Replace path implementation.

Path and PathFragment have been replaced with String-based implementations. They are pretty similar, but each method is dissimilar enough that I did not feel sharing code was appropriate.

A summary of changes:

PATH
====

* Subsumes LocalPath (deleted, its tests repurposed)
* Use a simple string to back Path
* Path instances are no longer interned; Reference equality will no longer work
* Always normalized (same as before)
* Some operations will now be slower, like instance compares (which were previously just a reference check)
* Multiple identical paths will now consume more memory since they are not interned

PATH FRAGMENT
=============

* Use a simple string to back PathFragment
* No more segment arrays with interned strings
* Always normalized
* Remove isNormalized
* Replace some isNormalizied uses with containsUpLevelReferences() to check if path fragments try to escape their scope
* To check if user input is normalized, supply static methods on PathFragment to validate the string before constructing a PathFragment
* Because PathFragments are always normalized, we have to replace checks for literal "." from PathFragment#getPathString to PathFragment#getSafePathString. The latter returns "." for the empty string.
* The previous implementation supported efficient segment semantics (segment count, iterating over segments). This is now expensive since we do longer have a segment array.

ARTIFACT
========

* Remove Path instance. It is instead dynamically constructed on request. This is necessary to avoid this CL becoming a memory regression.

RELNOTES: None
PiperOrigin-RevId: 185062932

2 files changed, 11 insertions, 5 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/cmdline/Label.java b/src/main/java/com/google/devtools/build/lib/cmdline/Label.java
index 2fbb2a4217..054648dd18 100644
--- a/src/main/java/com/google/devtools/build/lib/cmdline/Label.java
+++ b/src/main/java/com/google/devtools/build/lib/cmdline/Label.java
@@ -345,8 +345,17 @@ public final class Label
     return packageIdentifier.getPackageFragment();
   }
 
-  /** Returns the label as a path fragment, using the package and the label name. */
+  /**
+   * Returns the label as a path fragment, using the package and the label name.
+   *
+   * <p>Make sure that the label refers to a file. Non-file labels do not necessarily have
+   * PathFragment representations.
+   */
   public PathFragment toPathFragment() {
+    // PathFragments are normalized, so if we do this on a non-file target named '.'
+    // then the package would be returned. Detect this and throw.
+    // A target named '.' can never refer to a file.
+    Preconditions.checkArgument(!name.equals("."));
     return packageIdentifier.getPackageFragment().getRelative(name);
   }
 
diff --git a/src/main/java/com/google/devtools/build/lib/cmdline/PackageIdentifier.java b/src/main/java/com/google/devtools/build/lib/cmdline/PackageIdentifier.java
index ac62a3ae96..2067b641f0 100644
--- a/src/main/java/com/google/devtools/build/lib/cmdline/PackageIdentifier.java
+++ b/src/main/java/com/google/devtools/build/lib/cmdline/PackageIdentifier.java
@@ -87,7 +87,7 @@ public final class PackageIdentifier
       // TODO(ulfjack): Remove this when kchodorow@'s exec root rearrangement has been rolled out.
       RepositoryName repository = RepositoryName.create("@" + tofind.getSegment(1));
       return PackageIdentifier.create(repository, tofind.subFragment(2));
-    } else if (!tofind.normalize().isNormalized()) {
+    } else if (tofind.containsUplevelReferences()) {
       RepositoryName repository = RepositoryName.create("@" + tofind.getSegment(1));
       return PackageIdentifier.create(repository, tofind.subFragment(2));
     } else {
@@ -112,9 +112,6 @@ public final class PackageIdentifier
 
   private PackageIdentifier(RepositoryName repository, PathFragment pkgName) {
     this.repository = Preconditions.checkNotNull(repository);
-    if (!pkgName.isNormalized()) {
-      pkgName = pkgName.normalize();
-    }
     this.pkgName = Canonicalizer.fragments().intern(Preconditions.checkNotNull(pkgName));
     this.hashCode = Objects.hash(repository, pkgName);
   }