Handle plan outputs when they are too long to comment

action.yml

@@ -277,13 +277,17 @@ runs:
       id: plan
       if: inputs.action == 'plan'
       working-directory: ${{ inputs.directory }}
+      env:
+        TF_CLI: ${{ inputs.tf-cli }}
+        TF_PLAN_NO_COLOR: ${{ github.event_name == 'pull_request' && '-no-color' || '' }}
+        TF_PLAN_DESTROY: ${{ fromJSON(inputs.destroy) && '-destroy' || '' }}
+        TF_PLAN_OUT: ${{ inputs.plan-file-name && format('-out={0}', inputs.plan-file-name) || '' }}
+        TF_PLAN_ACTION_ARGS: ${{ inputs.action-args }}
+        PLAN_COMMENT_MAX_BYTES: '60000'
+        PLAN_COMMENT_EXCERPT_MAX_BYTES: '12288'
       shell: bash
       run: |
-        ${{ inputs.tf-cli }} plan -input=false \
-          ${{ github.event_name == 'pull_request' && '-no-color' || '' }} \
-          ${{ fromJSON(inputs.destroy) && '-destroy' || '' }} \
-          ${{ inputs.plan-file-name && format('-out={0}', inputs.plan-file-name) || '' }} \
-          ${{ inputs.action-args }}
+        bash "${{ github.action_path }}/scripts/terraform_plan.sh"
 
     - name: Encrypt Plan
       if: inputs.action == 'plan' && inputs.plan-file-name && inputs.encrypted-plan-password
@@ -367,8 +371,11 @@ runs:
         validateStderr: ${{ steps.validate.outputs.stderr }}
         testStdout: ${{ steps.test.outputs.stdout }}
         testStderr: ${{ steps.test.outputs.stderr }}
-        planStdout: ${{ steps.plan.outputs.stdout }}
-        planStderr: ${{ steps.plan.outputs.stderr }}
+        planCommentStdout: ${{ steps.plan.outputs.comment_stdout }}
+        planCommentStderr: ${{ steps.plan.outputs.comment_stderr }}
+        planCommentOverflow: ${{ steps.plan.outputs.comment_overflow }}
+        planCommentExcerptSource: ${{ steps.plan.outputs.comment_excerpt_source }}
+        workflowRunUrl: ${{ github.server_url }}/${{ github.repository }}/actions/runs/${{ github.run_id }}/job/${{ job.check_run_id }}
         outputStdout: ${{ steps.output.outputs.stdout }}
         outputStderr: ${{ steps.output.outputs.stderr }}
       with:
@@ -410,8 +417,11 @@ runs:
             plan: {
               enabled: ${{ inputs.action == 'plan' }},
               outcome: "${{ steps.plan.outcome }}",
-              stdout: `${process.env.planStdout}`,
-              stderr: `${process.env.planStderr}`
+              stdout: `${process.env.planCommentStdout}`,
+              stderr: `${process.env.planCommentStderr}`,
+              overflowed: `${process.env.planCommentOverflow}` === 'true',
+              excerptSource: `${process.env.planCommentExcerptSource}`,
+              logsUrl: `${process.env.workflowRunUrl}`
             },
             output: {
               enabled: ${{ inputs.action == 'output' }},

