Move linters into the tree

This MR moves the GHC linters into the tree, so that they can be run directly using Hadrian.

* Query all files tracked by Git instead of using changed files, so that we can run the exact same linting step locally and in a merge request.
* Only check that the changelogs don't contain TBA when RELEASE=YES.
* Add hadrian/lint script, which runs all the linting steps.
* Ensure the hlint job exits with a failure if hlint is not installed (otherwise we were ignoring the failure). Given that hlint doesn't seem to be available in CI at the moment, I've temporarily allowed failure in the hlint job.
* Run all linting tests in CI using hadrian.

10 files changed, 388 insertions, 30 deletions

diff --git a/testsuite/tests/linters/Makefile b/testsuite/tests/linters/Makefile
index 559d0bba3e..54ef4db132 100644
--- a/testsuite/tests/linters/Makefile
+++ b/testsuite/tests/linters/Makefile
@@ -1,11 +1,96 @@
 TOP=../..
 
-ifeq "$(NOTES_UTIL)" ""
-NOTES_UTIL := $(abspath $(TOP)/../inplace/bin/notes-util)
+ifeq "$(LINT_NOTES)" ""
+LINT_NOTES := $(abspath $(TOP)/../inplace/bin/lint-notes)
+endif
+
+ifeq "$(LINT_WHITESPACE)" ""
+LINT_WHITESPACE := $(abspath $(TOP)/../inplace/bin/lint-whitespace)
 endif
 
 uniques:
 	python3 checkUniques/check-uniques.py $(TOP)/..
 
+makefiles:
+	(cd $(TOP)/tests/linters/ && python3 regex-linters/check-makefiles.py tracked)
+
+version-number:
+	regex-linters/check-version-number.sh ${TOP}/..
+
+cpp:
+	(cd $(TOP)/tests/linters/ && python3 regex-linters/check-cpp.py tracked)
+
+changelogs:
+	regex-linters/check-changelogs.sh $(TOP)/..
+
 notes:
-	(cd $(TOP)/.. && $(NOTES_UTIL) broken-refs)
+	(cd $(TOP)/.. && $(LINT_NOTES) broken-refs)
+
+whitespace:
+	(cd $(TOP)/.. &&\
+	  $(LINT_WHITESPACE) tracked\
+			--ignore-dirs\
+				testsuite\
+				libraries/base/cbits\
+				libraries/base/tests\
+				utils/hp2ps\
+				utils/hpc\
+				utils/unlit\
+			--ignore-files\
+				libraries/base/GHC/IO/Encoding/CodePage/Table.hs\
+				libraries/base/Control/Concurrent/QSem.hs\
+				libraries/base/Control/Concurrent/QSemN.hs\
+				libraries/base/Control/Monad/ST/Imp.hs\
+				libraries/base/Control/Monad/ST/Lazy.hs\
+				libraries/base/Data/Char.hs\
+				libraries/base/Data/Eq.hs\
+				libraries/base/Data/IORef.hs\
+				libraries/base/Data/Int.hs\
+				libraries/base/Data/Ix.hs\
+				libraries/base/Data/Ratio.hs\
+				libraries/base/Data/STRef/Lazy.hs\
+				libraries/base/Data/STRef/Strict.hs\
+				libraries/base/Foreign.hs\
+				libraries/base/Foreign/C.hs\
+				libraries/base/Foreign/Concurrent.hs\
+				libraries/base/Foreign/ForeignPtr.hs\
+				libraries/base/Foreign/ForeignPtr/Imp.hs\
+				libraries/base/Foreign/ForeignPtr/Safe.hs\
+				libraries/base/Foreign/ForeignPtr/Unsafe.hs\
+				libraries/base/Foreign/Marshal.hs\
+				libraries/base/Foreign/Marshal/Alloc.hs\
+				libraries/base/Foreign/Marshal/Error.hs\
+				libraries/base/Foreign/Marshal/Safe.hs\
+				libraries/base/Foreign/Marshal/Unsafe.hs\
