From e412a2d5a9014b58439f0580abbf8c0248271bb1 Mon Sep 17 00:00:00 2001
From: Matthew Flatt <mflatt@racket-lang.org>
Date: Thu, 17 Mar 2016 13:11:48 -0600
Subject: [PATCH] raco pkg {install,update,...}: add --dry-run

---
 pkgs/racket-doc/pkg/scribblings/lib.scrbl    | 25 ++++---
 pkgs/racket-doc/pkg/scribblings/pkg.scrbl    | 18 +++--
 pkgs/racket-test/tests/pkg/tests-install.rkt | 37 +++++++---
 pkgs/racket-test/tests/pkg/tests-migrate.rkt |  2 +
 pkgs/racket-test/tests/pkg/tests-remove.rkt  |  8 ++-
 pkgs/racket-test/tests/pkg/tests-update.rkt  | 20 +++++-
 racket/collects/pkg/lib.rkt                  | 12 ++--
 racket/collects/pkg/main.rkt                 | 13 +++-
 racket/collects/pkg/private/git.rkt          |  7 +-
 racket/collects/pkg/private/install.rkt      | 75 ++++++++++++--------
 racket/collects/pkg/private/migrate.rkt      |  6 +-
 racket/collects/pkg/private/print.rkt        |  6 ++
 racket/collects/pkg/private/remove.rkt       | 68 ++++++++++--------
 13 files changed, 206 insertions(+), 91 deletions(-)

diff --git a/pkgs/racket-doc/pkg/scribblings/lib.scrbl b/pkgs/racket-doc/pkg/scribblings/lib.scrbl
index f582239550..d027899dc4 100644
--- a/pkgs/racket-doc/pkg/scribblings/lib.scrbl
+++ b/pkgs/racket-doc/pkg/scribblings/lib.scrbl
@@ -265,7 +265,8 @@ is true, error messages may suggest specific command-line flags for
                            [#:force-strip? force-string? boolean? #f]
                            [#:multi-clone-mode multi-clone-mode (or/c 'fail 'force 'convert 'ask) 'fail]
                            [#:pull-mode pull-mode (or/c 'ff-only 'try 'rebase) 'ff-only]
-                           [#:link-dirs? link-dirs? boolean? #f])
+                           [#:link-dirs? link-dirs? boolean? #f]
+                           [#:dry-run? dry-run? boolean? #f])
          (or/c 'skip
                #f
                (listof (or/c path-string?
@@ -299,7 +300,8 @@ The package lock must be held; see @racket[with-pkg-lock].
 @history[#:changed "6.1.1.5" @elem{Added the @racket[#:multi-clone-mode] 
                                    and @racket[#:infer-clone-from-dir?] arguments.}
          #:changed "6.1.1.6" @elem{Added the @racket[#:use-trash?] argument.}
-         #:changed "6.1.1.8" @elem{Added the @racket[#:pull-mode] argument.}]}
+         #:changed "6.1.1.8" @elem{Added the @racket[#:pull-mode] argument.}
+         #:changed "6.4.0.14" @elem{Added the @racket[#:dry-run] argument.}]}
 
 
 @defproc[(pkg-update      [sources (listof (or/c string? pkg-desc?))]
@@ -322,7 +324,8 @@ The package lock must be held; see @racket[with-pkg-lock].
                           [#:multi-clone-mode multi-clone-mode (or/c 'fail 'force 'convert 'ask) 'fail]
                           [#:pull-mode pull-mode (or/c 'ff-only 'try 'rebase) 'ff-only]
                           [#:link-dirs? link-dirs? boolean? #f]
-                          [#:infer-clone-from-dir? infer-clone-from-dir? boolean? #f])
+                          [#:infer-clone-from-dir? infer-clone-from-dir? boolean? #f]
+                          [#:dry-run? dry-run? boolean? #f])
         (or/c 'skip
               #f
               (listof (or/c path-string?
@@ -357,7 +360,8 @@ The package lock must be held; see @racket[with-pkg-lock].
 @history[#:changed "6.1.1.5" @elem{Added the @racket[#:multi-clone-mode] 
                                    and @racket[#:infer-clone-from-dir?] arguments.}
          #:changed "6.1.1.6" @elem{Added the @racket[#:use-trash?] argument.}
-         #:changed "6.1.1.8" @elem{Added the @racket[#:skip-uninstalled?] and @racket[#:pull-mode] arguments.}]}
+         #:changed "6.1.1.8" @elem{Added the @racket[#:skip-uninstalled?] and @racket[#:pull-mode] arguments.}
+         #:changed "6.4.0.14" @elem{Added the @racket[#:dry-run] argument.}]}
 
 
 @defproc[(pkg-remove      [names (listof string?)]
@@ -366,7 +370,8 @@ The package lock must be held; see @racket[with-pkg-lock].
                           [#:force? force? boolean? #f]
                           [#:quiet? quiet? boolean? #f]
                           [#:use-trash? boolean? use-trash? #f]
-                          [#:from-command-line? from-command-line? boolean? #f])
+                          [#:from-command-line? from-command-line? boolean? #f]
+                          [#:dry-run? dry-run? boolean? #f])
          (or/c 'skip
                #f
                (listof (or/c path-string? 
@@ -381,7 +386,8 @@ specific command-line flags for @command-ref{remove}.
 
 The package lock must be held; see @racket[with-pkg-lock].
 
-@history[#:changed "6.1.1.6" @elem{Added the @racket[#:use-trash?] argument.}]}
+@history[#:changed "6.1.1.6" @elem{Added the @racket[#:use-trash?] argument.}
+         #:changed "6.4.0.14" @elem{Added the @racket[#:dry-run] argument.}]}
 
 
 @defproc[(pkg-new [name path-string?])
@@ -419,7 +425,8 @@ The package lock must be held to allow reads; see
                            [#:quiet? quiet? boolean? #f]
                            [#:from-command-line? from-command-line? boolean? #f]
                            [#:strip strip (or/c #f 'source 'binary 'binary-lib) #f]
-                           [#:force-strip? force-string? boolean? #f])
+                           [#:force-strip? force-string? boolean? #f]
+                           [#:dry-run? dry-run? boolean? #f])
          (or/c 'skip
                #f
                (listof (or/c path-string?
@@ -431,7 +438,9 @@ Implements @racket[pkg-migrate-command].  The result is the same as for
 If @racket[from-command-line?]  is true, error messages may suggest
 specific command-line flags for @command-ref{migrate}.
 
-The package lock must be held; see @racket[with-pkg-lock].}
+The package lock must be held; see @racket[with-pkg-lock].
+
+@history[#:changed "6.4.0.14" @elem{Added the @racket[#:dry-run] argument.}]}
 
 
 @defproc[(pkg-catalog-show [names (listof string?)]
diff --git a/pkgs/racket-doc/pkg/scribblings/pkg.scrbl b/pkgs/racket-doc/pkg/scribblings/pkg.scrbl
index 82db0b2af1..058ac1b72b 100644
--- a/pkgs/racket-doc/pkg/scribblings/pkg.scrbl
+++ b/pkgs/racket-doc/pkg/scribblings/pkg.scrbl
@@ -596,6 +596,9 @@ sub-commands.
     ]}
 
 
+  @item{@DFlag{dry-run} --- Prevents changes to the current installation. All installation and update work is
+                            staged and checked, but the final installation step is skipped.}
+
   @item{@DFlag{no-setup} --- Does not run @exec{raco setup} after installation. This behavior is also the case if the
         environment variable @envvar{PLT_PKG_NOSETUP} is set to any non-empty value.}
 
@@ -613,7 +616,8 @@ sub-commands.
                                    @DFlag{multi-clone} flags.}
          #:changed "6.1.1.6" @elem{Added the @DFlag{no-trash} flag, and changed
                                    the @DFlag{deps} default to depend only on interactive mode.}
-         #:changed "6.1.1.8" @elem{Added the @DFlag{pull} flag.}]}
+         #:changed "6.1.1.8" @elem{Added the @DFlag{pull} flag.}
+         #:changed "6.4.0.14" @elem{Added the @DFlag{dry-run} flag.}]}
 
 
 @subcommand{@command/toc{update} @nonterm{option} ... @nonterm{pkg-source} ... 
@@ -723,6 +727,7 @@ the given @nonterm{pkg-source}s.
 
  @item{@DFlag{pull} @nonterm{mode} --- Same as for @command-ref{install}}
 
+ @item{@DFlag{dry-run} --- Same as for @command-ref{install}.}
  @item{@DFlag{no-setup} --- Same as for @command-ref{install}.}
  @item{@DFlag{jobs} @nonterm{n} or @Flag{j} @nonterm{n} --- Same as for @command-ref{install}.}
  @item{@DFlag{batch} --- Same as for @command-ref{install}.}
@@ -735,7 +740,8 @@ the given @nonterm{pkg-source}s.
                                    when no arguments are provided.}
          #:changed "6.1.1.6" @elem{Added the @DFlag{no-trash} flag, and changed
                                    the @DFlag{deps} default to depend only on interactive mode.}
-         #:changed "6.1.1.8" @elem{Added the @DFlag{skip-uninstalled} and @DFlag{pull} flags.}]}
+         #:changed "6.1.1.8" @elem{Added the @DFlag{skip-uninstalled} and @DFlag{pull} flags.}]
+         #:changed "6.4.0.14" @elem{Added the @DFlag{dry-run} flag.}}
 
 @subcommand{@command/toc{remove} @nonterm{option} ... @nonterm{pkg} ... 
 --- Attempts to remove the given packages. By default, if a package is the dependency
@@ -761,6 +767,7 @@ the given @nonterm{pkg}s.
  @item{@Flag{i} or @DFlag{installation} --- Shorthand for @exec{--scope installation}.}
  @item{@Flag{u} or @DFlag{user} --- Shorthand for @exec{--scope user}.}
  @item{@DFlag{scope-dir} @nonterm{dir} --- Selects @nonterm{dir} as the @tech{package scope}, the same as for @command-ref{install}.}
+ @item{@DFlag{dry-run} --- Same as for @command-ref{install}.}
  @item{@DFlag{no-setup} --- Same as for @command-ref{install}.}
  @item{@DFlag{jobs} @nonterm{n} or @Flag{j} @nonterm{n} --- Same as for @command-ref{install}.}
  @item{@DFlag{batch} --- Same as for @command-ref{install}.}
@@ -768,7 +775,8 @@ the given @nonterm{pkg}s.
  ]
 
 @history[#:changed "6.1.1.5" @elem{Added the @DFlag{batch} flag.}
-         #:changed "6.1.1.6" @elem{Added the @DFlag{no-trash} flag.}]}
+         #:changed "6.1.1.6" @elem{Added the @DFlag{no-trash} flag.}
+         #:changed "6.4.0.14" @elem{Added the @DFlag{dry-run} flag.}]}
 
 
 @subcommand{@command/toc{new} @nonterm{pkg} ---
@@ -848,10 +856,12 @@ package is created.
   @item{@DFlag{ignore-checksums} --- Same as for @command-ref{install}.}
   @item{@DFlag{strict-doc-conflicts} --- Same as for @command-ref{install}.}
   @item{@DFlag{no-cache} --- Same as for @command-ref{install}.}
+  @item{@DFlag{dry-run} --- Same as for @command-ref{install}.}
   @item{@DFlag{no-setup} --- Same as for @command-ref{install}.}
   @item{@DFlag{jobs} @nonterm{n} or @Flag{j} @nonterm{n} --- Same as for @command-ref{install}.}
  ]
-}
+
+@history[#:changed "6.4.0.14" @elem{Added the @DFlag{dry-run} flag.}]}
 
 @subcommand{@command/toc{create} @nonterm{option} ... @nonterm{directory-or-package}
 --- Bundles a package into an archive. Bundling
diff --git a/pkgs/racket-test/tests/pkg/tests-install.rkt b/pkgs/racket-test/tests/pkg/tests-install.rkt
index 68f70a048d..c2cff03092 100644
--- a/pkgs/racket-test/tests/pkg/tests-install.rkt
+++ b/pkgs/racket-test/tests/pkg/tests-install.rkt
@@ -22,18 +22,35 @@
  (shelly-begin
   (initialize-catalogs)
 
+  (define-syntax-rule (shelly-install-dry-run what src)
+    (shelly-case
+     (format "Test dry-run installation of ~a" what)
+     $ "racket -e '(require pkg-test1)'" =exit> 1
+     $ (~a "raco pkg install --dry-run " src)
+     $ "racket -e '(require pkg-test1)'" =exit> 1))
+
+  (define-syntax-rule (shelly-install/d what src)
+    (begin
+      (shelly-install-dry-run what src)
+      (shelly-install what src)))
+
+  (define-syntax-rule (shelly-install*/d what srcs pkgs)
+    (begin
+      (shelly-install-dry-run what srcs)
+      (shelly-install* what srcs pkgs)))
+
   (shelly-case
    "raco pkg install tests"
-   (shelly-install "local package (tgz)" "test-pkgs/pkg-test1.tgz")
-   (shelly-install "local package (zip)" "test-pkgs/pkg-test1.zip")
-   (shelly-install "local package (file://zip)" (url->string (path->url (path->complete-path "test-pkgs/pkg-test1.zip"))))
-   (shelly-install "local package (plt)" "test-pkgs/pkg-test1.plt")
-   (shelly-install* "local package (zip, compiled)" "test-pkgs/pkg-test1b.zip" "pkg-test1b")
-   (shelly-install* "local package (zip, single-collection)" 
-                    "test-pkgs/pkg-test1.zip test-pkgs/pkg-test3.zip" 
-                    "pkg-test1 pkg-test3")
-   (shelly-install "local package (dir)" (url->string (path->url (path->complete-path "test-pkgs/pkg-test1"))))
-   (shelly-install "local package (file://dir)" (url->string (path->url (path->complete-path "test-pkgs/pkg-test1"))))
+   (shelly-install/d "local package (tgz)" "test-pkgs/pkg-test1.tgz")
+   (shelly-install/d "local package (zip)" "test-pkgs/pkg-test1.zip")
+   (shelly-install/d "local package (file://zip)" (url->string (path->url (path->complete-path "test-pkgs/pkg-test1.zip"))))
+   (shelly-install/d "local package (plt)" "test-pkgs/pkg-test1.plt")
+   (shelly-install*/d "local package (zip, compiled)" "test-pkgs/pkg-test1b.zip" "pkg-test1b")
+   (shelly-install*/d "local package (zip, single-collection)" 
+                      "test-pkgs/pkg-test1.zip test-pkgs/pkg-test3.zip" 
+                      "pkg-test1 pkg-test3")
+   (shelly-install/d "local package (dir)" (url->string (path->url (path->complete-path "test-pkgs/pkg-test1"))))
+   (shelly-install/d "local package (file://dir)" (url->string (path->url (path->complete-path "test-pkgs/pkg-test1"))))
 
