Move hard-coded logic to generate C main out of the compiler and into druntime

src/dmd/compiler.d

@@ -32,8 +32,6 @@ import dmd.tokens;
 
 extern (C++) __gshared
 {
-    /// DMD-generated module `__entrypoint` where the C main resides
-    Module entrypoint = null;
     /// Module in which the D main is
     Module rootHasMain = null;
 
@@ -50,61 +48,6 @@ extern (C++) __gshared
  */
 extern (C++) struct Compiler
 {
-    /**
-     * Generate C main() in response to seeing D main().
-     *
-     * This function will generate a module called `__entrypoint`,
-     * and set the globals `entrypoint` and `rootHasMain`.
-     *
-     * This used to be in druntime, but contained a reference to _Dmain
-     * which didn't work when druntime was made into a dll and was linked
-     * to a program, such as a C++ program, that didn't have a _Dmain.
-     *
-     * Params:
-     *   sc = Scope which triggered the generation of the C main,
-     *        used to get the module where the D main is.
-     */
-    extern (C++) static void genCmain(Scope* sc)
-    {
-        if (entrypoint)
-            return;
-        /* The D code to be generated is provided as D source code in the form of a string.
-         * Note that Solaris, for unknown reasons, requires both a main() and an _main()
-         */
-        immutable cmaincode =
-        q{
-            extern(C)
-            {
-                int _d_run_main(int argc, char **argv, void* mainFunc);
-                int _Dmain(char[][] args);
-                int main(int argc, char **argv)
-                {
-                    return _d_run_main(argc, argv, &_Dmain);
-                }
-                version (Solaris) int _main(int argc, char** argv) { return main(argc, argv); }
-            }
-        };
-        Identifier id = Id.entrypoint;
-        auto m = new Module("__entrypoint.d", id, 0, 0);
-        scope diagnosticReporter = new StderrDiagnosticReporter(global.params.useDeprecated);
-        scope p = new Parser!ASTCodegen(m, cmaincode, false, diagnosticReporter);
-        p.scanloc = Loc.initial;
-        p.nextToken();
-        m.members = p.parseModule();
-        assert(p.token.value == TOK.endOfFile);
-        assert(!p.errors); // shouldn't have failed to parse it
-        bool v = global.params.verbose;
-        global.params.verbose = false;
-        m.importedFrom = m;
-        m.importAll(null);
-        m.dsymbolSemantic(null);
-        m.semantic2(null);
-        m.semantic3(null);
-        global.params.verbose = v;
-        entrypoint = m;
-        rootHasMain = sc._module;
-    }
-
     /******************************
      * Encode the given expression, which is assumed to be an rvalue literal
      * as another type for use in CTFE.

src/dmd/compiler.h

@@ -21,8 +21,6 @@ class Type;
 struct Scope;
 struct UnionExp;
 
-// DMD-generated module `__entrypoint` where the C main resides
-extern Module *entrypoint;
 // Module in which the D main is
 extern Module *rootHasMain;
 
@@ -37,6 +35,5 @@ struct Compiler
     static Expression *paintAsType(UnionExp *, Expression *, Type *);
     // Backend
     static void loadModule(Module *);
-    static void genCmain(Scope *);
     static bool onImport(Module *);
 };

src/dmd/dsymbolsem.d

@@ -1685,7 +1685,6 @@ private extern(C++) final class DsymbolSemanticVisitor : Visitor
         // https://issues.dlang.org/show_bug.cgi?id=11117
         // https://issues.dlang.org/show_bug.cgi?id=11164
         if (global.params.moduleDeps !is null && !(imp.id == Id.object && sc._module.ident == Id.object) &&
-            sc._module.ident != Id.entrypoint &&
             strcmp(sc._module.ident.toChars(), "__main") != 0)
         {
             /* The grammar of the file is:
@@ -3992,7 +3991,29 @@ private extern(C++) final class DsymbolSemanticVisitor : Visitor
         }
 
         if (funcdecl.fbody && funcdecl.isMain() && sc._module.isRoot())
-            Compiler.genCmain(sc);
+        {
+            // check if `_d_cmain` is defined
+            bool cmainTemplateExists()
+            {
+                auto rootSymbol = sc.search(funcdecl.loc, Id.empty, null);
+                if (auto moduleSymbol = rootSymbol.search(funcdecl.loc, Id.object))
+                    if (moduleSymbol.search(funcdecl.loc, Id.CMain))
+                        return true;
+
+                return false;
+            }
+
+            // Only mixin `_d_cmain` if it is defined
+            if (cmainTemplateExists())
+            {
+                // add `mixin _d_cmain!();` to the declaring module
+                auto tqual = new TypeIdentifier(funcdecl.loc, Id.CMain);
+                auto tm = new TemplateMixin(funcdecl.loc, null, tqual, null);
+                sc._module.members.push(tm);
+            }
+
+            rootHasMain = sc._module;
+        }
 
         assert(funcdecl.type.ty != Terror || funcdecl.errors);
 

src/dmd/glue.d

@@ -325,21 +325,6 @@ void genObjFile(Module m, bool multiobj)
 
     //printf("Module.genobjfile(multiobj = %d) %s\n", multiobj, m.toChars());
 
-    if (m.ident == Id.entrypoint)
-    {
-        bool v = global.params.verbose;
-        global.params.verbose = false;
-
-        foreach (member; *m.members)
-        {
-            //printf("toObjFile %s %s\n", member.kind(), member.toChars());
-            toObjFile(member, multiobj);
-        }
-
-        global.params.verbose = v;
-        return;
-    }
-
     lastmname = m.srcfile.toChars();
 
     objmod.initfile(lastmname, null, m.toPrettyChars());

src/dmd/id.d

@@ -339,7 +339,7 @@ immutable Msgtable[] msgtable =
     { "main" },
     { "WinMain" },
     { "DllMain" },
-    { "entrypoint", "__entrypoint" },
+    { "CMain", "_d_cmain" },
     { "rt_init" },
     { "__cmp" },
     { "__equals"},

src/dmd/mars.d

@@ -702,8 +702,6 @@ private int tryMain(size_t argc, const(char)** argv, ref Param params)
             if (params.verbose)
                 message("code      %s", m.toChars());
             genObjFile(m, false);
-            if (entrypoint && m == rootHasMain)
-                genObjFile(entrypoint, false);
         }
         if (!global.errors && firstm)
         {
@@ -720,8 +718,6 @@ private int tryMain(size_t argc, const(char)** argv, ref Param params)
                 message("code      %s", m.toChars());
             obj_start(m.srcfile.toChars());
             genObjFile(m, params.multiobj);
-            if (entrypoint && m == rootHasMain)
-                genObjFile(entrypoint, params.multiobj);
             obj_end(library, m.objfile.toChars());
             obj_write_deferred(library);
             if (global.errors && !params.lib)

test/runnable/extra-files/minimal/object.d

@@ -1,7 +1,8 @@
 module object;
 
-private alias extern(C) int function(char[][] args) MainFunc;
-private extern (C) int _d_run_main(int argc, char** argv, MainFunc mainFunc)
+extern(C) void _Dmain();
+
+extern(C) void main()
 {
-    return mainFunc(null);
+    _Dmain();
 }