+				libraries/base/Foreign/Safe.hs\
+				libraries/base/Foreign/StablePtr.hs\
+				libraries/base/Foreign/Storable.hs\
+				libraries/base/GHC/IO/Encoding/Latin1.hs\
+				libraries/base/GHC/IO/Encoding/Types.hs\
+				libraries/base/GHC/IO/Handle/FD.hs\
+				libraries/base/GHC/IO/IOMode.hs\
+				libraries/base/System/Console/GetOpt.hs\
+				libraries/base/System/IO/Unsafe.hs\
+				libraries/base/System/Mem.hs\
+				libraries/base/Text/Show.hs\
+				libraries/base/include/HsBase.h\
+				libraries/base/include/HsEvent.h\
+				libraries/base/include/md5.h\
+				libraries/ghc-prim/GHC/Tuple.hs\
+				libraries/template-haskell/Language/Haskell/TH/Quote.hs\
+				rts/STM.h\
+				rts/Sparks.h\
+				rts/Threads.h\
+				rts/hooks/OnExit.c\
+				rts/sm/Evac.h\
+				rts/sm/MarkStack.h\
+				rts/sm/MarkWeak.h\
+				rts/sm/Scav.h\
+				rts/sm/Sweep.c\
+				rts/sm/Sweep.h\
+				rts/win32/veh_excn.h\
+				utils/genprimopcode/Parser.y\
+				utils/genprimopcode/Syntax.hs\
+				utils/lndir/lndir-Xos.h\
+				utils/lndir/lndir-Xosdefs.h\
+  )
diff --git a/testsuite/tests/linters/all.T b/testsuite/tests/linters/all.T
index ef3ea5441f..0eefb0f9a4 100644
--- a/testsuite/tests/linters/all.T
+++ b/testsuite/tests/linters/all.T
@@ -14,8 +14,27 @@ def has_ls_files() -> bool:
   except subprocess.CalledProcessError:
     return False
 
+test('makefiles', [ no_deps if has_ls_files() else skip
+                  , extra_files(["regex-linters"]) ]
+                , makefile_test, ['makefiles'])
 
-test('notes', [no_deps if has_ls_files() else skip
-              , req_hadrian_deps(["lint:notes-util"])
+test('changelogs', [ no_deps if has_ls_files() else skip
+                   , extra_files(["regex-linters"]) ]
+                 , makefile_test, ['changelogs'])
+
+test('cpp', [ no_deps if has_ls_files() else skip
+            , extra_files(["regex-linters"]) ]
+            , makefile_test, ['cpp'])
+
+test('version-number', [ no_deps if has_ls_files() else skip
+                       , extra_files(["regex-linters"]) ]
+                     , makefile_test, ['version-number'])
+
+test('notes', [ no_deps if has_ls_files() else skip
+              , req_hadrian_deps(["lint:notes"])
               , normalise_fun(normalise_nos) ]
-              , makefile_test, ['notes'])
+            , makefile_test, ['notes'])
+
+test('whitespace', [ no_deps if has_ls_files() else skip
+                   , req_hadrian_deps(["lint:whitespace"]) ]
+                 , makefile_test, ['whitespace'])
diff --git a/testsuite/tests/linters/changelogs.stdout b/testsuite/tests/linters/changelogs.stdout
new file mode 100644
index 0000000000..9547d7b24b
--- /dev/null
+++ b/testsuite/tests/linters/changelogs.stdout
@@ -0,0 +1 @@
+Changelogs look OK (no "TBA"s, or RELEASE=NO)
diff --git a/testsuite/tests/linters/notes.stdout b/testsuite/tests/linters/notes.stdout
index 8e4ad38ac8..57d2aa1367 100644
--- a/testsuite/tests/linters/notes.stdout
+++ b/testsuite/tests/linters/notes.stdout
