mdiff/patch: fix bad hunk handling for unified diffs with zero context Prior to this patch "hg diff -U0", i.e., zero lines of context, would output hunk headers with a start line one greater than what GNU patch and git output. Guido van Rossum documents the unified diff format[1] as having a start line value "one lower than one would expect" for zero length hunks. Comparing the behaviour of the three systems prior to this patch in transforming c1 c3 to c1 c2 c3 - GNU "diff -U0" reports the hunk as "@@ -1,0 +2 @@" - "git diff -U0" reports the hunk as "@@ -1,0 +2 @@" - "hg diff -U0" reports the hunk as "@@ -2,0 +2,1 @@" After this patch, "hg diff -U0" reports "@@ -1,0 +2,1 @@". Since "hg export --config diff.unified=0" outputs zero-context unified diffs, "hg import" has also been updated to account for start lines one less than expected for zero length hunk ranges. [1]: http://www.artima.com/weblogs/viewpost.jsp?thread=164293

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  $ hg init repo

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  $ cd repo

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  $ cat > a <<EOF

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  > c

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  > c

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  > a

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  > a

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  > b

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  > a

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  > a

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  > c

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  > c

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  > EOF

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  $ hg ci -Am adda

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  adding a

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  $ cat > a <<EOF

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  > c

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  > c

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  > a

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  > a

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  > dd

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  > a

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  > a

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  > c

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  > c

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  > EOF

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default context

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  $ hg diff --nodates

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  diff -r cf9f4ba66af2 a

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  --- a/a

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  +++ b/a

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  @@ -2,7 +2,7 @@

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   c

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   a

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   a

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  -b

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  +dd

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   a

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   a

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   c

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invalid --unified

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  $ hg diff --nodates -U foo

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  abort: diff context lines count must be an integer, not 'foo'

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  [255]

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  $ hg diff --nodates -U 2

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  diff -r cf9f4ba66af2 a

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  --- a/a

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  +++ b/a

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  @@ -3,5 +3,5 @@

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   a

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   a

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  -b

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  +dd

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   a

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   a

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  $ hg --config diff.unified=2 diff --nodates

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  diff -r cf9f4ba66af2 a

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  --- a/a

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  +++ b/a

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  @@ -3,5 +3,5 @@

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   a

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   a

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  -b

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  +dd

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   a

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   a

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  $ hg diff --nodates -U 1

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  diff -r cf9f4ba66af2 a

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  --- a/a

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  +++ b/a

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  @@ -4,3 +4,3 @@

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   a

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  -b

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  +dd

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   a

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invalid diff.unified

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  $ hg --config diff.unified=foo diff --nodates

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  abort: diff context lines count must be an integer, not 'foo'

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  [255]

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0 lines of context hunk header matches gnu diff hunk header

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  $ hg init diffzero

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  $ cd diffzero

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  $ cat > f1 << EOF

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  > c2

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  > c4

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  > c5

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  > EOF

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  $ hg commit -Am0

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  adding f1

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  $ cat > f2 << EOF

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  > c1

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  > c2

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  > c3

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  > c4

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  > EOF

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  $ diff -U0 f1 f2

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  --- f1	* (glob)

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  +++ f2	* (glob)

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  @@ -0,0 +1 @@

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  +c1

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  @@ -1,0 +3 @@

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  +c3

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  @@ -3 +4,0 @@

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  -c5

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  [1]

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  $ mv f2 f1

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  $ hg diff -U0 --nodates

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  diff -r 55d8ff78db23 f1

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  --- a/f1

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  +++ b/f1

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  @@ -0,0 +1,1 @@

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  +c1

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  @@ -1,0 +3,1 @@

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  +c3

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  @@ -3,1 +4,0 @@

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  -c5

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  $ hg diff -U0 --nodates --git

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  diff --git a/f1 b/f1

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  --- a/f1

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  +++ b/f1

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  @@ -0,0 +1,1 @@

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  +c1

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  @@ -1,0 +3,1 @@

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  +c3

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  @@ -3,1 +4,0 @@

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  -c5

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  $ hg diff -U0 --nodates -p

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  diff -r 55d8ff78db23 f1

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  --- a/f1

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  +++ b/f1

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  @@ -0,0 +1,1 @@

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  +c1

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  @@ -1,0 +3,1 @@ c2

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  +c3

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  @@ -3,1 +4,0 @@ c4

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  -c5