add a DUK_HOBJECT_FLAG_NOTAIL flag and 'use duk notail' directive

src/duk_api.c

@@ -2802,6 +2802,7 @@ int duk_push_c_function(duk_context *ctx, duk_c_function func, int nargs) {
 	        DUK_HOBJECT_FLAG_NATIVEFUNCTION |
 	        DUK_HOBJECT_FLAG_NEWENV |
 	        DUK_HOBJECT_FLAG_STRICT |
+	        DUK_HOBJECT_FLAG_NOTAIL |
 	        DUK_HOBJECT_FLAG_EXOTIC_DUKFUNC |
 	        DUK_HOBJECT_CLASS_AS_FLAGS(DUK_HOBJECT_CLASS_FUNCTION);
 	
@@ -2816,6 +2817,7 @@ void duk_push_c_function_noexotic(duk_context *ctx, duk_c_function func, int nar
 	        DUK_HOBJECT_FLAG_NATIVEFUNCTION |
 	        DUK_HOBJECT_FLAG_NEWENV |
 	        DUK_HOBJECT_FLAG_STRICT |
+	        DUK_HOBJECT_FLAG_NOTAIL |
 	        DUK_HOBJECT_CLASS_AS_FLAGS(DUK_HOBJECT_CLASS_FUNCTION);
 	
 	(void) duk__push_c_function_raw(ctx, func, nargs, flags);
@@ -2828,6 +2830,7 @@ void duk_push_c_function_noconstruct_noexotic(duk_context *ctx, duk_c_function f
 	        DUK_HOBJECT_FLAG_NATIVEFUNCTION |
 	        DUK_HOBJECT_FLAG_NEWENV |
 	        DUK_HOBJECT_FLAG_STRICT |
+	        DUK_HOBJECT_FLAG_NOTAIL |
 	        DUK_HOBJECT_CLASS_AS_FLAGS(DUK_HOBJECT_CLASS_FUNCTION);
 	
 	(void) duk__push_c_function_raw(ctx, func, nargs, flags);