@@ -22,11 +22,11 @@ ref    compiler/GHC/Core/Unfold.hs:1242:50:     Note [Unfold info lazy contexts]
 ref    compiler/GHC/Core/Unfold/Make.hs:157:34:     Note [DFunUnfoldings]
 ref    compiler/GHC/Core/Unify.hs:544:16:     Note [Unification result]
 ref    compiler/GHC/Core/Unify.hs:1390:9:     Note [INLINE pragmas and (>>)]
-ref    compiler/GHC/Core/Utils.hs:944:40:     Note [ _       -> [con1]
-ref    compiler/GHC/CoreToStg.hs:460:15:     Note [Nullary unboxed tuple]
-ref    compiler/GHC/Driver/Main.hs:1551:34:     Note [simpleTidyPgm - mkBootModDetailsTc]
-ref    compiler/GHC/Driver/Session.hs:1949:36:     Note [GHC.Driver.Main . Safe Haskell Inference]
-ref    compiler/GHC/Driver/Session.hs:3910:49:     Note [Eta-reduction in -O0]
+ref    compiler/GHC/Core/Utils.hs:947:40:     Note [ _       -> [con1]
+ref    compiler/GHC/CoreToStg.hs:462:15:     Note [Nullary unboxed tuple]
+ref    compiler/GHC/Driver/Main.hs:1566:34:     Note [simpleTidyPgm - mkBootModDetailsTc]
+ref    compiler/GHC/Driver/Session.hs:1947:36:     Note [GHC.Driver.Main . Safe Haskell Inference]
+ref    compiler/GHC/Driver/Session.hs:3916:49:     Note [Eta-reduction in -O0]
 ref    compiler/GHC/Hs/Extension.hs:140:5:     Note [Strict argument type constraints]
 ref    compiler/GHC/HsToCore/Binds.hs:313:33:     Note [AbsBinds wrappers]
 ref    compiler/GHC/HsToCore/Binds.hs:849:46:     Note [Free dictionaries]
@@ -39,8 +39,8 @@ ref    compiler/GHC/HsToCore/Docs.hs:130:0:     Note [1]
 ref    compiler/GHC/HsToCore/Pmc/Solver.hs:853:20:     Note [COMPLETE sets on data families]
 ref    compiler/GHC/HsToCore/Types.hs:61:13:     Note [Generating fresh names for FFI wrappers]
 ref    compiler/GHC/HsToCore/Utils.hs:939:62:     Note [Don't CPR join points]
-ref    compiler/GHC/Iface/Syntax.hs:705:0:     Note [Minimal complete definition]
-ref    compiler/GHC/Iface/Syntax.hs:765:44:     Note [Minimal complete definition]
+ref    compiler/GHC/Iface/Syntax.hs:708:0:     Note [Minimal complete definition]
+ref    compiler/GHC/Iface/Syntax.hs:768:44:     Note [Minimal complete definition]
 ref    compiler/GHC/Parser/Lexer.x:185:7:     Note [Lexing NumericUnderscores extension]
 ref    compiler/GHC/Parser/Lexer.x:502:3:     Note [Lexing NumericUnderscores extension]
 ref    compiler/GHC/Rename/Expr.hs:2013:9:     Note [ApplicativeDo and strict patterns]
@@ -52,10 +52,10 @@ ref    compiler/GHC/Rename/Pat.hs:888:29:     Note [Disambiguating record fields
 ref    compiler/GHC/Rename/Splice.hs:450:27:     Note [Splices]
 ref    compiler/GHC/Runtime/Eval.hs:996:2:     Note [Querying instances for a type]
 ref    compiler/GHC/Runtime/Interpreter.hs:198:30:     Note [uninterruptibleMask_]
-ref    compiler/GHC/StgToCmm.hs:107:18:     Note [codegen-split-init]
-ref    compiler/GHC/StgToCmm.hs:110:18:     Note [pipeline-split-init]
-ref    compiler/GHC/StgToCmm/Expr.hs:491:4:     Note [case on bool]
-ref    compiler/GHC/StgToCmm/Expr.hs:751:3:     Note [alg-alt heap check]
