git - git diff hunk header 中的摘录来自哪里？

Question

当我在 C# 文件上使用 git diff 时，我看到如下内容:

diff --git a/foo.cs b/foo.cs
index ff61664..dd8a3e3 100644
--- a/foo.cs
+++ b/foo.cs
@@ -15,6 +15,7 @@ static void Main(string[] args)
                    string name = Console.ReadLine();
             }
             Console.WriteLine("Hello {0}!", name);
+            Console.WriteLine("Goodbye");
         }
     }
 }

hunk 标题行包含当前方法的第一行 (static void Main(string[] args))，这很棒。然而它似乎不是很可靠......我看到很多情况下它不起作用。

所以我想知道，这段摘录是从哪里来的？ git diff 是否以某种方式识别语言语法？有没有办法自定义它？

Answer 1

Is there a way to customize it?

配置在 .gitattributes , section "Defining a custom hunk-header"中定义:

First, in .gitattributes, you would assign the diff attribute for paths.

*.tex diff=tex

Then, you would define a "diff.tex.xfuncname" configuration to specify a regular expression that matches a line that you would want to appear as the hunk header "TEXT". Add a section to your $GIT_DIR/config file (or $HOME/.gitconfig file) like this:

[diff "tex"]
   xfuncname = "^(\\\\(sub)*section\\{.*)$"

Note. A single level of backslashes are eaten by the configuration file parser, so you would need to double the backslashes; the pattern above picks a line that begins with a backslash, and zero or more occurrences of sub followed by section followed by open brace, to the end of line.

There are a few built-in patterns to make this easier, and tex is one of them, so you do not have to write the above in your configuration file (you still need to enable this with the attribute mechanism, via .gitattributes).

('csharp'是当前内置模式的一部分)

---

---

---

Where does this excerpt come from?
Does git diff somehow recognize the language syntax?

最初，该算法对于函数名称检测非常粗糙:
参见 commit acb7257 (Git 1.3.0，2006 年 4 月，作者:Mark Wooding)

xdiff : 在 block 头中显示函数名称。

The speed of the built-in diff generator is nice; but the function namesshown by diff -p are really nice. And I hate having to choose.
So, we hack xdiff to find the function names and print them.

The function names are parsed by a particularly stupid algorithm at themoment: it just tries to find a line in the 'old' file, from before thestart of the hunk, whose first character looks plausible. Still, it'smost definitely a start.

---

它是用 get_func_line() 精炼的, 本身来自 commit f258475 (Git 1.5.3，2007 年 9 月，作者 Junio C Hamano ( gitster ))

您可以在该提交中看到测试 t/t4018-diff-funcname.sh , 以测试自定义 diff 函数名称模式。

基于每个路径属性的 block 头选择。

This makes "diff -p" hunk headers customizable via gitattributes mechanism.
It is based on Johannes's earlier patch that allowed to define a singleregexp to be used for everything.

The mechanism to arrive at the regexp that is used to define hunk headeris the same as other use of gitattributes.
You assign an attribute, funcname (because "diff -p" typically uses the name of the function the patch is about as the hunk header), a simple string value.
This can be one of the names of built-in pattern (currently, java" is defined) or a custom pattern name, to be looked up from the configuration file.

 (in .gitattributes)
 *.java   funcname=java
 *.perl   funcname=perl

 (in .git/config)
 [funcname]
   java = ... # ugly and complicated regexp to override the built-in one.
   perl = ... # another ugly and complicated regexp to define a new one.

---

当前xfuncname commit 45d9414 中介绍了语法, Git 1.6.0.3，2008 年 10 月，由 Brandon Casey 撰写

diff.*.xfuncname它使用“扩展的”正则表达式来选择大块标题

Currently, the hunk headers produced by 'diff -p' are customizable bysetting the diff.*.funcname option in the config file. The 'funcname' option takes a basic regular expression. This functionality was designed using the GNU regex library which, by default, allows using backslashed versions of some extended regular expression operators, even in Basic Regular Expression mode. For example, the following characters, when backslashed, are interpreted according to the extended regular expression rules: ?, +, and |.
As such, the builtin funcname patterns were created using some extendedregular expression operators.

Other platforms which adhere more strictly to the POSIX spec do notinterpret the backslashed extended RE operators in Basic Regular Expressionmode. This causes the pattern matching for the builtin funcname patterns tofail on those platforms.

