Improve wording for URI schemes, checkout URI for third party integrations (github#30146)

Author: hharen

content/code-security/code-scanning/integrating-with-code-scanning/sarif-support-for-code-scanning.md

@@ -71,6 +71,29 @@ SARIF files support both rules and results. The information stored in these elem
 
 When you compare SARIF files generated by analyzing different codebases with the same tool and rules, you should see differences in the results of the analyses but not in the rules.
 
+## Specifying the root for source files
+
+{% data variables.product.prodname_code_scanning_capc %} interprets results that are reported with relative paths as relative to the root of the repository analyzed. If a result contains an absolute URI, the URI is converted to a relative URI. The relative URI can then be matched against a file committed to the repository.
+
+You can provide the source root for conversion from absolute to relative URIs in one of the following ways.
+
+- [`checkout_path`](https://github.com/github/codeql-action/blob/c2c0a2908e95769d01b907f9930050ecb5cf050d/analyze/action.yml#L44-L47) input to the `github/codeql-action/analyze` action
+- `checkout_uri` parameter to the SARIF upload API endpoint. For more information, see "[{% data variables.product.prodname_code_scanning_capc %}](/rest/code-scanning#upload-an-analysis-as-sarif-data)" in the REST API documentation
+- [`invocation.workingDirectory.uri`](https://docs.oasis-open.org/sarif/sarif/v2.1.0/csprd01/sarif-v2.1.0-csprd01.html#_Toc9244365) property in the SARIF file
+
+If you provide a source root, any location of an artifact specified using an absolute URI must use the same URI scheme. If there is a mismatch between the URI scheme for the source root and one or more of the absolute URIs, the upload is rejected.
+
+For example, a SARIF file is uploaded using a source root of `file:///github/workspace`. 
+
+```
+# Conversion of absolute URIs to relative URIs for location artifacts
+
+file:///github/workspace/src/main.go -> src/main.go
+file:///tmp/go-build/tmp.go          -> file:///tmp/go-build/tmp.go
+```
+
+The file is successfully uploaded as both absolute URIs use the same URI scheme as the source root.
+
 ## Validating your SARIF file
 
 <!--UI-LINK: When code scanning fails, the error banner shown in the Security > Code scanning alerts view links to this anchor.-->
@@ -107,6 +130,7 @@ Any valid SARIF 2.1.0 output file can be uploaded, however, {% data variables.pr
 |----|----|
 | `tool.driver` | **Required.** A `toolComponent` object that describes the analysis tool. For more information, see the [`toolComponent` object](#toolcomponent-object). |
 | `tool.extensions[]` | **Optional.** An array of `toolComponent` objects that represent any plugins or extensions used by the tool during analysis. For more information, see the [`toolComponent` object](#toolcomponent-object). |
+| `invocation.workingDirectory.uri` | **Optional.** This field is used only when `checkout_uri` (SARIF upload API only) or `checkout_path` (% data variables.product.prodname_actions %} only) are not provided. The value is used to convert absolute URIs used in [`physicalLocation` objects](#physicallocation-object) to relative URIs. For more information, see "[Specifying the root for source files](#specifying-the-root-for-source-files)."|
 | `results[]` | **Required.** The results of the analysis tool. {% data variables.product.prodname_code_scanning_capc %} displays the results on {% data variables.product.prodname_dotcom %}. For more information, see the [`result` object](#result-object).
 
 ### `toolComponent` object
@@ -168,7 +192,7 @@ A location within a programming artifact, such as a file in the repository or a
 
 | Name | Description |
 |----|----|
-| `artifactLocation.uri`| **Required.** A URI indicating the location of an artifact, usually a file either in the repository or generated during a build. If the URI is relative, it should be relative to the root of the {% data variables.product.prodname_dotcom %} repository being analyzed. For example, main.js or src/script.js are relative to the root of the repository. If the URI is absolute, {% data variables.product.prodname_code_scanning %} can use the URI to checkout the artifact and match up files in the repository. For example, `https://github.com/ghost/example/blob/00/src/promiseUtils.js`.
+| `artifactLocation.uri`| **Required.** A URI indicating the location of an artifact, usually a file either in the repository or generated during a build. For the best results we recommend that this is a relative path from the root of the GitHub repository being analyzed. For example, `src/main.js`. For more information about artifact URIs, see "[Specifying the root for source files](#specifying-the-root-for-source-files)."|
 | `region.startLine` | **Required.** The line number of the first character in the region.
 | `region.startColumn` | **Required.** The column number of the first character in the region.
 | `region.endLine` | **Required.** The line number of the last character in the region.