    ;; Check ".zip" file with extra directory layer:
    (let ([dir (make-temporary-file "zip~a" 'directory)]
diff --git a/pkgs/racket-test/tests/pkg/tests-migrate.rkt b/pkgs/racket-test/tests/pkg/tests-migrate.rkt
index 43b92cc909..5d5a3e7088 100644
--- a/pkgs/racket-test/tests/pkg/tests-migrate.rkt
+++ b/pkgs/racket-test/tests/pkg/tests-migrate.rkt
@@ -29,5 +29,7 @@
          "                            (build-path (find-system-path 'addon-dir) (symbol->string 'other)))\"")
    $ "raco pkg remove -u --auto pkg-b"
    $ "raco pkg show -l -u -a" =stdout> " [none]\n"
+   $ "raco pkg migrate --dry-run -u other"
+   $ "raco pkg show -l -u -a" =stdout> " [none]\n"
    $ "raco pkg migrate -u other"
    $ "raco pkg show -l -u -a" =stdout> #rx"Package\\[\\*=auto\\] +Checksum +Source\npkg-a\\* +[a-f0-9.]+    \\(catalog \"pkg-a\"\\)\npkg-b +[a-f0-9.]+ +\\(catalog \"pkg-b\"\\)\n")))
diff --git a/pkgs/racket-test/tests/pkg/tests-remove.rkt b/pkgs/racket-test/tests/pkg/tests-remove.rkt
index e9e9a83e62..95c5bcac73 100644
--- a/pkgs/racket-test/tests/pkg/tests-remove.rkt
+++ b/pkgs/racket-test/tests/pkg/tests-remove.rkt
@@ -21,7 +21,8 @@
    "remove and show"
    (shelly-case "remove of not installed package fails"
                 $ "raco pkg show -l -u -a" =stdout> " [none]\n"
-                $ "raco pkg remove not-there" =exit> 1)
+                $ "raco pkg remove not-there" =exit> 1
+                $ "raco pkg remove --dry-run not-there" =exit> 1)
    (shelly-case "remove of bad name"
                 $ "raco pkg remove bad/" =exit> 1
                 =stderr> #rx"disallowed")
@@ -39,12 +40,17 @@
                    $ "raco pkg install test-pkgs/pkg-test2.zip"
                    $ "raco pkg show -l -u -a" =stdout> #rx"Package +Checksum +Source\npkg-test1 +[a-f0-9.]+ +\\(file .+/test-pkgs/pkg-test1.zip\"\\)\npkg-test2 +[a-f0-9.]+ +\\(file .+/test-pkgs/pkg-test2.zip\"\\)\n"
                    $ "raco pkg remove pkg-test1" =exit> 1 =stderr> #rx"pkg-test1 \\(required by: \\(pkg-test2\\)\\)"
+                   $ "raco pkg remove --dry-run pkg-test1" =exit> 1 =stderr> #rx"pkg-test1 \\(required by: \\(pkg-test2\\)\\)"
+                   $ "raco pkg remove --dry-run pkg-test2"
+                   $ "raco pkg show -l -u -a" =stdout> #rx"Package +Checksum +Source\npkg-test1 +[a-f0-9.]+ +\\(file .+/test-pkgs/pkg-test1.zip\"\\)\npkg-test2 +[a-f0-9.]+ +\\(file .+/test-pkgs/pkg-test2.zip\"\\)\n"
                    $ "raco pkg remove pkg-test2"
                    $ "raco pkg show -l -u -a" =stdout>  #rx"Package +Checksum +Source\npkg-test1 +[a-f0-9.]+ +\\(file .+/test-pkgs/pkg-test1.zip\"\\)\n")
    (shelly-install "remove of dep can be forced"
                    "test-pkgs/pkg-test1.zip"
                    $ "raco pkg install test-pkgs/pkg-test2.zip"
                    $ "racket -e '(require pkg-test2/contains-dep)'" =exit> 0
+                   $ "raco pkg remove --dry-run --force pkg-test1"
+                   $ "racket -e '(require pkg-test2/contains-dep)'" =exit> 0
                    $ "raco pkg remove --force pkg-test1"
                    $ "racket -e '(require pkg-test2/contains-dep)'" =exit> 1
                    $ "raco pkg install test-pkgs/pkg-test1.zip"
diff --git a/pkgs/racket-test/tests/pkg/tests-update.rkt b/pkgs/racket-test/tests/pkg/tests-update.rkt
index e1164b54f1..8f3969d310 100644
--- a/pkgs/racket-test/tests/pkg/tests-update.rkt
+++ b/pkgs/racket-test/tests/pkg/tests-update.rkt
@@ -45,6 +45,8 @@
                      "test-pkgs/pkg-test1.zip"
                      "pkg-test1"
                      $ "racket -e '(require pkg-test1/update)'" =exit> 42
+                     $ "raco pkg update --dry-run test-pkgs/update-test/pkg-test1.zip"
+                     $ "racket -e '(require pkg-test1/update)'" =exit> 42
                      $ "raco pkg update test-pkgs/update-test/pkg-test1.zip"
                      $ "racket -e '(require pkg-test1/update)'" =exit> 43)
     (finally
@@ -52,6 +54,8 @@
    (shelly-install "packages can be replaced with local packages (file + name)"
                    "test-pkgs/pkg-test1.zip"
                    $ "racket -e '(require pkg-test1/update)'" =exit> 42
+                   $ "raco pkg update --dry-run --name pkg-test1 test-pkgs/pkg-test1-v2.zip"
+                   $ "racket -e '(require pkg-test1/update)'" =exit> 42
                    $ "raco pkg update --name pkg-test1 test-pkgs/pkg-test1-v2.zip"
                    $ "racket -e '(require pkg-test1/update)'" =exit> 43)
    (define tmp2-dir (path->directory-path (make-temporary-file "pkg~a" 'directory)))
@@ -60,6 +64,8 @@
     (shelly-install "packages can be replaced with local packages (directory)"
                     "test-pkgs/pkg-test1.zip"
                     $ "racket -e '(require pkg-test1/update)'" =exit> 42
+                    $ (~a "raco pkg update --dry-run --name pkg-test1 "tmp2-dir"pkg-test1-v2")
+                    $ "racket -e '(require pkg-test1/update)'" =exit> 42
                     $ (~a "raco pkg update --name pkg-test1 "tmp2-dir"pkg-test1-v2")
                     $ "racket -e '(require pkg-test1/update)'" =exit> 43)
     (shelly-install "replacement checksum can be checked"
@@ -68,6 +74,8 @@
     (shelly-install "checksum can be supplied for local directory"
                     "test-pkgs/pkg-test1.zip"
                     $ "racket -e '(require pkg-test1/update)'" =exit> 42
+                    $ (~a "raco pkg update --dry-run --name pkg-test1 --checksum abcdef "tmp2-dir"pkg-test1-v2")
+                    $ "racket -e '(require pkg-test1/update)'" =exit> 42
                     $ (~a "raco pkg update --name pkg-test1 --checksum abcdef "tmp2-dir"pkg-test1-v2")
                     $ "racket -e '(require pkg-test1/update)'" =exit> 43
                     $ "raco pkg show" =stdout> #rx"abcdef"
@@ -92,6 +100,8 @@
                      $ "racket -e '(require pkg-test1/update)'" =exit> 42
                      $ "cp -f test-pkgs/pkg-test1-v2.zip test-pkgs/update-test/pkg-test1.zip"
                      $ "cp -f test-pkgs/pkg-test1-v2.zip.CHECKSUM test-pkgs/update-test/pkg-test1.zip.CHECKSUM"
+                     $ "raco pkg update --dry-run pkg-test1" =exit> 0
+                     $ "racket -e '(require pkg-test1/update)'" =exit> 42
                      $ "raco pkg update pkg-test1" =exit> 0
                      $ "racket -e '(require pkg-test1/update)'" =exit> 43)
     (finally
@@ -105,9 +115,12 @@
     (shelly-install* "remote packages can be updated, single-collection to multi-collection"
                      "test-pkgs/pkg-test1.zip http://localhost:9997/update-test/pkg-test3.zip"
                      "pkg-test1 pkg-test3"
+                     $ "racket -e '(require pkg-test3)'" =stdout> "pkg-test3/main loaded\n"
                      $ "raco pkg update pkg-test3" =exit> 0 =stdout> "Downloading checksum for pkg-test3\nNo updates available\n"
                      $ "cp -f test-pkgs/pkg-test3-v2.zip test-pkgs/update-test/pkg-test3.zip"
                      $ "cp -f test-pkgs/pkg-test3-v2.zip.CHECKSUM test-pkgs/update-test/pkg-test3.zip.CHECKSUM"
+                     $ "raco pkg update --dry-run pkg-test3" =exit> 0
+                     $ "racket -e '(require pkg-test3)'" =stdout> "pkg-test3/main loaded\n"
                      $ "raco pkg update pkg-test3" =exit> 0
                      $ "racket -e '(require pkg-test3)'" =stdout> "pkg-test3/main version 2 loaded\n")
     (finally
@@ -118,12 +131,15 @@
     $ "mkdir -p test-pkgs/update-test"
     $ "cp -f test-pkgs/pkg-test3-v2.zip test-pkgs/update-test/pkg-test3.zip"
     $ "cp -f test-pkgs/pkg-test3-v2.zip.CHECKSUM test-pkgs/update-test/pkg-test3.zip.CHECKSUM"
-    (shelly-install* "remote packages can be updated, multi-colelction to single-collection"
+    (shelly-install* "remote packages can be updated, multi-collection to single-collection"
                      "test-pkgs/pkg-test1.zip http://localhost:9997/update-test/pkg-test3.zip"
                      "pkg-test1 pkg-test3"
+                     $ "racket -e '(require pkg-test3)'" =stdout> "pkg-test3/main version 2 loaded\n"
                      $ "raco pkg update pkg-test3" =exit> 0 =stdout> "Downloading checksum for pkg-test3\nNo updates available\n"
                      $ "cp -f test-pkgs/pkg-test3.zip test-pkgs/update-test/pkg-test3.zip"
                      $ "cp -f test-pkgs/pkg-test3.zip.CHECKSUM test-pkgs/update-test/pkg-test3.zip.CHECKSUM"
+                     $ "raco pkg update --dry-run pkg-test3" =exit> 0
+                     $ "racket -e '(require pkg-test3)'" =stdout> "pkg-test3/main version 2 loaded\n"
                      $ "raco pkg update pkg-test3" =exit> 0
                      $ "racket -e '(require pkg-test3)'" =stdout> "pkg-test3/main loaded\n")
     (finally
@@ -145,6 +161,8 @@
                      $ "racket -e '(require pkg-test1/update)'" =exit> 42
                      $ "cp -f test-pkgs/pkg-test1-v2.zip test-pkgs/update-test/pkg-test1.zip"
                      $ "cp -f test-pkgs/pkg-test1-v2.zip.CHECKSUM test-pkgs/update-test/pkg-test1.zip.CHECKSUM"
+                     $ "raco pkg update --dry-run --update-deps pkg-test2" =exit> 0
+                     $ "racket -e '(require pkg-test1/update)'" =exit> 42
                      $ "raco pkg update --update-deps pkg-test2" =exit> 0
                      $ "racket -e '(require pkg-test1/update)'" =exit> 43
                      $ "raco pkg remove pkg-test2")
diff --git a/racket/collects/pkg/lib.rkt b/racket/collects/pkg/lib.rkt
index a4a51c8795..9b686a63ed 100644
--- a/racket/collects/pkg/lib.rkt
+++ b/racket/collects/pkg/lib.rkt
@@ -119,7 +119,8 @@
                         #:infer-clone-from-dir? boolean?
                         #:lookup-for-clone? boolean?
                         #:multi-clone-behavior (or/c 'fail 'force 'convert 'ask)
-                        #:pull-behavior (or/c 'ff-only 'rebase 'try))
+                        #:pull-behavior (or/c 'ff-only 'rebase 'try)
+                        #:dry-run? boolean?)
         (or/c #f 'skip (listof (or/c path-string? (non-empty-listof path-string?)))))]
   [pkg-remove
    (->* ((listof string?))
@@ -128,7 +129,8 @@
                  #:quiet? boolean?
                  #:use-trash? boolean?
                  #:from-command-line? boolean?
-                 #:demote? boolean?)
+                 #:demote? boolean?
+                 #:dry-run? boolean?)
         (or/c #f 'skip (listof (or/c path-string? (non-empty-listof path-string?)))))]
   [pkg-show
    (->* (string? (or/c #f (listof string?)))
@@ -156,7 +158,8 @@
                         #:force-strip? boolean?
                         #:link-dirs? boolean?
                         #:multi-clone-behavior (or/c 'fail 'force 'convert 'ask)
-                        #:pull-behavior (or/c 'ff-only 'rebase 'try))
+                        #:pull-behavior (or/c 'ff-only 'rebase 'try)
+                        #:dry-run? boolean?)
         (or/c #f 'skip (listof (or/c path-string? (non-empty-listof path-string?)))))]
   [pkg-migrate
    (->* (string?)
@@ -169,7 +172,8 @@
                         #:quiet? boolean?
                         #:from-command-line? boolean?
                         #:strip (or/c #f 'source 'binary 'binary-lib)
-                        #:force-strip? boolean?)
+                        #:force-strip? boolean?
+                        #:dry-run? boolean?)
