Explicitly define cmp_pandas_datetimestruct

[jbrockmendel]

Fixes build warning

pandas/_libs/tslib.c:78967:17: warning: implicit declaration of function 'cmp_pandas_datetimestruct' is invalid in C99 [-Wimplicit-function-declaration]

[jreback]

lgtm. ping on green.

[codecov]

Codecov Report

Merging #17750 into master will decrease coverage by 0.04%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #17750      +/-   ##
==========================================
- Coverage   91.25%   91.21%   -0.05%     
==========================================
  Files         163      163              
  Lines       49856    49856              
==========================================
- Hits        45496    45474      -22     
- Misses       4360     4382      +22

Flag	Coverage Δ
#multiple	89.01% <ø> (-0.03%)	⬇️
#single	40.25% <ø> (-0.07%)	⬇️

Impacted Files	Coverage Δ
pandas/io/gbq.py	25% <0%> (-58.34%)	⬇️
pandas/plotting/_converter.py	63.38% <0%> (-1.82%)	⬇️
pandas/core/frame.py	97.73% <0%> (-0.1%)	⬇️
pandas/core/indexes/datetimes.py	95.48% <0%> (-0.1%)	⬇️

---

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[codecov]

Codecov Report

Merging #17750 into master will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #17750      +/-   ##
==========================================
- Coverage   91.25%   91.24%   -0.02%     
==========================================
  Files         163      163              
  Lines       49856    49869      +13     
==========================================
+ Hits        45496    45502       +6     
- Misses       4360     4367       +7

Flag	Coverage Δ
#multiple	89.04% <ø> (ø)	⬆️
#single	40.24% <ø> (-0.07%)	⬇️

Impacted Files	Coverage Δ
pandas/io/gbq.py	25% <0%> (-58.34%)	⬇️
pandas/core/frame.py	97.73% <0%> (-0.1%)	⬇️
pandas/plotting/_style.py	74.28% <0%> (ø)	⬆️
pandas/core/internals.py	94.38% <0%> (ø)	⬆️
pandas/core/indexing.py	93.97% <0%> (+0.03%)	⬆️
pandas/io/formats/excel.py	96.69% <0%> (+0.04%)	⬆️
pandas/core/indexes/base.py	96.46% <0%> (+0.11%)	⬆️

---

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[jreback]

this is causing some more warnings have a look at the travis logs

[jbrockmendel]

Are you referring to

In file included from pandas/_libs/period.c:250:0:
pandas/_libs/src/datetime/np_datetime.h:106:5: note: expected ‘struct pandas_datetimestruct *’ but argument is of type ‘const struct pandas_datetimestruct *’
 int cmp_pandas_datetimestruct(pandas_datetimestruct *a,
     ^
pandas/_libs/period.c:20547:3: warning: passing argument 2 of ‘cmp_pandas_datetimestruct’ discards ‘const’ qualifier from pointer target type [enabled by default]

? AFAICT there's not much to be done about that unless we want to un-declare the const in np_datetime.c.

[jreback]

so how does this PR help then?

[jreback]

the warning currently s

pandas/_libs/tslib.c:81135:3: warning: implicit declaration of function ‘cmp_pandas_datetimestruct’ [-Wimplicit-function-declaration]
   __pyx_t_2 = ((cmp_pandas_datetimestruct(__pyx_v_dts, (&_NS_MIN_DTS)) == -1L) != 0);
   ^
pandas/_libs/tslib.c: In function ‘__pyx_pymod_exec_tslib’:

[jreback]

you need to declare const * the structure args in .h and change in .c

[jreback]

thanks!