+ref    compiler/GHC/StgToCmm.hs:108:18:     Note [codegen-split-init]
+ref    compiler/GHC/StgToCmm.hs:111:18:     Note [pipeline-split-init]
+ref    compiler/GHC/StgToCmm/Expr.hs:585:4:     Note [case on bool]
+ref    compiler/GHC/StgToCmm/Expr.hs:848:3:     Note [alg-alt heap check]
 ref    compiler/GHC/Tc/Errors.hs:180:13:     Note [Fail fast on kind errors]
 ref    compiler/GHC/Tc/Errors.hs:2016:0:     Note [Highlighting ambiguous type variables]
 ref    compiler/GHC/Tc/Errors/Ppr.hs:1760:11:     Note [Highlighting ambiguous type variables]
@@ -82,10 +82,10 @@ ref    compiler/GHC/Tc/Gen/Pat.hs:1376:16:     Note [Pattern coercions]
 ref    compiler/GHC/Tc/Gen/Sig.hs:78:10:     Note [Overview of type signatures]
 ref    compiler/GHC/Tc/Instance/Family.hs:515:35:     Note [Constrained family instances]
 ref    compiler/GHC/Tc/Module.hs:698:15:     Note [Extra dependencies from .hs-boot files]
-ref    compiler/GHC/Tc/Module.hs:1901:19:     Note [Root-main id]
-ref    compiler/GHC/Tc/Module.hs:1971:6:     Note [Root-main id]
+ref    compiler/GHC/Tc/Module.hs:1904:19:     Note [Root-main id]
+ref    compiler/GHC/Tc/Module.hs:1974:6:     Note [Root-main id]
 ref    compiler/GHC/Tc/Solver.hs:2541:36:     Note [Kind generalisation and SigTvs]
-ref    compiler/GHC/Tc/Solver/Canonical.hs:1228:33:     Note [Canonical LHS]
+ref    compiler/GHC/Tc/Solver/Canonical.hs:1229:33:     Note [Canonical LHS]
 ref    compiler/GHC/Tc/Solver/Interact.hs:1638:9:     Note [No touchables as FunEq RHS]
 ref    compiler/GHC/Tc/Solver/Interact.hs:2292:12:     Note [The equality class story]
 ref    compiler/GHC/Tc/Solver/Rewrite.hs:1032:7:     Note [Stability of rewriting]
@@ -96,9 +96,9 @@ ref    compiler/GHC/Tc/TyCl.hs:4366:16:     Note [rejigCon and c.f. Note [Check
 ref    compiler/GHC/Tc/TyCl/Instance.hs:947:26:     Note [Generalising in tcFamTyPatsGuts]
 ref    compiler/GHC/Tc/Types.hs:647:17:     Note [Generating fresh names for FFI wrappers]
 ref    compiler/GHC/Tc/Types.hs:696:33:     Note [Extra dependencies from .hs-boot files]
-ref    compiler/GHC/Tc/Types.hs:1145:28:     Note [Don't promote data constructors with non-equality contexts]
-ref    compiler/GHC/Tc/Types.hs:1221:36:     Note [Bindings with closed types]
-ref    compiler/GHC/Tc/Types.hs:1457:47:     Note [Care with plugin imports]
+ref    compiler/GHC/Tc/Types.hs:1154:28:     Note [Don't promote data constructors with non-equality contexts]
+ref    compiler/GHC/Tc/Types.hs:1230:36:     Note [Bindings with closed types]
+ref    compiler/GHC/Tc/Types.hs:1466:47:     Note [Care with plugin imports]
 ref    compiler/GHC/Tc/Types/Constraint.hs:238:34:     Note [NonCanonical Semantics]
 ref    compiler/GHC/Tc/Utils/Concrete.hs:246:2:     Note [Concrete and Concrete#]
 ref    compiler/GHC/Tc/Utils/Env.hs:556:7:     Note [Bindings with closed types]
@@ -109,8 +109,8 @@ ref    compiler/GHC/Tc/Utils/TcMType.hs:793:7:     Note [Kind checking for GADTs