scripts/terraform_plan.sh

@@ -0,0 +1,89 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+plan_stdout_file=$(mktemp)
+plan_stderr_file=$(mktemp)
+plan_excerpt_file=$(mktemp)
+plan_combined_file=$(mktemp)
+
+cleanup_plan_files() {
+  rm -f "$plan_stdout_file" "$plan_stderr_file" "$plan_excerpt_file" "$plan_combined_file"
+}
+trap cleanup_plan_files EXIT
+
+PLAN_COMMENT_MAX_BYTES="${PLAN_COMMENT_MAX_BYTES:-60000}"
+PLAN_COMMENT_EXCERPT_MAX_BYTES="${PLAN_COMMENT_EXCERPT_MAX_BYTES:-12288}"
+
+write_multiline_output() {
+  local output_name="$1"
+  local file_path="$2"
+  local delimiter="${output_name}_$(date +%s)_$RANDOM"
+
+  {
+    echo "${output_name}<<${delimiter}"
+    cat "$file_path"
+    printf '\n%s\n' "$delimiter"
+  } >> "$GITHUB_OUTPUT"
+}
+
+plan_command="${TF_CLI} plan -input=false"
+
+if [ -n "${TF_PLAN_NO_COLOR:-}" ]; then
+  plan_command="${plan_command} ${TF_PLAN_NO_COLOR}"
+fi
+
+if [ -n "${TF_PLAN_DESTROY:-}" ]; then
+  plan_command="${plan_command} ${TF_PLAN_DESTROY}"
+fi
+
+if [ -n "${TF_PLAN_OUT:-}" ]; then
+  plan_command="${plan_command} ${TF_PLAN_OUT}"
+fi
+
+if [ -n "${TF_PLAN_ACTION_ARGS:-}" ]; then
+  plan_command="${plan_command} ${TF_PLAN_ACTION_ARGS}"
+fi
+
+set +e
+eval "$plan_command" \
+  > >(tee "$plan_stdout_file") \
+  2> >(tee "$plan_stderr_file" >&2)
+plan_exit_code=$?
+set -e
+
+plan_stdout_bytes=$(wc -c < "$plan_stdout_file" | tr -d '[:space:]')
+plan_stderr_bytes=$(wc -c < "$plan_stderr_file" | tr -d '[:space:]')
+plan_total_bytes=$((plan_stdout_bytes + plan_stderr_bytes))
+
+if [ "$plan_total_bytes" -le "$PLAN_COMMENT_MAX_BYTES" ]; then
+  {
+    echo "comment_overflow=false"
+    echo "comment_excerpt_source=full"
+  } >> "$GITHUB_OUTPUT"
+
+  write_multiline_output "comment_stdout" "$plan_stdout_file"
+  write_multiline_output "comment_stderr" "$plan_stderr_file"
+else
+  plan_summary_match=$(grep -nE -m 1 '^Plan: [0-9]+ to add, [0-9]+ to change, [0-9]+ to destroy\.$' "$plan_stdout_file" || true)
+
+  if [ -n "$plan_summary_match" ]; then
+    plan_summary_line="${plan_summary_match%%:*}"
+    tail -n +"$plan_summary_line" "$plan_stdout_file" > "$plan_combined_file"
+    head -c "$PLAN_COMMENT_EXCERPT_MAX_BYTES" "$plan_combined_file" > "$plan_excerpt_file"
+    comment_excerpt_source="plan-summary"
+  else
+    cat "$plan_stdout_file" "$plan_stderr_file" > "$plan_combined_file"
+    tail -c "$PLAN_COMMENT_EXCERPT_MAX_BYTES" "$plan_combined_file" > "$plan_excerpt_file"
+    comment_excerpt_source="tail"
+  fi
+
+  {
+    echo "comment_overflow=true"
+    echo "comment_excerpt_source=${comment_excerpt_source}"
+    echo "comment_stderr="
+  } >> "$GITHUB_OUTPUT"
+  write_multiline_output "comment_stdout" "$plan_excerpt_file"
+fi
+
+exit "$plan_exit_code"

terraform_comment.js

@@ -110,7 +110,48 @@ ${outcome !== 'skipped' ? createTestDetails(stdout, stderr) : ''}
     ` : '';
 }
 
-const createPlanDetails = (stdout, stderr) => {
+const createPlanExcerptSourceNote = (excerptSource) => {
+    if (excerptSource === 'plan-summary') {
+        return 'This excerpt starts at the Terraform summary line (`Plan: ...`).';
+    }
+
+    if (excerptSource === 'tail') {
+        return 'The Terraform summary line was not found, so this excerpt shows the tail of combined stdout/stderr output.';
+    }
+
+    return 'This excerpt shows a truncated portion of the Terraform plan output.';
+};
+
+const createPlanDetails = ({stdout, stderr, overflowed, excerptSource, logsUrl}) => {
+    if (overflowed) {
+        const workflowLogs = logsUrl ? `[workflow run logs](${logsUrl})` : 'workflow run logs';
+        const excerptSourceNote = createPlanExcerptSourceNote(excerptSource);
+        const excerptOutput = stdout
+            ? `
+\`\`\`hcl\n
+${stdout}
+\`\`\`
+`
+            : `
+_No plan excerpt was available in this comment._
+`;
+
+        return `
+
+<details><summary>Show Plan</summary>
+
+Terraform plan output exceeded size constraints, so this comment includes only a partial excerpt.
+
+${excerptSourceNote}
+
+View the full plan output in the ${workflowLogs}.
+
+${excerptOutput}
+
+</details>
+    `;
+    }
+
     return `
 
 <details><summary>Show Plan</summary>
@@ -123,11 +164,11 @@ ${stdout}${stderr ? `\n${stderr}` : ''}
     `;
 };
 
-const createPlanOutput = ({enabled, outcome, stdout, stderr}) => {
+const createPlanOutput = ({enabled, outcome, stdout, stderr, overflowed, excerptSource, logsUrl}) => {
     return enabled ? `
 
 #### Terraform Plan 📖 \`${outcome}\`
-${outcome !== 'skipped' ? createPlanDetails(stdout, stderr) : ''}
+${outcome !== 'skipped' ? createPlanDetails({stdout, stderr, overflowed, excerptSource, logsUrl}) : ''}
     ` : '';
 };