zip: add CheckFiles, CheckDir, and CheckZip

These functions may be used to check whether the files in an abstract
list, a directory, or a module zip file satisfy the module name and
size constraints listed in the package documentation. Each function
returns a CheckedFiles record that lists valid, omitted, and invalid
files, as well as any size-related error for the whole set of
files. The omitted and invalid lists have an error for each file,
saying why it was omitted or invalid.

Create, CreateFromDir, and Unzip are now implemented using these
functions (or common code). They now return errors based on
CheckedFiles errors. Most error messages won't change, but if multiple
files are invalid, they will be all be listed instead of just the
first one.

Fixes golang/go#36058
Updates golang/go#39091

Change-Id: I9d4d508288bbd821f93423e712232d8a68356529
Reviewed-on: https://go-review.googlesource.com/c/mod/+/235597
Run-TryBot: Jay Conrod <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>
Reviewed-by: Bryan C. Mills <[email protected]>
Reviewed-by: Michael Matloob <[email protected]>

Author: Jay Conrod

zip/testdata/check_dir/empty.txt

@@ -0,0 +1,6 @@
+-- want --
+valid:
+
+omitted:
+
+invalid:

zip/testdata/check_dir/various.txt

@@ -0,0 +1,20 @@
+-- want --
+valid:
+$work/valid.go
+
+omitted:
+$work/.hg_archival.txt: file is inserted by 'hg archive' and is always omitted
+$work/.git: directory is a version control repository
+$work/sub: directory is in another module
+$work/vendor/x/y: file is in vendor directory
+
+invalid:
+$work/GO.MOD: go.mod files must have lowercase names
+$work/invalid.go': malformed file path "invalid.go'": invalid char '\''
+-- valid.go --
+-- GO.MOD --
+-- invalid.go' --
+-- vendor/x/y --
+-- sub/go.mod --
+-- .hg_archival.txt --
+-- .git/x --

zip/testdata/check_files/empty.txt

@@ -0,0 +1,6 @@
+-- want --
+valid:
+
+omitted:
+
+invalid:

zip/testdata/check_files/various.txt

@@ -0,0 +1,25 @@
+-- want --
+valid:
+valid.go
+
+omitted:
+vendor/x/y: file is in vendor directory
+sub/go.mod: file is in another module
+.hg_archival.txt: file is inserted by 'hg archive' and is always omitted
+
+invalid:
+not/../clean: file path is not clean
+GO.MOD: go.mod files must have lowercase names
+invalid.go': malformed file path "invalid.go'": invalid char '\''
+valid.go: multiple entries for file "valid.go"
+-- valid.go --
+-- not/../clean --
+-- GO.MOD --
+-- invalid.go' --
+-- vendor/x/y --
+-- sub/go.mod --
+-- .hg_archival.txt --
+-- valid.go --
+duplicate
+-- valid.go --
+another duplicate

zip/testdata/check_zip/empty.txt

@@ -0,0 +1,8 @@
+path=example.com/empty
+version=v1.0.0
+-- want --
+valid:
+
+omitted:
+
+invalid:

zip/testdata/check_zip/various.txt

@@ -0,0 +1,21 @@
+path=example.com/various
+version=v1.0.0
+-- want --
+valid:
+example.com/[email protected]/valid.go
+
+omitted:
+
+invalid:
+noprefix: path does not have prefix "example.com/[email protected]/"
+example.com/[email protected]/not/../clean: file path is not clean
+example.com/[email protected]/invalid.go': malformed file path "invalid.go'": invalid char '\''
+example.com/[email protected]/GO.MOD: go.mod files must have lowercase names
+example.com/[email protected]/valid.go: multiple entries for file "valid.go"
+-- noprefix --
+-- example.com/[email protected]/valid.go --
+-- example.com/[email protected]/not/../clean --
+-- example.com/[email protected]/invalid.go' --
+-- example.com/[email protected]/GO.MOD --
+-- example.com/[email protected]/valid.go --
+duplicate

zip/testdata/create/bad_gomod_case.txt

@@ -1,5 +1,5 @@
 path=example.com/m
 version=v1.0.0
-wantErr=found file named GO.MOD, want all lower-case go.mod
+wantErr=GO.MOD: go.mod files must have lowercase names
 -- GO.MOD --
 module example.com/m

zip/testdata/create_from_dir/bad_gomod_case.txt

@@ -1,5 +1,5 @@
 path=example.com/m
 version=v1.0.0
-wantErr=found file named GO.MOD, want all lower-case go.mod
+wantErr=GO.MOD: go.mod files must have lowercase names
 -- GO.MOD --
 module example.com/m

zip/testdata/unzip/bad_gomod_case.txt

@@ -1,5 +1,5 @@
 path=example.com/m
 version=v1.0.0
-wantErr=found file named example.com/[email protected]/GO.MOD, want all lower-case go.mod
+wantErr=go.mod files must have lowercase names
 -- example.com/[email protected]/GO.MOD --
 module example.com/m

zip/testdata/unzip/bad_submodule.txt

@@ -1,6 +1,6 @@
 path=example.com/m
 version=v1.0.0
-wantErr=found go.mod file not in module root directory
+wantErr=go.mod file not in module root directory
 -- example.com/[email protected]/go.mod --
 module example.com/m
 

zip/testdata/unzip/cap_go_mod_not_submodule.txt

@@ -1,6 +1,6 @@
 path=example.com/m
 version=v1.0.0
-wantErr=found go.mod file not in module root directory
+wantErr=go.mod file not in module root directory
 -- example.com/[email protected]/a.go --
 package a
 -- example.com/[email protected]/b/GO.MOD --

zip/testdata/unzip/prefix_only.txt

@@ -1,6 +1,6 @@
 path=example.com/m
 version=v1.0.0
-wantErr=unexpected file name example.com/[email protected]
+wantErr=example.com/[email protected]: path does not have prefix "example.com/[email protected]/"
 -- example.com/[email protected] --
 -- example.com/[email protected]/go.mod --
 module example.com/m