         (or/c #f 'skip (listof (or/c path-string? (non-empty-listof path-string?)))))]
   [pkg-catalog-show
    (->* ((listof string?))
diff --git a/racket/collects/pkg/main.rkt b/racket/collects/pkg/main.rkt
index fa015657ac..6091fbbe2b 100644
--- a/racket/collects/pkg/main.rkt
+++ b/racket/collects/pkg/main.rkt
@@ -140,6 +140,7 @@
   (define-syntax (make-commands stx)
     (syntax-case stx ()
       [(_ #:scope-flags (scope-flags ...)
+          #:dry-run-flags (dry-run-flags ...)
           #:job-flags (job-flags ...)
           #:trash-flags (trash-flags ...)
           #:catalog-flags (catalog-flags ...)
@@ -181,6 +182,7 @@
              [#:bool pkgs () ("Install only the specified packages, even when none are provided")]
              install-force-flags ...
              install-clone-flags ...
+             dry-run-flags ...
              job-flags ...
              trash-flags ...
              [#:bool fail-fast () ("Break `raco setup' when it discovers an error")]
@@ -242,6 +244,7 @@
                                                                       'ask))
                                        #:pull-behavior pull
                                        #:link-dirs? link-dirs?
+                                       #:dry-run? dry-run
                                        #:use-trash? (not no-trash)
                                        (for/list ([p (in-list sources)])
                                          (pkg-desc p a-type* name checksum #f
@@ -274,6 +277,7 @@
              [#:bool skip-uninstalled () ("Skip a given <pkg-source> if not installed")]
              install-force-flags ...
              install-clone-flags ...
+             dry-run-flags ...
              job-flags ...
              trash-flags ...
              #:args pkg-source
@@ -345,6 +349,7 @@
                                       #:pull-behavior pull
                                       #:link-dirs? link-dirs?
                                       #:infer-clone-from-dir? (not (or link static-link copy))
+                                      #:dry-run? dry-run
                                       #:use-trash? (not no-trash)))))
                   (setup "updated" no-setup #f setup-collects jobs))))]
             ;; ----------------------------------------
@@ -357,6 +362,7 @@
              #:once-any
              scope-flags ...
              #:once-each
+             dry-run-flags ...
              job-flags ...
              trash-flags ...
              #:args pkg
@@ -371,6 +377,7 @@
                                #:demote? demote
                                #:auto? auto
                                #:force? force
+                               #:dry-run? dry-run
                                #:use-trash? (not no-trash))))
                 (setup "removed" no-setup #f setup-collects jobs)))]
             ;; ----------------------------------------
@@ -445,6 +452,7 @@
              #:once-each
              catalog-flags ...
              install-force-flags ...
+             dry-run-flags ...
              job-flags ...
              #:args (from-version)
              (call-with-package-scope
@@ -466,7 +474,8 @@
                                   #:strip (or (and source 'source)
                                               (and binary 'binary)
                                               (and binary-lib 'binary-lib))
-                                  #:force-strip? force))))
+                                  #:force-strip? force
+                                  #:dry-run? dry-run))))
                 (setup "migrated" no-setup #f setup-collects jobs)))]
             ;; ----------------------------------------
             [create
@@ -654,6 +663,8 @@
     [#:bool installation ("-i") "Shorthand for `--scope installation'"]
     [#:bool user ("-u") "Shorthand for `--scope user'"]
     [(#:str dir #f) scope-dir () "Select package scope <dir>"])
+   #:dry-run-flags
+   ([#:bool dry-run () ("Don't actually change package installation")])
    #:job-flags
    ([#:bool no-setup () ("Don't `raco setup' after changing packages (usually a bad idea)")]
     [(#:num n #f) jobs ("-j") "Setup with <n> parallel jobs"]
diff --git a/racket/collects/pkg/private/git.rkt b/racket/collects/pkg/private/git.rkt
index 1ee7c4d540..688046f5b9 100644
--- a/racket/collects/pkg/private/git.rkt
+++ b/racket/collects/pkg/private/git.rkt
@@ -14,6 +14,7 @@
 (define (git #:status [status void]
              #:quiet-stderr? [quiet-stderr? #t] ; suppress stderr unless error
              #:fail-mode [fail-mode 'error]
+             #:dry-run? [dry-run? #f]
              . args)
   (define exe (force git-exe))
   (unless exe
@@ -28,7 +29,11 @@
                (with-handlers ([values (lambda (exn)
                                          ;; re-raise after restoring stderr:
                                          (lambda () (raise exn)))])
-                 (define r (apply system* exe args))
+                 (define r
+                   (cond
+                    [dry-run? #t]
+                    [else
+                     (apply system* exe args)]))
                  (lambda () r)))))
   (cond
    [r #t]
diff --git a/racket/collects/pkg/private/install.rkt b/racket/collects/pkg/private/install.rkt
index 2df70b180d..39c552f816 100644
--- a/racket/collects/pkg/private/install.rkt
+++ b/racket/collects/pkg/private/install.rkt
@@ -167,6 +167,7 @@
          #:ai-cache ai-cache
          #:clone-info clone-info
          #:pull-behavior pull-behavior
+         #:dry-run? dry-run?
          descs)
   (define download-printf (if quiet? void printf/flush))
   (define check-sums? (not ignore-checksums?))
@@ -240,8 +241,11 @@
           ;; The `do-it` thunk:
           (lambda (fail-repos)
             (unless quiet?
-              (download-printf "Promoting ~a from auto-installed to explicitly installed\n" pkg-name))
-            (update-pkg-db! pkg-name (update-auto existing-pkg-info #f))))]
+              (download-printf "Promoting ~a from auto-installed to explicitly installed~a\n"
+                               pkg-name
+                               (dry-run-explain dry-run?)))
+            (unless dry-run?
+              (update-pkg-db! pkg-name (update-auto existing-pkg-info #f)))))]
         [else
          ;; Fail --- already installed
          (clean!)
@@ -453,7 +457,7 @@
                (let ()
                  (define (continue conversation)
                    (raise (vector #t infos pkg-name update-pkgs
-                                  (λ () (for-each (compose (remove-package #t quiet? use-trash?) pkg-desc-name) update-pkgs))
+                                  (λ () (for-each (compose (remove-package #t quiet? use-trash? dry-run?) pkg-desc-name) update-pkgs))
                                   conversation
                                   clone-info)))
                  (match (if (andmap (lambda (dep) (set-member? implies (pkg-desc-name dep)))
@@ -558,7 +562,7 @@
                                                                   #:link-dirs? link-dirs?)])
                                  (for ([pkg (in-list update-pkgs)]) (updater #:prefetch? #t pkg))
                                  (append-map updater update-pkgs))])
-                (λ () (for-each (compose (remove-package #t quiet? use-trash?) pkg-desc-name) to-update))))
+                (λ () (for-each (compose (remove-package #t quiet? use-trash? dry-run?) pkg-desc-name) to-update))))
             (match this-dep-behavior
               ['fail
                (clean!)
@@ -591,17 +595,19 @@
         ;; The "do-it" function (see `repos+do-its` below):
         (λ (fail-repos)
           (when updating?
-            (download-printf "Re-installing ~a\n" pkg-name))
+            (download-printf "Re-installing ~a~a\n" pkg-name (dry-run-explain dry-run?)))
           (define final-pkg-dir
             (cond
              [clean?
               (define final-pkg-dir (or git-dir
                                         (select-package-directory
-                                         (build-path (pkg-installed-dir) pkg-name))))
-              (unless git-dir
-                (make-parent-directory* final-pkg-dir)
-                (copy-directory/files pkg-dir final-pkg-dir #:keep-modify-seconds? #t))
-              (clean!)
+                                         (build-path (pkg-installed-dir) pkg-name)
+                                         dry-run?)))
+              (unless dry-run?
+                (unless git-dir
+                  (make-parent-directory* final-pkg-dir)
+                  (copy-directory/files pkg-dir final-pkg-dir #:keep-modify-seconds? #t))
+                (clean!))
               final-pkg-dir]
              [else
               pkg-dir]))
@@ -612,14 +618,15 @@
                          (if single-collect "single-collection " "") 
                          final-pkg-dir)
           (define scope (current-pkg-scope))
-          (links final-pkg-dir
-                 #:name single-collect
-                 #:user? (not (or (eq? 'installation scope)
-                                  (path? scope)))
-                 #:file (scope->links-file scope)
-                 #:root? (not single-collect)
-                 #:static-root? (and (pair? orig-pkg)
-                                     (eq? 'static-link (car orig-pkg))))
+          (unless dry-run?
+            (links final-pkg-dir
+                   #:name single-collect
+                   #:user? (not (or (eq? 'installation scope)
+                                    (path? scope)))
+                   #:file (scope->links-file scope)
+                   #:root? (not single-collect)
+                   #:static-root? (and (pair? orig-pkg)
+                                       (eq? 'static-link (car orig-pkg)))))
           (define alt-dir-name
             ;; If we had to pick an alternate dir name, then record it:
             (let-values ([(base name dir?) (split-path final-pkg-dir)])
@@ -635,7 +642,8 @@
           (define this-pkg-info
             (make-pkg-info orig-pkg new-checksum auto? single-collect alt-dir-name))
           (log-pkg-debug "updating db with ~e to ~e" pkg-name this-pkg-info)
-          (update-pkg-db! pkg-name this-pkg-info)))]))
+          (unless dry-run?
+            (update-pkg-db! pkg-name this-pkg-info))))]))
   (define metadata-ns (make-metadata-namespace))
   (define infos
     (for/list ([v (in-list descs)])
@@ -694,8 +702,9 @@
   (define fail-repos
     (for/fold ([fail-repos #hash()]) ([(git-dir checksums) (in-hash repos)])
       (parameterize ([current-directory git-dir])
-        (download-printf "Merging commits at ~a\n"
-                         git-dir)
+        (download-printf "Merging commits at ~a~a\n"
+                         git-dir
+                         (dry-run-explain dry-run?))
         (when ((length checksums) . > . 1)
           (download-printf (~a "Multiple packages in the of the clone\n"
                                "  " git-dir "\n"
@@ -706,6 +715,7 @@
           (define ok?
             (git #:status (lambda (s) (download-printf "~a\n" s))
                  #:fail-mode 'status
+                 #:dry-run? dry-run?
                  (if rebase? "rebase" "merge")
                  (if rebase? "--onto" "--ff-only")
                  checksum))
@@ -762,7 +772,8 @@
 