 ref    compiler/GHC/Tc/Utils/TcType.hs:529:7:     Note [TyVars and TcTyVars]
 ref    compiler/GHC/ThToHs.hs:1738:11:     Note [Adding parens for splices]
 ref    compiler/GHC/ThToHs.hs:1749:3:     Note [Adding parens for splices]
-ref    compiler/GHC/Types/Basic.hs:586:17:     Note [Safe Haskell isSafeOverlap]
-ref    compiler/GHC/Types/Basic.hs:1326:7:     Note [Activation competition]
+ref    compiler/GHC/Types/Basic.hs:619:17:     Note [Safe Haskell isSafeOverlap]
+ref    compiler/GHC/Types/Basic.hs:1359:7:     Note [Activation competition]
 ref    compiler/GHC/Types/Demand.hs:307:25:     Note [Preserving Boxity of results is rarely a win]
 ref    compiler/GHC/Types/Demand.hs:1100:4:     Note [Use one-shot information]
 ref    compiler/GHC/Types/Error.hs:358:3:     Note [Suppressing Messages]
@@ -124,14 +124,16 @@ ref    compiler/Language/Haskell/Syntax/Expr.hs:1561:32:     Note [Quasi-quote o
 ref    compiler/Language/Haskell/Syntax/Pat.hs:336:12:     Note [Disambiguating record fields]
 ref    configure.ac:212:10:     Note [Linking ghc-bin against threaded stage0 RTS]
 ref    docs/core-spec/core-spec.mng:177:6:     Note [TyBinders]
-ref    ghc/GHCi/UI.hs:3630:25:     Note [ModBreaks.decls]
+ref    ghc/GHCi/UI.hs:3646:25:     Note [ModBreaks.decls]
 ref    ghc/ghc.mk:62:6:     Note [Linking ghc-bin against threaded stage0 RTS]
 ref    hadrian/src/Expression.hs:130:30:     Note [Linking ghc-bin against threaded stage0 RTS]
 ref    libraries/base/GHC/ST.hs:139:7:     Note [Definition of runRW#]
+ref    linters/lint-notes/Notes.hs:32:29:     Note [" <> T.unpack x <> "]
+ref    linters/lint-notes/Notes.hs:69:22:     Note [...]
 ref    testsuite/config/ghc:212:10:     Note [WayFlags]
 ref    testsuite/driver/testlib.py:152:10:     Note [Why is there no stage1 setup function?]
 ref    testsuite/driver/testlib.py:156:2:     Note [Why is there no stage1 setup function?]
-ref    testsuite/mk/boilerplate.mk:259:2:     Note [WayFlags]
+ref    testsuite/mk/boilerplate.mk:263:2:     Note [WayFlags]
 ref    testsuite/tests/indexed-types/should_fail/ExtraTcsUntch.hs:30:27:     Note [Extra TcS Untouchables]
 ref    testsuite/tests/perf/join_points/join005.hs:19:63:     Note [Don't CPR join points]
 ref    testsuite/tests/perf/should_run/all.T:3:6:     Note [Solving from instances when interacting Dicts]
@@ -149,7 +151,5 @@ ref    testsuite/tests/typecheck/should_compile/tc228.hs:9:7:     Note [Inferenc
 ref    testsuite/tests/typecheck/should_compile/tc231.hs:12:16:     Note [Important subtlety in oclose]
 ref    testsuite/tests/typecheck/should_fail/UnliftedNewtypesMultiFieldGadt.hs:11:28:     Note [Kind-checking the field type]
 ref    testsuite/tests/typecheck/should_fail/tcfail093.hs:13:7:     Note [Important subtlety in oclose]
-ref    utils/notes-util/Notes.hs:33:29:     Note [" <> T.unpack x <> "]
-ref    utils/notes-util/Notes.hs:70:22:     Note [...]
-ref    validate:413:14:     Note [Why is there no stage1 setup function?]
