create: Fix non-deterministic conflict detection in hugo new content

The contentInclusionFilter used strings.Contains to match filenames
against the target path. Because strings.Contains is a substring check,
a directory entry like "content/about" matches "content/about.md",
causing unrelated files to be pulled into the mini-build. Whether the
conflict was then detected depended on whether the filesystem walker
delivered a directory entry or a full file path.

Also adds an upfront check for the directory-conflict case, since
a corrected filter alone would allow about.md to be created alongside
an existing about/ directory.

Closes #12602
Closes #12786
Closes #14112
Closes #14769

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

create/content.go

@@ -162,9 +162,8 @@ func (b *contentBuilder) buildDir() error {
 	if !b.dirMap.siteUsed {
 		// We don't need to build everything.
 		contentInclusionFilter = hglob.NewFilenameFilterForInclusionFunc(func(filename string) bool {
-			filename = strings.TrimPrefix(filename, string(os.PathSeparator))
 			for _, cn := range contentTargetFilenames {
-				if strings.Contains(cn, filename) {
+				if strings.HasSuffix(cn, filename) {
 					return true
 				}
 			}
@@ -219,6 +218,9 @@ func (b *contentBuilder) buildDir() error {
 func (b *contentBuilder) buildFile() (string, error) {
 	contentPlaceholderAbsFilename, err := b.cf.CreateContentPlaceHolder(b.targetPath, b.force)
 	if err != nil {
+		if fi, serr := b.sourceFs.Stat(contentPlaceholderAbsFilename); serr == nil && !fi.IsDir() {
+			return "", errTargetConflict(contentPlaceholderAbsFilename)
+		}
 		return "", err
 	}
 
@@ -231,11 +233,17 @@ func (b *contentBuilder) buildFile() (string, error) {
 	if !usesSite {
 		// We don't need to build everything.
 		contentInclusionFilter = hglob.NewFilenameFilterForInclusionFunc(func(filename string) bool {
-			filename = strings.TrimPrefix(filename, string(os.PathSeparator))
-			return strings.Contains(contentPlaceholderAbsFilename, filename)
+			return strings.HasSuffix(contentPlaceholderAbsFilename, filename)
 		})
 	}
 
+	// If a directory with the target's name (sans extension) exists, this file
+	// would produce a URL conflict with the existing section or leaf bundle.
+	targetDir := strings.TrimSuffix(contentPlaceholderAbsFilename, filepath.Ext(contentPlaceholderAbsFilename))
+	if fi, err := b.sourceFs.Stat(targetDir); err == nil && fi.IsDir() {
+		return "", errTargetConflict(contentPlaceholderAbsFilename)
+	}
+
 	if err := b.h.Build(hugolib.BuildCfg{NoBuildLock: true, SkipRender: true, ContentInclusionFilter: contentInclusionFilter}); err != nil {
 		return "", err
 	}
@@ -268,10 +276,14 @@ func (b *contentBuilder) setArcheTypeFilenameToUse(ext string) {
 	}
 }
 
+func errTargetConflict(path string) error {
+	return fmt.Errorf("no page found for %q; the target path conflicts with existing content", path)
+}
+
 func (b *contentBuilder) applyArcheType(contentFilename string, archetypeFi hugofs.FileMetaInfo) error {
 	p := b.h.GetContentPage(contentFilename)
 	if p == nil {
-		return fmt.Errorf("no page found for %q; if a file with the same name but different case already exists, please use a different filename or remove the existing file", contentFilename)
+		return errTargetConflict(contentFilename)
 	}
 
 	f, err := b.sourceFs.Create(contentFilename)

testscripts/commands/new_content.txt

@@ -5,8 +5,8 @@ hugo new content --kind post post/first-post.md
 grep 'draft = true' content/post/first-post.md
 
 # Issue 12599
-cd $WORK
 
+cd $WORK
 hugo new project --format toml --force issue-12599
 cp hugo.toml issue-12599/hugo.toml
 cd issue-12599
@@ -16,6 +16,33 @@ grep 'DATE _2099-12-31_' public/s1/p1/index.html
 grep 'SLUG _p1_' public/s1/p1/index.html
 grep 'TITLE _2099 12 31 P1_' public/s1/p1/index.html
 
+# Issue 12602
+
+cd $WORK
+hugo new project issue-12602
+cd issue-12602
+hugo new content about/_index.md
+! hugo new content about.md
+stderr 'the target path conflicts with existing content'
+
+# Issue 12786
+
+cd $WORK
+hugo new project issue-12786
+cd issue-12786
+hugo new content content/p1/index.md
+! hugo new content content/p1/p2.md
+stderr 'the target path conflicts with existing content'
+
+# Issue 14112
+
+cd $WORK
+hugo new project issue-14112
+cd issue-14112
+hugo new content P1.md
+! hugo new content p1.md
+stderr 'the target path conflicts with existing content'
+
 -- hugo.toml --
 disableKinds = ['home','rss','section','sitemap','taxonomy','term']
 [frontmatter]