Add MDS034 markdown-flavor rule for flavor validation

PLAN.md

@@ -43,7 +43,7 @@ footer: |
 | 83  | 🔳     | [Security hardening batch](plan/83_security-hardening-batch.md)                                                 |
 | 84  | 🔲     | [Symlink default-deny for file discovery](plan/84_symlink-default-deny.md)                                      |
 | 85  | 🔳     | [Increase test coverage to 95% by extracting shared rule helpers](plan/85_coverage-to-95-percent.md)            |
-| 86  | 🔲     | [Markdown flavor validation](plan/86_markdown-flavor-validation.md)                                             |
+| 86  | 🔳     | [Markdown flavor validation](plan/86_markdown-flavor-validation.md)                                             |
 | 87  | 🔲     | [Flavor validation for GitHub Alerts](plan/87_markdown-flavor-github-alerts.md)                                 |
 | 88  | ✅     | [TOC directive migration aid](plan/88_toc-directive-migration.md)                                               |
 | 89  | 🔲     | [TOC generator directive and MDS035 auto-fix](plan/89_toc-generator-directive.md)                               |

cmd/mdsmith/main.go

@@ -39,6 +39,7 @@ import (
 	_ "github.com/jeduden/mdsmith/internal/rules/include"
 	_ "github.com/jeduden/mdsmith/internal/rules/linelength"
 	_ "github.com/jeduden/mdsmith/internal/rules/listindent"
+	_ "github.com/jeduden/mdsmith/internal/rules/markdownflavor"
 	_ "github.com/jeduden/mdsmith/internal/rules/maxfilelength"
 	_ "github.com/jeduden/mdsmith/internal/rules/maxsectionlength"
 	_ "github.com/jeduden/mdsmith/internal/rules/nobareurls"

internal/integration/rules_test.go

@@ -22,7 +22,7 @@ import (
 	_ "github.com/jeduden/mdsmith/internal/rules/catalog"
 	_ "github.com/jeduden/mdsmith/internal/rules/concisenessscoring"
 	_ "github.com/jeduden/mdsmith/internal/rules/crossfilereferenceintegrity"
-	_ "github.com/jeduden/mdsmith/internal/rules/directorystructure"
+	"github.com/jeduden/mdsmith/internal/rules/directorystructure"
 	_ "github.com/jeduden/mdsmith/internal/rules/emptysectionbody"
 	_ "github.com/jeduden/mdsmith/internal/rules/fencedcodelanguage"
 	_ "github.com/jeduden/mdsmith/internal/rules/fencedcodestyle"
@@ -32,6 +32,7 @@ import (
 	_ "github.com/jeduden/mdsmith/internal/rules/include"
 	_ "github.com/jeduden/mdsmith/internal/rules/linelength"
 	_ "github.com/jeduden/mdsmith/internal/rules/listindent"
+	_ "github.com/jeduden/mdsmith/internal/rules/markdownflavor"
 	_ "github.com/jeduden/mdsmith/internal/rules/maxfilelength"
 	_ "github.com/jeduden/mdsmith/internal/rules/maxsectionlength"
 	_ "github.com/jeduden/mdsmith/internal/rules/nobareurls"
@@ -140,9 +141,15 @@ func applySettingsToRule(
 }
 
 func TestRuleFixtures(t *testing.T) {
-	primeDirectoryStructureWarnOnce(t)
 	dirs := discoverFixtureDirs(t)
 
+	// MDS033's "no allowed patterns" warning is gated by a
+	// process-level sync.Once. After MDS033's own fixtures run, the
+	// rule is left in configured=true / allowed=[] state by the
+	// defaults-based cleanup. Silence the guard explicitly so later
+	// checkAllRules walks do not depend on warning emission order.
+	directorystructure.SilenceConfigWarningForTesting()
+
 	for _, dir := range dirs {
 		base := filepath.Base(dir)
 		m := ruleIDPattern.FindStringSubmatch(base)
@@ -388,28 +395,6 @@ func runFixSingleFile(
 
 // --- shared helpers ---
 
-// primeDirectoryStructureWarnOnce fires MDS033's "no allowed patterns"
-// sync.Once warning up front. Without this, test cleanup in
-// applySettingsToRule leaves MDS033 in a configured-but-empty state,
-// so the warning would fire the first time any post-MDS033 fixture
-// calls checkAllRules, producing a spurious diagnostic.
-func primeDirectoryStructureWarnOnce(t *testing.T) {
-	t.Helper()
-	r := rule.ByID("MDS033")
-	if r == nil {
-		return
-	}
-	cr, ok := r.(rule.Configurable)
-	if !ok {
-		return
-	}
-	require.NoError(t, cr.ApplySettings(map[string]any{"allowed": []any{}}))
-	f, err := lint.NewFile("prime.md", []byte("# x\n"))
-	require.NoError(t, err)
-	_ = r.Check(f)
-	require.NoError(t, cr.ApplySettings(cr.DefaultSettings()))
-}
-
 func discoverFixtureDirs(t *testing.T) []string {
 	t.Helper()
 	dirs, err := filepath.Glob("../../internal/rules/MDS*-*")