   (cond
    [(or (null? repo+do-its)
-        (and (not updating-any?) (andmap is-promote? all-infos)))
+        (and (not updating-any?) (andmap is-promote? all-infos))
+        dry-run?)
     ;; No actions, so no setup:
     'skip]
    [else
@@ -792,7 +803,7 @@
       (loop new-check
             (set-union setup-pkgs new-check))])))
 
-(define (select-package-directory dir #:counter [counter 0])
+(define (select-package-directory dir dry-run? #:counter [counter 0])
   (define full-dir (if (zero? counter)
                        dir
                        (let-values ([(base name dir?) (split-path dir)])
@@ -804,7 +815,8 @@
                              (build-path base new-name)
                              new-name))))
   (cond
-   [(directory-exists? full-dir)
+   [(and (directory-exists? full-dir)
+         (not dry-run?))
     ;; If the directory exists, assume that we'd like to replace it.
     ;; Maybe the directory couldn't be deleted when a package was
     ;; uninstalled, and maybe it will work now (because some process
@@ -813,7 +825,7 @@
                      (lambda (exn)
                        (log-pkg-warning "error deleting old directory: ~a" 
                                         (exn-message exn))
-                       (select-package-directory dir #:counter (add1 counter)))])
+                       (select-package-directory dir #f #:counter (add1 counter)))])
       (delete-directory/files full-dir)
       ;; delete succeeded:
       full-dir)]
@@ -856,7 +868,8 @@
                                                    (read-pkg-db)
                                                    (if quiet? void printf/flush))]
                      #:pull-behavior [pull-behavior 'ff-only]
-                     #:convert-to-non-clone? [convert-to-non-clone? #f])
+                     #:convert-to-non-clone? [convert-to-non-clone? #f]
+                     #:dry-run? [dry-run? #f])
   (define download-printf (if quiet? void printf/flush))
   
