From dd3aa8410572ddf7331588594caa0172ba3d5219 Mon Sep 17 00:00:00 2001
From: JoostK <joost.koehoorn@gmail.com>
Date: Wed, 9 Jun 2021 21:25:43 +0200
Subject: [PATCH] fix(compiler-cli): prevent prior compilations from being
 retained in watch builds

In watch builds, the compiler attempts to reuse as much information from
a prior compilation as possible. To accomplish this, it keeps a
reference to the most recently succeeded `TraitCompiler`, which contains
all analysis data for the program. However, `TraitCompiler` has an
internal reference to an `IncrementalBuild`, which is itself built on
top of its prior state. Consequently, all prior compilations continued
to be referenced, preventing garbage collection from cleaning up these
instances.

This commit changes the `AnalyzedIncrementalState` to no longer retain
a `TraitCompiler` instance, but only the analysis data it contains. This
breaks the retainer path to the prior incremental state, allowing it to
be garbage collected.
---
 .../src/ngtsc/incremental/src/incremental.ts         |  8 ++++++--
 .../compiler-cli/src/ngtsc/incremental/src/state.ts  |  9 ++++++---
 .../src/ngtsc/transform/src/compilation.ts           | 12 ++++++++++++
 3 files changed, 24 insertions(+), 5 deletions(-)

diff --git a/packages/compiler-cli/src/ngtsc/incremental/src/incremental.ts b/packages/compiler-cli/src/ngtsc/incremental/src/incremental.ts
index e0ef06c463750..1f466dc968c01 100644
--- a/packages/compiler-cli/src/ngtsc/incremental/src/incremental.ts
+++ b/packages/compiler-cli/src/ngtsc/incremental/src/incremental.ts
@@ -259,7 +259,7 @@ export class IncrementalCompilation implements IncrementalBuild<ClassRecord, Fil
       versions: this.versions,
       depGraph: this.depGraph,
       semanticDepGraph: newGraph,
-      traitCompiler,
+      priorAnalysis: traitCompiler.getAnalyzedRecords(),
       typeCheckResults: null,
       emitted,
     };
@@ -303,7 +303,11 @@ export class IncrementalCompilation implements IncrementalBuild<ClassRecord, Fil
       return null;
     }
 
-    return this.step.priorState.traitCompiler.recordsFor(sf);
+    const priorAnalysis = this.step.priorState.priorAnalysis;
+    if (!priorAnalysis.has(sf)) {
+      return null;
+    }
+    return priorAnalysis.get(sf)!;
   }
 
   priorTypeCheckingResultsFor(sf: ts.SourceFile): FileTypeCheckingData|null {
diff --git a/packages/compiler-cli/src/ngtsc/incremental/src/state.ts b/packages/compiler-cli/src/ngtsc/incremental/src/state.ts
index bda9a28527a09..5526affe5c055 100644
--- a/packages/compiler-cli/src/ngtsc/incremental/src/state.ts
+++ b/packages/compiler-cli/src/ngtsc/incremental/src/state.ts
@@ -6,8 +6,10 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
+import * as ts from 'typescript';
+
 import {AbsoluteFsPath} from '../../file_system';
-import {TraitCompiler} from '../../transform';
+import {ClassRecord} from '../../transform';
 import {FileTypeCheckingData} from '../../typecheck/src/checker';
 import {SemanticDepGraph} from '../semantic_graph';
 
@@ -51,9 +53,10 @@ export interface AnalyzedIncrementalState {
   semanticDepGraph: SemanticDepGraph;
 
   /**
-   * `TraitCompiler` which contains records of all analyzed classes within the build.
+   * The analysis data from a prior compilation. This stores the trait information for all source
+   * files that was present in a prior compilation.
    */
-  traitCompiler: TraitCompiler;
+  priorAnalysis: Map<ts.SourceFile, ClassRecord[]>;
 
   /**
    * All generated template type-checking files produced as part of this compilation, or `null` if
diff --git a/packages/compiler-cli/src/ngtsc/transform/src/compilation.ts b/packages/compiler-cli/src/ngtsc/transform/src/compilation.ts
index 6c8ba0da9ccfc..a189f5d4a93b5 100644
--- a/packages/compiler-cli/src/ngtsc/transform/src/compilation.ts
+++ b/packages/compiler-cli/src/ngtsc/transform/src/compilation.ts
@@ -166,6 +166,18 @@ export class TraitCompiler implements ProgramTypeCheckAdapter {
     return records;
   }
 
+  getAnalyzedRecords(): Map<ts.SourceFile, ClassRecord[]> {
+    const result = new Map<ts.SourceFile, ClassRecord[]>();
+    for (const [sf, classes] of this.fileToClasses) {
+      const records: ClassRecord[] = [];
+      for (const clazz of classes) {
+        records.push(this.classes.get(clazz)!);
+      }
+      result.set(sf, records);
+    }
+    return result;
+  }
+
   /**
    * Import a `ClassRecord` from a previous compilation.
    *