Add shared library for filepath normalization

Author: joefarebrother

csharp/ql/test/library-tests/utils/FilepathNormalizeTest.expected

@@ -0,0 +1,10 @@
+|  | . |
+| ./a/b/c/../d | a/b/d |
+| / | / |
+| /a/b/../c | /a/c |
+| /a/b/c/../../d/ | /a/d |
+| a/.. | . |
+| a/b/../c | a/c |
+| a/b//////c/./d/../e//d// | a/b/c/e/d |
+| a/b/c | a/b/c |
+| a/b/c/../../../../d/e/../f | ../d/f |

csharp/ql/test/library-tests/utils/FilepathNormalizeTest.ql

@@ -0,0 +1,14 @@
+import codeql.util.FilePath
+
+class FilepathTest extends NormalizableFilepath {
+  FilepathTest() {
+    this =
+      [
+        "a/b/c", "a/b/../c", "a/..", "/a/b/../c", "a/b/c/../../../../d/e/../f", "", "/",
+        "./a/b/c/../d", "a/b//////c/./d/../e//d//", "/a/b/c/../../d/"
+      ]
+  }
+}
+
+from FilepathTest s
+select s, s.getNormalizedPath()

shared/util/change-notes/2023-10-13-filepath-normalization.md

@@ -0,0 +1,4 @@
+category: feature
+---
+* Added `FilePath` API for normalizing filepaths.
+```

shared/util/codeql/util/FilePath.qll

@@ -0,0 +1,74 @@
+/** Provides a utility for normalizing filepaths. */
+
+/**
+ * A filepath that should be normalized.
+ * Extend to provide additional strings that should be normalized as filepaths.
+ */
+abstract class NormalizableFilepath extends string {
+  bindingset[this]
+  NormalizableFilepath() { any() }
+
+  private string getComponent(int i) { result = this.splitAt("/", i) }
+
+  private int getNumComponents() { result = strictcount(int i | exists(this.getComponent(i))) }
+
+  /** count .. segments in prefix in normalization from index i */
+  private int dotdotCountFrom(int i) {
+    result = 0 and i = this.getNumComponents()
+    or
+    exists(string c | c = this.getComponent(i) |
+      if c = ""
+      then result = this.dotdotCountFrom(i + 1)
+      else
+        if c = "."
+        then result = this.dotdotCountFrom(i + 1)
+        else
+          if c = ".."
+          then result = this.dotdotCountFrom(i + 1) + 1
+          else result = (this.dotdotCountFrom(i + 1) - 1).maximum(0)
+    )
+  }
+
+  /** count non-.. segments in postfix in normalization from index 0 to i-1 */
+  private int segmentCountUntil(int i) {
+    result = 0 and i = 0
+    or
+    exists(string c | c = this.getComponent(i - 1) |
+      if c = ""
+      then result = this.segmentCountUntil(i - 1)
+      else
+        if c = "."
+        then result = this.segmentCountUntil(i - 1)
+        else
+          if c = ".."
+          then result = (this.segmentCountUntil(i - 1) - 1).maximum(0)
+          else result = this.segmentCountUntil(i - 1) + 1
+    )
+  }
+
+  private string part(int i) {
+    result = this.getComponent(i) and
+    result != "." and
+    if result = ""
+    then i = 0
+    else (
+      result != ".." and
+      0 = this.dotdotCountFrom(i + 1)
+      or
+      result = ".." and
+      0 = this.segmentCountUntil(i)
+    )
+  }
+
+  /** Gets the normalized filepath for this string; traversing `/../` paths. */
+  string getNormalizedPath() {
+    exists(string norm | norm = concat(string s, int i | s = this.part(i) | s, "/" order by i) |
+      if norm != ""
+      then result = norm
+      else
+        if this.matches("/%")
+        then result = "/"
+        else result = "."
+    )
+  }
+}