Using git to find first introduction of token on a specific line of a file

Question

Let's say I have a file A.cpp, and I notice an error on line 15 of the file. Let's say the error is a "const" on a function that returns a pointer to a member variable, meaning using const on the function is technically correct but semantically wrong. I would like to discuss the semantics with the author who made the change.

Using git, is there a way to find out which revision introduced the "const" token? More specifically, I'd like to know who introduced the token.

"git blame" shows who made the last change to the line, but I would actually like to find the first commit containing the token.

Answer 1

There are a few possible ways of doing it.

• git blame, or better graphical blame tool (like git gui blame or the blame view in git instaweb / gitweb) to browse history of a line, going back in history until you find appropriate commit.

• so called "pickaxe search", i.e. git log -S with appropriate token / regexp, to find (list) all commits where number of given tokens changed (which usually means where given token was added or deleted), e.g.:

  git log --reverse -p -S'const int foobar' -- A.cpp
  

• git bisect where "bad" commit would mean the one with 'const' where there it shouldn't be (testing using e.g. grep).