bpo-34876: Change the lineno of the AST for decorated function and class. (GH-9731)

It was overridden by the lineno of the first decorator. Now it is
the lineno of 'def' or 'class'.

Python/ast.c

@@ -1659,12 +1659,6 @@ ast_for_decorated(struct compiling *c, const node *n)
     } else if (TYPE(CHILD(n, 1)) == async_funcdef) {
       thing = ast_for_async_funcdef(c, CHILD(n, 1), decorator_seq);
     }
-    /* we count the decorators in when talking about the class' or
-     * function's line number */
-    if (thing) {
-        thing->lineno = LINENO(n);
-        thing->col_offset = n->n_col_offset;
-    }
     return thing;
 }
 

Python/compile.c

@@ -1950,6 +1950,7 @@ compiler_function(struct compiler *c, stmt_ty s, int is_async)
     Py_ssize_t i, funcflags;
     int annotations;
     int scope_type;
+    int firstlineno;
 
     if (is_async) {
         assert(s->kind == AsyncFunctionDef_kind);
@@ -1976,6 +1977,11 @@ compiler_function(struct compiler *c, stmt_ty s, int is_async)
     if (!compiler_decorators(c, decos))
         return 0;
 
+    firstlineno = s->lineno;
+    if (asdl_seq_LEN(decos)) {
+        firstlineno = ((expr_ty)asdl_seq_GET(decos, 0))->lineno;
+    }
+
     funcflags = compiler_default_arguments(c, args);
     if (funcflags == -1) {
         return 0;
@@ -1989,7 +1995,7 @@ compiler_function(struct compiler *c, stmt_ty s, int is_async)
         funcflags |= 0x04;
     }
 
-    if (!compiler_enter_scope(c, name, scope_type, (void *)s, s->lineno)) {
+    if (!compiler_enter_scope(c, name, scope_type, (void *)s, firstlineno)) {
         return 0;
     }
 
@@ -2032,12 +2038,17 @@ compiler_class(struct compiler *c, stmt_ty s)
 {
     PyCodeObject *co;
     PyObject *str;
-    int i;
+    int i, firstlineno;
     asdl_seq* decos = s->v.ClassDef.decorator_list;
 
     if (!compiler_decorators(c, decos))
         return 0;
 
+    firstlineno = s->lineno;
+    if (asdl_seq_LEN(decos)) {
+        firstlineno = ((expr_ty)asdl_seq_GET(decos, 0))->lineno;
+    }
+
     /* ultimately generate code for:
          <name> = __build_class__(<func>, <name>, *<bases>, **<keywords>)
        where:
@@ -2052,7 +2063,7 @@ compiler_class(struct compiler *c, stmt_ty s)
 
     /* 1. compile the class body into a code object */
     if (!compiler_enter_scope(c, s->v.ClassDef.name,
-                              COMPILER_SCOPE_CLASS, (void *)s, s->lineno))
+                              COMPILER_SCOPE_CLASS, (void *)s, firstlineno))
         return 0;
     /* this block represents what we do in the new scope */
     {