fix(cli): stack monitor prints over error messages (aws#19859)

In aws#19742, we limited the amount of text that the status printer
would produce, and tried to get rid of the empty lines at the end
of the rewritable block as well.

Unfortunately, we scrolled up too far, overwriting the error messages
that may occur during resource provisioning. Since these were the only
place where error messages were displayed, it is now not possible to see
why a stack deployment fails.

This PR fixes that.


----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

packages/aws-cdk/lib/api/util/cloudformation/stack-activity-monitor.ts

@@ -682,7 +682,7 @@ export class CurrentActivityPrinter extends ActivityPrinterBase {
 
     // Display in the same block space, otherwise we're going to have silly empty lines.
     this.block.displayLines(lines);
-    this.block.removeEmptyLines(lines);
+    this.block.removeEmptyLines();
   }
 
   private progressBar(width: number) {
@@ -745,7 +745,7 @@ function colorFromStatusActivity(status?: string) {
     return chalk.red;
   }
 
-  if (status.startsWith('CREATE_') || status.startsWith('UPDATE_')) {
+  if (status.startsWith('CREATE_') || status.startsWith('UPDATE_') || status.startsWith('IMPORT_')) {
     return chalk.green;
   }
   // For stacks, it may also be 'UPDDATE_ROLLBACK_IN_PROGRESS'

packages/aws-cdk/lib/api/util/display.ts

@@ -7,6 +7,7 @@ const wrapAnsi = require('wrap-ansi');
  */
 export class RewritableBlock {
   private lastHeight = 0;
+  private trailingEmptyLines = 0;
 
   constructor(private readonly stream: NodeJS.WriteStream) {
   }
@@ -22,23 +23,27 @@ export class RewritableBlock {
   }
 
   public displayLines(lines: string[]) {
-    lines = terminalWrap(this.width, expandNewlines(lines)).slice(0, getMaxBlockHeight(this.height, this.lastHeight, lines));
+    lines = terminalWrap(this.width, expandNewlines(lines));
+    lines = lines.slice(0, getMaxBlockHeight(this.height, this.lastHeight, lines));
 
     this.stream.write(cursorUp(this.lastHeight));
     for (const line of lines) {
       this.stream.write(cll() + line + '\n');
     }
+
+    this.trailingEmptyLines = Math.max(0, this.lastHeight - lines.length);
+
     // Clear remainder of unwritten lines
-    for (let i = 0; i < this.lastHeight - lines.length; i++) {
+    for (let i = 0; i < this.trailingEmptyLines; i++) {
       this.stream.write(cll() + '\n');
     }
 
     // The block can only ever get bigger
     this.lastHeight = Math.max(this.lastHeight, lines.length);
   }
 
-  public removeEmptyLines(lines: string[]) {
-    this.stream.write(cursorUp(this.lastHeight - lines.length));
+  public removeEmptyLines() {
+    this.stream.write(cursorUp(this.trailingEmptyLines));
   }
 }
 
@@ -62,26 +67,18 @@ function cll() {
 function terminalWrap(width: number | undefined, lines: string[]) {
   if (width === undefined) { return lines; }
 
-  const ret = new Array<string>();
-  for (const line of lines) {
-    ret.push(...wrapAnsi(line, width - 1, {
-      hard: true,
-      trim: true,
-      wordWrap: false,
-    }).split('\n'));
-  }
-  return ret;
+  return lines.flatMap(line => wrapAnsi(line, width - 1, {
+    hard: true,
+    trim: true,
+    wordWrap: false,
+  }).split('\n'));
 }
 
 /**
  * Make sure there are no hidden newlines in the gin strings
  */
 function expandNewlines(lines: string[]): string[] {
-  const ret = new Array<string>();
-  for (const line of lines) {
-    ret.push(...line.split('\n'));
-  }
-  return ret;
+  return lines.flatMap(line => line.split('\n'));
 }
 
 function getMaxBlockHeight(windowHeight: number | undefined, lastHeight: number, lines: string[]): number {

packages/aws-cdk/test/api/util/display.test.ts

@@ -36,4 +36,27 @@ describe('Rewritable Block Tests', () => {
 
     expect(output.length).toEqual(6);
   });
+
+  test('display accounts for newlines in output', () => {
+    const output = stderr.inspectSync(() => {
+      block.displayLines(['before\nafter']);
+    });
+    expect(output.length).toEqual(3); // cursorup + 2 lines
+  });
+
+  test('removeEmptyLines only removes trailing lines', () => {
+    stderr.inspectSync(() => {
+      block.displayLines(Array.from(Array(5).keys()).map(x => `${x}`));
+    });
+    stderr.inspectSync(() => {
+      // Leaves 3 empty lines
+      block.displayLines(Array.from(Array(2).keys()).map(x => `${x}`));
+    });
+
+    const output = stderr.inspectSync(() => {
+      block.removeEmptyLines();
+    });
+    const expectedEmptyLines = 3;
+    expect(JSON.stringify(output)).toEqual(JSON.stringify([`\u001b[${expectedEmptyLines}A`]));
+  });
 });