add bitfields to D

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/cli.d

@@ -843,6 +843,7 @@ dmd -cov -unittest myprog.d
             "implement https://github.com/dlang/DIPs/blob/master/DIPs/other/DIP1008.md (@nogc Throwable)"),
         Feature("dip1021", "useDIP1021",
             "implement https://github.com/dlang/DIPs/blob/master/DIPs/accepted/DIP1021.md (Mutable function arguments)"),
+        Feature("bitfields", "bitfields", "add bitfields https://github.com/dlang/dlang.org/pull/3190"),
         Feature("fieldwise", "fieldwise", "use fieldwise comparisons for struct equality"),
         Feature("fixAliasThis", "fixAliasThis",
             "when a symbol is resolved, check alias this scope before going to upper scopes"),

src/dmd/declaration.d

@@ -1691,6 +1691,32 @@ extern (C++) class BitFieldDeclaration : VarDeclaration
         v.visit(this);
     }
 
+    /***********************************
+     * Retrieve the .min or .max values.
+     * Only valid after semantic analysis.
+     * Params:
+     *  id = Id.min or Id.max
+     * Returns:
+     *  the min or max value
+     */
+    final ulong getMinMax(Identifier id)
+    {
+        const width = fieldWidth;
+        const uns = type.isunsigned();
+        const min = id == Id.min;
+        ulong v;
+        assert(width != 0);  // should have been rejected in semantic pass
+        if (width == ulong.sizeof * 8)
+            v = uns ? (min ? ulong.min : ulong.max)
+                    : (min ?  long.min :  long.max);
+        else
+            v = uns ? (min ? 0
+                           : (1L << width) - 1)
+                    : (min ? -(1L << (width - 1))
+                           :  (1L << (width - 1)) - 1);
+        return v;
+    }
+
     override final void setFieldOffset(AggregateDeclaration ad, ref FieldState fieldState, bool isunion)
     {
         //printf("BitFieldDeclaration::setFieldOffset(ad: %s, field: %s)\n", ad.toChars(), toChars());

src/dmd/dsymbolsem.d

@@ -1204,6 +1204,11 @@ 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/expressionsem.d

@@ -12605,6 +12605,22 @@ Expression semanticY(DotIdExp exp, Scope* sc, int flag)
         Expression e = new IntegerExp(exp.loc, actualAlignment, Type.tsize_t);
         return e;
     }
+    else if ((exp.ident == Id.max || exp.ident == Id.min) &&
+             exp.e1.isVarExp() &&
+             exp.e1.isVarExp().var.isBitFieldDeclaration())
+    {
+        // For `x.max` and `x.min` get the max/min of the bitfield, not the max/min of its type
+        auto bf = exp.e1.isVarExp().var.isBitFieldDeclaration();
+        return new IntegerExp(exp.loc, bf.getMinMax(exp.ident), bf.type);
+    }
+    else if ((exp.ident == Id.max || exp.ident == Id.min) &&
+             exp.e1.isDotVarExp() &&
+             exp.e1.isDotVarExp().var.isBitFieldDeclaration())
+    {
+        // For `x.max` and `x.min` get the max/min of the bitfield, not the max/min of its type
+        auto bf = exp.e1.isDotVarExp().var.isBitFieldDeclaration();
+        return new IntegerExp(exp.loc, bf.getMinMax(exp.ident), bf.type);
+    }
     else if (cfile && exp.ident == Id.__sizeof && exp.e1.isStringExp())
     {
         // Sizeof string literal includes the terminating 0
@@ -12618,7 +12634,9 @@ Expression semanticY(DotIdExp exp, Scope* sc, int flag)
             flag = 0;
         Expression e = exp.e1.type.dotExp(sc, exp.e1, exp.ident, flag | (exp.noderef ? DotExpFlag.noDeref : 0));
         if (e)
+        {
             e = e.expressionSemantic(sc);
+        }
         return e;
     }
 }

