qapi: Improve source file read error handling

qapi-gen.py crashes when it can't open the main schema file, and when
it can't read from any schema file.  Lazy.

Change QAPISchema.__init__() to take a file name instead of a file
object.  Move the open code from _include() to __init__(), so it's
used for the main schema file, too.

Move the read into the try for good measure, and rephrase the error
message.

Reporting open or read failure for the main schema file needs a
QAPISourceInfo representing "no source".  Make QAPISourceInfo cope
with fname=None.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20190927134639.4284-27-armbru@redhat.com>

scripts/qapi/common.py

@@ -53,7 +53,12 @@ class QAPISourceInfo(object):
         return info
 
     def loc(self):
-        return '%s:%d' % (self.fname, self.line)
+        if self.fname is None:
+            return sys.argv[0]
+        ret = self.fname
+        if self.line is not None:
+            ret += ':%d' % self.line
+        return ret
 
     def in_defn(self):
         if self.defn_name:
@@ -383,14 +388,26 @@ class QAPIDoc(object):
 
 class QAPISchemaParser(object):
 
-    def __init__(self, fp, previously_included=[], incl_info=None):
+    def __init__(self, fname, previously_included=[], incl_info=None):
-        self.fname = fp.name
+        previously_included.append(os.path.abspath(fname))
-        previously_included.append(os.path.abspath(fp.name))
+
-        self.src = fp.read()
+        try:
+            if sys.version_info[0] >= 3:
+                fp = open(fname, 'r', encoding='utf-8')
+            else:
+                fp = open(fname, 'r')
+            self.src = fp.read()
+        except IOError as e:
+            raise QAPISemError(incl_info or QAPISourceInfo(None, None, None),
+                               "can't read %s file '%s': %s"
+                               % ("include" if incl_info else "schema",
+                                  fname,
+                                  e.strerror))
+
         if self.src == '' or self.src[-1] != '\n':
             self.src += '\n'
         self.cursor = 0
-        self.info = QAPISourceInfo(self.fname, 1, incl_info)
+        self.info = QAPISourceInfo(fname, 1, incl_info)
         self.line_pos = 0
         self.exprs = []
         self.docs = []
@@ -414,7 +431,7 @@ class QAPISchemaParser(object):
                 if not isinstance(include, str):
                     raise QAPISemError(info,
                                        "value of 'include' must be a string")
-                incl_fname = os.path.join(os.path.dirname(self.fname),
+                incl_fname = os.path.join(os.path.dirname(fname),
                                           include)
                 self.exprs.append({'expr': {'include': incl_fname},
                                    'info': info})
@@ -466,14 +483,7 @@ class QAPISchemaParser(object):
         if incl_abs_fname in previously_included:
             return None
 
-        try:
+        return QAPISchemaParser(incl_fname, previously_included, info)
-            if sys.version_info[0] >= 3:
-                fobj = open(incl_fname, 'r', encoding='utf-8')
-            else:
-                fobj = open(incl_fname, 'r')
-        except IOError as e:
-            raise QAPISemError(info, "%s: %s" % (e.strerror, incl_fname))
-        return QAPISchemaParser(fobj, previously_included, info)
 
     def _pragma(self, name, value, info):
         global doc_required, returns_whitelist, name_case_whitelist
@@ -1734,11 +1744,7 @@ class QAPISchemaEvent(QAPISchemaEntity):
 class QAPISchema(object):
     def __init__(self, fname):
         self.fname = fname
-        if sys.version_info[0] >= 3:
+        parser = QAPISchemaParser(fname)
-            f = open(fname, 'r', encoding='utf-8')
-        else:
-            f = open(fname, 'r')
-        parser = QAPISchemaParser(f)
         exprs = check_exprs(parser.exprs)
         self.docs = parser.docs
         self._entity_list = []

tests/qapi-schema/include-no-file.err

@@ -1 +1 @@
-tests/qapi-schema/include-no-file.json:1: No such file or directory: tests/qapi-schema/include-no-file-sub.json
+tests/qapi-schema/include-no-file.json:1: can't read include file 'tests/qapi-schema/include-no-file-sub.json': No such file or directory