src/duk_hobject.h

@@ -41,17 +41,17 @@
 #define DUK_HOBJECT_FLAG_THREAD                DUK_HEAPHDR_USER_FLAG(6)   /* object is a thread (duk_hthread) */
 #define DUK_HOBJECT_FLAG_ARRAY_PART            DUK_HEAPHDR_USER_FLAG(7)   /* object has an array part (a_size may still be 0) */
 #define DUK_HOBJECT_FLAG_STRICT                DUK_HEAPHDR_USER_FLAG(8)   /* function: function object is strict */
-#define DUK_HOBJECT_FLAG_NEWENV                DUK_HEAPHDR_USER_FLAG(9)   /* function: create new environment when called (see duk_hcompiledfunction) */
-#define DUK_HOBJECT_FLAG_NAMEBINDING           DUK_HEAPHDR_USER_FLAG(10)  /* function: create binding for func name (function templates only, used for named function expressions) */
-#define DUK_HOBJECT_FLAG_CREATEARGS            DUK_HEAPHDR_USER_FLAG(11)  /* function: create an arguments object on function call */
-#define DUK_HOBJECT_FLAG_ENVRECCLOSED          DUK_HEAPHDR_USER_FLAG(12)  /* envrec: (declarative) record is closed */
-#define DUK_HOBJECT_FLAG_EXOTIC_ARRAY          DUK_HEAPHDR_USER_FLAG(13)  /* 'Array' object, array length and index exotic behavior */
-#define DUK_HOBJECT_FLAG_EXOTIC_STRINGOBJ      DUK_HEAPHDR_USER_FLAG(14)  /* 'String' object, array index exotic behavior */
-#define DUK_HOBJECT_FLAG_EXOTIC_ARGUMENTS      DUK_HEAPHDR_USER_FLAG(15)  /* 'Arguments' object and has arguments exotic behavior (non-strict callee) */
-#define DUK_HOBJECT_FLAG_EXOTIC_DUKFUNC        DUK_HEAPHDR_USER_FLAG(16)  /* Duktape/C (nativefunction) object, exotic 'length' */
-#define DUK_HOBJECT_FLAG_EXOTIC_BUFFEROBJ      DUK_HEAPHDR_USER_FLAG(17)  /* 'Buffer' object, array index exotic behavior, virtual 'length' */
-#define DUK_HOBJECT_FLAG_EXOTIC_PROXYOBJ       DUK_HEAPHDR_USER_FLAG(18)  /* 'Proxy' object */
-/* bit 19 unused */
+#define DUK_HOBJECT_FLAG_NOTAIL                DUK_HEAPHDR_USER_FLAG(9)   /* function: function must not be tailcalled */
+#define DUK_HOBJECT_FLAG_NEWENV                DUK_HEAPHDR_USER_FLAG(10)  /* function: create new environment when called (see duk_hcompiledfunction) */
+#define DUK_HOBJECT_FLAG_NAMEBINDING           DUK_HEAPHDR_USER_FLAG(11)  /* function: create binding for func name (function templates only, used for named function expressions) */
+#define DUK_HOBJECT_FLAG_CREATEARGS            DUK_HEAPHDR_USER_FLAG(12)  /* function: create an arguments object on function call */
+#define DUK_HOBJECT_FLAG_ENVRECCLOSED          DUK_HEAPHDR_USER_FLAG(13)  /* envrec: (declarative) record is closed */
+#define DUK_HOBJECT_FLAG_EXOTIC_ARRAY          DUK_HEAPHDR_USER_FLAG(14)  /* 'Array' object, array length and index exotic behavior */
+#define DUK_HOBJECT_FLAG_EXOTIC_STRINGOBJ      DUK_HEAPHDR_USER_FLAG(15)  /* 'String' object, array index exotic behavior */
+#define DUK_HOBJECT_FLAG_EXOTIC_ARGUMENTS      DUK_HEAPHDR_USER_FLAG(16)  /* 'Arguments' object and has arguments exotic behavior (non-strict callee) */
+#define DUK_HOBJECT_FLAG_EXOTIC_DUKFUNC        DUK_HEAPHDR_USER_FLAG(17)  /* Duktape/C (nativefunction) object, exotic 'length' */
+#define DUK_HOBJECT_FLAG_EXOTIC_BUFFEROBJ      DUK_HEAPHDR_USER_FLAG(18)  /* 'Buffer' object, array index exotic behavior, virtual 'length' */
+#define DUK_HOBJECT_FLAG_EXOTIC_PROXYOBJ       DUK_HEAPHDR_USER_FLAG(19)  /* 'Proxy' object */
 /* bit 20 unused */
 
