Remove the unify mode

The unify mode has not received enough attention and has at least these
bugs:

1. The direct mode doesn’t work if the unify mode is enabled. This is
   because the unify mode doesn’t call into process_preprocessed_file
   which stores the paths and hashes of included files needed by the
   direct mode.
2. The .incbin directive detection has no effect when using the unify
   mode. This is again because the unify mode doesn’t use
   process_preprocessed_file which is where the .incbin detection takes
   place.
3. The unifier’s tokenizer doesn’t understand C++11 raw string literals.
4. The unifier ignores comments, but comments may have semantic meaning
   to modern compilers, e.g. “fall through” comments.

Bugs 3 and 4 are fixable by improving the unifier’s tokenization
algorithm, but since it’s a bit tricky it likely won’t be worth the
effort, especially not as a bug fix.

Bugs 1 and 2 are also fixable by unifying the two code paths, but that’s
a non-trivial effort.

In addition to the bugs, I believe that the usefullness of the unify
mode is low:

* It’s only applicable when not using -g.
* It won't be enabled for C++ unless somebody fixes bug 3.
* It can make line numbers in warning messages and __LINE__ expansions
  incorrect.
* Since comments should not be ignored, the unify mode can only make a
  difference for some types of whitespace changes, like adding or
  removing blank lines or changing a+b to a + b. (a + b is already
  normalized to a + b by the preprocessor.)

Therefore I’ll just remove the unify mode to fix the bugs.

Fixes #497.

(cherry picked from commit 947a72ce3712a6901e7ddc43a50c5df40739113e)

1 files changed, 0 insertions, 13 deletions

diff --git a/doc/MANUAL.adoc b/doc/MANUAL.adoc
index e4af9982..b9820e0f 100644
--- a/doc/MANUAL.adoc
+++ b/doc/MANUAL.adoc
@@ -704,18 +704,6 @@ NOTE: In previous versions of ccache, *CCACHE_TEMPDIR* had to be on the same
     with other users. Note that this also affects the file permissions set on
     the object files created from your compilations.
 
-[[config_unify]] *unify* (*CCACHE_UNIFY* or *CCACHE_NOUNIFY*, see <<_boolean_values,Boolean values>> above)::
-
-    If true, ccache will use a C/C++ unifier when hashing the preprocessor
-    output if the *-g* option is not used. The unifier is slower than a normal
-    hash, so setting this environment variable loses a little bit of speed, but
-    it means that ccache can take advantage of not recompiling when the changes
-    to the source code consist of reformatting only. Note that enabling the
-    unifier changes the hash, so cached compilations produced when the unifier
-    is enabled cannot be reused when the unifier is disabled, and vice versa.
-    Enabling the unifier may result in incorrect line number information in
-    compiler warning messages and expansions of the `__LINE__` macro.
-
 
 Cache size management
 ---------------------
@@ -1073,7 +1061,6 @@ The depend mode will be disabled if any of the following holds:
 
 * the configuration setting <<config_depend_mode,*depend_mode*>> is false
 * the configuration setting <<config_run_second_cpp,*run_second_cpp*>> is false
-* the configuration setting <<config_unify,*unify*>> is true
 * the compiler is not generating dependencies using *-MD* or *-MMD*