Add a derived `Show SrcLoc` instance

Test Plan:
```
ghci> import GHC.Stack
ghci> SrcLoc "f" "b" "c" 1 2 3 4
SrcLoc {srcLocPackage = "f", srcLocModule = "b", srcLocFile = "c",
srcLocStartLine = 1, srcLocStartCol = 2, srcLocEndLine = 3,
srcLocEndCol = 4}
```

Reviewers: austin, hvr, bgamari

Reviewed By: bgamari

Subscribers: thomie

Projects: #ghc

Differential Revision: https://phabricator.haskell.org/D1886

GHC Trac Issues: #11510

6 files changed, 9 insertions, 6 deletions

diff --git a/libraries/base/GHC/Show.hs b/libraries/base/GHC/Show.hs
index 4322aff2e8..a3807bbf32 100644
--- a/libraries/base/GHC/Show.hs
+++ b/libraries/base/GHC/Show.hs
@@ -52,6 +52,7 @@ module GHC.Show
 import GHC.Base
 import GHC.List ((!!), foldr1, break)
 import GHC.Num
+import GHC.Stack.Types
 
 -- | The @shows@ functions return a function that prepends the
 -- output 'String' to an existing 'String'.  This allows constant-time
@@ -204,6 +205,8 @@ instance Show TrName where
 instance Show Module where
   showsPrec _ (Module p m) = shows p . (':' :) . shows m
 
+deriving instance Show SrcLoc
+
 --------------------------------------------------------------
 -- Show instances for the first few tuple
 --------------------------------------------------------------
diff --git a/testsuite/tests/ghci.debugger/scripts/break006.stderr b/testsuite/tests/ghci.debugger/scripts/break006.stderr
index 3b57eb3a64..b04dd169a0 100644
--- a/testsuite/tests/ghci.debugger/scripts/break006.stderr
+++ b/testsuite/tests/ghci.debugger/scripts/break006.stderr
@@ -10,7 +10,7 @@
         instance Show Ordering -- Defined in ‘GHC.Show’
         instance Show Integer -- Defined in ‘GHC.Show’
         ...plus 23 others
-        ...plus 19 instance involving out-of-scope typess
+        ...plus 20 instance involving out-of-scope typess
         (use -fprint-potential-instances to see them all)
     • In a stmt of an interactive GHCi command: print it
 
@@ -25,6 +25,6 @@
         instance Show Ordering -- Defined in ‘GHC.Show’
         instance Show Integer -- Defined in ‘GHC.Show’
         ...plus 23 others
-        ...plus 19 instance involving out-of-scope typess
+        ...plus 20 instance involving out-of-scope typess
         (use -fprint-potential-instances to see them all)
     • In a stmt of an interactive GHCi command: print it
diff --git a/testsuite/tests/ghci.debugger/scripts/print019.stderr b/testsuite/tests/ghci.debugger/scripts/print019.stderr
index 0dcc854245..428abb15fa 100644
--- a/testsuite/tests/ghci.debugger/scripts/print019.stderr
+++ b/testsuite/tests/ghci.debugger/scripts/print019.stderr
@@ -9,6 +9,6 @@
         instance Show Ordering -- Defined in ‘GHC.Show’
         instance Show Integer -- Defined in ‘GHC.Show’
         ...plus 30 others
-        ...plus 8 instance involving out-of-scope typess
+        ...plus 9 instance involving out-of-scope typess
         (use -fprint-potential-instances to see them all)
     • In a stmt of an interactive GHCi command: print it
diff --git a/testsuite/tests/overloadedlists/should_fail/overloadedlistsfail01.stderr b/testsuite/tests/overloadedlists/should_fail/overloadedlistsfail01.stderr
index 7a43f4f778..9a72957573 100644
--- a/testsuite/tests/overloadedlists/should_fail/overloadedlistsfail01.stderr
+++ b/testsuite/tests/overloadedlists/should_fail/overloadedlistsfail01.stderr
@@ -8,7 +8,7 @@ overloadedlistsfail01.hs:5:8: error:
         instance Show Integer -- Defined in ‘GHC.Show’
         instance Show a => Show (Maybe a) -- Defined in ‘GHC.Show’
         ...plus 22 others
-        ...plus four instance involving out-of-scope typess
+        ...plus five instance involving out-of-scope typess
         (use -fprint-potential-instances to see them all)
     • In the expression: print [1]
       In an equation for ‘main’: main = print [1]
diff --git a/testsuite/tests/typecheck/should_compile/holes2.stderr b/testsuite/tests/typecheck/should_compile/holes2.stderr
index 5541689c83..f10ea95e61 100644
--- a/testsuite/tests/typecheck/should_compile/holes2.stderr
+++ b/testsuite/tests/typecheck/should_compile/holes2.stderr
@@ -8,7 +8,7 @@ holes2.hs:3:5: warning:
         instance Show Integer -- Defined in ‘GHC.Show’
         instance Show a => Show (Maybe a) -- Defined in ‘GHC.Show’
         ...plus 22 others
-        ...plus three instance involving out-of-scope typess
+        ...plus four instance involving out-of-scope typess
         (use -fprint-potential-instances to see them all)
     • In the expression: show _
       In an equation for ‘f’: f = show _
diff --git a/testsuite/tests/typecheck/should_fail/tcfail133.stderr b/testsuite/tests/typecheck/should_fail/tcfail133.stderr
index a178f02801..d8795eab90 100644
--- a/testsuite/tests/typecheck/should_fail/tcfail133.stderr
+++ b/testsuite/tests/typecheck/should_fail/tcfail133.stderr
@@ -12,7 +12,7 @@ tcfail133.hs:68:7: error:
         instance (Show a, Show b, Number a, Digit b) => Show (a :@ b)
           -- Defined at tcfail133.hs:11:54
         ...plus 25 others
-        ...plus three instance involving out-of-scope typess
+        ...plus four instance involving out-of-scope typess
         (use -fprint-potential-instances to see them all)
     • In the expression: show $ add (One :@ Zero) (One :@ One)
       In an equation for ‘foo’: