[cfe-dev] Parsing ObjC source file with precompiled headers in libclang

Nikita Zhuk nikita at zhuk.fi
Tue Jan 17 11:43:59 PST 2012

Hi Gregory,

index.read is mapped to the clang_createTranslationUnit function in libclang, which is documented to "Create a translation unit from an AST file (-emit-ast).". Since the precompiled header isn't AST file, I don't think that function should be used.

On 16.1.2012, at 8.31, Gregory Szorc wrote:

> On 1/15/2012 9:14 AM, Nikita Zhuk wrote:
>> Hi,
>> I'm parsing an ObjC source file with libclang by using Python bindings. Parsing itself works fine but since I'm parsing source files which #import framework headers such as UIKit.h and Foundation.h, the parsing is a pretty heavy operation even for the most simple main source files. I would like to use precompiled prefix headers to make the parsing faster, but apparently I'm doing something wrong. Here is the Python code I use:
>> ---
>> import sys
>> import clang.cindex
>> index = clang.cindex.Index.create()
>> args = ["-include", "/Users/nzhuk/Desktop/MyTestApp/MyTestApp-Prefix.o.pch"]
>> sourceFile = "/Users/nzhuk/Desktop/MyTestApp/MyTestApp/NZMasterViewController.m"
>> tu = index.parse(sourceFile, args)
>> if(tu == None):
>> 	print "Parsing failed"
>> 	sys.exit(1)
>> print 'Translation unit:', tu.spelling
>> for diag in tu.diagnostics:
>> 	print diag
>> ---
>> The "MyTestApp-Prefix.o.pch" file is a precompiled header which was compiled from prefix header called "MyTestApp-Prefix.pch" with "clang -x objective-c-header [...other CC flags...] MyTestApp-Prefix.pch -o MyTestApp-Prefix.o.pch". The precompiled header is a 4.1 MB binary file which starts with characters "CPCH".
>> I get the translation unit back from the parse method, but apparently the parser tries to read the PCH file as text. The diagnostics output looks like this:
>> <Diagnostic severity 3, location <SourceLocation file '/Users/nzhuk/Desktop/MyTestApp/MyTestApp-Prefix.o.pch', line 1, column 1>, spelling "unknown type name 'CPCH'">
>> <Diagnostic severity 3, location <SourceLocation file '/Users/nzhuk/Desktop/MyTestApp/MyTestApp-Prefix.o.pch', line 1, column 5>, spelling "expected identifier or '('">
>> <Diagnostic severity 2, location <SourceLocation file '/Users/nzhuk/Desktop/MyTestApp/MyTestApp-Prefix.o.pch', line 1, column 7>, spelling 'null character ignored'>
>> [ ... ]
>> <Diagnostic severity 2, location <SourceLocation file '/Users/nzhuk/Desktop/MyTestApp/MyTestApp-Prefix.o.pch', line 446, column 175>, spelling 'null character ignored'>
>> <Diagnostic severity 4, location <SourceLocation file None, line 0, column 0>, spelling 'too many errors emitted, stopping now'>
>> I've tried replacing "-include" with "-include-pch", but that just returns a None (= null) translation unit from the parse method, without any diagnostics. Have I misunderstood the usage of precompiled headers? Any pointers would be greatly appreciated.
> I /think/ you should be using Index.read() instead of Index.parse() to
> load PCH files. Try:
>  tu = index.read(sourceFile)
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