   (define descs
@@ -929,6 +942,7 @@
                          #:multi-clone-behavior (vector-ref clone-info 0)
                          #:repo-descs (vector-ref clone-info 1)
                          #:pull-behavior pull-behavior
+                         #:dry-run? dry-run?
                          (for/list ([dep (in-list deps)])
                            (if (pkg-desc? dep)
                                dep
@@ -951,7 +965,7 @@
         #:remote-checksum-cache remote-checksum-cache
         #:pre-succeed (λ ()
                         (for ([pkg-name (in-hash-keys extra-updating)])
-                          ((remove-package #t quiet? use-trash?) pkg-name))
+                          ((remove-package #t quiet? use-trash? dry-run?) pkg-name))
                         (pre-succeed))
         #:updating? updating?
         #:extra-updating extra-updating
@@ -967,6 +981,7 @@
         #:clone-info (vector clone-behavior
                              repo-descs)
         #:pull-behavior pull-behavior
+        #:dry-run? dry-run?
         new-descs)
        (unless (empty? summary-deps)
          (unless quiet?
@@ -1243,7 +1258,8 @@
                     #:infer-clone-from-dir? [infer-clone-from-dir? #f]
                     #:lookup-for-clone? [lookup-for-clone? #f]
                     #:multi-clone-behavior [clone-behavior 'fail]
-                    #:pull-behavior [pull-behavior 'ff-only])
+                    #:pull-behavior [pull-behavior 'ff-only]
+                    #:dry-run? [dry-run? #f])
   (define download-printf (if quiet? void printf/flush))
   (define metadata-ns (make-metadata-namespace))
   (define db (read-pkg-db))
@@ -1337,7 +1353,7 @@
          (flush-output))
        (pkg-install
         #:updating? #t
-        #:pre-succeed (λ () (for-each (compose (remove-package #t quiet? use-trash?) pkg-desc-name) to-update))
+        #:pre-succeed (λ () (for-each (compose (remove-package #t quiet? use-trash? dry-run?) pkg-desc-name) to-update))
         #:dep-behavior dep-behavior
         #:update-deps? update-deps?
         #:update-implies? update-implies?
@@ -1362,6 +1378,7 @@
                                      (andmap pkg-desc? in-pkgs)
                                      (not (ormap pkg-desc-extra-path in-pkgs)))
         #:pull-behavior pull-behavior
+        #:dry-run? dry-run?
         to-update)]))))
 