+ref    validate:412:14:     Note [Why is there no stage1 setup function?]
 
diff --git a/testsuite/tests/linters/regex-linters/check-changelogs.sh b/testsuite/tests/linters/regex-linters/check-changelogs.sh
new file mode 100755
index 0000000000..10fca9d5c0
--- /dev/null
+++ b/testsuite/tests/linters/regex-linters/check-changelogs.sh
@@ -0,0 +1,16 @@
+#!/usr/bin/env bash
+
+set -e
+
+COLOR_RED="\e[31m"
+COLOR_GREEN="\e[32m"
+COLOR_NONE="\e[0m"
+
+if grep -E -q 'RELEASE=YES' ${1}/configure.ac && grep TBA ${1}/libraries/*/changelog.md
+then
+    echo -e "${COLOR_RED}Error: Found \"TBA\"s in changelogs.${COLOR_NONE}"
+    exit 1
+else
+    echo -e "${COLOR_GREEN}Changelogs look OK (no \"TBA\"s, or RELEASE=NO)${COLOR_NONE}"
+    exit 0
+fi
diff --git a/testsuite/tests/linters/regex-linters/check-cpp.py b/testsuite/tests/linters/regex-linters/check-cpp.py
new file mode 100644
index 0000000000..4cc2257984
--- /dev/null
+++ b/testsuite/tests/linters/regex-linters/check-cpp.py
@@ -0,0 +1,44 @@
+#!/usr/bin/env python3
+
+# A linter to warn for ASSERT macros which are separated from their argument
+# list by a space, which Clang's CPP barfs on
+
+from pathlib import Path
+from linter import run_linters, RegexpLinter
+
+linters = [
+    RegexpLinter(r'WARN\s+\(',
+                 message='CPP macros should not have a space between the macro name and their argument list'),
+    RegexpLinter(r'ASSERT\s+\(',
+                 message='CPP macros should not have a space between the macro name and their argument list'),
+    RegexpLinter(r'ASSERT2\s+\(',
+                 message='CPP macros should not have a space between the macro name and their argument list'),
+    RegexpLinter(r'#ifdef\s+',
+                 message='`#if defined(x)` is preferred to `#ifdef x`'),
+    RegexpLinter(r'#if\s+defined\s+',
+                 message='`#if defined(x)` is preferred to `#if defined x`'),
+    RegexpLinter(r'#ifndef\s+',
+                 message='`#if !defined(x)` is preferred to `#ifndef x`'),
+]
+
+for l in linters:
+    # Need do document rules!
+    l.add_path_filter(lambda path: path != Path('docs', 'coding-style.html'))
+    l.add_path_filter(lambda path: path != Path('docs', 'users_guide', 'utils.rst'))
+    # Don't lint vendored code
+    l.add_path_filter(lambda path: not path.name == 'config.guess')
+    # Don't lint files from external xxhash projects
+    l.add_path_filter(lambda path: path != Path('rts', 'xxhash.h')),
+    # Don't lint font files
+    l.add_path_filter(lambda path: not path.parent == Path('docs','users_guide',
+        'rtd-theme', 'static', 'fonts'))
+    # Don't lint image files
+    l.add_path_filter(lambda path: not path.parent == Path('docs','users_guide',
+        'images'))
+    # Don't lint core spec
+    l.add_path_filter(lambda path: not path.name == 'core-spec.pdf')
+    # Don't lint the linter itself
+    l.add_path_filter(lambda path: not path.name == 'check-cpp.py')
+
+if __name__ == '__main__':
+    run_linters(linters)
diff --git a/testsuite/tests/linters/regex-linters/check-makefiles.py b/testsuite/tests/linters/regex-linters/check-makefiles.py
new file mode 100644
index 0000000000..5a8286c6a7
--- /dev/null
+++ b/testsuite/tests/linters/regex-linters/check-makefiles.py
@@ -0,0 +1,45 @@
+#!/usr/bin/env python3
+
+"""
+Linters for testsuite makefiles
+"""
+
+from linter import run_linters, RegexpLinter
+
+"""
+Warn for use of `--interactive` inside Makefiles (#11468).