Introduce a new option 'xfuncname' which uses extended regular expressions, and advertise it instead of funcname.
Since most users are on GNU platforms, the majority of funcname patterns are created and tested there.
Advertising only xfuncname should help to avoid the creation of non-portable patterns which work with GNU regex but not elsewhere.

Additionally, the extended regular expressions may be less ugly andcomplicated compared to the basic RE since many common special operators do not need to be backslashed.

For example, the GNU Basic RE:

^[    ]*\\(\\(public\\|static\\).*\\)$

becomes the following Extended RE:

^[    ]*((public|static).*)$

---

最后，它被扩展为commit 14937c2 ，适用于 git 1.7.8(2011 年 12 月)，由 René Scharfe 撰写。

diff : 添加选项以将整个函数显示为上下文

Add the option -W/--function-context to git diff.
It is similar to the same option of git grep and expands the context of change hunks so that the whole surrounding function is shown.
This "natural" context can allow changes to be understood better.

---

它仍在 Git 2.15(2017 年第 4 季度)中进行调整

The built-in pattern to detect the "function header" for HTML didnot match <H1>..<H6> elements without any attributes, which hasbeen fixed.

在 2.15 之前，它无法匹配 <h1>...</h1> , 而 <h1 class="smth">...</h1>匹配。

参见 commit 9c03cac (2017 年 9 月 23 日)Ilya Kantor ( iliakan ) .
^{(由 Junio C Hamano -- gitster -- merge 于 commit 376a1da ，2017 年 9 月 28 日)}

---

检测函数边界的模式称为 xfuncref .

参见 commit a807200 (2019 年 11 月 8 日)Łukasz Niemier ( hauleth ) .
^{(由 Junio C Hamano -- gitster -- merge 于 commit 376e730，2019 年 12 月 1 日)}，适用于 Git 2.25(2020 年第一季度)

userdiff: add Elixir to supported userdiff languages

^{Signed-off-by: Łukasz Niemier
Acked-by: Johannes Sixt}

Adds support for xfuncref in Elixir language which is Ruby-like language that runs on Erlang Virtual Machine (BEAM).

和:

参见 commit d1b1384 (2019 年 12 月 13 日)Ed Maste ( emaste ) .
^{(由 Junio C Hamano -- gitster -- merge 于 commit ba6b662 ，2019 年 12 月 25 日)}

userdiff: remove empty subexpression from elixir regex

^{Signed-off-by: Ed Maste
Reviewed-by: Jeff King
Helped-by: Johannes Sixt}

The regex failed to compile on FreeBSD.

Also add /* -- */ mark to separate the two regex entries given to the PATTERNS() macro, to make it consistent with patterns for other content types.

---

Git 2.27(2020 年第二季度)添加了 Markdown 文档的 userdiff 模式。

参见 commit 09dad92 (2020 年 5 月 2 日)Ash Holland ( sersorrel ) .
^{(由 Junio C Hamano -- gitster -- merge 于 commit dc4c393，2020 年 5 月 8 日)}

userdiff: support Markdown

^{Signed-off-by: Ash Holland
Acked-by: Johannes Sixt}

It's typical to find Markdown documentation alongside source code, and having better context for documentation changes is useful; see also commit 69f9c87d4 ("userdiff: add support for Fountain documents", 2015-07-21, Git v2.6.0-rc0 -- merge listed in batch #1).

The pattern is based on the CommonMark specification 0.29, section 4.2 https://spec.commonmark.org/ but doesn't match empty headings, as seeing them in a hunk header is unlikely to be useful.

Only ATX headings are supported, as detecting setext headings would require printing the line before a pattern matches, or matching a multiline pattern. The word-diff pattern is the same as the pattern for HTML, because many Markdown parsers accept inline HTML.

---

在 Git 2.30(2021 年第一季度)中，userdiff 模式学会了识别 POSIX shell 中的函数定义和 bash .

参见 commit 2ff6c34 (2020 年 10 月 22 日)Victor Engmark ( l0b0 ) .
^{(由 Junio C Hamano -- gitster -- merge 于 commit 292e53f，2020 年 11 月 2 日)}

userdiff: support Bash

^{Signed-off-by: Victor Engmark
Acked-by: Johannes Sixt}

Support POSIX, bashism and mixed function declarations, all four compound command types, trailing comments and mixed whitespace.

