[cfe-dev] Replacing the non-portable diff invocation coded as %diff_plist (and friends)

Artem Dergachev via cfe-dev cfe-dev at lists.llvm.org
Wed Apr 3 16:23:37 PDT 2019


Yup, sounds reasonable!

Traditionally these tests were using FileCheck. The point of replacing 
FileCheck with diff was that FileCheck failure reports for incorrectly 
produced plist files on tests were very hard to understand, especially 
when it was happening on a remote buildbot. This was happening because 
plists are XML files and most bugs in them usually look like large 
(10-20) lines suddenly appearing or disappearing, with the most 
important information being in the innermost XML tag in the middle of 
the chunk. Because FileCheck reports only the first line that doesn't 
match, it made it very annoying to debug. Diffs, on the other hand, are 
outright perfect for the task.

An external normalization script doesn't anyhow contradict this purpose, 
and if i understand correctly it was in fact one of the possible 
solutions that was considered back in 

On 4/2/19 1:07 PM, Hubert Tong via cfe-dev wrote:
> Various tests in `clang/test/Analysis/` invoke `diff` with a 
> non-portable `-I` option. I do not believe that a requirement for a 
> `diff` utility that supports such an extension is intended by the 
> community. I believe that replacing `diff -I` with `diff` on files 
> that have been normalized using `grep -v` is a reasonable solution. A 
> minor detail is that the output being checked is produced without a 
> newline at the end of the file. As part of the proposed solution, the 
> file is rehabilitated as a text file (as required by `grep`) by adding 
> such a newline. The same is done for the reference expected files that 
> are missing a newline at the end of the file. The solution is sketched 
> out below for feedback.
> The normalization is in many cases encoded in a lit substitution 
> `%diff_plist`. A sample application of the proposed change would look 
> like the following. See further below for additional rationale on the 
> particulars.
> Replace the RUN line:
> -// RUN: cat %t.plist | %diff_plist 
> %S/Inputs/expected-plists/unix-fns.c.plist -
> +// RUN: %normalize_plist <%S/Inputs/expected-plists/unix-fns.c.plist 
> >%t.expected.sed.plist && echo >>%t.plist && %normalize_plist 
> <%t.plist | diff -u %t.expected.sed.plist -
> Replace the lit substitution:
> -# Diff command used by Clang Analyzer tests (when comparing .plist files
> +# Filtering command used by Clang Analyzer tests (when comparing 
> .plist files
>  # with reference output)
> -config.substitutions.append(('%diff_plist',
> -    'diff -u -w -I "<string>/" -I "<string>.:" -I "version"'))
> +config.substitutions.append(('%normalize_plist',
> +    "grep -Ev '%s|%s|%s'" %
> +        ('^[[:space:]]*<string>.* version .*</string>$',
> +         '^[[:space:]]*<string>/.*</string>$',
> +         '^[[:space:]]*<string>.:.*</string>$')))
> Why not use more `RUN` lines?
> The output being checked is line-number sensitive. Keeping the same 
> number of `RUN` lines minimizes unnecessary noise and risk of errors.
> Why not use `sed`?
> `sed` can be used to normalize the lines that are expected to vary; 
> however, the some of the expected-output files have these lines omitted.
> The `grep` replacement is more compatible with the behaviour of `diff 
> -I`. The filtered files are nevertheless named with "sed" for the 
> connotation that substitution took place.
> Why remove `-w` from `diff`?
> It appears that the `-w` option was being used for its effect (in some 
> implementations) of ignoring the difference between a file that ends 
> with a newline and one which does not. Following normalization of both 
> files to end in a newline, this is no longer necessary. Since the 
> effect is non-portable, keeping the option (and thus allowing the 
> non-portable effect to occur, and perhaps become relied upon during 
> development) is potentially harmful.
> Why not add the newline via `cat`?
> The newline can be added (in this context) using `echo | cat file -` 
> as opposed to using `echo >>file`; however, the `lit` implementation 
> of `cat` does not operate as expected on the standard input.
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