+
+Encourage the use of `$(TEST_HC_OPTS_INTERACTIVE)` instead of
+`$(TEST_HC_OPTS) --interactive -ignore-dot-ghci -v0`. It's too easy to
+forget one of those flags when adding a new test.
+"""
+interactive_linter = \
+    RegexpLinter(r'--interactive',
+                 message = "Warning: Use `$(TEST_HC_OPTS_INTERACTIVE)` instead of `--interactive -ignore-dot-ghci -v0`."
+                ).add_path_filter(lambda path: path.name == 'Makefile')
+
+test_hc_quotes_linter = \
+    RegexpLinter('\t\\$\\(TEST_HC\\)',
+                 message = "Warning: $(TEST_HC) should be quoted in Makefiles.",
+                ).add_path_filter(lambda path: path.name == 'Makefile')
+
+ghc_pkg_quotes_linter = \
+    RegexpLinter('\t\\$\\(GHC_PKG\\)',
+                 message = "Warning: $(GHC_PKG) should be quoted in Makefiles.",
+                ).add_path_filter(lambda path: path.name == 'Makefile')
+
+haddock_quotes_linter = \
+    RegexpLinter('\t\\$\\(HADDOCK\\)',
+                 message = "Warning: $(HADDOCK) should be quoted in Makefiles.",
+                ).add_path_filter(lambda path: path.name == 'Makefile')
+
+linters = [
+    interactive_linter,
+    test_hc_quotes_linter,
+    ghc_pkg_quotes_linter,
+    haddock_quotes_linter
+]
+
+if __name__ == '__main__':
+    run_linters(linters,
+                subdir='testsuite')
diff --git a/testsuite/tests/linters/regex-linters/check-version-number.sh b/testsuite/tests/linters/regex-linters/check-version-number.sh
new file mode 100755
index 0000000000..2ce68627f4
--- /dev/null
+++ b/testsuite/tests/linters/regex-linters/check-version-number.sh
@@ -0,0 +1,7 @@
+#!/usr/bin/env bash
+
+set -e
+
+grep -E -q 'RELEASE=NO' ${1}/configure.ac ||
+  grep -E -q '\[[0-9]+\.[0-9]+\.[0-9]+\]' ${1}/configure.ac ||
+  ( echo "error: configure.ac: GHC version number must have three components when RELEASE=YES."; exit 1 )
diff --git a/testsuite/tests/linters/regex-linters/linter.py b/testsuite/tests/linters/regex-linters/linter.py
new file mode 100644
index 0000000000..2246dcce30
--- /dev/null
+++ b/testsuite/tests/linters/regex-linters/linter.py
@@ -0,0 +1,140 @@
+"""
+Utilities for linters
+"""
+
+import os
+import sys
+import re
+import textwrap
+import subprocess
+from pathlib import Path
+from typing import List, Optional, Callable, Sequence
+from collections import namedtuple
+
+def lint_failure(file, line_no: int, line_content: str, message: str):
+    """ Print a lint failure message. """
+    wrapper = textwrap.TextWrapper(initial_indent='  ',
+                                   subsequent_indent='    ')
+    body = wrapper.fill(message)
+    msg = '''
+    {file}:
+
+             |
+      {line_no:5d}  |  {line_content}
+             |
+
+    {body}
+    '''.format(file=file, line_no=line_no,
+               line_content=line_content,
+               body=body)
+
+    print(textwrap.dedent(msg))
+
+def get_changed_files(base_commit: str, head_commit: str,
+                      subdir: str = '.'):
+    """ Get the files changed by the given range of commits. """
+    cmd = ['git', 'diff', '--name-only',
+           base_commit, head_commit, '--', subdir]
+    files = subprocess.check_output(cmd)
+    return files.decode('UTF-8').split('\n')
+
+def get_tracked_files(subdir: str = '.'):
+    """ Get the files tracked by git in the given subdirectory. """
+    cmd = ['git', 'ls-tree', '--name-only', '-r', 'HEAD', subdir]
+    files = subprocess.check_output(cmd)
+    return files.decode('UTF-8').split('\n')
+
+Warning = namedtuple('Warning', 'path,line_no,line_content,message')
+
+class Linter(object):
+    """
+    A :class:`Linter` must implement :func:`lint`, which looks at the
+    given path and calls :func:`add_warning` for any lint issues found.