src/dmd/frontend.h

@@ -507,6 +507,7 @@ struct Param final
     bool ehnogc;
     FeatureState dtorFields;
     bool fieldwise;
+    bool bitfields;
     FeatureState rvalueRefParam;
     CppStdRevision cplusplus;
     bool markdown;
@@ -632,6 +633,7 @@ struct Param final
         inclusiveInContracts(),
         ehnogc(),
         fieldwise(),
+        bitfields(),
         cplusplus((CppStdRevision)201103u),
         markdown(true),
         vmarkdown(),
@@ -705,7 +707,7 @@ struct Param final
         mapfile()
     {
     }
-    Param(bool obj, bool link = true, bool dll = false, bool lib = false, bool multiobj = false, bool oneobj = false, bool trace = false, bool tracegc = false, bool verbose = false, bool vcg_ast = false, bool showColumns = false, bool vtls = false, bool vtemplates = false, bool vtemplatesListInstances = false, bool vgc = false, bool vfield = false, bool vcomplex = true, bool vin = false, uint8_t symdebug = 0u, bool symdebugref = false, bool optimize = false, DiagnosticReporting useDeprecated = (DiagnosticReporting)1u, bool stackstomp = false, bool useUnitTests = false, bool useInline = false, FeatureState useDIP25 = (FeatureState)-1, FeatureState useDIP1000 = (FeatureState)-1, bool useDIP1021 = false, bool release = false, bool preservePaths = false, DiagnosticReporting warnings = (DiagnosticReporting)2u, PIC pic = (PIC)0u, bool color = false, bool cov = false, uint8_t covPercent = 0u, bool ctfe_cov = false, bool nofloat = false, bool ignoreUnsupportedPragmas = false, bool useModuleInfo = true, bool useTypeInfo = true, bool useExceptions = true, bool noSharedAccess = false, bool previewIn = false, bool shortenedMethods = false, bool betterC = false, bool addMain = false, bool allInst = false, bool fix16997 = true, bool fixAliasThis = false, bool inclusiveInContracts = false, bool ehnogc = false, FeatureState dtorFields = (FeatureState)-1, bool fieldwise = false, FeatureState rvalueRefParam = (FeatureState)-1, CppStdRevision cplusplus = (CppStdRevision)201103u, bool markdown = true, bool vmarkdown = false, bool showGaggedErrors = false, bool printErrorContext = false, bool manual = false, bool usage = false, bool mcpuUsage = false, bool transitionUsage = false, bool checkUsage = false, bool checkActionUsage = false, bool revertUsage = false, bool previewUsage = false, bool externStdUsage = false, bool hcUsage = false, bool logo = false, CHECKENABLE useInvariants = (CHECKENABLE)0u, CHECKENABLE useIn = (CHECKENABLE)0u, CHECKENABLE useOut = (CHECKENABLE)0u, CHECKENABLE useArrayBounds = (CHECKENABLE)0u, CHECKENABLE useAssert = (CHECKENABLE)0u, CHECKENABLE useSwitchError = (CHECKENABLE)0u, CHECKENABLE boundscheck = (CHECKENABLE)0u, CHECKACTION checkAction = (CHECKACTION)0u, uint32_t errorLimit = 20u, _d_dynamicArray< const char > argv0 = {}, Array<const char* > modFileAliasStrings = Array<const char* >(), Array<const char* >* imppath = nullptr, Array<const char* >* fileImppath = nullptr, _d_dynamicArray< const char > objdir = {}, _d_dynamicArray< const char > objname = {}, _d_dynamicArray< const char > libname = {}, bool doDocComments = false, _d_dynamicArray< const char > docdir = {}, _d_dynamicArray< const char > docname = {}, Array<const char* > ddocfiles = Array<const char* >(), bool doHdrGeneration = false, _d_dynamicArray< const char > hdrdir = {}, _d_dynamicArray< const char > hdrname = {}, bool hdrStripPlainFunctions = true, CxxHeaderMode doCxxHdrGeneration = (CxxHeaderMode)0u, _d_dynamicArray< const char > cxxhdrdir = {}, _d_dynamicArray< const char > cxxhdrname = {}, bool doJsonGeneration = false, _d_dynamicArray< const char > jsonfilename = {}, JsonFieldFlags jsonFieldFlags = (JsonFieldFlags)0u, OutBuffer* mixinOut = nullptr, const char* mixinFile = nullptr, int32_t mixinLines = 0, uint32_t debuglevel = 0u, Array<const char* >* debugids = nullptr, uint32_t versionlevel = 0u, Array<const char* >* versionids = nullptr, _d_dynamicArray< const char > defaultlibname = {}, _d_dynamicArray< const char > debuglibname = {}, _d_dynamicArray< const char > mscrtlib = {}, _d_dynamicArray< const char > moduleDepsFile = {}, OutBuffer* moduleDeps = nullptr, bool emitMakeDeps = false, _d_dynamicArray< const char > makeDepsFile = {}, Array<const char* > makeDeps = Array<const char* >(), MessageStyle messageStyle = (MessageStyle)0u, bool run = false, Array<const char* > runargs = Array<const char* >(), Array<const char* > objfiles = Array<const char* >(), Array<const char* > linkswitches = Array<const char* >(), Array<bool > linkswitchIsForCC = Array<bool >(), Array<const char* > libfiles = Array<const char* >(), Array<const char* > dllfiles = Array<const char* >(), _d_dynamicArray< const char > deffile = {}, _d_dynamicArray< const char > resfile = {}, _d_dynamicArray< const char > exefile = {}, _d_dynamicArray< const char > mapfile = {}) :
