add shell script to debug repeatable builds

to aid reproduce #647

.github/workflows/rust.yml

@@ -13,7 +13,7 @@ name: Continuous integration
 # https://github.com/googlefonts/fontations/blob/main/.github/workflows/rust.yml.
 # other than the list of crates for cargo check no std
 
-jobs:  
+jobs:
   check:
     name: Rustfmt
     runs-on: ubuntu-latest
@@ -178,55 +178,35 @@ jobs:
       - name: Build and install fontc (release mode)
         run: cd fontc && pwd && cargo install --path .
 
+      - name: Fetch OTS
+        run: |
+            curl -OL "https://github.com/khaledhosny/ots/releases/download/v9.1.0/ots-9.1.0-Linux.zip"
+            unzip "ots-9.1.0-Linux.zip" "ots-9.1.0-Linux/ots-sanitize"
+
+      - name: Install ttx
+        run: |
+          pipx install fonttools
+          which ttx
+          ttx --version
+
       - name: Check out font project source repository
         uses: actions/checkout@v4
         with:
           repository: googlefonts/googlesans
+          path: googlesans
           token: ${{ secrets.GS_READ_FONTC }}
 
       - name: Pin SOURCE_DATE_EPOCH
         run: echo "SOURCE_DATE_EPOCH=$(date +%s)" >> "$GITHUB_ENV"
 
-      - name: Compile me once, shame on you
-        run: |
-          rm -rf build
-          fontc source/GoogleSans/GoogleSans.designspace
-          cp build/font.ttf ./first-roman.ttf
-          rm -rf build
-          fontc source/GoogleSans/GoogleSans-Italic.designspace
-          cp build/font.ttf ./first-italic.ttf
+      - name: Compile Roman twice
+        run: ./resources/scripts/repeatable-builds.sh googlesans/source/GoogleSans/GoogleSans.designspace
 
-      - name: Fetch OTS
-        run: |
-            curl -OL "https://github.com/khaledhosny/ots/releases/download/v9.1.0/ots-9.1.0-Linux.zip"
-            unzip "ots-9.1.0-Linux.zip" "ots-9.1.0-Linux/ots-sanitize"
+      - name: Compile Italic twice
+        run: ./resources/scripts/repeatable-builds.sh googlesans/source/GoogleSans/GoogleSans-Italic.designspace
 
       - name: OTS tests, Roman
-        run: ots-9.1.0-Linux/ots-sanitize build/font.ttf
+        run: ots-9.1.0-Linux/ots-sanitize build/GoogleSans.ttf
 
       - name: OTS tests, Italic
-        run: ots-9.1.0-Linux/ots-sanitize build/font.ttf
-
-      - name: Compile me twice, shame on me
-        run: |
-          rm -rf build
-          fontc source/GoogleSans/GoogleSans.designspace
-          cp build/font.ttf ./second-roman.ttf
-          rm -rf build
-          fontc source/GoogleSans/GoogleSans-Italic.designspace
-          cp build/font.ttf ./second-italic.ttf
-
-      - name: ttx, it might be handy to troubleshoot
-        # tail -n +2 to skip past the first line because it emits the filename
-        run: |
-          pipx install fonttools
-          which ttx
-          ttx --version
-          diff -u <(ttx -l first-roman.ttf | tail -n +2) <(ttx -l second-roman.ttf | tail -n +2)
-          diff -u <(ttx -l first-italic.ttf | tail -n +2) <(ttx -l second-italic.ttf | tail -n +2)
-
-      - name: Stable Roman?
-        run: cmp first-roman.ttf second-roman.ttf
-
-      - name: Stable Italic?
-        run: cmp first-italic.ttf second-italic.ttf
+        run: ots-9.1.0-Linux/ots-sanitize build/GoogleSans-Italic.ttf

resources/scripts/repeatable-builds.sh

@@ -0,0 +1,44 @@
+#!/bin/bash
+
+# This script is used to test that fontc produces repeatable builds.
+
+if [ -z "$1" ]; then
+  echo "Error: Please provide path to a font source to compile"
+  exit 1
+fi
+
+INPUT_SOURCE="$1"
+filename=$(basename "$INPUT_SOURCE")
+first="build/${filename%.*}.ttf"
+second="build/${filename%.*}#1.ttf"
+
+ttcmp() {
+  if [ "$#" -lt 2 ]
+  then
+    echo "Usage: ttcmp FONT1.ttf FONT2.ttf"
+    return 1
+  fi
+  cmp $1 $2
+  if [ $? -ne 0 ]; then
+    # tail -n +2 to skip past the first line because it emits the filename
+    diff -u <(ttx -l $1 | tail -n +2) <(ttx -l $2 | tail -n +2)
+  fi
+}
+
+echo "$ which fontc"
+which fontc
+
+echo "$ fontc $INPUT_SOURCE -o $first"
+fontc "$INPUT_SOURCE" -o $first
+
+echo "$ fontc $INPUT_SOURCE -o $second"
+fontc "$INPUT_SOURCE" -o $second
+
+echo "$ ttcmp $first $second"
+ttcmp $first $second
+if [ $? -eq 0 ]; then
+  echo "Success: $first and $second are identical"
+else
+  echo "Error: $first and $second are different"
+  exit 1
+fi