patch 8.1.0956: using context:0 in 'diffopt' does not work well
Problem: Using context:0 in 'diffopt' does not work well.
Solution: Make zero context do the same as one line context. (closes #4005)
diff --git a/src/testdir/dumps/Test_diff_06.0.dump b/src/testdir/dumps/Test_diff_06.0.dump
new file mode 100644
index 0000000..8d73089
--- /dev/null
+++ b/src/testdir/dumps/Test_diff_06.0.dump
@@ -0,0 +1,20 @@
+|++0#0000e05#a8a8a8255| >+|-@1| @1|3| |l|i|n|e|s|:| |1|-@19||+1#0000000#ffffff0|++0#0000e05#a8a8a8255| |+|-@1| @1|3| |l|i|n|e|s|:| |1|-@19
+| @1|4+0#0000000#ffffff0| @33||+1&&| +0#0000e05#a8a8a8255@1|4+0#0000000#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|4+0#0000000#5fd7ff255| @33||+1&#ffffff0| +0#0000e05#a8a8a8255@1|-+0#4040ff13#afffff255@34
+| +0#0000e05#a8a8a8255@1|5+0#0000000#ffffff0| @33||+1&&| +0#0000e05#a8a8a8255@1|5+0#0000000#ffffff0| @33
+|++0#0000e05#a8a8a8255| |+|-@1| @1|4| |l|i|n|e|s|:| |6|-@19||+1#0000000#ffffff0|++0#0000e05#a8a8a8255| |+|-@1| @1|4| |l|i|n|e|s|:| |6|-@19
+| @1|1+0#0000000#ffffff0|0| @32||+1&&| +0#0000e05#a8a8a8255@1|1+0#0000000#ffffff0|0| @32
+| +0#0000e05#a8a8a8255@1|-+0#4040ff13#afffff255@34||+1#0000000#ffffff0| +0#0000e05#a8a8a8255@1|1+0#0000000#5fd7ff255@1| @32
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+|X+3#0000000&|f|i|l|e|1| @12|1|,|1| @11|A|l@1| |X+1&&|f|i|l|e|2| @12|1|,|1| @11|A|l@1
+|:+0&&|s|e|t| |d|i|f@1|o|p|t|+|=|c|o|n|t|e|x|t|:|0| @51
diff --git a/src/testdir/dumps/Test_diff_06.1.dump b/src/testdir/dumps/Test_diff_06.1.dump
new file mode 100644
index 0000000..b2b6583
--- /dev/null
+++ b/src/testdir/dumps/Test_diff_06.1.dump
@@ -0,0 +1,20 @@
+|++0#0000e05#a8a8a8255| >+|-@1| @1|3| |l|i|n|e|s|:| |1|-@19||+1#0000000#ffffff0|++0#0000e05#a8a8a8255| |+|-@1| @1|3| |l|i|n|e|s|:| |1|-@19
+| @1|4+0#0000000#ffffff0| @33||+1&&| +0#0000e05#a8a8a8255@1|4+0#0000000#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|4+0#0000000#5fd7ff255| @33||+1&#ffffff0| +0#0000e05#a8a8a8255@1|-+0#4040ff13#afffff255@34
+| +0#0000e05#a8a8a8255@1|5+0#0000000#ffffff0| @33||+1&&| +0#0000e05#a8a8a8255@1|5+0#0000000#ffffff0| @33
+|++0#0000e05#a8a8a8255| |+|-@1| @1|4| |l|i|n|e|s|:| |6|-@19||+1#0000000#ffffff0|++0#0000e05#a8a8a8255| |+|-@1| @1|4| |l|i|n|e|s|:| |6|-@19
+| @1|1+0#0000000#ffffff0|0| @32||+1&&| +0#0000e05#a8a8a8255@1|1+0#0000000#ffffff0|0| @32
+| +0#0000e05#a8a8a8255@1|-+0#4040ff13#afffff255@34||+1#0000000#ffffff0| +0#0000e05#a8a8a8255@1|1+0#0000000#5fd7ff255@1| @32
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+|X+3#0000000&|f|i|l|e|1| @12|1|,|1| @11|A|l@1| |X+1&&|f|i|l|e|2| @12|1|,|1| @11|A|l@1
+|:+0&&|s|e|t| |d|i|f@1|o|p|t|+|=|c|o|n|t|e|x|t|:|1| @51
diff --git a/src/testdir/dumps/Test_diff_06.2.dump b/src/testdir/dumps/Test_diff_06.2.dump