+    Param(bool obj, bool link = true, bool dll = false, bool lib = false, bool multiobj = false, bool oneobj = false, bool trace = false, bool tracegc = false, bool verbose = false, bool vcg_ast = false, bool showColumns = false, bool vtls = false, bool vtemplates = false, bool vtemplatesListInstances = false, bool vgc = false, bool vfield = false, bool vcomplex = true, bool vin = false, uint8_t symdebug = 0u, bool symdebugref = false, bool optimize = false, DiagnosticReporting useDeprecated = (DiagnosticReporting)1u, bool stackstomp = false, bool useUnitTests = false, bool useInline = false, FeatureState useDIP25 = (FeatureState)-1, FeatureState useDIP1000 = (FeatureState)-1, bool useDIP1021 = false, bool release = false, bool preservePaths = false, DiagnosticReporting warnings = (DiagnosticReporting)2u, PIC pic = (PIC)0u, bool color = false, bool cov = false, uint8_t covPercent = 0u, bool ctfe_cov = false, bool nofloat = false, bool ignoreUnsupportedPragmas = false, bool useModuleInfo = true, bool useTypeInfo = true, bool useExceptions = true, bool noSharedAccess = false, bool previewIn = false, bool shortenedMethods = false, bool betterC = false, bool addMain = false, bool allInst = false, bool fix16997 = true, bool fixAliasThis = false, bool inclusiveInContracts = false, bool ehnogc = false, FeatureState dtorFields = (FeatureState)-1, bool fieldwise = false, bool bitfields = false, FeatureState rvalueRefParam = (FeatureState)-1, CppStdRevision cplusplus = (CppStdRevision)201103u, bool markdown = true, bool vmarkdown = false, bool showGaggedErrors = false, bool printErrorContext = false, bool manual = false, bool usage = false, bool mcpuUsage = false, bool transitionUsage = false, bool checkUsage = false, bool checkActionUsage = false, bool revertUsage = false, bool previewUsage = false, bool externStdUsage = false, bool hcUsage = false, bool logo = false, CHECKENABLE useInvariants = (CHECKENABLE)0u, CHECKENABLE useIn = (CHECKENABLE)0u, CHECKENABLE useOut = (CHECKENABLE)0u, CHECKENABLE useArrayBounds = (CHECKENABLE)0u, CHECKENABLE useAssert = (CHECKENABLE)0u, CHECKENABLE useSwitchError = (CHECKENABLE)0u, CHECKENABLE boundscheck = (CHECKENABLE)0u, CHECKACTION checkAction = (CHECKACTION)0u, uint32_t errorLimit = 20u, _d_dynamicArray< const char > argv0 = {}, Array<const char* > modFileAliasStrings = Array<const char* >(), Array<const char* >* imppath = nullptr, Array<const char* >* fileImppath = nullptr, _d_dynamicArray< const char > objdir = {}, _d_dynamicArray< const char > objname = {}, _d_dynamicArray< const char > libname = {}, bool doDocComments = false, _d_dynamicArray< const char > docdir = {}, _d_dynamicArray< const char > docname = {}, Array<const char* > ddocfiles = Array<const char* >(), bool doHdrGeneration = false, _d_dynamicArray< const char > hdrdir = {}, _d_dynamicArray< const char > hdrname = {}, bool hdrStripPlainFunctions = true, CxxHeaderMode doCxxHdrGeneration = (CxxHeaderMode)0u, _d_dynamicArray< const char > cxxhdrdir = {}, _d_dynamicArray< const char > cxxhdrname = {}, bool doJsonGeneration = false, _d_dynamicArray< const char > jsonfilename = {}, JsonFieldFlags jsonFieldFlags = (JsonFieldFlags)0u, OutBuffer* mixinOut = nullptr, const char* mixinFile = nullptr, int32_t mixinLines = 0, uint32_t debuglevel = 0u, Array<const char* >* debugids = nullptr, uint32_t versionlevel = 0u, Array<const char* >* versionids = nullptr, _d_dynamicArray< const char > defaultlibname = {}, _d_dynamicArray< const char > debuglibname = {}, _d_dynamicArray< const char > mscrtlib = {}, _d_dynamicArray< const char > moduleDepsFile = {}, OutBuffer* moduleDeps = nullptr, bool emitMakeDeps = false, _d_dynamicArray< const char > makeDepsFile = {}, Array<const char* > makeDeps = Array<const char* >(), MessageStyle messageStyle = (MessageStyle)0u, bool run = false, Array<const char* > runargs = Array<const char* >(), Array<const char* > objfiles = Array<const char* >(), Array<const char* > linkswitches = Array<const char* >(), Array<bool > linkswitchIsForCC = Array<bool >(), Array<const char* > libfiles = Array<const char* >(), Array<const char* > dllfiles = Array<const char* >(), _d_dynamicArray< const char > deffile = {}, _d_dynamicArray< const char > resfile = {}, _d_dynamicArray< const char > exefile = {}, _d_dynamicArray< const char > mapfile = {}) :
         obj(obj),
         link(link),
         dll(dll),
@@ -759,6 +761,7 @@ struct Param final
         ehnogc(ehnogc),
         dtorFields(dtorFields),
         fieldwise(fieldwise),
+        bitfields(bitfields),
         rvalueRefParam(rvalueRefParam),
         cplusplus(cplusplus),
         markdown(markdown),
@@ -5855,6 +5858,7 @@ class BitFieldDeclaration : public VarDeclaration
     BitFieldDeclaration* syntaxCopy(Dsymbol* s);
     BitFieldDeclaration* isBitFieldDeclaration();
     void accept(Visitor* v);
+    uint64_t getMinMax(Identifier* id);
     void setFieldOffset(AggregateDeclaration* ad, FieldState& fieldState, bool isunion);
 };
 