internal/rules/MDS034-markdown-flavor/README.md

@@ -0,0 +1,145 @@
+---
+id: MDS034
+name: markdown-flavor
+status: ready
+description: >-
+  Flags Markdown syntax that the declared target
+  flavor does not render.
+---
+# MDS034: markdown-flavor
+
+Flags Markdown syntax that the declared target
+flavor does not render.
+
+- **ID**: MDS034
+- **Name**: `markdown-flavor`
+- **Status**: ready
+- **Default**: disabled
+- **Fixable**: no (fix pipeline lands in a follow-up)
+- **Implementation**:
+  [source](./)
+- **Category**: meta
+
+## Settings
+
+| Key    | Type   | Description                     |
+|--------|--------|---------------------------------|
+| flavor | string | Target flavor; see table below. |
+
+The flavor name is case-sensitive. Supported
+values:
+
+- `commonmark` — strict CommonMark; rejects every
+  tracked feature.
+- `gfm` — GitHub Flavored Markdown; adds tables,
+  task lists, strikethrough, and bare-URL
+  autolinks.
+- `goldmark` — mdsmith-defined profile; GFM plus
+  heading IDs.
+- `pandoc` — Pandoc's default markdown; GFM plus
+  footnotes, definition lists, heading IDs,
+  superscript, subscript, math block, and inline
+  math. Rejects abbreviations (non-default
+  extension).
+- `phpextra` — PHP Markdown Extra; tables,
+  footnotes, definition lists, heading IDs, and
+  abbreviations. Rejects GFM features and math.
+- `multimarkdown` — MultiMarkdown; PHP Extra plus
+  math block and inline math.
+- `myst` — MyST (Sphinx documentation flavor);
+  tables, strikethrough, footnotes, definition
+  lists, heading IDs, math block, and inline math.
+- `any` — accepts every tracked feature. Use when
+  the target renderer is unknown or permissive and
+  you want to silence flavor diagnostics without
+  disabling the rule.
+
+## Config
+
+Enable with a target flavor:
+
+```yaml
+rules:
+  markdown-flavor:
+    flavor: gfm
+```
+
+Disable (default):
+
+```yaml
+rules:
+  markdown-flavor: false
+```
+
+## Detected features
+
+MDS034 tracks twelve syntax features whose
+support varies across Markdown flavors.
+
+Eleven features are detected from the goldmark AST
+of a dual parse. That parse enables five built-in
+extensions: table, strikethrough, task list,
+footnote, and definition list. It also enables the
+heading-ID attribute parser. Five custom parsers
+add superscript, subscript, math block, inline
+math, and abbreviations.
+
+Bare-URL autolinks are detected separately. The
+detector scans text nodes from the main parse for
+URL-shaped text. It skips links, autolinks, code
+spans, and code blocks.
+
+`flavor: any` accepts every feature and is omitted
+from the table below.
+
+| Feature            | commonmark | gfm | goldmark | pandoc | phpextra | multimarkdown | myst |
+|--------------------|------------|-----|----------|--------|----------|---------------|------|
+| tables             | no         | yes | yes      | yes    | yes      | yes           | yes  |
+| task lists         | no         | yes | yes      | yes    | no       | no            | no   |
+| strikethrough      | no         | yes | yes      | yes    | no       | no            | yes  |
+| bare-URL autolinks | no         | yes | yes      | yes    | no       | no            | no   |
+| footnotes          | no         | no  | no       | yes    | yes      | yes           | yes  |
+| definition lists   | no         | no  | no       | yes    | yes      | yes           | yes  |
+| heading IDs        | no         | no  | yes      | yes    | yes      | yes           | yes  |
+| superscript        | no         | no  | no       | yes    | no       | no            | no   |
+| subscript          | no         | no  | no       | yes    | no       | no            | no   |
+| math blocks        | no         | no  | no       | yes    | no       | yes           | yes  |
+| inline math        | no         | no  | no       | yes    | no       | yes           | yes  |
+| abbreviations      | no         | no  | no       | no     | yes      | yes           | no   |
+
+## Examples
+
+### Good
+
+<?include
+file: good/gfm.md
+wrap: markdown
+?>
+
+```markdown
+# Heading
+
+Text with ~~old~~ markup and a task list:
+
+- [x] done
+- [ ] todo
+```
+
+<?/include?>
+
+### Bad
+
+<?include
+file: bad/commonmark-table.md
+wrap: markdown
+?>
+
+```markdown
+# Heading
+
+| a | b |
+| - | - |
+| 1 | 2 |
+```
+
+<?/include?>

