patchgit-p4: ignore P4 changelists that only touch files

git-p4.py, t/t9826-git-p4-keep-empty-commits.sh

diff --git a/git-p4.py b/git-p4.py
index 7a9dd6a..c38a8f7 100755
--- a/git-p4.py
+++ b/git-p4.py
@@ -328,6 +328,15 @@ def split_p4_type(p4type):
     return (base, mods)
 
 #
+# converts P4 mods to Git file modes
+#
+def convert_to_git_mode(p4_mods):
+    if 'x' in p4_mods:
+        return '100755'
+    else:
+        return '100644'
+
+#
 # return the raw p4 type of a file (text, text+ko, etc)
 #
 def p4_type(f):
@@ -335,6 +344,35 @@ def p4_type(f):
     return results[0]['headType']
 
 #
+# Returns true if Git would mark the diff of a file `f` in `changelist1`
+# and `changelist2` as modified. The change detection is very conservative
+# as a P4 file type change would usually not change the Git content.
+# However, in case of symlinks or UTF-16 files that might happen.
+#
+def p4_file_changed(f, changelist1, changelist2):
+    if not changelist1 or not changelist2:
+        return True
+    results = p4CmdList([
+        'diff2',
+        '{}@{}'.format(wildcard_encode(f), changelist1),
+        '{}@{}'.format(wildcard_encode(f), changelist2)
+    ])
+    if len(results) != 1:
+        return True
+    elif ('status' not in results[0] or
+          'type' not in results[0] or
+          'type2' not in results[0]):
+        return True
+    else:
+        (type1, mods1) = split_p4_type(results[0]['type'])
+        (type2, mods2) = split_p4_type(results[0]['type2'])
+        return (
+            results[0]['status'] != 'identical' or
+            convert_to_git_mode(mods1) != convert_to_git_mode(mods2) or
+            type1 != type2
+        )
+
+#
 # Given a type base and modifier, return a regexp matching
 # the keywords that can be expanded in the file
 #
@@ -2394,10 +2432,8 @@ class P4Sync(Command, P4UserMap):
             sys.stdout.flush()
 
         (type_base, type_mods) = split_p4_type(file["type"])
+        git_mode = convert_to_git_mode(type_mods)
 
-        git_mode = "100644"
-        if "x" in type_mods:
-            git_mode = "100755"
         if type_base == "symlink":
             git_mode = "120000"
             # p4 print on a symlink sometimes contains "target\n";
@@ -2656,6 +2692,14 @@ class P4Sync(Command, P4UserMap):
         files = [f for f in files
             if self.inClientSpec(f['path']) and self.hasBranchPrefix(f['path'])]
 
+        files = [f for f in files
+            if not f['action'] == 'edit' or p4_file_changed(
+                f['path'],
+                details.get('previous_change', None),
+                details['change']
+            )
+        ]
+
         if not files and not gitConfigBool('git-p4.keepEmptyCommits'):
             print('Ignoring revision {0} as it would produce an empty commit.'
                 .format(details['change']))
@@ -2993,8 +3037,10 @@ class P4Sync(Command, P4UserMap):
 
     def importChanges(self, changes):
         cnt = 1
+        previous_change = None
         for change in changes:
             description = p4_describe(change)
+            description['previous_change'] = previous_change
             self.updateOptionDict(description)
 
             if not self.silent:
@@ -3069,6 +3115,8 @@ class P4Sync(Command, P4UserMap):
                                 self.initialParent)
                     # only needed once, to connect to the previous commit
                     self.initialParent = ""
+
+                previous_change = change
             except IOError:
                 print self.gitError.read()
                 sys.exit(1)
diff --git a/t/t9826-git-p4-keep-empty-commits.sh b/t/t9826-git-p4-keep-empty-commits.sh
index be12960..23a300a 100755
--- a/t/t9826-git-p4-keep-empty-commits.sh
+++ b/t/t9826-git-p4-keep-empty-commits.sh
@@ -15,7 +15,7 @@ test_expect_success 'Create a repo' '
 
 		mkdir -p subdir &&
 
-		>subdir/file1.txt &&
+		echo "content1" >subdir/file1.txt &&
 		p4 add subdir/file1.txt &&
 		p4 submit -d "Add file 1" &&
 
@@ -35,7 +35,21 @@ test_expect_success 'Create a repo' '
 		p4 submit -d "Remove file 3" &&
 
 		p4 delete file4.txt &&
-		p4 submit -d "Remove file 4"
+		p4 submit -d "Remove file 4" &&
+
+		p4 edit subdir/file1.txt &&
+		touch subdir/file1.txt &&
+		p4 submit -d "Touch file1 - no changes" subdir/file1.txt
+
+		p4 edit -t text+x subdir/file1.txt &&
+		p4 submit -d "Change execution bit" subdir/file1.txt
+
+		p4 edit -t binary+x subdir/file1.txt &&
+		p4 submit -d "Change filetype" subdir/file1.txt
+
+		p4 edit subdir/file1.txt &&
+		echo "content1 changed" >subdir/file1.txt &&
+		p4 submit -d "Change content" subdir/file1.txt
 	)
 '
 
@@ -47,6 +61,15 @@ test_expect_success 'Clone repo root path with all history' '
 		git init . &&
 		git p4 clone --use-client-spec --destination="$git" //depot@all &&
 		cat >expect <<-\EOF &&
+Change content
+[git-p4: depot-paths = "//depot/": change = 10]
+
+Change filetype
+[git-p4: depot-paths = "//depot/": change = 9]
+
+Change execution bit
+[git-p4: depot-paths = "//depot/": change = 8]
+
 Remove file 4
 [git-p4: depot-paths = "//depot/": change = 6]
 
@@ -80,6 +103,18 @@ test_expect_success 'Clone repo subdir with all history but keep empty commits'
 		git config git-p4.keepEmptyCommits true &&
 		git p4 clone --use-client-spec --destination="$git" //depot@all &&
 		cat >expect <<-\EOF &&
+Change content
+[git-p4: depot-paths = "//depot/": change = 10]
+
+Change filetype
+[git-p4: depot-paths = "//depot/": change = 9]
+
+Change execution bit
+[git-p4: depot-paths = "//depot/": change = 8]
+
+Touch file1 - no changes
+[git-p4: depot-paths = "//depot/": change = 7]
+
 Remove file 4
 [git-p4: depot-paths = "//depot/": change = 6]
 
@@ -112,6 +147,15 @@ test_expect_success 'Clone repo subdir with all history' '
 		git init . &&
 		git p4 clone --use-client-spec --destination="$git" --verbose //depot@all &&
 		cat >expect <<-\EOF &&
+Change content
+[git-p4: depot-paths = "//depot/": change = 10]
+
+Change filetype
+[git-p4: depot-paths = "//depot/": change = 9]
+
+Change execution bit
+[git-p4: depot-paths = "//depot/": change = 8]
+
 Remove file 3
 [git-p4: depot-paths = "//depot/": change = 5]