src/dmd/globals.d

@@ -162,6 +162,7 @@ extern (C++) struct Param
     FeatureState dtorFields; // destruct fields of partially constructed objects
                             // https://issues.dlang.org/show_bug.cgi?id=14246
     bool fieldwise;         // do struct equality testing field-wise rather than by memcmp()
+    bool bitfields;         // support C style bit fields
     FeatureState rvalueRefParam; // allow rvalues to be arguments to ref parameters
                                  // https://dconf.org/2019/talks/alexandrescu.html
                                  // https://gist.github.com/andralex/e5405a5d773f07f73196c05f8339435a

src/dmd/globals.h

@@ -147,6 +147,7 @@ struct Param
     FeatureState dtorFields;  // destruct fields of partially constructed objects
                               // https://issues.dlang.org/show_bug.cgi?id=14246
     bool fieldwise;         // do struct equality testing field-wise rather than by memcmp()
+    bool bitfields;         // support C style bit fields
     FeatureState rvalueRefParam;    // allow rvalues to be arguments to ref parameters
     CppStdRevision cplusplus;  // version of C++ name mangling to support
     bool markdown;          // enable Markdown replacements in Ddoc

src/dmd/parse.d

@@ -289,6 +289,15 @@ class Parser(AST, Lexer = dmd.lexer.Lexer) : 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
@@ -4298,7 +4307,8 @@ class Parser(AST, Lexer = dmd.lexer.Lexer) : 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)
     {
@@ -4459,6 +4469,12 @@ class Parser(AST, Lexer = dmd.lexer.Lexer) : 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);
@@ -4591,19 +4607,39 @@ class Parser(AST, Lexer = dmd.lexer.Lexer) : 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 (!global.params.bitfields)
+                        error("use -preview=bitfields for bitfield support");
+                    if (_init)
+                        error("initializer not allowed for bit-field declaration");
+                    if (storage_class)
+                        error("storage class not allowed 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)
                 {
@@ -4616,7 +4652,7 @@ class Parser(AST, Lexer = dmd.lexer.Lexer) : 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)
                 {
@@ -4646,12 +4682,12 @@ class Parser(AST, Lexer = dmd.lexer.Lexer) : 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;
                 }