git-gui: Add support for calling out to the prepare-commit-msg hook

Signed-off-by: Joshua Williams <joshua.williams@qlogic.com>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

git-gui.sh

@@ -1170,6 +1170,7 @@ proc rescan {after {honor_trustmtime 1}} {
 		|| [string trim [$ui_comm get 0.0 end]] eq {})} {
 		if {[string match amend* $commit_type]} {
 		} elseif {[load_message GITGUI_MSG]} {
+		} elseif {[run_prepare_commit_msg_hook]} {
 		} elseif {[load_message MERGE_MSG]} {
 		} elseif {[load_message SQUASH_MSG]} {
 		}
@@ -1269,6 +1270,70 @@ proc load_message {file} {
 	return 0
 }
 
+proc run_prepare_commit_msg_hook {} {
+	global pch_error
+
+	# prepare-commit-msg requires PREPARE_COMMIT_MSG exist.  From git-gui
+	# it will be .git/MERGE_MSG (merge), .git/SQUASH_MSG (squash), or an
+	# empty file but existant file.
+
+	set fd_pcm [open [gitdir PREPARE_COMMIT_MSG] a]
+
+	if {[file isfile [gitdir MERGE_MSG]]} {
+		set pcm_source "merge"
+		set fd_mm [open [gitdir MERGE_MSG] r]
+		puts -nonewline $fd_pcm [read $fd_mm]
+		close $fd_mm
+	} elseif {[file isfile [gitdir SQUASH_MSG]]} {
+		set pcm_source "squash"
+		set fd_sm [open [gitdir SQUASH_MSG] r]
+		puts -nonewline $fd_pcm [read $fd_sm]
+		close $fd_sm
+	} else {
+		set pcm_source ""
+	}
+
+	close $fd_pcm
+
+	set fd_ph [githook_read prepare-commit-msg \
+			[gitdir PREPARE_COMMIT_MSG] $pcm_source]
+	if {$fd_ph eq {}} {
+		catch {file delete [gitdir PREPARE_COMMIT_MSG]}
+		return 0;
+	}
+
+	ui_status [mc "Calling prepare-commit-msg hook..."]
+	set pch_error {}
+
+	fconfigure $fd_ph -blocking 0 -translation binary -eofchar {}
+	fileevent $fd_ph readable \
+		[list prepare_commit_msg_hook_wait $fd_ph]
+
+	return 1;
+}
+
+proc prepare_commit_msg_hook_wait {fd_ph} {
+	global pch_error
+
+	append pch_error [read $fd_ph]
+	fconfigure $fd_ph -blocking 1
+	if {[eof $fd_ph]} {
+		if {[catch {close $fd_ph}]} {
+			ui_status [mc "Commit declined by prepare-commit-msg hook."]
+			hook_failed_popup prepare-commit-msg $pch_error
+			catch {file delete [gitdir PREPARE_COMMIT_MSG]}
+			exit 1
+		} else {
+			load_message PREPARE_COMMIT_MSG
+		}
+		set pch_error {}
+		catch {file delete [gitdir PREPARE_COMMIT_MSG]}
+		return
+        }
+	fconfigure $fd_ph -blocking 0
+	catch {file delete [gitdir PREPARE_COMMIT_MSG]}
+}
+
 proc read_diff_index {fd after} {
 	global buf_rdi