview_in.d(1):        parameter `__anonymous_param` declared as `in` here
 ---
 */

compiler/test/fail_compilation/fail183.d

@@ -2,13 +2,13 @@
 TEST_OUTPUT:
 ---
 fail_compilation/fail183.d(17): Error: attribute `const` is redundant with previously-applied `in`
-fail_compilation/fail183.d(18): Error: attribute `scope` cannot be applied with `in`, use `-preview=in` instead
+fail_compilation/fail183.d(18): Error: attribute `scope` is redundant with previously-applied `in`
 fail_compilation/fail183.d(19): Error: attribute `const` is redundant with previously-applied `in`
-fail_compilation/fail183.d(19): Error: attribute `scope` cannot be applied with `in`, use `-preview=in` instead
-fail_compilation/fail183.d(20): Error: attribute `scope` cannot be applied with `in`, use `-preview=in` instead
+fail_compilation/fail183.d(19): Error: attribute `scope` is redundant with previously-applied `in`
+fail_compilation/fail183.d(20): Error: attribute `scope` is redundant with previously-applied `in`
 fail_compilation/fail183.d(20): Error: attribute `const` is redundant with previously-applied `in`
 fail_compilation/fail183.d(22): Error: attribute `in` cannot be added after `const`: remove `const`
-fail_compilation/fail183.d(23): Error: attribute `in` cannot be added after `scope`: remove `scope` and use `-preview=in`
+fail_compilation/fail183.d(23): Error: attribute `in` cannot be added after `scope`: remove `scope`
 fail_compilation/fail183.d(24): Error: attribute `in` cannot be added after `const`: remove `const`
 fail_compilation/fail183.d(25): Error: attribute `in` cannot be added after `const`: remove `const`
 ---

compiler/test/run.d

@@ -158,7 +158,7 @@ Options:
         args = ["all"];
 
     // move any long-running tests to the front
-    static size_t sortKey(in ref Target target)
+    static size_t sortKey(const scope ref Target target)
     {
         const name = target.normalizedTestName;
         if (name.startsWith("runnable"))