 #define DUK_HOBJECT_FLAG_CLASS_BASE            DUK_HEAPHDR_USER_FLAG_NUMBER(21)
@@ -126,6 +126,7 @@
 #define DUK_HOBJECT_HAS_THREAD(h)              DUK_HEAPHDR_CHECK_FLAG_BITS(&(h)->hdr, DUK_HOBJECT_FLAG_THREAD)
 #define DUK_HOBJECT_HAS_ARRAY_PART(h)          DUK_HEAPHDR_CHECK_FLAG_BITS(&(h)->hdr, DUK_HOBJECT_FLAG_ARRAY_PART)
 #define DUK_HOBJECT_HAS_STRICT(h)              DUK_HEAPHDR_CHECK_FLAG_BITS(&(h)->hdr, DUK_HOBJECT_FLAG_STRICT)
+#define DUK_HOBJECT_HAS_NOTAIL(h)              DUK_HEAPHDR_CHECK_FLAG_BITS(&(h)->hdr, DUK_HOBJECT_FLAG_NOTAIL)
 #define DUK_HOBJECT_HAS_NEWENV(h)              DUK_HEAPHDR_CHECK_FLAG_BITS(&(h)->hdr, DUK_HOBJECT_FLAG_NEWENV)
 #define DUK_HOBJECT_HAS_NAMEBINDING(h)         DUK_HEAPHDR_CHECK_FLAG_BITS(&(h)->hdr, DUK_HOBJECT_FLAG_NAMEBINDING)
 #define DUK_HOBJECT_HAS_CREATEARGS(h)          DUK_HEAPHDR_CHECK_FLAG_BITS(&(h)->hdr, DUK_HOBJECT_FLAG_CREATEARGS)
@@ -145,6 +146,7 @@
 #define DUK_HOBJECT_SET_THREAD(h)              DUK_HEAPHDR_SET_FLAG_BITS(&(h)->hdr, DUK_HOBJECT_FLAG_THREAD)
 #define DUK_HOBJECT_SET_ARRAY_PART(h)          DUK_HEAPHDR_SET_FLAG_BITS(&(h)->hdr, DUK_HOBJECT_FLAG_ARRAY_PART)
 #define DUK_HOBJECT_SET_STRICT(h)              DUK_HEAPHDR_SET_FLAG_BITS(&(h)->hdr, DUK_HOBJECT_FLAG_STRICT)
+#define DUK_HOBJECT_SET_NOTAIL(h)              DUK_HEAPHDR_SET_FLAG_BITS(&(h)->hdr, DUK_HOBJECT_FLAG_NOTAIL)
 #define DUK_HOBJECT_SET_NEWENV(h)              DUK_HEAPHDR_SET_FLAG_BITS(&(h)->hdr, DUK_HOBJECT_FLAG_NEWENV)
 #define DUK_HOBJECT_SET_NAMEBINDING(h)         DUK_HEAPHDR_SET_FLAG_BITS(&(h)->hdr, DUK_HOBJECT_FLAG_NAMEBINDING)
 #define DUK_HOBJECT_SET_CREATEARGS(h)          DUK_HEAPHDR_SET_FLAG_BITS(&(h)->hdr, DUK_HOBJECT_FLAG_CREATEARGS)
@@ -164,6 +166,7 @@
 #define DUK_HOBJECT_CLEAR_THREAD(h)            DUK_HEAPHDR_CLEAR_FLAG_BITS(&(h)->hdr, DUK_HOBJECT_FLAG_THREAD)
 #define DUK_HOBJECT_CLEAR_ARRAY_PART(h)        DUK_HEAPHDR_CLEAR_FLAG_BITS(&(h)->hdr, DUK_HOBJECT_FLAG_ARRAY_PART)
 #define DUK_HOBJECT_CLEAR_STRICT(h)            DUK_HEAPHDR_CLEAR_FLAG_BITS(&(h)->hdr, DUK_HOBJECT_FLAG_STRICT)
+#define DUK_HOBJECT_CLEAR_NOTAIL(h)            DUK_HEAPHDR_CLEAR_FLAG_BITS(&(h)->hdr, DUK_HOBJECT_FLAG_NOTAIL)
 #define DUK_HOBJECT_CLEAR_NEWENV(h)            DUK_HEAPHDR_CLEAR_FLAG_BITS(&(h)->hdr, DUK_HOBJECT_FLAG_NEWENV)
 #define DUK_HOBJECT_CLEAR_NAMEBINDING(h)       DUK_HEAPHDR_CLEAR_FLAG_BITS(&(h)->hdr, DUK_HOBJECT_FLAG_NAMEBINDING)
 #define DUK_HOBJECT_CLEAR_CREATEARGS(h)        DUK_HEAPHDR_CLEAR_FLAG_BITS(&(h)->hdr, DUK_HOBJECT_FLAG_CREATEARGS)

src/duk_js_call.c

@@ -1890,6 +1890,9 @@ void duk_handle_ecma_call_setup(duk_hthread *thr,
 		/* See: test-bug-tailcall-preventyield-assert.c. */
 		DUK_DDD(DUK_DDDPRINT("tailcall prevented by current activation having DUK_ACT_FLAG_PREVENTYIELD"));
 		use_tailcall = 0;
+	} else if (DUK_HOBJECT_HAS_NOTAIL(func)) {
+		DUK_D(DUK_DPRINT("tailcall prevented by function having a notail flag"));
+		use_tailcall = 0;
 	}
 
 	if (use_tailcall) {

src/duk_js_compiler.c

@@ -677,6 +677,11 @@ static void duk__convert_to_func_template(duk_compiler_ctx *comp_ctx) {
 		DUK_HOBJECT_SET_STRICT((duk_hobject *) h_res);
 	}
 
