From `gn help inputs`:

"Inputs for binary targets will be treated as order-only dependencies, meaning 
that they will be forced up-to-date before compiling or any files in the target, 
but changes in the inputs will not necessarily force the target to compile. 
This is because it is expected that the compiler will report the precise list 
of input dependencies required to recompile each file once the initial build is done."

I'm not sure why brettw@ thought this was the right thing to do. 
AFAIK `ar`, `ld` and friends don't have a concept of -MMD or any 
other way to generate a deps file, and it doesn't really make sense to 
specify `inputs` to individual object files either.

This also affects the .saves file inputs to the linker for striping: https://codereview.chromium.org/1999513002/

Re-assigning this to brettw@ now that he's back in the office. 

Brett, we discussed this briefly last week or the week before; I think the thing to do here is to make inputs a proper dependency on links, not just an order-only dependency, since link commands have no concept of deps files that they could dump precise lists into.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/57ac2eae0f67ef9310e2fad40258b1d45ac82435

commit 57ac2eae0f67ef9310e2fad40258b1d45ac82435
Author: phosek <phosek@chromium.org>
Date: Fri Jun 17 21:49:02 2016

GN: Use implicit dependency for binary input deps

This is to ensure that the input gets rebuilt when the depencies change
even when they are not included in the depfile generated by the
compiler.

BUG=612623

Review-Url: https://codereview.chromium.org/2071573003
Cr-Commit-Position: refs/heads/master@{#400515}

[modify] https://crrev.com/57ac2eae0f67ef9310e2fad40258b1d45ac82435/tools/gn/docs/reference.md
[modify] https://crrev.com/57ac2eae0f67ef9310e2fad40258b1d45ac82435/tools/gn/ninja_binary_target_writer.cc
[modify] https://crrev.com/57ac2eae0f67ef9310e2fad40258b1d45ac82435/tools/gn/ninja_binary_target_writer.h
[modify] https://crrev.com/57ac2eae0f67ef9310e2fad40258b1d45ac82435/tools/gn/ninja_binary_target_writer_unittest.cc
[modify] https://crrev.com/57ac2eae0f67ef9310e2fad40258b1d45ac82435/tools/gn/ninja_target_writer.cc
[modify] https://crrev.com/57ac2eae0f67ef9310e2fad40258b1d45ac82435/tools/gn/ninja_target_writer_unittest.cc
[modify] https://crrev.com/57ac2eae0f67ef9310e2fad40258b1d45ac82435/tools/gn/variables.cc

bouncing this back to rsesek@; I think just listing this in `inputs` should work now.

This seems to work for executable but not shared_library targets.

WIP patch https://codereview.chromium.org/2119843004

Is this still an issue?

Yeah, when I tested this in #8/#9 this wasn't fully done.