new file mode 100644
index 0000000..ce07d07
--- /dev/null
+++ b/src/testdir/dumps/Test_diff_06.2.dump
@@ -0,0 +1,20 @@
+|++0#0000e05#a8a8a8255| >+|-@1| @1|2| |l|i|n|e|s|:| |1|-@19||+1#0000000#ffffff0|++0#0000e05#a8a8a8255| |+|-@1| @1|2| |l|i|n|e|s|:| |1|-@19
+| @1|3+0#0000000#ffffff0| @33||+1&&| +0#0000e05#a8a8a8255@1|3+0#0000000#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|4+0#0000000#ffffff0| @33||+1&&| +0#0000e05#a8a8a8255@1|4+0#0000000#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|4+0#0000000#5fd7ff255| @33||+1&#ffffff0| +0#0000e05#a8a8a8255@1|-+0#4040ff13#afffff255@34
+| +0#0000e05#a8a8a8255@1|5+0#0000000#ffffff0| @33||+1&&| +0#0000e05#a8a8a8255@1|5+0#0000000#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|6+0#0000000#ffffff0| @33||+1&&| +0#0000e05#a8a8a8255@1|6+0#0000000#ffffff0| @33
+|++0#0000e05#a8a8a8255| |+|-@1| @1|2| |l|i|n|e|s|:| |7|-@19||+1#0000000#ffffff0|++0#0000e05#a8a8a8255| |+|-@1| @1|2| |l|i|n|e|s|:| |7|-@19
+| @1|9+0#0000000#ffffff0| @33||+1&&| +0#0000e05#a8a8a8255@1|9+0#0000000#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|1+0#0000000#ffffff0|0| @32||+1&&| +0#0000e05#a8a8a8255@1|1+0#0000000#ffffff0|0| @32
+| +0#0000e05#a8a8a8255@1|-+0#4040ff13#afffff255@34||+1#0000000#ffffff0| +0#0000e05#a8a8a8255@1|1+0#0000000#5fd7ff255@1| @32
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+|X+3#0000000&|f|i|l|e|1| @12|1|,|1| @11|A|l@1| |X+1&&|f|i|l|e|2| @12|1|,|1| @11|A|l@1
+|:+0&&@1|s|e|t| |d|i|f@1|o|p|t|+|=|c|o|n|t|e|x|t|:|2| @50
diff --git a/src/testdir/test_diffmode.vim b/src/testdir/test_diffmode.vim
index 84fb451..5a3a6be 100644
--- a/src/testdir/test_diffmode.vim
+++ b/src/testdir/test_diffmode.vim
@@ -783,6 +783,17 @@
call WriteDiffFiles(buf, [1, 2, 3, 4, 4, 5, 6, 7, 8, 9, 10], [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11])
call VerifyBoth(buf, 'Test_diff_06', '')
+ " Variants on test 6 with different context settings
+ call term_sendkeys(buf, ":set diffopt+=context:2\<cr>")
+ call VerifyScreenDump(buf, 'Test_diff_06.2', {})
+ call term_sendkeys(buf, ":set diffopt-=context:2\<cr>")
+ call term_sendkeys(buf, ":set diffopt+=context:1\<cr>")
+ call VerifyScreenDump(buf, 'Test_diff_06.1', {})
+ call term_sendkeys(buf, ":set diffopt-=context:1\<cr>")
+ call term_sendkeys(buf, ":set diffopt+=context:0\<cr>")
+ call VerifyScreenDump(buf, 'Test_diff_06.0', {})
+ call term_sendkeys(buf, ":set diffopt-=context:0\<cr>")
+
" Test 7 - 9: Test normal/patience/histogram diff algorithm
call WriteDiffFiles(buf, ['#include <stdio.h>', '', '// Frobs foo heartily', 'int frobnitz(int foo)', '{',
\ ' int i;', ' for(i = 0; i < 10; i++)', ' {', ' printf("Your answer is: ");',