+	if (func->is_notail) {
+		DUK_DDD(DUK_DDDPRINT("function is notail -> set NOTAIL"));
+		DUK_HOBJECT_SET_NOTAIL((duk_hobject *) h_res);
+	}
+
 	/*
 	 *  Build function fixed size 'data' buffer, which contains bytecode,
 	 *  constants, and inner function references.
@@ -5877,6 +5882,8 @@ static void duk__parse_stmt(duk_compiler_ctx *comp_ctx, duk_ivalue *res, int all
 				/* XXX: how to compare 'use strict' most compactly?
 				 * We don't necessarily want to add it to the built-ins
 				 * because it's not needed at run time.
+				 * The length comparisons are present to handle
+				 * strings like "use strict\u0000foo" as required.
 				 */
 
 				if (DUK_HSTRING_GET_BYTELEN(h_dir) == 10 &&
@@ -5884,6 +5891,11 @@ static void duk__parse_stmt(duk_compiler_ctx *comp_ctx, duk_ivalue *res, int all
 					DUK_DDD(DUK_DDDPRINT("use strict directive detected: strict flag %d -> %d",
 					                     comp_ctx->curr_func.is_strict, 1));
 					comp_ctx->curr_func.is_strict = 1;
+				} else if (DUK_HSTRING_GET_BYTELEN(h_dir) == 14 &&
+				           DUK_STRNCMP((const char *) DUK_HSTRING_GET_DATA(h_dir), "use duk notail", 14) == 0) {
+					DUK_DDD(DUK_DDDPRINT("use duk notail directive detected: notail flag %d -> %d",
+					                     comp_ctx->curr_func.is_notail, 1));
+					comp_ctx->curr_func.is_notail = 1;
 				} else {
 					DUK_DD(DUK_DDPRINT("unknown directive: '%!O', ignoring but not terminating "
 					                   "directive prologue", (duk_hobject *) h_dir));
@@ -6814,9 +6826,10 @@ static int duk__parse_func_like_fnum(duk_compiler_ctx *comp_ctx, int is_decl, in
 	/* inherit initial strictness from parent */
 	comp_ctx->curr_func.is_strict = old_func.is_strict;
 
+	DUK_ASSERT(comp_ctx->curr_func.is_notail == 0);
 	comp_ctx->curr_func.is_function = 1;
-	comp_ctx->curr_func.is_eval = 0;
-	comp_ctx->curr_func.is_global = 0;
+	DUK_ASSERT(comp_ctx->curr_func.is_eval == 0);
+	DUK_ASSERT(comp_ctx->curr_func.is_global == 0);
 	comp_ctx->curr_func.is_setget = is_setget;
 	comp_ctx->curr_func.is_decl = is_decl;
 

src/duk_js_compiler.h

@@ -129,6 +129,7 @@ struct duk_compiler_func {
 	int is_setget;                      /* is a setter/getter */
 	int is_decl;                        /* is a function declaration (as opposed to function expression) */
 	int is_strict;                      /* function is strict */
+	int is_notail;                      /* function must not be tailcalled */
 	int in_directive_prologue;          /* parsing in "directive prologue", recognize directives */
 	int in_scanning;                    /* parsing in "scanning" phase (first pass) */
 	int may_direct_eval;                /* function may call direct eval */

src/duk_js_var.c

@@ -180,6 +180,9 @@ void duk_js_push_closure(duk_hthread *thr,
 	if (DUK_HOBJECT_HAS_STRICT(&fun_temp->obj)) {
 		DUK_HOBJECT_SET_STRICT(&fun_clos->obj);
 	}
+	if (DUK_HOBJECT_HAS_NOTAIL(&fun_temp->obj)) {
+		DUK_HOBJECT_SET_NOTAIL(&fun_clos->obj);
+	}
 	/* DUK_HOBJECT_FLAG_NEWENV: handled below */
 	DUK_ASSERT(!DUK_HOBJECT_HAS_NAMEBINDING(&fun_clos->obj));
 	if (DUK_HOBJECT_HAS_CREATEARGS(&fun_temp->obj)) {