add bitfields to D

Author: WalterBright

changelog/bitfields.dd

@@ -0,0 +1,21 @@
+Add bit fields to D
+
+They work just like the bit fields in ImportC do.
+
+https://github.com/dlang/dlang.org/pull/3190
+
+---
+struct B
+{
+    int x:3, y:2;
+}
+
+static assert(B.sizeof == 4);
+
+int vaporator(B b)
+{
+    b.x = 4;
+    b.y = 2;
+    return b.x + b.y; // returns 6
+}
+---

src/dmd/dsymbolsem.d

@@ -1229,6 +1229,11 @@ private extern(C++) final class DsymbolSemanticVisitor : Visitor
         if (dsym.errors)
             return;
 
+        if (!dsym.parent.isStructDeclaration() && !dsym.parent.isClassDeclaration())
+        {
+            dsym.error("bit-field must be member of struct, union, or class");
+        }
+
         sc = sc.startCTFE();
         auto width = dsym.width.expressionSemantic(sc);
         sc = sc.endCTFE();

src/dmd/parse.d

@@ -496,6 +496,15 @@ class Parser(AST) : Lexer
         return true;
     }
 
+    /************************************
+     * Parse declarations and definitions
+     * Params:
+     *  once = !=0 means parse exactly one decl or def
+     *  pLastDecl = set to last decl or def parsed
+     *  pAttrs = keep track of attributes
+     * Returns:
+     *  array of declared symbols
+     */
     AST.Dsymbols* parseDeclDefs(int once, AST.Dsymbol* pLastDecl = null, PrefixAttributes!AST* pAttrs = null)
     {
         AST.Dsymbol lastDecl = null; // used to link unittest to its previous declaration
@@ -4456,7 +4465,8 @@ class Parser(AST) : Lexer
      * These can be:
      *      1. declarations at global/class level
      *      2. declarations at statement level
-     * Return array of Declaration *'s.
+     * Returns:
+     *  array of Declarations.
      */
     private AST.Dsymbols* parseDeclarations(bool autodecl, PrefixAttributes!AST* pAttrs, const(char)* comment)
     {
@@ -4841,6 +4851,12 @@ class Parser(AST) : Lexer
             else if (t != tfirst)
                 error("multiple declarations must have the same type, not `%s` and `%s`", tfirst.toChars(), t.toChars());
 
+            if (token.value == TOK.colon && !ident && t.ty != Tfunction)
+            {
+                // Unnamed bit field
+                ident = Identifier.generateAnonymousId("BitField");
+            }
+
             bool isThis = (t.ty == Tident && (cast(AST.TypeIdentifier)t).ident == Id.This && token.value == TOK.assign);
             if (ident)
                 checkCstyleTypeSyntax(loc, t, alt, ident);
@@ -4973,19 +4989,37 @@ class Parser(AST) : Lexer
             }
             else if (ident)
             {
+                AST.Expression width;
+                if (token.value == TOK.colon)
+                {
+                    nextToken();
+                    width = parseCondExp();
+                }
+
                 AST.Initializer _init = null;
                 if (token.value == TOK.assign)
                 {
                     nextToken();
                     _init = parseInitializer();
                 }
 
-                auto v = new AST.VarDeclaration(loc, t, ident, _init);
-                v.storage_class = storage_class;
-                if (pAttrs)
-                    pAttrs.storageClass = STC.undefined_;
-
-                AST.Dsymbol s = v;
+                AST.Dsymbol s;
+                if (width)
+                {
+                    if (_init)
+                        error("no initializer for bit-field declaration");
+                    if (storage_class)
+                        error("no storage class for bit-field declaration");
+                    s = new AST.BitFieldDeclaration(width.loc, t, ident, width);
+                }
+                else
+                {
+                    auto v = new AST.VarDeclaration(loc, t, ident, _init);
+                    v.storage_class = storage_class;
+                    if (pAttrs)
+                        pAttrs.storageClass = STC.undefined_;
+                    s = v;
+                }
 