+    """
+    def __init__(self):
+        self.warnings = [] # type: List[Warning]
+        self.path_filters = [] # type: List[Callable[[Path], bool]]
+
+    def add_warning(self, w: Warning):
+        self.warnings.append(w)
+
+    def add_path_filter(self, f: Callable[[Path], bool]) -> "Linter":
+        self.path_filters.append(f)
+        return self
+
+    def do_lint(self, path: Path):
+        if all(f(path) for f in self.path_filters):
+            self.lint(path)
+
+    def lint(self, path: Path):
+        raise NotImplementedError
+
+class LineLinter(Linter):
+    """
+    A :class:`LineLinter` must implement :func:`lint_line`, which looks at
+    the given line from a file and calls :func:`add_warning` for any lint
+    issues found.
+    """
+    def lint(self, path: Path):
+        if path.is_file():
+            with path.open('r') as f:
+                for line_no, line in enumerate(f):
+                    self.lint_line(path, line_no+1, line)
+
+    def lint_line(self, path: Path, line_no: int, line: str):
+        raise NotImplementedError
+
+class RegexpLinter(LineLinter):
+    """
+    A :class:`RegexpLinter` produces the given warning message for
+    all lines matching the given regular expression.
+    """
+    def __init__(self, regex: str, message: str):
+        LineLinter.__init__(self)
+        self.re = re.compile(regex)
+        self.message = message
+
+    def lint_line(self, path: Path, line_no: int, line: str):
+        if self.re.search(line):
+            w = Warning(path=path, line_no=line_no, line_content=line[:-1],
+                        message=self.message)
+            self.add_warning(w)
+
+def run_linters(linters: Sequence[Linter],
+                subdir: str = '.') -> None:
+    import argparse
+    parser = argparse.ArgumentParser()
+    subparsers = parser.add_subparsers()
+
+    subparser = subparsers.add_parser('commits', help='Lint a range of commits')
+    subparser.add_argument('base', help='Base commit')
+    subparser.add_argument('head', help='Head commit')
+    subparser.set_defaults(get_linted_files=lambda args:
+                            get_changed_files(args.base, args.head, subdir))
+
+    subparser = subparsers.add_parser('files', help='Lint the given files')
+    subparser.add_argument('file', nargs='+', help='File to lint')
+    subparser.set_defaults(get_linted_files=lambda args: args.file)
+
+    subparser = subparsers.add_parser('tracked', help="Lint files tracked by Git")
+    subparser.set_defaults(get_linted_files=lambda args:
+                            get_tracked_files(subdir))
+
+    args = parser.parse_args()
+
+    linted_files = args.get_linted_files(args)
+    for path in linted_files:
+        if path.startswith('linters'):
+            continue
+        for linter in linters:
+            linter.do_lint(Path(path))
+
+    warnings = [warning
+                for linter in linters
+                for warning in linter.warnings]
+    warnings = sorted(warnings, key=lambda x: (x.path, x.line_no))
+    for w in warnings:
+        lint_failure(w.path, w.line_no, w.line_content, w.message)
+
+    if len(warnings) > 0:
+        sys.exit(1)
diff --git a/testsuite/tests/linters/whitespace.stdout b/testsuite/tests/linters/whitespace.stdout
new file mode 100644
index 0000000000..b773a1831d
--- /dev/null
+++ b/testsuite/tests/linters/whitespace.stdout
@@ -0,0 +1 @@
+whitespace validation passed!