patch 9.1.0976: Vim9: missing return statement with throw

Problem:  Vim9: missing return statement with throw
          (atitcreate)
Solution: Treat a throw statement at the end of an if-else block as a
          return statement (Yegappan Lakshmanan)

fixes: #16312
closes: #16338

Signed-off-by: Yegappan Lakshmanan <yegappan@yahoo.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

src/testdir/test_vim9_func.vim

@@ -550,6 +550,47 @@ def Test_not_missing_return()
   v9.CheckScriptSuccess(lines)
 enddef
 
+" Test for an if-else block ending in a throw statement
+def Test_if_else_with_throw()
+  var lines =<< trim END
+      def Ifelse_Throw1(): number
+        if false
+          return 1
+        else
+          throw 'Error'
+        endif
+      enddef
+      defcompile
+  END
+  v9.CheckScriptSuccess(lines)
+
+  lines =<< trim END
+      def Ifelse_Throw2(): number
+        if true
+          throw 'Error'
+        else
+          return 2
+        endif
+      enddef
+      defcompile
+  END
+  v9.CheckScriptSuccess(lines)
+
+  lines =<< trim END
+      def Ifelse_Throw3(): number
+        if true
+          return 1
+        elseif false
+          throw 'Error'
+        else
+          return 3
+        endif
+      enddef
+      defcompile
+  END
+  v9.CheckScriptSuccess(lines)
+enddef
+
 def Test_return_bool()
   var lines =<< trim END
       vim9script

src/version.c

@@ -704,6 +704,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    976,
 /**/
     975,
 /**/

src/vim9cmds.c

@@ -602,7 +602,9 @@ compile_elseif(char_u *arg, cctx_T *cctx)
 	return NULL;
     }
     unwind_locals(cctx, scope->se_local_count, TRUE);
-    if (!cctx->ctx_had_return)
+    if (!cctx->ctx_had_return && !cctx->ctx_had_throw)
+	// the previous if block didn't end in a "return" or a "throw"
+	// statement.
 	scope->se_u.se_if.is_had_return = FALSE;
 
     if (cctx->ctx_skip == SKIP_NOT)
@@ -749,7 +751,9 @@ compile_else(char_u *arg, cctx_T *cctx)
 	return NULL;
     }
     unwind_locals(cctx, scope->se_local_count, TRUE);
-    if (!cctx->ctx_had_return)
+    if (!cctx->ctx_had_return && !cctx->ctx_had_throw)
+	// the previous if block didn't end in a "return" or a "throw"
+	// statement.
 	scope->se_u.se_if.is_had_return = FALSE;
     scope->se_u.se_if.is_seen_else = TRUE;
 
@@ -821,7 +825,9 @@ compile_endif(char_u *arg, cctx_T *cctx)
     }
     ifscope = &scope->se_u.se_if;
     unwind_locals(cctx, scope->se_local_count, TRUE);
-    if (!cctx->ctx_had_return)
+    if (!cctx->ctx_had_return && !cctx->ctx_had_throw)
+	// the previous if block didn't end in a "return" or a "throw"
+	// statement.
 	ifscope->is_had_return = FALSE;
 
     if (scope->se_u.se_if.is_if_label >= 0)

src/vim9compile.c

@@ -4407,7 +4407,16 @@ compile_def_function_body(
 				     cctx->ctx_had_return ? "return" : "throw");
 	    return FAIL;
 	}
-	cctx->ctx_had_throw = FALSE;
+
+	// When processing the end of an if-else block, don't clear the
+	// "ctx_had_throw" flag.  If an if-else block ends in a "throw"
+	// statement, then it is considered to end in a "return" statement.
+	// The "ctx_had_throw" is cleared immediately after processing the
+	// if-else block ending statement.
+	// Otherwise, clear the "had_throw" flag.
+	if (ea.cmdidx != CMD_else && ea.cmdidx != CMD_elseif
+						&& ea.cmdidx != CMD_endif)
+	    cctx->ctx_had_throw = FALSE;
 
 	p = skipwhite(p);
 	if (ea.cmdidx != CMD_SIZE
@@ -4474,13 +4483,16 @@ compile_def_function_body(
 	    case CMD_elseif:
 		    line = compile_elseif(p, cctx);
 		    cctx->ctx_had_return = FALSE;
+		    cctx->ctx_had_throw = FALSE;
 		    break;
 	    case CMD_else:
 		    line = compile_else(p, cctx);
 		    cctx->ctx_had_return = FALSE;
+		    cctx->ctx_had_throw = FALSE;
 		    break;
 	    case CMD_endif:
 		    line = compile_endif(p, cctx);
+		    cctx->ctx_had_throw = FALSE;
 		    break;
 
 	    case CMD_while:
@@ -4695,7 +4707,7 @@ compile_dfunc_scope_end_missing(cctx_T *cctx)
 }
 
 /*
- * When compiling a def function, if it doesn not have an explicit return
+ * When compiling a def function, if it doesn't have an explicit return
  * statement, then generate a default return instruction.  For an object
  * constructor, return the object.
  */