internal/rules/MDS034-markdown-flavor/bad/commonmark-abbreviation.md

@@ -0,0 +1,16 @@
+---
+settings:
+  flavor: commonmark
+diagnostics:
+  - line: 3
+    column: 1
+    message: "abbreviations are not supported by commonmark"
+  - line: 5
+    column: 5
+    message: "abbreviations are not supported by commonmark"
+---
+# Heading
+
+*[HTML]: Hyper Text Markup Language
+
+Use HTML here.

internal/rules/MDS034-markdown-flavor/bad/commonmark-bare-url.md

@@ -0,0 +1,11 @@
+---
+settings:
+  flavor: commonmark
+diagnostics:
+  - line: 3
+    column: 7
+    message: "bare-URL autolinks are not supported by commonmark"
+---
+# Heading
+
+Visit https://example.com for details.

internal/rules/MDS034-markdown-flavor/bad/commonmark-heading-id.md

@@ -0,0 +1,11 @@
+---
+settings:
+  flavor: commonmark
+diagnostics:
+  - line: 1
+    column: 11
+    message: "heading IDs are not supported by commonmark"
+---
+# Heading {#top}
+
+Body text.

internal/rules/MDS034-markdown-flavor/bad/commonmark-math-block.md

@@ -0,0 +1,13 @@
+---
+settings:
+  flavor: commonmark
+diagnostics:
+  - line: 3
+    column: 1
+    message: "math blocks are not supported by commonmark"
+---
+# Heading
+
+$$
+a^2 + b^2 = c^2
+$$

internal/rules/MDS034-markdown-flavor/bad/commonmark-math-inline.md

@@ -0,0 +1,11 @@
+---
+settings:
+  flavor: commonmark
+diagnostics:
+  - line: 3
+    column: 5
+    message: "inline math is not supported by commonmark"
+---
+# Heading
+
+See $x+1$ above.

internal/rules/MDS034-markdown-flavor/bad/commonmark-strikethrough.md

@@ -0,0 +1,11 @@
+---
+settings:
+  flavor: commonmark
+diagnostics:
+  - line: 3
+    column: 6
+    message: "strikethrough is not supported by commonmark"
+---
+# Heading
+
+Text ~~crossed out~~ here.

internal/rules/MDS034-markdown-flavor/bad/commonmark-subscript.md

@@ -0,0 +1,11 @@
+---
+settings:
+  flavor: commonmark
+diagnostics:
+  - line: 3
+    column: 2
+    message: "subscript is not supported by commonmark"
+---
+# Heading
+
+H~2~O is water.

internal/rules/MDS034-markdown-flavor/bad/commonmark-superscript.md

@@ -0,0 +1,11 @@
+---
+settings:
+  flavor: commonmark
+diagnostics:
+  - line: 3
+    column: 7
+    message: "superscript is not supported by commonmark"
+---
+# Heading
+
+E = mc^2^ is famous.

internal/rules/MDS034-markdown-flavor/bad/commonmark-table.md

@@ -0,0 +1,13 @@
+---
+settings:
+  flavor: commonmark
+diagnostics:
+  - line: 3
+    column: 1
+    message: "tables are not supported by commonmark"
+---
+# Heading
+
+| a | b |
+| - | - |
+| 1 | 2 |

internal/rules/MDS034-markdown-flavor/bad/commonmark-task-list.md

@@ -0,0 +1,15 @@
+---
+settings:
+  flavor: commonmark
+diagnostics:
+  - line: 3
+    column: 3
+    message: "task lists are not supported by commonmark"
+  - line: 4
+    column: 3
+    message: "task lists are not supported by commonmark"
+---
+# Heading
+
+- [x] done
+- [ ] todo

internal/rules/MDS034-markdown-flavor/bad/gfm-definition-list.md

@@ -0,0 +1,12 @@
+---
+settings:
+  flavor: gfm
+diagnostics:
+  - line: 3
+    column: 1
+    message: "definition lists are not supported by gfm"
+---
+# Heading
+
+term
+:   definition

internal/rules/MDS034-markdown-flavor/bad/gfm-footnote.md

@@ -0,0 +1,16 @@
+---
+settings:
+  flavor: gfm
+diagnostics:
+  - line: 3
+    column: 1
+    message: "footnotes are not supported by gfm"
+  - line: 5
+    column: 1
+    message: "footnotes are not supported by gfm"
+---
+# Heading
+
+A paragraph.[^1]
+
+[^1]: footnote body.