Even though Bash allows locale-dependent characters in function names, only detect function names with characters allowed by POSIX.1-2017 for simplicity.
This should cover the vast majority of use cases, and produces system-agnostic results.

Since a word pattern has to be specified, but there is no easy way to know the default word pattern, use the default IFS characters for a starter. A later patch can improve this.

gitattributes现在包含在其 man page 中:

• bash suitable for source code in the Bourne-Again SHell language.
  Covers a superset of POSIX shell function definitions.

---

在 Git 2.32(2021 年第 2 季度)中，添加了“方案”的用户差异模式。

参见 commit a437390 (2021 年 4 月 8 日)Atharva Raykar ( tfidfwastaken ) .
^{(由 Junio C Hamano -- gitster -- merge 于 commit 6d7a62d，2021 年 4 月 20 日)}

userdiff: add support for Scheme

^{Signed-off-by: Atharva Raykar}

Add a diff driver for Scheme-like languages which recognizes top level and local define forms, whether it is a function definition, binding, syntax definition or a user-defined define-xyzzy form.

Also supports R6RS library forms, module forms along with class and struct declarations used in Racket (PLT Scheme).

Alternate "def" syntax such as those in Gerbil Scheme are also supported, like defstruct, defsyntax and so on.

The rationale for picking define forms for the hunk headers is because it is usually the only significant form for defining the structure of the program, and it is a common pattern for schemers to have local function definitions to hide their visibility, so it is not only the top level define's that are of interest.
Schemers also extend the language with macros to provide their own define forms (for example, something like a define-test-suite) which is also captured in the hunk header.

Since it is common practice to extend syntax with variants of a form like module+, class* etc, those have been supported as well.

The word regex is a best-effort attempt to conform to R7RS (section 2.1) valid identifiers, symbols and numbers.

gitattributes现在包含在其 man page 中:

• scheme suitable for source code in the Scheme language.

---

在 Git 2.33(2021 年第 3 季度)中，C# 的 userdiff 模式学习了 token “record”。

参见 commit c4e3178 (2021 年 3 月 2 日)作者:Julian Verdurmen ( 304NotModified ) .
^{(由 Junio C Hamano -- gitster -- merge 于 commit f741069 ，2021 年 7 月 8 日)}

userdiff: add support for C# record types

^{Signed-off-by: Julian Verdurmen
Reviewed-by: Johannes Schindelin}

Records are added in C# 9

Code example :

public record Person(string FirstName, string LastName);

For more information, see https://learn.microsoft.com/en-us/dotnet/csharp/whats-new/csharp-9

---

在 Git 2.34(2021 年第 4 季度)中，“java”语言的 userdiff 模式已经更新。

参见 commit a8cbc89 (2021 年 8 月 11 日)Tassilo Horn ( tsdh ) .
^{(由 Junio C Hamano -- gitster -- merge 于 commit a896086 ，2021 年 8 月 30 日)}

userdiff: improve java hunk header regex

^{Signed-off-by: Tassilo Horn}

Currently, the git diff^(man) hunk headers show the wrong method signature if the method has a qualified return type, an array return type, or a generic return type because the regex doesn't allow dots (.), [], or < and > in the return type.
Also, type parameter declarations couldn't be matched.

Add several t4018 tests asserting the right hunk headers for different cases:

• enum constant change
• change in generic method with bounded type parameters
• change in generic method with wildcard
• field change in a nested class

并且，仍然使用 Git 2.34(2021 年第 4 季度)，更新了 C++ 语言的用户差异模式。

参见 commit 386076e (2021 年 10 月 24 日)，commit c4fdba3 , commit 637b80c , commit bfaaf19 (2021 年 10 月 10 日)，和 commit 350b87c , commit 3e063de , commit 1cf9384 (2021 年 10 月 8 日)Johannes Sixt ( j6t ) .
^{(由 Junio C Hamano -- gitster -- merge 于 commit f3f157f，2021 年 10 月 25 日)}

例如:

userdiff-cpp: permit the digit-separating single-quote in numbers

^{Signed-off-by: Johannes Sixt}

Since C++17, the single-quote can be used as digit separator:

3.141'592'654
1'000'000
0xdead'beaf

Make it known to the word regex of the cpp driver, so that numbers are not split into separate tokens at the single-quotes.