gnodet commented on issue #12306:
URL: https://github.com/apache/maven/issues/12306#issuecomment-4738562108
## Root Cause Analysis: `<targetPath>.</targetPath>` → empty string →
absolute path at filesystem root
### The triggering config in `taglibs-rdc/pom.xml`
```xml
<resource>
<directory>src/main/resources</directory>
<targetPath>.</targetPath> <!-- a literal dot -->
</resource>
```
### The bug chain (Maven 4 only)
1. **`DefaultSourceRoot.java:111`** — constructor normalizes targetPath via
Java NIO:
```java
this.targetPathOrNull = (targetPathOrNull != null) ?
targetPathOrNull.normalize() : null;
```
`Path.of(".").normalize()` returns an **empty path** (zero name elements,
`toString()=""`) because `.` is a redundant element. The result is **not
null**, so it gets stored as a non-null empty Path.
2. **`ConnectedResource.java:46`** — converts it to an empty string for the
legacy plugin:
```java
.targetPath(sourceRoot.targetPath().map(Path::toString).orElse(null))
// → "" (empty string, NOT null)
```
3. **`DefaultMavenResourcesFiltering.getDestinationFile()`** — the plugin
concatenates:
```java
destination = "" + "/" +
"org/apache/taglibs/rdc/resources/RDCBundle_en_US.properties"
=
"/org/apache/taglibs/rdc/resources/RDCBundle_en_US.properties" // absolute!
```
Java's `File("/org/...").isAbsolute() == true`, so `outputDirectory`
(`/project/target/classes`) is **completely bypassed**. Maven tries to write to
the filesystem root → `NoSuchFileException`.
### Why Maven 3 worked
Maven 3 passed the original `"."` string to the plugin without NIO
normalization. The plugin computed `"." + "/" + filename = "./filename"`
(relative), which was correctly resolved against the output directory.
### Fix location
**`DefaultSourceRoot.java:111`** — treat empty normalized paths as null
(same semantics as no targetPath):
```java
if (targetPathOrNull != null) {
Path normalized = targetPathOrNull.normalize();
// "." normalizes to empty path = "copy to output root" = same as null
this.targetPathOrNull = (normalized.getNameCount() == 0) ? null :
normalized;
} else {
this.targetPathOrNull = null;
}
```
The existing test `testHandlesEmptyTargetPathFromResource` tests explicit
`""` (handled by `nonBlank()` → null, never reaches the normalization path),
but **there's no test for `"."` which takes a completely different code path**.
A test for `targetPath="."` would have caught this.
_Claude Code on behalf of Guillaume Nodet_
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