                 if (tpl && _init)
                 {
@@ -4998,7 +5032,7 @@ class Parser(AST) : Lexer
                 {
                     auto ax = new AST.Dsymbols();
                     ax.push(s);
-                    s = new AST.AlignDeclaration(v.loc, ealign, ax);
+                    s = new AST.AlignDeclaration(s.loc, ealign, ax);
                 }
                 if (link != linkage)
                 {
@@ -5028,12 +5062,12 @@ class Parser(AST) : Lexer
                 default:
                     if (loc.linnum != token.loc.linnum)
                     {
-                        error("semicolon needed to end declaration of `%s`, instead of `%s`", v.toChars(), token.toChars());
-                        errorSupplemental(loc, "`%s` declared here", v.toChars());
+                        error("semicolon needed to end declaration of `%s`, instead of `%s`", s.toChars(), token.toChars());
+                        errorSupplemental(loc, "`%s` declared here", s.toChars());
                     }
                     else
                     {
-                        error("semicolon needed to end declaration of `%s` instead of `%s`", v.toChars(), token.toChars());
+                        error("semicolon needed to end declaration of `%s` instead of `%s`", s.toChars(), token.toChars());
                     }
                     break;
                 }

test/fail_compilation/biterrors.d

@@ -0,0 +1,14 @@
+/* TEST_OUTPUT:
+---
+fail_compilation/biterrors.d(103): Error: no initializer for bit-field declaration
+fail_compilation/biterrors.d(104): Error: no storage class for bit-field declaration
+---
+ */
+
+#line 100
+
+struct S
+{
+    int i : 3 = 7;
+    static int j : 3;
+}

test/fail_compilation/biterrors2.d

@@ -0,0 +1,8 @@
+/* TEST_OUTPUT:
+---
+fail_compilation/biterrors2.d(100): Error: variable `biterrors2.a` bit-field must be member of struct, union, or class
+---
+*/
+
+#line 100
+int a : 2;

test/fail_compilation/test16188.d

@@ -1,8 +1,7 @@
-TEST_OUTPUT:
+/* TEST_OUTPUT:
 ---
-fail_compilation/test16188.d(1): Error: no identifier for declarator `TEST_OUTPUT`
-fail_compilation/test16188.d(1): Error: declaration expected, not `:`
-fail_compilation/test16188.d(18): Error: unmatched closing brace
+fail_compilation/test16188.d(101): Error: no property `name` for type `test16188.Where`
+fail_compilation/test16188.d(101):        potentially malformed `opDispatch`. Use an explicit instantiation to get a better error message
 ---
  */
 
@@ -15,6 +14,8 @@ fail_compilation/test16188.d(18): Error: unmatched closing brace
  * I don't understand why.
  */
 
+#line 100
+
 void where() { Where().name; }
 
 struct Where

test/fail_compilation/test17284.d

@@ -1,8 +1,9 @@
 TEST_OUTPUT:
 ---
-fail_compilation/test17284.d(1): Error: no identifier for declarator `TEST_OUTPUT`
-fail_compilation/test17284.d(1): Error: declaration expected, not `:`
-fail_compilation/test17284.d(12): Error: unmatched closing brace
+fail_compilation/test17284.d(3): Error: semicolon needed to end declaration of `__anonBitField1`, instead of `:`
+fail_compilation/test17284.d(1):        `__anonBitField1` declared here
+fail_compilation/test17284.d(3): Error: declaration expected, not `:`
+fail_compilation/test17284.d(13): Error: unmatched closing brace
 ---
 */
 

test/runnable/bit.d

@@ -0,0 +1,21 @@
+
+struct S
+{
+    uint x : 2, y : 3, :0;
+    int :0;
+}
+
+uint foo(S s)
+{
+    return s.x + s.y;
+}
+
+int main()
+{
+    S s;
+    s.x = 2;
+    s.y = 4;
+    uint u = foo(s);
+    assert(u == 6);
+    return 0;
+}