 ;; ----------------------------------------
diff --git a/racket/collects/pkg/private/migrate.rkt b/racket/collects/pkg/private/migrate.rkt
index e26e06160b..e9befec449 100644
--- a/racket/collects/pkg/private/migrate.rkt
+++ b/racket/collects/pkg/private/migrate.rkt
@@ -23,7 +23,8 @@
                      #:use-cache? [use-cache? #t]
                      #:dep-behavior [dep-behavior #f]
                      #:strip [strip-mode #f]
-                     #:force-strip? [force-strip? #f])
+                     #:force-strip? [force-strip? #f]
+                     #:dry-run? [dry-run? #f])
   (define from-db
     (parameterize ([current-pkg-scope-version from-version])
       (installed-pkg-table #:scope 'user)))
@@ -77,6 +78,7 @@
                     #:quiet? quiet? 
                     #:from-command-line? from-command-line?
                     #:strip strip-mode
-                    #:force-strip? force-strip?)
+                    #:force-strip? force-strip?
+                    #:dry-run? dry-run?)
        (unless quiet?
          (printf "Packages migrated\n")))))
diff --git a/racket/collects/pkg/private/print.rkt b/racket/collects/pkg/private/print.rkt
index abb19dc94d..8bc340d6a3 100644
--- a/racket/collects/pkg/private/print.rkt
+++ b/racket/collects/pkg/private/print.rkt
@@ -67,3 +67,9 @@
                 (if default-yes? "" "nothing or "))
        (eprintf " `a' or `A' for \"yes for all\", or `c' or `C' for \"cancel\".\n")
        (loop)])))
+
+
+(define (dry-run-explain dry-run?)
+  (if dry-run?
+      " (but not really)"
+      ""))
diff --git a/racket/collects/pkg/private/remove.rkt b/racket/collects/pkg/private/remove.rkt
index 1c6792ec67..18ad59db28 100644
--- a/racket/collects/pkg/private/remove.rkt
+++ b/racket/collects/pkg/private/remove.rkt
@@ -16,51 +16,57 @@
 (provide remove-package
          pkg-remove)
 
-(define (demote-packages quiet? pkg-names)
+(define (demote-packages quiet? dry-run? pkg-names)
   (define db (read-pkg-db))
   (for ([pkg-name (in-list pkg-names)])
     (define pi (package-info pkg-name #:db db))
     (unless (pkg-info-auto? pi)
       (unless quiet?
-        (printf/flush "Demoting ~a to auto-installed\n" pkg-name))
-      (update-pkg-db! pkg-name (update-auto pi #t)))))
+        (printf/flush "Demoting ~a to auto-installed~a\n"
+                      pkg-name 
+                      (dry-run-explain dry-run?)))
+      (unless dry-run?
+        (update-pkg-db! pkg-name (update-auto pi #t))))))
 
-(define ((remove-package for-install? quiet? use-trash?) pkg-name)
+(define ((remove-package for-install? quiet? use-trash? dry-run?) pkg-name)
   (unless quiet?
-    (printf/flush "~a ~a\n"
+    (printf/flush "~a ~a~a\n"
                   (if for-install?
                       "Uninstalling to prepare re-install of"
                       "Removing")
-                  pkg-name))
+                  pkg-name
+                  (dry-run-explain dry-run?)))
   (define db (read-pkg-db))
   (define pi (package-info pkg-name #:db db))
   (match-define (pkg-info orig-pkg checksum _) pi)
   (define pkg-dir (pkg-directory* pkg-name #:db db))
-  (remove-from-pkg-db! pkg-name)
+  (unless dry-run?
+    (remove-from-pkg-db! pkg-name))
   (define scope (current-pkg-scope))
   (define user? (not (or (eq? scope 'installation)
                          (path? scope))))
-  (match orig-pkg
-    [`(,(or 'link 'static-link 'clone) ,_ . ,_)
-     (links pkg-dir
-            #:remove? #t
-            #:user? user?
-            #:file (scope->links-file scope)
-            #:root? (not (sc-pkg-info? pi)))]
-    [_
-     (links pkg-dir
-            #:remove? #t
-            #:user? user?
-            #:file (scope->links-file scope)
-            #:root? (not (sc-pkg-info? pi)))
-     (cond
-      [(and use-trash?
-            (select-trash-dest pkg-name))
-       => (lambda (trash-dest)
-            (printf/flush "Moving ~a to trash: ~a\n" pkg-name trash-dest)
-            (rename-file-or-directory pkg-dir trash-dest))]
-      [else
-       (delete-directory/files pkg-dir)])]))
+  (unless dry-run?
+    (match orig-pkg
+      [`(,(or 'link 'static-link 'clone) ,_ . ,_)
+       (links pkg-dir
+              #:remove? #t
+              #:user? user?
+              #:file (scope->links-file scope)
+              #:root? (not (sc-pkg-info? pi)))]
+      [_
+       (links pkg-dir
+              #:remove? #t
+              #:user? user?
+              #:file (scope->links-file scope)
+              #:root? (not (sc-pkg-info? pi)))
+       (cond
+        [(and use-trash?
+              (select-trash-dest pkg-name))
+         => (lambda (trash-dest)
+              (printf/flush "Moving ~a to trash: ~a\n" pkg-name trash-dest)
+              (rename-file-or-directory pkg-dir trash-dest))]
+        [else
+         (delete-directory/files pkg-dir)])])))
       
 
 (define (pkg-remove given-pkgs
@@ -69,6 +75,7 @@
                     #:auto? [auto? #f]
                     #:quiet? [quiet? #f]
                     #:use-trash? [use-trash? #f]
+                    #:dry-run? [dry-run? #f]
                     #:from-command-line? [from-command-line? #f])
   (define db (read-pkg-db))
   (define all-pkgs
@@ -143,14 +150,15 @@
     ;; Demote any package that is not going to be removed:
     (demote-packages
      quiet?
+     dry-run?
      (set->list (set-subtract (list->set in-pkgs)
                               (list->set remove-pkgs)))))
 
-  (for-each (remove-package #f quiet? use-trash?)
+  (for-each (remove-package #f quiet? use-trash? dry-run?)
             remove-pkgs)
 
   (cond
-   [(or (null? remove-pkgs) demote?)
+   [(or (null? remove-pkgs) demote? dry-run?)
     ;; Did nothing, so no setup:
     'skip]
    [else